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The United States Congress legislates pesticide laws
to manage health and environmental risk. Pesticides are
currently regulated under two major federal laws: the Federal
Insecticide, Fungicide, and Rodenticide Act (FIFRA); and the Federal
Food, Drug, and Cosmetic Act (FFDCA). FIFRA gives the U.S.
Environmental Protection Agency (EPA) the authority to
register pesticides; to require appropriate chemical, toxicological,
and environmental studies; and to prescribe labeling use
restrictions aimed to prevent unreasonable adverse effects on human
health and the environment. Pesticides that come into contact with
food and animal feed are regulated under FFDCA, which gives
EPA the authority to establish tolerances (maximum pesticide
residues allowed) in food and feed. The FQPA of 1996
modified FFDCA and FIFRA to broadly extend the authority to
conduct risk assessments.
Regulations for pesticide registration specify data
requirements, methods for conducting studies, procedures for
risk assessment, and labeling content. EPA uses these as tools
to determine whether a pesticide can be used without
unreasonable effects on human and environmental health. EPA's
assessment also addresses specific risks to humans and the
environment and appraises potential economic, social, and
environmental impact associated with use of the pesticide. In effect,
the decision-making process balances potential risk to humans
and the environment against projected economic, social, and
environmental benefits.
There have been many changes in pesticide products
and registration requirements during the last decade. What
was acceptable risk, yesterday, may not be, today. Policies
and decisions on acceptable risk change, over time; and as
public awareness and concerns over pesticide risk increase, so
do registration requirements.
The Insecticide Act (1910) prevented the manufacture,
sale, or transport of impure or improperly labeled insecticides
and fungicides. Its primary focus was to ensure that products
were labeled adequately and that container contents were
stated precisely on the label. The Insecticide Act contained no
registration requirements and did not set safety standards.
The Insecticide Act was replaced in 1947 by a more
comprehensive law: the Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA). FIFRA was the first law to require
pesticide manufacturers to register their products with the United
States Department of Agriculture (USDA), which was responsible
for registering all pesticides prior to sale or movement via
interstate or foreign commerce.
Pesticide regulations were expanded again in 1954 with
an amendment to the Federal Food, Drug, and Cosmetic Act.
The amendment required tolerance limits for pesticide residues
on agricultural commodities; and it limited the amount of
residue that could remain in or on a food crop after application,
according to "good agricultural practices." A 1958 amendment,
the Delaney Clause, prohibited establishment of tolerances
for carcinogenic food additives. However, it applied only to
pesticides for which residues were greater in the actual food
item than in the raw agricultural commodity. The registration
process was changed in 1964 when FIFRA was modified to give
USDA the authority to deny or cancel product registration.
Increases in environmental awareness in the 1960s,
exemplified by Rachel Carson's Silent
Spring, changed forever how pesticides would be viewed by the American public. The
most commonly used insecticides at that time were part of a
chemical class of compounds called chlorinated hydrocarbons
which includes the well-known insecticide DDT. Emerging
environmental groups and the news media accurately portrayed
these pesticides as chemicals that bioaccumulate in the
environment, disrupt links in the food chain, and poison wildlife.
Silent Spring captured the public's attention and rallied a cry for greater
public awareness of environmental issues.
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The environmental movement added balance to
discussion on the benefits of pesticide use, providing awareness of the
risks posed to people, wildlife, and ecosystems. FIFRA 1964
established procedures for suspending the registration of
pesticides determined to be unsafe, and the growing environmental
movement formed powerful lobbies that supported additional
legislation. Politically astute individuals and organizations directed
their attention to Congress, lobbying for legislation that would
help protect the economy, the environment, and public health. As
a result, manufacturers and users were held more accountable
for reducing both short- and long-term risks of pesticide use.
The public looked to Congress to pass enforceable
legislation requiring pesticides to be scientifically evaluated prior to
release for agricultural, commercial, or consumer use. While the
debate has shifted over the years as issues have emerged
and changed, it remains a primary obligation of
manufacturers, through government oversight, to understand and minimize
risks posed by pesticides.
In 1970, Congress created the United States
Environmental Protection Agency (EPA) and, in 1972, strengthened
FIFRA dramatically to give EPA more regulatory authority.
Changes in FIFRA, since 1970, have resulted in a
major philosophical shift in pesticide regulation. Originally,
FIFRA required regulators to review and register pesticide products.
But in 1972, in the interest of risk reduction and pollution
prevention, Congress changed FIFRA from a labeling law to a
comprehensive statute designed to regulate the manufacture,
distribution, and use of pesticides. Pesticide manufacturers were
then required to support all registrations by providing
prescribed scientific studies showing that use of the product would
not cause "unreasonable adverse effects on human health or
the environment."
In addition to requiring scientific data in support of
pesticide registration, FIFRA was modified to prohibit any use of a
pesticide inconsistent with its labeling. In other words, the
label became the law; and violations for not following the label
could result in label enforcement via license revocation and
fines. Recognition that not all pesticides pose the same risk
led to the FIFRA statute (1972) whereby pesticides deemed safe for application by the
general public are commonly referred to as general-use pesticides,
while those posing greater risk are classified as
restricted-use pesticides. The purchase
and application of restricted-use pesticides are limited to
certified applicators or persons supervised by certified individuals.
To ensure that adverse effects on human health and the
environment can be prevented, pesticide registration, product
labeling, government enforcement, and applicator education form the foundation of
a comprehensive framework to regulate the manufacture, use, and disposal of pesticides.
Because Congress did not intend FIFRA to be solely an environmental bill,
an industry bill, or a farm bill, sincere efforts were made to balance the needs of
all stakeholders. Since benefits play an important role in decision-making under the act, Congress amended FIFRA to
allow USDA and interested parties to explain how cancellation
of pesticides might impact the public adversely by
denying potential benefits along with potential risks. Regulatory
decisions are based on the balance of risk versus benefit
(risk-benefit analysis).
As required under the revised FIFRA, EPA publishes
scientific testing guidelines and regulations to ensure that studies
in support of pesticide registration employ the best scientific
tests and methods. The regulations stipulate what testing is
required and how the studies are to be performed. Prior to the
inclusion of testing guidelines, pesticide manufacturers conducted
many studies on the impact of their products on mammals, birds,
fish, and the environment. EPA guidelines stipulated for the first
time certain toxicological, ecological, residual, and environmental
fate studies.
Risk assessments require data on toxicological end
points and exposure. FIFRA guidelines and regulations place a
formaland increasedresponsibility for testing
requirements on pesticide manufacturers. The data developed as the result
of the guidelines, combined with the available tools to
estimate exposure levels, formed the beginning of EPA's risk
assessment process.
The generation of new data has allowed the
registration process to improve and mature. Advances in science,
new experimental tools, and new thinking (driven by desire on
the part of EPA and manufacturers to improve the science of
risk assessment) yield more complex data for review; thus, EPA
is obligated to review growing numbers of massive and
intricate data sets supporting pesticide registration and to upgrade
its work force with scientists schooled in such specific disciplines
as environmental chemistry and toxicology.
Defensible scientific data from standardized
procedures (protocols) are required if regulators are to credibly
assess product registration. In the mid 1970s, fraudulent
practices surfaced in one large-contract toxicology laboratory,
triggering questions within EPA as to the quality of data used as a
basis for registration decisions. EPA's concern led to
Good Laboratory
Practice Standards describing how studies must be
conducted. These standards are commonly called Good Laboratory
Practices (GLPs).
