Summary of the Revised OP Cumulative Risk Assessment

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 Although the information provided here was accurate and current when first created, it is now outdated.

June 10, 2002

Background

The Food Quality Protection Act (FQPA) directs EPA to consider the effects on human health that can result from exposure to two or more chemicals that act the same way in the body.
EPA designed and conducted a sophisticated and complex cumulative risk assessment for the organophosphate pesticides.
This assessment is based on evaluation 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 Agency's methods result in measurements of the probability of exposure to more than one organophophate pesticide and an assessment of such combined exposure.
The methods used to generate the results have received numerous scientific reviews by the FIFRA Scientific Advisory Panel before completion of the cumulative risk assessment.
In December 2001, EPA released the preliminary assessment for public comment and scientific review. The results of those comment and review processes are incorporated in this revised assessment.
The food assessment is national in scope because food consumption and residues in food generally do not vary significantly across the U.S. or during the year.
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.

Status and Results of the Risk Assessment

EPA has completed and released the revised cumulative risk assessment for the organophosphate pesticides after considering public comment and additional scientific review on the preliminary assessment.
This assessment represents a new way of analyzing data about potential exposure to pesticides. The revised assessment being released for public review incorporates, as appropriate, public comments received on the preliminary assessment as well as advice provided by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) Scientific Advisory Panel (SAP). The major differences between this assessment and the preliminary assessment include:

The revised assessment includes consideration of the Food Quality Protection Act (FQPA) safety factor as it relates to the organophospate pesticide cumulative risk assessment. The available data support differences among the pesticides, which led the Agency to incorporate the safety factor determination into the relative potency factors.

Specific information on dimethoate, omethoate (a metabolite of dimethoate), chlorpyrifos, and methamidophos showed no age-dependent sensitivity, allowing the FQPA safety factor to be removed.

For the pesticides for which such a conclusion could not be reached, EPA retained a 3X FQPA safety factor in calculating the relative potencies of the pesticides.

Any potentially harmful neurodevelopmental effects from exposure to organophosphate pesticides from a mechanism other than cholinesterase inhibition are examined and dealt with in the individual chemical assessments.

The revised assessment includes an analysis of the upper tail of the exposure distribution. This analysis shows that particular high-end consumption and/or residue values are not responsible for the exposure estimates at the higher percentiles of the exposure distribution.
The assessment presents a range of margins of exposure at various percentiles of exposure as well as the percentiles at which the margins of exposure approach 100.
The assessment includes risk estimates for two time periods of exposure: one-day exposures and seven-day exposures. In addition, for one region, the assessment includes ranges of margin of exposure at various percentiles using 14-day and 21-day rolling average exposures.
EPA has calculated relative potency factors for four additional chemicals (chlorethoxyphos, phostebupirim, profenofos, and omethoate, a metabolite of dimethoate).
New data on exposure from the pet uses of tetrachlorvinphos have been used to include tetrachlorvinphos in the residential assessment.
The residential assessment for the indoor uses of DDVP has been revised to account for the size of the pest strip.
Chlorpyrifos methyl has been removed from the assessment to reflect the phase-out agreements with the registrants of those chemicals. Fenamiphos is included in the residential assessment, with use only on golf courses. However, the Agency has concluded a phase-out agreement with the registrant. Other use pattern changes are reflected in the assessment either as the result of corrections or additional risk mitigation actions.
New information provided in the comment period has been incorporated, as appropriate, in the assessment. This includes revisions to processing factors used in the dietary assessment.
The number of regions used in the regional assessment for water and residential exposure has been reduced to seven, based on similarities in climate, soils, and geography.

In the last several years, EPA has taken a variety of regulatory actions on the organophosphates pesticides, ranging from lowering application rates to complete cancellations on specific uses. These actions have substantially reduced the risks and have contributed to the high level of safety found in the cumulative risk assessment.

The revised assessment underscores EPA's continued confidence in the overall safety of the nation's food supply and the benefits of eating a varied diet rich in fruits and vegetables.
The assessment finds that virtually all the tolerances are expected to meet the stringent FQPA safety standard.
This organophosphate cumulative risk assessment presents results showing a range of estimated risks depending on the exposure period considered (one-day or seven-day average) and the percentile of exposure.
EPA is evaluating the appropriateness of consideration of these estimates throughout the full scope of the range.
It appears that one of the major factors influencing the results at the highest portion of the range derives from the fact that not all individual organophospate pesticide risk assessments have not been completed and resulting risk management actions have not been taken. This is particularly true for DDVP and dimethoate. EPA is continuing the scientific and regulatory work to evaluate and address these potential risks.

Pesticide residues in drinking water are not a significant contributor to risk.
Although most indoor uses of organophophorous pesticides have been eliminated through earlier risk reduction actions, some remaining uses have not yet been addressed through the individual chemical assessments.

Developing the Methods

Shortly after enactment of FQPA, EPA began developing new methods and tools that would allow the consideration of combined risks from exposures to several pesticides via several pathways and routes of exposure.
This process included consulting with a wide variety of scientific experts on possible approaches, working with stakeholders to develop improved sources of data, and implementing ways to increase the transparency of EPA's deliberations and decision-making processes.
For example:
- EPA has presented aspects of the methods for this assessment to the FIFRA Scientific Advisory Panel for independent scientific peer review at more than 30 meetings.
- There have been numerous science policy papers related to the cumulative assessment process released for public comment
- EPA has held numerous public technical briefings on the cumulative assessment guidance and the methods for various portions of the cumulative assessment process.

