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Preliminary Cumulative Risk Assessment for the Organophosphorus Pesticides Questions & Answers

Information provided for informational purposes only

Note: This information is provided for reference purposes only. Although the information provided here was accurate and current when first created, it is now outdated.

EPA has released its preliminary cumulative risk assessment for the organophosphorus pesticides. This assessment is based on evaulation of the potential for people to be exposed to more than one member of this group of pesticides at a time and considers exposures from food, drinking water, and residential sources. The assessment incorporates regional exposures from residential and drinking water sources, as the most appropriate way to account for the considerable variation in potential exposures across the country. EPA has developed an overview of the various aspects of the assessment, as well as detailed regional evaluations. Appendices to the risk assessment provide detailed views of the results.

What is cumulative risk assessment and why is it necessary?

What does this preliminary cumulative risk assessment show about risks from the organophosphorus pesticides?

What is EPA's approach to doing cumulative risk assessment?

How is EPA combining results of the food, water, and residential assessments?

Are all organophosphorus pesticides included in the assessment?

Does the preliminary cumulative assessment include all food uses of the pesticides?

How will EPA use the results of the cumulative risk assessment in making tolerance reassessment decisions?

What data sources is the Agency using for this preliminary assessment?

What are the next steps on cumulative risk assessment?

How can I get more information?


What is cumulative risk assessment and why is it necessary?

A cumulative risk assessment is the process of combining exposure (the amount of a pesticide to which an individual is exposed) and hazard (the health effects a pesticide could cause) from all substances that share a common mechanism of toxicity. The Food Quality Protection Act (FQPA) directs EPA to consider the combined effects to human health that can result from exposure to such pesticides and other substances.

The risk presented by a pesticide depends on the toxicity of the pesticide and the amount of the pesticide to which a person is exposed. It is important to note that a pesticide having low toxicity but the potential for high exposure can present a risk similar to that of a pesticide having high toxicity but very little potential for exposure. Since people can be exposed to several pesticides that act the same way in the body at the same time through various foods, drinking water, and from uses in and around the home, school, or recreational areas, it is also necessary to assess the effects of cumulative exposure.

What does this preliminary cumulative risk assessment show about risks from the organophosphorus pesticides?

EPA considered data about potential sources of exposure from food, drinking water, and residential uses (for example, in-home, lawn and garden, public health uses, and golf courses). The assessment is a preliminary view of the results of a new way of analyzing data about potential exposure to pesticides. The Agency's methods result in measurements of the probability of exposure to more than one organophosphorus pesticide. While we are examining the results of these analyses, it is too soon to draw firm conclusions about risks or consider risk management possibilities. The risk mitigation measures that have already been taken on individual members of this group of pesticides have led to significant reduction in potential risk; EPA will continue to address risks as they are identified for individual organophosphorus pesticides. EPA has confidence in the continued safety of our food supply and emphasizes the importance of eating a varied diet rich in fruits and vegetables. Drinking water does not appear to be a significant contributor to risk. Although most indoor uses of organophophorous pesticides have been eliminated through earlier risk reduction actions, some remaining uses may be of concern.

What is EPA's approach to doing cumulative risk assessment?

EPA's approach to cumulative risk assessment relies on a careful review of the data on toxicity of individual pesticides and information on potential for exposure. The process generally follows the steps laid out here.

Before beginning the cumulative assessment process, EPA generally assesses risks associated with individual pesticides. For each individual pesticide, EPA performs an aggregate risk assessment (considering all combined sources of exposure). In the aggregate assessment, EPA considers exposures to the pesticide from food, drinking water, and residential uses. At this stage, if risks exceed EPA's level of concern, the Agency would take steps to reduce risks associated with the chemical to acceptable levels. EPA's revised guidance on aggregate risk assessment ("General Principles for Performing Aggregate Exposure and Risk Assessment") is available on the web at www.epa.gov/pesticides/trac/science.

Identify Pesticides with a Common Mechanism

EPA identifies pesticides that have a common mechanism of toxicity. Once identified, these pesticides are called a "common mechanism group." Such a group consists of pesticides for which scientifically reliable data demonstrate that the same toxic effect occurs in or at the same organ or tissue by essentially the same sequence of major biochemical events. EPA guidance on the process for identifying whether pesticides have a common mechanism ("Guidance for Identifying Pesticides and Other Substances that Have a Common Mechanism of Toxicity") is available on the web at www.epa.gov/pesticides/trac/science.