The registration of a pesticide requires well-designed
studies conducted by trained scientists and reported accurately,
with documentation. GLPs ensure quality, integrity, credibility,
and consistency of data used in assessing risk. GLPs describe
how laboratory and field studies must be planned, performed,
monitored, recorded, and reported. They require pesticide
manufacturers to comply with a set of standard quality assurance
procedures for generating experimental data. This
documentation provides an audit trail which facilitates verification that
studies were properly performed and reported; and it affords
EPA reviewers confidence in their conclusions.
In the early years of pesticide regulation, comprehensive
risk assessments were uncommon because the technology
and scientific knowledge necessary to accurately interpret the
data were unavailable. But in the late 1980s, risk assessors began
to develop a new philosophy. They recognized that the
emphasis
should shift from toxicity assessment, alone, to include
exposure studies, uncertainty, and professional judgment. The
implementation of these additional considerations, coupled with
improved scientific applications, has greatly enhanced EPA's
decision-making process.
In the late 1980s and 1990s, EPA developed a policy
focused on reduced-risk pesticides, offering manufacturers the
incentive of quicker registration decisions for development of
"safer" products. The policy favors pesticides that have less potential
to cause adverse health and environmental effects than
those currently registered. Registration applications
documenting reduced, low-risk characteristics are granted priority
consideration in the review process, reducing the usual two- to
four-year registration process to as little as six months. Expedient
reviews allow "reduced-risk" pesticides to move more quickly to
the marketplace; and the use of this incentive to encourage
the development of "safer" pesticides places EPA in a better
position to manage pesticide risk in the marketplace of tomorrow.
Congress passed the Food Quality Protection Act of
1996 (FQPA), amending both FIFRA and FFDCA to provide a
more comprehensive system for regulating pesticides. Under
previous pesticide laws, EPA was required to balance potential
risks against potential benefits of a pesticide during the
registration review process; but FQPA established a single,
health-based safety standard for all pesticide residues in all foods and
greatly reduced consideration of pesticidal benefits. FQPA requires
that tolerances must be determined to be explicitly "safe"; that
is, there must be "reasonable certainty" that tolerance levels
will result in "no harm." FQPA also requires EPA to consider
all nonoccupational sources of pesticide exposure, both dietary
and nondietary, when establishing tolerances; and exposure to
other chemicals that may have a common mechanism of toxicity
must be considered, as well.
FQPA further requires that EPA specifically address
potential risks to infants and children. It mandates that special
attention
be paid to the possibility that chemicals may disrupt the
endocrine system, and that periodic reevaluation of all
pesticide registrations and tolerances is essential to ensure
ongoing validity.
One of the consequences of FQPA is the need to
further refine the risk assessment process, particularly in regard
to assessing potential risks from multiple sources and routes
of exposure. It is clear that risk assessment plays an
increasingly critical role in the process of pesticide registration
and reregistration.
In FIFRA, the United States Congress set the standard
for making pesticide registration decisions: "...any unreasonable
risk to man or the environment, taking into account the
economic, social, and environmental costs and benefits of the use of
any pesticide." Thus, both human health and ecological risk
assessments are essential to the decision-making process
behind pesticide registration. Environment is defined to include
"water, air, land, and all plants and man and other animals living
therein, and the interrelationships which exist among these." The
environmental protection component weighs heavily in risk
assessment decisions.
The primary decisions that EPA must make
concerning pesticides are to
 register a new product,
reregister an existing product,
cancel a current registration, and
determine if labeling protects human health and the
environment.
Risk assessments are performed by EPA during
registration and reregistration processes. They are also conducted
whenever new findings suggest that adverse effects might result
from use of a previously registered product. There are four end
points to which assessments are directed: Experimental Use
Permit; Registration; Reregistration; and Special Review.
Experimental Use Permit
Prior to completing all studies required for full
registration, registrants often submit a smaller data package along with
a request for an Experimental Use Permit (EUP); an EUP allows
a registrant to apply the product to as many as 5,000 acres
to evaluate performance. EPA reviews the abbreviated
package and judges whether there is a potential for risk to humans or
the environment under limited use conditions; if there is no
such indication, an EUP is issued.
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Registration
During the registration process, EPA evaluates all data
in support of active ingredients not previously registered, as well
as new uses (for a registered product) that would require
label changes. When requesting product registration, the
pesticide manufacturer (registrant) must submit to EPA all data
required by FIFRA. When all individual studies have been reviewed,
the results are factored into human and ecological risk
assessments to evaluate whether requested uses for the product
present unacceptable risk to human health or the environment.
Review and assessment are conducted by representatives of all
disciplines within EPA: product, residue, and environmental
chemistry; human health; and ecological effects.
Reregistration
From the very beginning, FIFRA intended that all
registered pesticides be reregistered every five years; but
economics nullified that intent. FIFRA Amended 1988 required
additional feesreregistration feesto be paid by manufacturers
submitting a product for reregistration, thus helping to provide
the necessary funding. All data used to support pesticides
registered before 1984 became subject to reevaluation and upgrading,
if necessary, to comply with current guidelines and standards.
The refined data enhances the ability of EPA and the registrant
to judge whether risk conclusions and registration decisions
made during the initial product registration process meet
today's standards.
Policy changes alter the emphasis of regulatory actions
in reregistration programs. Instead of moving riskier pesticides
into the lengthy special review process, the focus is to reduce risk
by negotiation, e.g., by changing application rates,
increasing application intervals, or using alternative application
methods. These measures often take the form of label changes
designed to mitigate the amount and duration of exposure.
Special Review
FIFRA gives EPA the statutory responsibility not only
to register pesticides but also to take regulatory
actionsincluding cancellationunder certain unusual conditions: for
instance, when new information on a currently registered pesticide
indicates that normal use of the product may result in
unreasonable adverse effects. Special reviews are initiated when concern
is heightened by specific circumstances, such as
when new evidence from laboratory studies suggests
that the pesticide may pose higher or different risks than
were predicted;
when a pesticide is linked to fish or bird incidents; or
when workers become ill.
The risk assessment process and the resources expended
to conduct intensive special reviews provide benefits to EPA
and the public:
EPA's mission to protect public health and the
environment from unreasonable adverse effects can be more readily fulfilled.
The well-defined risk assessment process for both
human health and ecological effects helps EPA make consistent,
well-informed registration decisions.
Effective communication of the process to pesticide
manufacturers fosters timely registration decisions.
The risk assessment process encourages in-depth
review similar to peer review of basic research.
The process provides a forum where EPA scientists
can reach consensus on conclusions drawn from risk assessment.
In fact, scientists in academia and those from the private
sector canand doshare the consensus.
The process helps guide EPA's decision on
whether additional data are needed to clarify a potential risk.
Corporate decisions on whether or not to develop
potential pesticide products are based on risk assessment,
marketability, and projected cost of production. Risk assessments must
be conducted periodically throughout the development and
commercial life of a pesticide, oftentimes beginning with
limited, preliminary data acquired very early in the development
process. As more data become available, risk assessments are refined
by virtue of an enhanced understanding of the toxicological
properties and chemical fate of the pesticide, as well as better
exposure estimates. Scientists who develop data often serve
as experts who present and interpret it for risk
managers. The development team assesses data at various intervals to
decide whether to cancel or continue research and plans for
commercialization of the product.
