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Technical Overview of Ecological Risk Assessment

Analysis Phase: Ecological Effects Characterization


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:

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:

For screening-level assessments, the following toxicity endpoints are used to calculate risk:

Aquatic Animals Toxicity Endpoints
for screening-level risk assessments
Assessment TypeEndpoint
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

Terrestrial Animals Toxicity Endpoints
for screening-level risk assessments
Assessment TypeEndpoint
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 Toxicity Endpoints
for screening-level risk assessments
Plant TypeEndpoint
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.

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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

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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.

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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.

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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.

On June 27-29, 2001, EPA and the Pest Management Regulatory Agency of Health Canada Exit EPA Disclaimer, 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.

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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

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 10-5050-5000.1 - 110 - 50<2
moderately toxic 51-500501-1000>1 - 1051 - 5002 - 11
slightly toxic 501-20001001-5000>10 - 100501 - 2000 
practically nontoxic >2000>5000>100>2000>11

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