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Technical Overview of Ecological Risk Assessment
Analysis Phase: Ecological Effects Characterization
Contents
The analysis phase examines two major parts of risk, exposure and effects, and their relationship with each other. The process for examining effects is called ecological effects characterization, whereas the process for examining exposure is called exposure characterization. During the analysis phase, risk assessors:
select data that can be used to characterize exposure and ecological effects;
characterize exposure by examining sources of the pesticide(s) or stressors, distribution of the pesticides in the environment, and extent of contact with pesticides;
characterize effects by examining stressor-response relationships, evidence for cause and effect, relationship between measures of effect and assessment endpoints; and
summarize conclusions about exposure and effects.
About Ecological Effects Characterization
An ecological effects characterization describes how toxic a pesticide is to different organisms and/or to other ecological entities (e.g., community), what effects it produces, how the effects relate to the assessment endpoints, and how these effects change with varying levels of pesticide exposure. This characterization is based on a stressor-response profile that describes how toxic a pesticide is to various plants and animals, the cause-and-effect relationships, how fast the organism(s) recovers, relationships between the assessment endpoints and measures of effect, and the uncertainties and assumptions associated with the analysis. The stressor-response profile is the final product of the ecological effects characterization.
EPA estimates the toxicity or hazard of a pesticide by evaluating ecological effects tests that vary from short-term (acute) to long-term (chronic) laboratory studies and may also include field studies. In these tests, animals and plants are exposed to different amounts of pesticides, and their responses to these varying concentrations are measured. The results of these tests may be used to establish a dose-response or cause-and-effect relationship between the amount of pesticide to which the organism is exposed and the effects on the organism.
In most cases, toxicity tests are conducted on an active ingredient basis. If formulated product effects data are available, they will also be considered in the risk assessment. In addition, data on degradates of potential toxicological concern will be incorporated into the risk assessment.
In this testing system, surrogate or substitute organisms are used to represent a group of organisms. For example, the laboratory rat may be used to represent all mammalian species.
Some of the impacts or ecological effects that are measured in ecotoxicity tests include:
mortality,
reduction in growth,
reproductive impairment,
changes in numbers of species,
bioaccumulation of residues in non-target organisms, and
disruption of community and ecosystem-level functions.
For screening-level assessments, the following toxicity endpoints are used to calculate risk:
| Assessment Type | Endpoint |
|---|---|
| Acute assessment | Lowest tested EC50 or LC50 for freshwater fish and invertebrates and estuarine/marine fish and invertebrates from acute toxicity tests |
| Chronic assessment | Lowest NOAEC for freshwater fish and invertebrates and estuarine/marine fish and invertebrates from early life-stage or full life-cycle tests |
Aquatic toxicity endpoints for specific pesticides can be found at the following website: Office of Pesticide Programs' Aquatic Life Benchmarks
| Assessment Type | Endpoint |
|---|---|
| Acute avian assessment | Lowest LD50 (single oral dose) and LC50 (subacute dietary) |
| Chronic avian assessment | Lowest NOAEC for 21-week avian reproduction test |
| Acute mammalian assessment | Lowest LD50 from single oral dose test |
| Chronic mammalian assessment | Lowest NOAEC for two-generation reproduction test |
| Plant Type | Endpoint |
|---|---|
| Terrestrial non-endangered | Lowest EC25 values from both seedling emergence and vegetative vigor for both monocots and dicots |
| Aquatic vascular and algae | Lowest EC50 for both vascular and algae |
| Terrestrial endangered | Lowest EC5 or NOAEC for both seedling emergence and vegetative vigor for both monocots and dicots |
Other toxicity endpoints may be used if professional judgment and lines of evidence determine that they can be linked to assessment endpoints in a reasonable manner. Guidance for using non-definitive endpoints in evaluating risks to animal species (listed and non-listed) can be found at: Guidance for Using Non-Definitive Endpoints in Evaluating Risks to Listed and Non-listed Animal Species.
The toxicological tests for ecological risk assessments are conducted under approved Harmonized Test Guidelines and Good Laboratory Practices Standards.
The results of these tests may be used to determine the need for mitigation measures that will minimize potential harmful effects to non-target organisms.