A thorough, well-organized risk assessment process
defines guidelines for required tests and identifies
risk standards that will be used to quantify the data;
stipulates full reevaluation of studies that supported
initial (or former) registration of a product to verify sufficiency
according to current standards and to identify any need for
additional testing prior to reregistration;
enables manufacturers to identify and eliminate high
risk products early in the development process, thus
minimizing expenditures in support of a product that most likely would
not be granted registration; and
requires sound, factual documentation of the
registration process as a basis on which customers, company
management, and stockholders can calculate their commitment to
advancement of the product.
Registrants often use similar or more stringent criteria
than those used by EPA and conduct a preliminary review of
their own data; this assists registrants in gauging their
products' prospects for registration. Preliminary reviews also may serve
as indicators of the amount of time EPA might spend evaluating
the data, that is, how quickly products might be registered. If
potential adverse effects are identified during any risk
assessment, scientists must decide if and how the potential risk can
be reduced; for example, by changes in formulation, methods
of application, use rates, and marketing, or by use of
personal protective equipment. Strategies for reducing risk involve what
is known as risk refinement.
For example, suppose a pesticide applied at a rate of
one pound of active ingredient per acre has the potential to
cause unreasonable risk to foraging bobwhite quail in treated fields.
A risk assessment may indicate that rates at or below 0.75
pound per acre would negate that potential. So, to mitigate risk,
product development teams may be asked to reduce the proposed
use rate.
Lowering the application rate of a product requires
reassessment of its efficacy. For this example, an application rate of
0.75 pound per acre would control most broadleaf weeds in corn,
but two resistant perennial weeds would not be controlled at
that rate. Based on this information as well as data indicating
risk potential at higher rates, the product development team
might conclude that the product would not compete successfully in
the marketplace; if so, commercial development would cease.
As practiced by EPA, risk assessment provides the
regulated pesticide industry with straightforward methods and criteria
to estimate risk. It is a well defined formal decision-making
process which, ideally, incorporates scientific knowledge about a
pesticide into the risk assessment along with inherent
uncertainties. The result takes form as a set of science-based estimates
that describe the likelihood of the pesticide to adversely
impact human health, wildlife survival and fitness, and
environmental quality, and which are sufficiently conservative to account
for uncertainties in the process.
Human health and ecological risk assessments often
are preliminary in nature and may be based on limited data
and/or very conservative assumptions. As more research data
are compiled and more accurate assumptions considered, the
more precise and comprehensive the risk assessmentand
the greater the confidence in conclusions drawn. However, if
initial risk assessments indicate no cause for concern, a more
refined risk assessment may not be necessary.
Quantitative risk assessment is a function of toxicity
and exposure. The risk assessment process involves multiple
steps, beginning with an appraisal of toxicity and exposure and
concluding with a characterization of risk.
Toxicity Characterization
Toxicological characterization is commonly based on
laboratory studies; that is, it reflects adverse effects observed
when animals are intentionally administered a range of
concentrations of the pesticide being studied. Toxicity can be characterized
by mortality or by sublethal effects within the range of doses tested.
An important aspect of toxicological evaluation is
determination of the relationship between magnitude of exposure
and extent and severity of observed effectscommonly referred
to as dose-response. The dose-response relationship
identifies dose levels at which adverse effects occur, as well as the
no observed effect concentration (NOEC). For risk assessment,
the lowest NOEC, LD50, etc., is used to estimate risk.
Exposure Characterization
Contact with a chemical in the environmentin the
workplace, at home, or in air, food, water, or soilconstitutes
exposure. Exposure concentrations may be either estimated
or measured, based on the amounts and manner in which
the chemical is used, the physical properties of the chemical,
and data from laboratory and field experiments. Exposure
assessments ascertain the exposure of people, wildlife, and plants
to pesticides in the environment. The extent of exposure
depends on the type of use (crop, lawn, and garden treatment;
mosquito control; indoor pest control), application rate, method of
application, and frequency of application, along with the
breakdown, partitioning, and movement of the chemical in the
environment. An adverse effect is predicted only if exposure approaches
or exceeds dose levels that have resulted in adverse effects
in toxicology studies.
Risk Characterization
Risk characterization defines the likelihood that humans
or wildlife will be exposed to hazardous concentrations. Thus,
risk characterization describes the relationship between
exposure and toxicity. Risk assessors identify species likely to be
exposed, the probability of such exposure occurring, and
effects that might be expected.
Suppose that a sampling for a given pesticide in the
environment yields an estimated exposure level of 3 ppb (parts
per billion) in water, and that a short-term laboratory study
shows that an exposure level of 100 ppb produces an
adverse effect in bluegill sunfish. How could this
information be integrated to predict the outcome
of fish exposed to the chemical?
In this particular example, it is understood that fish may be exposed to 3
ppb without negative effects; but adverse effects do occur in bluegill exposed,
short-term, to 100 ppb. A risk assessor might express no concern for fish at an
exposure level of 3 ppb since it is significantly
below the 100 ppb threshold for injury. But risk characterization often is not that simple.
For example, the risk assessor may need to consider whether prolonged exposure of
the fish, at a level of 3 ppb, might trigger
adverse effects; whether another life stage (e.g.,
embryo) might be more vulnerable than the adult;
and whether another fish species might be more
sensitive than bluegill. Another consideration is that
organisms (predators) higher in the food chain might be at risk if
the pesticide accumulates in fish on which they prey.
Ecological risk assessment is a process whereby
toxicity (effects data) and exposure estimates (environmental
concentrations) are evaluated for the likelihood that the intended use of
a pesticide will adversely affect terrestrial and aquatic
wildlife, plants, and other organisms. Data required to conduct
an ecological risk assessment include the following:
Toxicity to wildlife, aquatic organisms, plants, and
nontarget insects
Environmental fate
Environmental transport
Estimated environmental concentrations
Where and how the pesticide will be used
What animals and plants will be exposed
Climatologic, meterologic, and soil information
Assessing and characterizing risk to ecological
systems, including a myriad of nontarget aquatic and terrestrial
organisms as well as surface and ground water, is a much younger
and more complex science than that of human health risk
consideration. Ecological risk assessment considers a greater range
of complex issues and covers more species than does
human health risk assessment: fish, aquatic invertebrates, aquatic
and terrestrial plants, nontarget insects, birds, wild
mammals, reptiles, and amphibians.
Each species within an ecosystem fulfills specific
ecological roles. Plants are the primary producers of chemical energy
in any terrestrial or aquatic ecosystem. They capture sunlight
and convert it to energize new plant growth, forming the bottom
of the food chain. Energy flows through the food chain
when organisms consume plant tissues and are, in turn,
consumed. For instance, green algae are one-celled microscopic
organisms that are a staple food item for invertebrates such as water
fleas and mysid shrimp; these invertebrates, in turn, become food
for young fish and small fish species. The fish are then
consumed by predators such as larger fish, amphibians, birds, and
aquatic mammals. Because of the dynamics of the flow of
energy, perturbations of the most seemingly minor species may lead
to observable (measurable) impact on the entire
ecosystem. However, because of the ability of organisms and populations
to adapt to perturbationsthat is, because they are
resilienteffects on one or more components of an ecosystem may
result in minimal ecological change.