Perform a Cumulative Assessment

After establishing the common mechanism group, EPA performs the cumulative risk assessment in four steps:

  1. Hazard Assessment and Characterization-This step identifies the potential health effects that can be caused by a pesticide. For the cumulative assessment, this includes the potential for health effects from exposure to multiple pesticides with a common mechanism of toxicity, including consideration of conditions that will allow the effects to cumulate and whether specific subgroups might have increased sensitivity to the common toxic effect.
  2. Dose-Response Assessment and Characterization-This step determines the relative toxic strength of each pesticide included in the assessment and establishes a dose that is used to estimate the potential combined risk.
  3. Exposure Assessment and Characterization-This step assesses who is potentially exposed, how they might be exposed, and how much of the pesticide people could be exposed to through food, drinking water, and various non-agricultural uses, such as use in and around the home. For the cumulative assessment, EPA will assess the potential for humans to be exposed to multiple members of the common mechanism group at the same time and whether there are regional or subpopulation concerns.
  4. Risk Characterization-This step identifies the the strengths and weaknesses of the analysis, potential sources of risk, and any subpopulations that are at increased risk. It describes the Agency's confidence in the results as well as assumptions used and uncertainties in the analysis.

The first two steps include use of a weight-of-the-evidence approach to determine the harmful effect that occurs through a common mechanism of toxicity and to establish a common measure of toxic potency. A weight-of-the-evidence approach involves reviewing all pertinent data and information, assessing the strengths and weaknesses of the data, and reaching conclusions based on the overall picture provided by the data, rather than based on any one specific study. One way of comparing toxic potency is by selecting one pesticide as the "index" pesticide (generally the one for which the Agency has the best information on effects at a variety of doses) and comparing the other pesticides to it to determine their relative potency (e.g., one might be half as toxic as the index pesticide, while another might be twice as toxic).

Steps 3 and 4 include estimating exposure and risks for the food, drinking water, and residential/non-occupational pathways. EPA combines these exposures using a calendar-based software modeling tool that allows the user to develop exposure estimates for a period of time, such as a day, a week, or a month.

EPA published draft guidance on conducting cumulative risk assessments in June 2000. This guidance has been reviewed by the FIFRA Scientific Advisory Panel. The revised guidance is expected shortly and will be available at www.epa.gov/pesticides/trac/science.

How is EPA combining results of the food, water, and residential assessments?

EPA is undertaking regional risk assessments for potential exposures from drinking water and residential pesticide uses. These regional assessments will allow the Agency to take into account the variation in uses of pesticides across the country, as well as the differences in both sources of drinking water and the potential for presence of pesticide residues in water sources.

The Agency's food risk assessment for the organophosphorus pesticides is based on residues reported in the U.S. Department of Agriculture's Pesticide Data Program. The estimate of food exposure is conducted on a national basis, since most food commodities are available in all areas of the country. EPA will combine this national food assessment with the regional drinking water and residential results.

Are all organophosphorus pesticides included in the assessment?

The currently registered organophosphorus pesticides are included in the preliminary cumulative assessment unless they:

Does the preliminary cumulative assessment include all food uses of the pesticides?

The foods included in the assessment comprise 96% of the diet of children age 3-5, according to the USDA's Continuing Survey of Food Intake by Individuals. The remaining foods are highly processed and are not expected to contribute any significant residues. EPA used data that are available from the U.S. Department of Agriculture's Pesticide Data Program to define the potential amount of pesticides in foods. For foods not included in PDP, EPA "translated" from PDP data. Translation means that crops for which PDP does not contain data are similar enough to crops in PDP that the residue data can be used as a surrogate (e.g., cauliflower is based on data for broccoli).

How will EPA use the results of the cumulative risk assessment in making tolerance reassessment decisions?

FQPA requires EPA to consider the cumulative effects of substances that share a common mechanism of toxicity in making decisions about the safety of pesticide residues in food. The current risk assessment is a preliminary version; it will not be used in making risk management decisions. EPA's tolerance reassessment decisions for the organophosphorus pesticides will take into account the public comment and scientific consultation planned for the next few months. When the risk assessment is revised, EPA will require any unacceptable risks to be reduced to acceptable levels. In the meantime, EPA has already taken significant actions and continues to act on risks associated with individual pesticides, based on the risk assessments for those pesticides.

What data sources is the Agency using for this preliminary assessment?

This preliminary risk assessment is rich in data. EPA has gone to great lengths to obtain data to use in conducting this risk assessment. Each component of the risk assessment uses the best-available data. The sources of data vary for the food, water, and residential components of the risk assessment.

The sources of data for the food component include:

For the water component of the assessment:

For the residential/non-occupational component:

What are the next steps on cumulative risk assessment?

EPA has provided opportunities for public comment on the guidance leading up to this assessment and has conducted technical briefings to explain the methods being used in the assessment. Continuing in this effort to ensure transparency of our decision processes, we are implementing several steps over the next few months following the December 3, 2001 release of the preliminary cumulative risk assessment for the organophosphorus pesticides:

How can I get more information?

The preliminary organophosphorus cumulative risk assessment and summary documents are available on EPA's web site: www.epa.gov/pesticides/cumulative/pra_op_methods. It also is available from the Office of Pesticide Programs docket. Call the docket at 703-305-5805 for information.

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