Ecological Effects Studies
The website, Data Requirements for Pesticide Registration, (Code of Federal Regulations - 40CFR Part 158: Subpart G 158.630 and 158.660) specifies the types and amounts of data that EPA may require to determine the risks of a pesticide to non-target terrestrial and aquatic animals and plants. The types of data needed may vary depending on where and how the pesticide is used. Individual studies that the Agency may require in support of the registration or approval of certain pesticides are listed below. In addition to registrant-submitted data, the Agency may use toxicity endpoints found in publicly available literature for ecological risk assessments. To identify open literature studies that may potentially be incorporated into the Agency's ecological risk assessments, EPA uses the ECOTOXicology (ECOTOX) Database as a search engine. Guidance for evaluating ecological toxicity data in the open literature can be found at: Evaluation Guidelines for Ecological Toxicity Data in the Open Literature.
Terrestrial Animals
Birds
EPA may require the following acute oral, subacute dietary, and chronic tests in birds:
Avian Acute Oral Toxicity test is conducted with either an upland game bird (e.g., bobwhite quail) or a waterfowl species (e.g., mallard duck) and a passerine species (e.g., songbird). It is an acute, single-dose laboratory study that is designed to determine the amount of pesticide that will cause 50% mortality (LD50) in a test population of birds. EPA's test guideline 850.2100 provides guidance on how to conduct avian acute oral toxicity tests. In addition, the agency has developed Guidance for Classifying Studies Conducted Using the OECD Test Guideline 223 (TG223).
Avian Subacute Dietary Toxicity test is conducted with an upland game bird (e.g., bobwhite quail) and a waterfowl species (e.g., mallard duck). It is an acute, eight-day dietary laboratory study designed to determine the amount of pesticide that will cause 50% mortality (LC50) in a test population of birds.
Avian Reproduction test uses both an upland game bird and a waterfowl species. It is a laboratory study (usually 20 weeks) designed to determine the amount of pesticide that will harm the reproductive capabilities of a test population of birds. Reproductive impairment is measured in terms of number of eggs laid per hen, number of cracked eggs, number of viable embryos, live three-week embryos of viable embryos, normal hatchlings of live three-week embryos, number of 14-day-old survivors. This test is used to determine the NOAEC (No Observed Adverse Effects Concentration) or LOAEC (Lowest Observed Adverse Effects Concentration) for the above parameters.
Simulated or Actual Field Testing is conducted either to quantify the actual risks in the field or to show that risks in the field under actual use are different than in the laboratory.
Non-Target Insects
EPA may require testing for effects in insect pollinators, such as honey bees, when the typical end-use product (TEP) is intended for outdoor use and honey bees may be exposed to the pesticide.
Honey Bee Acute Contact Toxicity is an acute, single-dose laboratory study designed to determine the quantity of pesticide that will cause 50% mortality (LD50) in a test population of bees.
Honey Bee Toxicity of Residues on Foliage is a laboratory test designed to determine the length of time over which field-weathered foliar residues (residues on leaves) remain toxic to honey bees.
Field Testing for Pollinators may be required if the above tests indicate adverse effects on insects.
In January 2011, EPA participated in a SETAC Pellston workshop, which was designed to identify test methods for measuring exposure and toxic effects of systemic and non-systemic pesticides to pollinators and to identify a risk assessment process for pollinators. After the workshop was held, EPA developed Interim Guidance on Honey Bee Data Requirements for determining what studies should be considered for measuring potential exposure and effects to pollinator species.
Mammals
Generally, EPA scientists use the following studies to evaluate effects on small mammals:
Mammalian acute test is an acute, single oral dose effects test conducted in laboratory rats and mice. This test measures the amount of pesticide that will produce mortality in 50% of the test animals (LD50).
Mammalian subacute test measures subacute dietary effects in rats and mice, i.e., the amount of pesticide in the diet that will produce mortality in 50% of the test animals (LD50).
Mammalian chronic tests measure reproduction and developmental effects in mice and rats. These tests include a two-generational reproductive study and a short-term teratogenic/developmental study.
Aquatic Animals
EPA may require acute and chronic effects testing in fish and invertebrates. Depending on the use of the pesticide, these tests may be conducted on freshwater and/or estuarine/marine animals. The testing scheme is a tiered one and is based on the use and toxicity of the pesticide active ingredient. Depending on the results of studies conducted at a lower level, testing can progress from basic laboratory tests to applied field tests in the highest level.
Tier I
Freshwater Fish Acute Toxicity test uses both a cold water (i.e., rainbow trout) and warm water (i.e., bluegill) species. It is an acute, 96-hour laboratory study designed to determine the concentration in water required to cause 50% mortality (LC50) in a test population of fish.
Freshwater Acute Invertebrate Toxicity test uses a freshwater invertebrate (Daphnia sp.) in an acute, 48-hour laboratory study to determine the concentration of pesticide in water that causes 50% mortality (LC50) or immobilization in a test population of invertebrates.