Adverse environmental effects at various levels may
involve more than energy flow. For instance, adult mussels are
nearly sedentary at the bottom of moderately flowing streams, but
they filter algae and other small organisms from the water.
Young mussels must attach to the gills or fins of certain fish, where
they remain as harmless parasites (for weeks or months) until
their internal organs develop; then they drop from their host into
the stream bank substrate. Without the host species, some
mussel populations cannot survive.
Toxicity testing identifies concentrations that, when
administered to surrogate animals, result in a measurable
adverse biological response. These measured concentrations
and associated toxicity end points basically describe
what the chemical does to the environmentin this case, a single
living organism.
Testing for Adverse Effects
on Wildlife
Specific terrestrial and aquatic tests are mandated by
federal law and described in the Code of Federal Regulations, 40
CFR Part 158. Subpart E of Part 158, Terrestrial and Aquatic
Nontarget Organisms Data Requirements, clearly describes the
tests required for registration of a pesticide. Some tests are
not required for every pesticide product, but are listed in the
regulations as conditionally required. Conditionally required tests
are not mandated unless the use pattern or information
generated from required tests indicates a need for additional testing.
For instance, early life stage fish tests or invertebrate life cycle
tests are conditionally required for most pesticide products.
These tests become mandatory when scientific data indicate that
the pesticide is relatively stable in the aquatic environment and
that concentrations at or below one part per million produce
significant acute mortality.
The technical grade of an active ingredient normally is
the substance used in pesticide screening tests. Federal
regulations specify the conditions under which the end use product
(the formulation) must be tested. In all cases, effects observed
and measurements recorded for animals and plants exposed
to pesticides must be compared to control species (fish,
invertebrates, birds, plants, or animals) held under identical
conditions but not exposed to the chemical.
Testing surrogate species allows scientists to
observe adverse effects that may result from short-term (acute) and
long-term (chronic) exposure. Exposure for short periods at
high concentrations is used to determine concentration levels
necessary to produce mortalitylethal dosesas well as
sublethal effects on one stage of an organism (e.g., juvenile or
adult). These tests, for example, address immediate consequences
to fish and wildlife exposed to concentrations of the pesticide.
The more complex chronic tests are used to examine,
in detail, how the pesticide will impact various stages of
an animal's life cycle (e.g., bird embryo development). As
noted previously, chronic data are required when acute tests
indicate
that the toxicity of the pesticide exceeds a trigger limit and
when the environmental fate or use of the pesticide indicates
that nontarget organisms may be impacted. The data from
chronic tests are essential to accurate prediction of long-term effects
on fish and wildlife.
Potential Impacts Modeled
by Indicator Species
Surrogate organisms used in toxicological testing are
selected to represent various trophic levels within an
ecosystem. For instance, adverse effect data on bobwhite quail exposed to
a pesticide are used to generalize how that pesticide
might adversely affect all upland game birds.
Daphnia (the water flea) models freshwater crustaceans, and the Eastern oyster
models freshwater and marine mollusks. An assumption key to
ecological risk assessment is that data on surrogate species
adequately describe how a pesticide will impact the broader spectrum
of plants and animals.
A Tiered Approach to Testing
Toxic levels of a pesticide and descriptions of
potential adverse effects are developed using a tiered
(sequential) approach. Tier 1 studies, the most fundamental, are
primarily acute laboratory studies that examine concentrations
necessary to cause mortality or acute sublethal effects. Tier 2
involves longer-term, reproduction and life-cycle studies that
provide more complex data on the pesticide's impact on the entire
life cycle of the test animal. Tier 3 studies examine the impact of
a pesticide on animals in simulated environmental or actual
field conditions.
Testing for Adverse Effects
on Avian Species
There are three major laboratory tests for avian effects:
Acute oral LD50
Acute dietary LC50
Reproduction
In both acute oral and acute dietary studies, the primary
route of exposure is through ingestion; either the pesticide is
introduced directly into the subjects' crops (acute oral exposure), or
it is incorporated into their diet (acute dietary exposure).
Examples: Acute oral exposure occurs when a bird ingests a
large single dose. Acute dietary exposure may result from ingestion
of pesticide residues on food items.
The acute avian oral LD50 test assesses the effect of a
single, oral dose of a pesticide administered to bobwhite quail
or mallard ducks. Birds that survive a dose are observed for
two weeks for subsequent mortality and sublethal effects such
as wing droop, disorientation, abnormal behavior, and reduced
food consumption. The test yields the
LD50 level and the NOEC. The
LD50 level represents the dose which can be expected to kill
50 percent of the test population; and the NOEC reflects
the maximum dose that produces no observed effect on the
test population.
Deriving the acute avian dietary
LC50 involves feeding bobwhite quail and mallard ducks a pesticide-treated diet for
five days. A three-day observation period follows, during which
the
Bobwhites from a one-generation reproduction study conducted to
assess pesticidal effects on reproductive success.
birds are fed a control diet; abnormal behavior and
food consumption are recorded. In addition to the
LC50 (lethal concentration of pesticide in the
diet, in ppb), the process yields the NOEC values for the
pesticide being tested.
Avian reproduction testing involves feeding birds a
pesticide-treated diet for ten weeks prior to egg laying and throughout
the laying season. Data generated from the reproduction
study include the number of eggs laid, the number of
normal hatchlings, the number of survivors at 14 days after hatch,
and eggshell thickness. The NOEC for any of these end points
can be used in risk assessment.
In addition to the three major tests, simulated
and actual field tests are conditional, i.e., they may be required by EPA on
a case-by-case basis.
Young bobwhite, approximately seven days old, from a reproduction
study monitored for effects on survival and growth.
A simulated field test might include placing mallards,
bobwhite quail, or geese in outdoor cages, under circumstances
that mock exposure in the wild, and exposing them to the pesticide
at a rate and frequency prescribed by the pesticide label.
An actual field study might involve a pesticide application
to an orchard, after which various data are recorded. Besides
the
Canada geese on turf plot. Studies are conducted to measure avoidance
of treated turf. Birds are monitored to determine amount of time spent in
the treated and untreated halves of the test plot.
number of dead and dying birds
observed, additional data might be gathered,
including survival of dependent young, residues on wildlife food sources,
and residues in animal tissues (as evidenced by autopsy and
tissue sampling).
Testing for Adverse Effects on Freshwater and Estuarine/Marine Fish
A single concentration of the test pesticide is added to the water in an aquarium, and soon thereafter the fish are placed in the water.
Acute LC50 tests most often employ rainbow trout and bluegill sunfish (tested separately) that are actively feeding but have yet to spawn. Fish are exposed to vari-ous concentrations of the pesticide to determine the dose-mortality response and, as well, the sublethal responses over 96 hours (4 days).
The results generated from acute LC50 tests include the 96-hour LC50 and the NOEC. A number of behavioral changes and pathological observations also are recorded, such as erratic movement and swimming at the surface. Gross pathological observations could include protrusion of the eyeball, sloughing of skin, and increased skin pigmentation.
The early life stage test examines how a pesticide will impact the embryonic and larval stages of fish. Data generated by early life stage tests include
number of embryos hatched,
amount of time embryos require to hatch,
embryo mortality,
larval weight, and
larval length.
The NOEC for these parameters is determined by
comparing treatment groups with controls.
Fish life cycle studies use fathead minnows to
represent freshwater fish species and sheepshead minnows as
surrogates for estuarine fish species. The time needed to complete a
fish life cycle study is 260 to 300 days. Fish are exposed to a
pesticide
from one stage of their life cycle to the same stage in the
subsequent generation (egg to egg). Fish embryos are placed into
water containing a known pesticide concentration, and observations
are made from the egg stage through spawning. The eggs laid by the
first generation and the larvae that emerge are followed for an
additional 28 days. NOEC determination is based on control response
and treatment response.
Fish bioaccumulation studies begin with fish exposed to a
known pesticide concentration in water. During specific time periods, fish
are sacrificed to determine the pesticide
concentration in their tissues. Fish are separated into
filet samples (edible portion) and samples with all other parts
combined [visceral (inedible) portion]. Bioconcentration studies
are conducted until concentrations identified in fish tissues
remain fairly level for at least 28 days. The fish are then placed in
clean water and the time required for residues to be removed
from their tissues determined. This provides information
regarding potential food chain effects.
Testing for Adverse Effects
on Freshwater Aquatic Invertebrates
Two primary tests are included in assessment
of pesticidal effects on invertebrate species: acute
EC50, and aquatic invertebrate life
cycle. Daphnia (fresh-water crustaceans in which females can
self-fertilize) are typically used in both studies.
Invertebrate acute EC50
tests provide information on how newly hatched daphnids respond to a
pesticide over a 48- or 96-hour exposure period. The objective is
to estimate the concentration of pesticide that will
immobilize the daphnid. Immobilization is measured by gently shaking
a vessel containing daphnids lying on the bottom. Those that
swim for less than 15 seconds are considered immobile. The
concentration calculated to immobilize 50 percent of the daphnids
is considered the EC50.
Testing for Adverse Effects
on Estuarine and Marine Organisms
The acute toxicity test is the primary study used to
address the toxicity of pesticides to estuarine organisms. A
crustacean (mysid shrimp), an estuarine/marine fish (sheepshead
minnow), and a marine mollusk (Eastern oyster) are used to
evaluate pesticides. Sheepshead minnows and mysid shrimp are
placed into separate aquariums containing specific concentrations
of the pesticide for 96 hours. The mortality data generated is
used to calculate the LC50 and/or the
EC50 .
Typically, one end pointthe pesticide concentration
that inhibits shell growth by 50 percentis sought to estimate
the impact of a pesticide on mollusk species. The shell growth
of young Eastern oysters is assessed by placing them in a series
of pesticide concentrations in water for 96 hours each. The
concentration that inhibits shell growth by 50 percent is
calculated. Such a study is regarded as an indirect measure of the impact
of the pesticide on the nutritional status of the animal. A
mollusk that closes its shell in the presence of a pesticide cannot
feed; thus, shell growth is severely limited.
Testing for Adverse Effects
on Mammals
Testing on wild mammals normally is not required. Data
from testing for human health risks (using rats, mice, dogs,
and rabbits) typically are used to predict toxicity to wild mammals.
A situation where wild mammal toxicity testing may be required
is when a highly toxic rodenticide or predacide is used as a
broadcast bait; minks often are used as test subjects to determine
the potential for secondary toxicity (toxic effects in predators
that have consumed poisoned animals).
Testing for Adverse Effects
on Nontarget Insect Pollinators
The honeybee (Apis mellifera) is used as the principal
insect pollinator. Tests used to measure effects of a pesticide
on nontarget insect pollinators are the honeybee acute contact
LD50 and the honeybee toxicity of residues on
foliage.
The acute contact
LD50 test requires that honeybees be anesthetized to
facilitate placement of the pesticide directly on
the abdomen or thorax. Afterward, the bees are monitored for 48 or 96 hours; the
LD50 is calculated and expressed in micrograms
(mg) of active ingredient per bee.
The honeybee toxicity of residue on foliage
test determines how honeybees can receive a toxic dose from dislodgeable residues
on foliage. The pesticide is applied to foliage which is then harvested over a number
of days. Harvested foliage is placed into cages containing
worker bees, and the number of bees that die from contact with
the foliage is recorded and compared with controls.
Testing for Adverse Effects
on Plants
Nontarget plants studies. Plants of various species are monitored
for seedling emergence and vegetative vigor.
Nontarget Terrestrial Plant Toxicity
Corn, soybeans, root crops, tomatoes,
cucumbers, lettuce, cabbage, oats, ryegrass, and onions often
are used to test effects on nontarget plants. The soil
is treated or the pesticide applied to the foliage at
the maximum rate allowed by the label, or at a
concentration three times the expected environmental
concentration. Data collected in specific tests include
root length,
percent germination,
percent emergence,
time to emergence,
plant height,
dry plant weight, and
percent of plants exhibiting phytotoxic
(morphologic) changes.
The NOEC is determined for each end point, such
as growth and root length. The most sensitive NOEC
may be used in risk assessment.
Nontarget Aquatic Plant Toxicity
Tier 1
The two aquatic plant species most commonly tested
for nontarget plant toxicity are Selenastrum
capricornutum (a freshwater green alga) and
Lemna gibba (a macrophyte duckweed). Water containing the two species is treated with either
a single dose representing the maximum allowed rate, or
a concentration three times the expected
environmental concentration.
Tier 2
Five aquatic plant species are used for Tier 2 testing:
S. capricornutum, L.
gibba; Anabaena flos-aquae (a
blue-green alga); Skeletonema costatum (a marine diatom); and
Navicula pelliculosa (a freshwater diatom). The focus is on growth
rate data measured either as increases in cells, or as fronds.
Effects are expressed as EC50 (the concentration of pesticide
that reduces cell growth by 50 percent). Follow-up tests determine
if the effects are temporary, permanent, or lethal.
Environmental processes result in transformation,
transfer, and transport of pesticides. And the characterization of
environmental fate assesses what the environment does to the
chemical so that environmental exposurethat is, concentrations
an organism might actually encountercan be estimated.
Knowledge of pesticide environmental fate and transport
characteristics is essential to accurate estimation of the form and amount
of the chemical that wildlife and aquatic organisms might
encounter in the environment. Laboratory and field studies make it
possible to predict how much of a molecule and its metabolites
might reach nontarget organisms.
Understanding how a pesticide can be modified by
the environment also is critical in judging how it will affect its
intended target. For instance, a herbicide may offer great
promise, in the laboratory, in suppressing hard-to-control perennial
weeds found in cantaloupe and tomato fields. But if
environmental factors in the field break down the herbicide before the
weeds can absorb a sufficient dose, weed control is diminished.
Conversely, if the pesticide is somewhat resistant to
environmental breakdown, concerns are raised about the product's
residual action impacting water quality, wildlife, soil, and rotational crops.
Complex Interactions
Must Be Studied
The environment plays a major role in determining
how much pesticide residue remains;
how long it remains;
where it goes, ultimately;
what form it might assume; and
the toxicity of the molecule as it is modified, over time.
How a pesticide reacts within a specific environment (the
site of application) is dependent on its physical and chemical
characteristics as well as environmental properties such as soil
type, landscape position, and weather. Soil properties such as
pH, temperature, moisture, and nutrient concentrations
influence how chemicals are changed in the environment.
Similarly, climatic factors such as temperature and rainfall impact
pesticide persistence and movement.