Estuarine and Marine Organisms Acute Toxicity test uses marine/estuarine fish, shrimp, and mollusc species and are acute, 48- or 96- hour laboratory studies. They are designed to determine the concentration of pesticide that will cause 50% mortality (LC50), incomplete shell growth (oyster larvae), or reduced shell growth (oyster).
Whole Sediment Acute Toxicity (Freshwater and Saltwater) tests may be conducted when a pesticide is applied directly to water or is expected to enter water in significant amounts. These tests may consist of a one-part test of 10 or 28 days and a three-part test (14 days for each part) for freshwater organisms, and a one-part test of 10-28 days for estuarine/marine organisms. Hyallela azteca and Chironomus dilutus or C. riparius are commonly used in the one-part test, and the endpoints may include survival, growth and emergence. The three-part test consists of a 14-day aqueous exposure with minimal sediment, a 14-day sediment exposure with spiked sediment, and a 14-day interstitial exposure with the compound added to overlying water. Chironomus dilutus is commonly used in the three-part test, and effect levels may include LC50, EC50, and BCF. The acute sediment test for estuarine/marine organisms is usually conducted with amphipods and measures LC50, EC50, NOAEC, and LOAEC.
Bioavailability, Biomagnification Toxicity tests are conducted with aquatic organisms to estimate the potential of a pesticide, under controlled laboratory conditions, to partition to the organisms from respiratory and dermal exposures. These studies provide information on the degree of availability and biomagnification of a pesticide or degradate and the degree to which a pesticide or degradate level can be reversed (depuration) should levels in the surrounding aquatic environment be reduced.
Tier II
Fish Early Life-Stage test is designed to determine the amount of pesticide that will adversely affect the reproductive capabilities of a test population of fish. Impaired reproduction and development in fish are measured in terms of number of embryos hatched, time to hatch, mortality of embryos, time to swim-up, and growth- weight and length.
Fish Life-Cycle test is designed to determine the amount of pesticide that will adversely affect the reproductive capabilities and various life stages of a test population of fish. Impaired reproduction and development are measured in terms of the number of days to complete hatching, number of embryos hatched, number of surviving larvae hatched, number of abnormal fish, length of survivors, weight of survivors, mean length and weight of first- and second- generation juveniles, number of survivors, and number of embryos.
Aquatic Invertebrate Life Cycle test is designed to determine the amount of pesticide that will adversely affect the reproductive capabilities of a test population of aquatic invertebrates. Impaired reproduction and development are measured in terms of survival of the first generation, production of young by the first generation, and length of the first-generation test.
Whole Sediment Chronic Toxicity testing may be conducted when mortality exceeds 20% for any concentration level used in acute sediment testing. The chronic freshwater sediment test is a 65-day test that measures survival, growth rate, reproduction, and behavior in Chironomus dilutus. The estuarine/marine chronic test is a 28-day test that measures percentage of neonates that survive, growth rate, reproduction, and behavior in Leptocheirus plumulosus.
Tier III
Simulated or Actual Field Testing may be conducted to quantify the actual risk in the field or to show that the risk in the field is different from what is observed in the laboratory.
Amphibians and Reptiles
In general, EPA uses bird toxicity data as a surrogate for terrestrial-phase reptiles and amphibians and fish toxicity data as a surrogate for aquatic-phase amphibians.
Non-Target Plants
In general, most pesticides are tested at the Tier I level for potential effects to both terrestrial and aquatic plants. EPA uses plant toxicity data to screen pesticides for their potential to move from the treated field to other crops or non-target plants. Currently only five aquatic plants and ten terrestrial crop plants are tested under EPA's non-target plant toxicity guidelines. The plant testing scheme is tiered, such that a limit concentration may be used in the first level. If the first level tests show effects, then additional tests are conducted at a higher level. In these tests, multiple species of aquatic plants (algae and duckweed) are tested for effects on growth (EC50), and multiple species of herbaceous plants (crop species) are tested for seedling emergence and vegetative vigor (NOAEC and EC25).
EPA scientists use the model TerrPlant, version 1.2.2 to provide screening-level estimates of exposure to terrestrial plants from single pesticide applications. TerrPlant estimates exposure to terrestrial plants in both dry and semi-aquatic areas from runoff and spray drift.