Site-specific differences such as how a pesticide reacts,
over time (when applied in a Louisiana sugarcane field versus
an Indiana corn field, for example) are critical in estimating
environmental exposure. The circumstances of use and the
uniqueness of each chemical molecule make predicting
environmental exposure across the United States very complex.
How will the pesticide be used?
Application rates and techniques have direct bearing on
how a pesticide enters the environment. Thus, a pesticide applied
at a rate of ounces or less per acre has a lower potential
for exposing fish and wildlife than the same chemical applied at
a rate of pounds per acre.
A pesticide may be so sensitive to sunlight that it
decomposes soon after application. If the same product is
protected from sunlight by incorporation into the soil, however, its
persistence in the environment may be extended.
An incorporated product is less likely to impact wildlife
than one which is left exposed on the soil surface. For instance,
a granular pesticide presents greater exposure potential for
birds than does the same chemical applied as a liquid. Thus,
formulation is considered a critical factor in estimating
environmental exposure.
How will the pesticide be
transformed by the environment?
Research has shown that the environment often
alters pesticide molecules dramatically. The original (parent)
molecule often is modified as it enters and interacts with the
environment. Pesticides often are degraded in water (hydrolysis), by
sunlight (photodegradation), and by soil and aquatic
microorganisms (microbial degradation). Knowledge of transformation rates
and the products and toxicity of transformation is key to
assessing ecological risk.
Chemical properties of pesticides, such as volatility or
water solubility, influence their transfer in the environment. For
instance, the initial distribution of a pesticide in soil and water,
or between soil particles and the air that surrounds them, might
be 90 percent in soil and 10 percent in water. The physical
characteristics of a molecule, in combination with chemical
properties of the environment, influence whether a pesticide
molecule resides mainly in soil, air, or water.
How long will the pesticide persist in
the environment?
A pesticide's continued presence in the
environmentpersistenceis a key factor in predicting potential exposure
of wildlife. Persistence is generally described as a half-life, that
is, the length of time it takes for the disappearance of one half
of the applied pesticide from an environmental
compartment. Biological and chemical processes that degrade or dissipate
the pesticide influence its persistence.
How will the pesticide be
transported from the original application site to
off-site environments?
Pesticides and their metabolites (breakdown products)
move in a number of ways. They can
leach downward into ground water,
attach to soil particles and be washed away in
surface water runoff,
volatilize into the atmosphere, or
drift off-target.
Leaching, runoff, volatilization, and drift often are modeled
to show how pesticides move in the environment. Compounds
that do not readily adsorb to soil particles often have a high
potential for leaching to ground water or entering streams via
surface water runoff. Highly volatile pesticides may escape the
soil environment and dissipate into the atmosphere; when
redeposited later, via rainfall, they may interact with nontarget plants
and animals.
What is the range of pesticide
concentrations expected to come in contact with biological systems?
Knowledge of the application rate and an understanding
of how a pesticide can be transformed, transferred, and
transported within the environment facilitate prediction of the range
of concentrations that will actually interact with other organisms.
Development of expected environmental
concentrations depends on information developed from a host of
environmental fate and residue chemistry studies that describe
transformation, transfer, and transport. The lists of studies on the following
page demonstrate the extensive laboratory and field data
required for estimation of environmental concentrations.
Gambrel's quail with radio transmitter. Studies with free-ranging but
trackable birds, conducted to monitor effects on survival and reproductive performance.
What organisms are expected to be exposed to a pesticide?
Characterization of environmental exposure
requires consideration of the inhabitantswildlife, aquatic
organisms, and nontarget plantsof sites where a pesticide is likely
to occur. An understanding of the natural history
(distribution, abundance, breeding habits, and food sources) of
nontarget species facilitates identification of the predominant route
of exposure.
Environmental Fate Data Requirements
Hydrolysis
Photodegradation in water
Photodegradation in air
Aerobic soil metabolism
Anaerobic soil metabolism
Anaerobic aquatic metabolism
Leaching and adsorption
Laboratory volatility
Field volatility
Field dissipation, terrestrial uses
Field dissipation, aquatic uses
Forestry field dissipation
Confined rotational crop
Field rotational crop
Accumulation in irrigated crop
Accumulation in fish
Accumulation in aquatic nontarget organisms
Residue Chemistry Data Requirements
Chemical identification
Nature of residue in plants
Residue analytical methods, plants/animals
Magnitude of the residue in potable water
Magnitude of the residue in fish
Spray Drift Data Requirements
Droplet size spectrum
Drift field evaluation
Estimated Environmental Concentration: A Key
Environmental End Point
Potentially, all pesticides pose some risk to nontarget
organisms; and environmental concentration estimates are critical
in estimating ecological risk. Data developed on the
environmental fate of a pesticide, along with use information as stated in
the proposed pesticide labeling, are used to generate a value
known as an Estimated Environmental Concentration (EEC). The
EEC is an estimate of how much of a pesticide might reach
nontarget areas, potentially exposing wildlife, bees, worms,
aquatic animals, and plants. EECs generally are predicted for
ground and surface water, soil, and nontarget food items.
The key word in Estimated Environmental
Concentration is estimated. Scientists cannot measure actual concentrations
for every conceivable environmental situation. An actual
concentration measured today most likely would not match
measurements taken sometime earlier or later. Therefore, EECs should not
be viewed as hard or fixed values, but as
estimates based on data availability. Actual concentrations can and do fluctuate
according to numerous variables: time of year, geographic
location, weather patterns, soil conditions, cropping systems, etc.
Mathematical models that simulate the fate of pesticides
in the environment are used for developing EECs. But
initial models based on preliminary data, very early in the
pesticide development and testing processes, leave a window of
uncertainty. This initial lack of specific pesticide
informationthe unknownleads to this uncertainty in determining
accurate EECs. Therefore, the degree of uncertainty is compensated
by very conservative assumptions.
As researchers gain a better understanding of the
molecule through refined laboratory data and in-depth analysisand as
it becomes known what influence factors such as weather
conditions and soil characteristics might haveinput assumptions
are modified and new EECs determined that are less uncertain,
that is, refined.
The challenge in refining the EEC is to provide
greater scientific certainty and improved interpretations of the
available data. In this way, an improved understanding and
approximation of the actual environmental concentration is achieved.
The better the prediction, the better the risk estimate.
Developing Estimated Environmental Concentrations
for Aquatic Organisms
There are four basic tiers used to estimate
environmental exposure concentrations for aquatic systems. Each tier
requires additional data or more refined data analysis than lower
tiers. The higher tiers employ sophisticated models where
principal parameters and site-specific scenarios have been developed.
Aquatic EEC Tier 1: Single Event
EEC Based on a High-Exposure Scenario
The Generic Estimated Environmental
Concentration (GENEEC) model was developed by EPA to determine a
generic EEC for aquatic environments. EECs derived from
GENEEC models reflect the pesticide concentration expected under
worst-case conditions: an application on a highly erosive and
very steep upland slope, with heavy rainfall occurring
immediately after. The watershed model is essentially ten acres of
surface area. It is assumed that the entire area is treated, and that
the treated area has uniformly high slopes so that runoff
drains directly into a six-foot-deep, one-acre pond.
The GENEEC model utilizes environmental fate
parameters identified by laboratory testing protocols, as well as
information obtained from the proposed pesticide labeling. It also
includes fixed soil and weather parameters. The model estimates
pesticide runoff to the pond on the basis of rate and method
of application, water solubility, soil binding (adsorption)
characteristics, and persistence of the pesticide; spray drift is also a factor.
Aquatic EEC Tier 2:
Single Site, Variable Weather
Tier 2 assessments determine EECs based on
geographic areas nationwide and use sites (e.g., corn) in close proximity
to ponds; many input variables are the same as those for
GENEEC models, but additional parameters more descriptive of use
site may be factored, as well. These data are used in more
comprehensive models (PRZM/EXAMS). Conditions typical of
product use sites, including specific soils and weather information
(a distribution of weather, including a one-in-ten-year
high-runoff incidence) are used. Single median values for chemical
characteristics are selected from laboratory-derived environmental
half-lives in the upper ten percent of the statistical
distribution. Contributions from spray drift also are factored into the
estimate. The goal of Tier 2 analysis is to better define the
range of EEC--as compared to the single, worst-case Tier 1
assessment--that can be reasonably expected under variable weather
conditions. Frequently, a case more typical of the intended site is
analyzed, as well, for comparison against the worst case scenario.
Aquatic EEC Tier 3: Multiple Sites,
Multiple Weather Conditions
Tier 3 differs from tiers 1 and 2 in that both use-site
and weather parameters are varied. Tier 3 assessments
examine hypothetical circumstances representative of the regions in
and conditions under which the pesticide is likely to be used. Tier
3 modeling results in development of a distribution of EECs
that might be expected across use markets, recognizing that
both soil properties and weather patterns will vary significantly
by market region and years of use. Tier 3 analysis is used
by pesticide registrants to address environmental exposure
concerns that arise during product reregistration processes.
Aquatic EEC Tier 4:
Watershed Site Assessment
Tier 4 assessments are complex analyses that
investigate how pesticides are likely to interact with a landscape
composed of hundreds of thousands of acres. The landscape has
diverse soils and climates, varied proximities of treated fields to
receiving waters, and randomly distributed bodies of water.
Geographic Information Systems (GISs) are commonly
used at Tier 4. GISs allow graphical evaluation of concurrent
risk factors (within the regions of use) that heighten concerns.
In other words, GISs distinguish high risk versus low risk areas
of use on a regional basis.
Tier 4 procedures sometimes shift from risk
characterization and modeling to actual environmental residue monitoring.
Risk assessment equations and exposure estimates for EECs
are validated by actual measurements in the environment,
called Actual Environmental Concentrations
(AECs). Although sampling provides actual residue data, each set of data is valid
only for the point in time when the corresponding samples are
taken. And each sample yields only a hint as to the scope of
residue incidence. Modeling and monitoring often are combined
within Tier 4 to provide a fuller understanding of the distribution
of exposure occurring within treated watersheds.
Predicting Environmental Concentrations for
Terrestrial Organisms
Terrestrial (unlike aquatic) wildlife are exposed to
pesticides primarily through the plant or animal material that they
consume as food. Other routes of exposure, such as dermal,
inhalation, and ocular, are considered less important and difficult to
measure, and effects are thought to at least resemble those
associated with oral and dietary routes. For birds, the primary route
of exposure is dietary exposure to residues on food items,
although there is a potential to ingest granular pesticides. EECs
are developed for these routes of exposure.
Exposure estimates for wildlife vary according to the
amount of pesticide residue on food items and the actual consumption
of those items. In determining EECs for terrestrial organisms, it
is assumed that residue levels on food items increase as
application rates per acre rise.
Predicting Concentrations
on Food Items
EPA and pesticide manufacturers, in performing Tier 1
risk assessments, use a series of tables that establish guidelines
on how much pesticide residue might be expected on various
types of plants and insects. The original tables were developed
by Fred Hoerger and Gene Kenega and refined by John
Fletcher, James Nellessen, and Thomas Pfleeger.
Predicting the total amount of residue available on
vegetation depends on two variables: application rate and plant type.
Plant types are assigned to a simple plant characterization scheme:
Short rangegrass
Long grass
Broadleaf plants/forage
Fruits
Seeds
A portion of the revised Kenega table (p. 37),
illustrates maximum expected residues per plant species as a function
of application rate. For instance, the table predicts a
maximum EEC of 240 parts per million (ppm) on rangegrass
immediately after a pesticide application at one pound per acre.
EECs also are calculated for birds and mammals
consuming pesticide-treated insects. It is important to note that these
EECs are based on application rates without regard to the
characteristics of the pesticide. When actual residue data are not
available, EECs of 58 and 135 (based on pounds applied per acre) can
be used as estimates of residues on large and small insects.
Models Can Account
for Residue Declines
Residue levels from the Kenaga table can be refined.
First, the most appropriate environmental fate half-life value is
selected. Then degraded residue values are calculated,
considering multiple applications and time intervals between
repeat applications. These values can be used as more realistic
estimates of terrestrial residues. Further refinements can factor
in more specific feeding habits, food sources, body weights,
and ingestion rates for sensitive species likely to inhabit or
infiltrate the treated area.
Food Consumption Patterns Dictate
the Amount of Exposure
Exposure of birds or mammals can be refined by
incorporating weight of the animal, percentage of food consumed
relative to body weight, and amount of pesticide residue on the
food item.
Example: A 100 gram (0.1 kilogam) bird is known to
consume seeds in an amount equivalent to 10 percent of its body
weight each day. The estimated EEC was predicted to be 23 ppm
by using the Kenega table for fruits and seeds, with 1.5 pound
of active ingredient applied per acre. We assume that this
avian species feeds exclusively on the seeds. What is the EEC
(total amount of pesticide per kilogram of seeds consumed daily)?
Granular Product LD50 Per Square Foot
There is a potential for birds and mammals to ingest
pesticide granules. The initial risk assessment of oral exposure
of terrestrial vertebrates to a granular insecticide considers
an estimated number of unincorporated granules per square foot
in relation to the number per square foot that results in 50
percent mortality, that is, LD50. This procedure is based on
application rate,
concentration of the pesticide per granule,
a laboratory-derived LD50, and
body weight of the bird or mammal in question.
The procedure assumes that the bird or mammal will
ingest all of the pesticide available within one square foot
of treated area, and that all granules will be consumed within a
short period of time. The greater the
LD50 per square foot, the greater the presumed risk. If a high level of risk is indicated,
additional research may be conducted to either confirm or refute
the original findings.
Risk characterization is the summarizing step of a
risk assessment. Once all available data on exposure (EEC)
and toxicity are assembled, the overall ecological risk for a
pesticide can be characterized. The exposure and toxicity
characterizations are integrated into a comprehensive, scientifically
defensible description of the potential risk to the environment from
use of the pesticide.
Key components of risk characterization include
calculation of risk quotients,
level-of-concern analysis, and
weight-of-evidence analysis.
Risk characterization should yield clear, concise information
on scientific rationale applied during the assessment process.
Risk Quotients: The Integration
of Toxicity and Exposure
Integrating toxicity and exposure is accomplished by
developing an index called the risk quotient (RQ). This begins with
a conservative Tier 1 assessment that utilizes the highest
EEC and the most sensitive end point to determine the quotient.
An RQ provides general guidance on potential risks posed by
a pesticide. It is derived by dividing the EEC for a
particular environmental compartment (such as water) by a
toxicological end point (such as LC50) for an organism (e.g., fish) subject
to exposure in that compartment.