Tier I
Non-Target Area Terrestrial Plant Phytotoxicity is a greenhouse or growth chamber test that consists of two parts: a test for seedling emergence and a test for vegetative vigor. Seedling emergence is a 14-21 day test conducted at one dose level. With this test the % emergence, plant height, plant dry weight, and % visual phytotoxicity of the treated plants are compared with an untreated control. Vegetative vigor is a 14-28 day foliar spray test conducted at one dose level, which compares the plant height, plant dry weight, and % visual phytotoxicity in the treated plants with an untreated control. The tests are usually conducted with crop species, such as corn, soybeans, and a root crop. Seven other species that may be used include tomato, cucumber, lettuce, cabbage, oat, ryegrass, and onion.
Non-Target Area Aquatic Plant Phytotoxicity is a laboratory test that evaluates the acute toxicity of fungicides at the highest application rate to a freshwater green alga (Pseudokirchneria subcapitata) and an aquatic macrophyte (Lemna gibba). For herbicides, five species are usually tested at the highest application rate: Skeletonema costatum, Lemna gibba, Anabaena flos-aquae, Pseudokirchneria subcapitata, and a freshwater diatom, usually Navicula sp.
Tier II
Non-Target Terrestrial Area Plant Phytotoxicity is a greenhouse, growth chamber, or small plot test that consists of two parts: a seedling emergence test and a vegetative vigor test. These tests evaluate the effects of multiple dosage levels on plant growth. This test is used to generate an EC25 and NOAEC for % emergence, plant height, plant dry weight, and % visual phytotoxicity.
Non-Target Aquatic Area Plant Phytotoxicity is a dose- response test that is designed to evaluate the acute toxicity of pesticides to five aquatic species: Pseudokirchneria subcapitata (a freshwater green alga), Lemna gibba (an aquatic macrophyte), Anabaena flos-aquae (a blue-green alga), Skeletonema costatum (a marine diatom), and an unspecified freshwater diatom, usually Navicula Pellicosa. This test is used to generate EC50 and NOAEC values.
Tier III
Non-Target Plant Phytotoxicity Field Studies are terrestrial and aquatic field tests that may be required on a case-by-case basis if terrestrial plants show greater than 25% adverse effects on plant growth and aquatic plants show greater than 50% adverse effects on plant growth. These tests provide critical information on harmful effects to plants during stages of development.
Target Area Phytotoxicity Testing provides data concerning the phytotoxic effects of a pesticide on desirable plants.
On June 27-29, 2001, EPA and the Pest Management Regulatory Agency of Health Canada
, presented a harmonized four-tiered testing design for aquatic and terrestrial plants to the Scientific Advisory Panel. As part of this testing scheme, the two agencies proposed expanding the number of tested plant species to account for the wide variability in plant responses to chemicals. Each tier or level of progression in the testing scheme requires a more refined assessment of hazard and exposure. Presentations and results of this meeting are available at 2001 SAP Meetings.
How OPP Uses Ecotoxicity Data
After reviewing an individual toxicity or ecological effects study for a pesticide, EPA scientists develop a data evaluation record (DER) for the study. A DER summarizes the toxicity to certain species groups that are expected to be exposed to the pesticide. The templates for these DERs can be accessed at Environmental Effects Data Evaluation Record (DER) Templates.
The conclusions from all the individual ecotoxicity DERs are then integrated and summarized in a stressor-response profile, the final product of the ecological effects characterization. The profile presents the suite of effects for various animals and plants and an interpretation of available incidents information and monitoring data. Guidance for using incident data in evaluating animal and plant species (listed and non-listed) can be found at: Guidance for Using Incident Data in Evaluating Listed and Non-listed Species under Registration Review. The Agency compares the stressor-response profile with potential exposure levels to determine the risk of exposure-related effects.
In developing its ecological effects characterization, EPA uses either a five-step or a three-step scale of toxicity categories to classify pesticides based on toxicity data:
Ecotoxicity Categories for Terrestrial and Aquatic Organisms
| Toxicity Category | Avian: Acute Oral Concentration (mg/kg) |
Avian: Dietary Concentration (ppm) |
Aquatic Organisms: Acute Concentration (ppm) |
Wild Mammals: Acute Oral Concentration (mg/kg) |
Non-Target Insects: Acute Concentration (µg/bee) |
|---|---|---|---|---|---|
| very highly toxic | <10 | <50 | <0.1 | <10 | |
| highly toxic | 10-50 | 50-500 | 0.1 - 1 | 10 - 50 | <2 |
| moderately toxic | 51-500 | 501-1000 | >1 - 10 | 51 - 500 | 2 - 11 |
| slightly toxic | 501-2000 | 1001-5000 | >10 - 100 | 501 - 2000 | |
| practically nontoxic | >2000 | >5000 | >100 | >2000 | >11 |
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