In other words, an EEC for water may be divided by an
LC50 for fish to determine the risk quotient. An RQ of less than
one indicates an estimated exposure concentration
below the toxicity end point. Risk quotients greater than
a level of concern indicate that exposure may
exceed levels shown in laboratory tests to produce
adverse effects; it may lead to refined estimates of
exposure and effects to gain a better understanding of
the risks which are likely to occur in the environment.
Levels of Concern
Establish Risk Parameters
Levels of Concern (LOCs) are trigger ratios used by
regulatory authorities for comparison against calculated RQs.
LOCs incorporate (into risk assessment) uncertainties due to
possible exposure of sensitive populations and estimated
environmental concentrations. It has long been recognized that the number
of organisms used to examine adverse effects is limited;
thus, there remains the possibility that untested organisms in
the same environment may be more sensitive to a particular
pesticide than those tested. EPA established LOC trigger values
to ensure adequate protection for more-sensitive, untested,
and/or endangered species.
There are two general categories of LOCs (acute
and chronic) for each of the nontarget fauna groups; and there is
one category (acute) for each nontarget floral group. To determine
if an LOC has been exceeded, a risk quotient must be
determined and compared to trigger values. The following table provides
risk quotients and LOCs.
LOCs are regulatory triggers used to categorize whether
the potential risk is of low, medium, or high concern. For instance,
a risk quotient less than 0.5 developed for an avian acute
response is of minimal concern to nonendangered species, while
a quotient of 0.5 or greater suggests potentially higher acute risk.
LOCs differ among biological indicators and types of tests,
as well as between nonendangered and endangered species. If
the risk quotient is categorized as minimal for a chemical where
no LOC is triggered, the use of the pesticide is predicted to cause no adverse
effects when used in accordance with the label; and registration
or reregistration generally is granted. A moderate risk
quotient indicates that applicators should be educated on
use of the pesticide to minimize the likelihood of
adverse environmental effects; pesticides with moderate
RQs usually are granted restricted-use registration.
Registrants of pesticides with risk
quotients that generally exceed the LOC supported
by the weight of evidence face extensive risk mitigation requirements prior to
product registration. Optimally, mitigation
efforts lower potential risk concerns below the LOC, frequently through a refined EEC.
Reduced rates of application and number of applications,
buffer strips, in-furrow application (vs. broadcast), and
ground application (vs. aerial) are examples of measures that
can be taken to minimize fish and wildlife exposure.
The following is an example of the use of toxicological
data and EEC values to calculate a risk quotient; it is based on
an application rate of one pound of active ingredient per acre.
The data and assessment show that the risk quotients
for pesticide A do not exceed LOCs of acute and chronic
exposures for fish and birds; thus, no additional testing or mitigation
is required. For pesticide B, which is more toxic, the risk
quotients are greater than the threshold for presumption of risk for
both acute and chronic exposure. Additional testing, or more
extensive evaluation of the EEC, may be required to demonstrate
a reduced risk; or, risk mitigation measures might be adopted.
This example illustrates how two pesticides with different
toxicological properties but similar application rates can have different
presumptions of risk, based on their toxicity.
Application rates also influence risk assessment. The
toxicological data provided (p. 43), assuming that Pesticide A has
an application rate three times that of Pesticide B, illustrate
that, although Pesticide B is more toxic to fish and birds, its
presumption of risk is similar to less toxic Compound A. In the
second illustration (p. 43) neither pesticide's RQ value exceeds
the triggers for presumption of risk, although pesticide B is
acutely toxic to fish and birds.
Weight of Evidence Analysis
Strengths, limitations, and uncertainties, as well as
magnitude, frequency, and spatial and temporal patterns of
previously identified adverse effects, are discussed. Monitoring
data and reported incidents of wildlife kills are included to
help confirm risk potential. Dissipation and
application characteristics of the pesticidedistance
from application site, duration of effects, and time
of year at which wildlife and aquatic organisms may be most
susceptibleare discussed in terms of likelihood of
the pesticide to affect wildlife and aquatic organisms. Very often,
discussions suggest a number of potential mitigation measures that may be used
to reduce risk while maintaining benefits from continued registration of
the pesticide.
Finally, potential risks of pesticide use are compared to potential
risks from pesticides already used on the same site and, typically, for the
same pests. This helps decision makers to view the overall picture of
potential ecological risk while making registration and reregistration decisions.
The process ends with a summary statement on the likelihood of
adverse effects based on evidence analysis and professional judgment.
Pesticides provide significant benefits to the American
public by controlling pests that invade agricultural crops,
industrial sites, homes, schools, restaurants, and hospitals. Public
health is enhanced when pesticides are targeted against
mosquitoes, ticks, and rodents that carry disease; head lice; fleas;
and allergy-producing cockroaches. Antimicrobial products
disinfect drinking water supplies and reduce hazards from organisms
that cause human diseases such as cholera. The motoring
public and transportation industries benefit when herbicides
eliminate plants that obscure roadway signs and encroach on
rights-of-way. Pesticides are instrumental in protecting native
habitats and indigenous flora from non-native plant species.
Other pesticides protect and preserve homes, museums, and
historic buildings from wood-destroying insects such as termites
and carpenter ants.
But there are risks associated with pesticide use, as well,
and they draw public attention. Obviously, in order to be useful,
most pesticides are toxic to the target pest. It is very
difficult to develop a chemical that will affect
only the targeted pest and carry no potential
to harm nontarget wildlife species. No pesticide is
risk-free, and certainly no pesticide is "safe" in all
situations: All carry the potential to cause adverse effects.
Ecological risk assessment is a process where
scientific information is used to address potential environmental
risks associated with pesticide use. Good regulatory
decisions depend on documented scientific research, an understanding
of the strengths and weaknesses of the specific risk
assessment, and sound professional judgment in drawing conclusions
from compiled data. Risk assessments should clearly identify
pertinent facts and any assumptions deemed necessary to
accurately evaluate the pesticide. If ecological risk assessments
are clear, concise, and thorough, they add a vitally important
dimension to EPA's decision making process. Clarity and openness
in the risk assessment process permit informed debate on
pesticide use; ultimately, the registration of a pesticide must
withstand scientific inquiry, public scrutiny, and legal review.
Paula Adduci, i2i Interactive
Steve Adduci, i2i Interactive
Dan Barber, DowElanco
Val Beasley, University of Illinois
William Benson, The University of Mississippi
Chris Berry, Imagix, Inc.
John Carbone, Rohm and Haas Company
Charles Crawford, United States Geological Survey
Gregory Dahl, North Dakota State University
Rob Dittmer, DuPont Agricultural Products
Sidney Draggan, United States Environmental Protection Agency
David Fischer, Bayer
Joseph Gorsuch, Eastman Kodak Company
Ronald Hellenthal, University of Notre Dame
Paul Hendley, ZENECA Ag Products
Jeffrey Lucas, Purdue University
Jeffrey Martin, United States Geological Survey
Ursula Petersen, Wisconsin Department of Agriculture
Joseph Wisk, American Cyanamid
Reviewed 3/03
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The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the Purdue
University Cooperative Extension Service is implied.
It is the policy of the Purdue University Cooperative Extension Service, David C. Petritz, Director, that all persons shall have
equal opportunity and access to the programs and facilities without regard to race, color, sex, religion, ntional origin, age, marital status,
parental status, sexual orientation, or disability. Purdue University is an Affirmative Action employer.
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