Pesticides and Uses Included in the Assessment

The revised cumulative assessment of potential exposure includes the following 30 pesticides. The letters following the names indicate in which assessment(s) they appear, food (F), water (W), residential (R):

acephate-F,W,R

azinphos-methyl-F,W

bensulide-W,R

chlorethoxyfos-W

chlorpyrifos-F,W

diazinon-F,W

dichlorvos (DDVP)-F,W,R

dicrotophos-W

dimethoate-F,W

disulfoton-F,W,R

ethoprop-F,W

fenamiphos-R*

fenthion-R

malathion-F,W,R

methamidophos-F,W

methidathion-F,W

methyl parathion-F,W

mevinphos-F

naled-W,R

oxydemeton-methyl (ODM)-F,W

phorate-F,W

phosolone-F

phosmet-F,W

phostebupirim-W

pirimiphos methyl-F

profenofos-W

terbufos-F,W

tetrachlorvinphos-R

tribufos-F,W

trichlorfon-R

*Fenamiphos is included in the residential assessment, with use only on golf courses. However, the Agency has concluded a phase-out agreement with the registrant.
The organophospate pesticides that are not included in the food assessment meet one of three criteria:
- They have been voluntarily canceled
- They have only residential or public health uses
- They have no detectable residues in food

Sources of Data

EPA considered data about potential sources of exposure from food, drinking water, and residential uses (for example, in-home, lawn and garden, public-health-related uses, and golf courses).
This risk assessment is rich in data; EPA has gone to great lengths to obtain appropriate data to use in conducting this risk assessment.
Each component of the risk assessment uses the best-available data; data mainly come from surveys of what people eat, their activities such as use of pesticides around the home, and monitoring studies of pesticide residues.
For the food assessment, data sources include:
- U.S. Department of Agriculture's (USDA) Pesticide Data Program
- USDA's Continuing Survey of Food Intake by Individuals
- The Food and Drug Administration (FDA) Center for Food Safety and Applied Nutrition monitoring data
Data sources for the water component of the assessment include:
- USDA Agricultural Chemical Usage Reports for Field Crops, Fruits, and Vegetables
- USDA Typical Planting and Harvesting Dates for Field Crops and Fresh Market and Processing Vegetables
- Local sources for refinements
- Monitoring studies from U.S. Geological Survey and other sources
For the residential assessment, data sources include:
- Information from surveys and task forces, e.g., National Home and Garden Pesticide Use Survey
- Special studies and reports from the published scientific literature, e.g., Non-Scripted Activities of Children Measured Using Fluorescent Tracers (Black, 1993)
- EPA's Exposure Factors Handbook
- Other sources, e.g., State Cooperative Extension Service

Analyzing the Data

In assessing hazard associated with the organophosphate pesticides, EPA analyzed the common mechanism of toxicity-inhibition of cholinesterase.
The Agency chose an index chemical- methamidophos-to use for comparison of degree of cholinesterase inhibition among these pesticides.
EPA's assessment constructs realistic scenarios using all the available data; these scenarios are the basis for analysis of the probability of exposure.
To perform the risk assessment, EPA used a calendar-based program called Calendex^TM to calculate probabilities of exposure from food, water, and residential use.
In developing the water assessment, EPA also used a computer modeling program called PRZM-EXAMS/IR, supplemented by water monitoring data. (The Pesticide Root Zone Model (PRZM) calculates what happens to a pesticide in a farmer's field on a day-to-day basis. It considers factors such as rainfall and how and when the pesticide is applied. EXAMS assesses the fate, exposure, and persistence of pesticides in aquatic ecosystems. The Index Reservoir (IR) is representative of a number of reservoirs in the central Midwest. These models provide a basis for assessing potential of pesticides to contaminate water.)
In assessing the potential exposure from food, EPA determined that the data supported looking at the exposure nationally, since food generally is distributed nationally.
In assessing potential exposure to pesticides in drinking water and from residential uses, the Agency used a geographic approach. People generally obtain drinking water from local sources, and there are different pest issues in different regions, so the use of pesticides varies in different parts of the country, as well as seasonally, requiring a more localized approach.

Next Steps

Continuing in the effort to ensure transparency of its decision processes, EPA is implementing several steps following the June 10, 2002 release of the revised cumulative risk assessment for the organophosphate pesticides:
- EPA opened a 30-day public comment period, which will close July 22, 2002 (EPA will publish a Federal Register notice that will include information on submitting comments).
- On June 18, 2002, EPA held a technical briefing on the assessment.
- On June 26-27, 2002, the FIFRA Scientific Advisory Panel:
  - reviewed the Agency's consideration of the FQPA safety factor as it relates to the organophosphate cumulative risk assessment, including certain science issues including the role of cholinesterase in development, interpretation of animal data and factors underlying age-dependent sensitivity, and relevance of animal data to children and
  - was consulted on the status of results from cumulative risk estimates for the organophosphate pesticides using alternative models (Calendex^™and Lifeline™).
- EPA will evaluate SAP comments as well as other comments or data received and will modify this assessment as appropriate. As existing analyses are revised or new information becomes available, EPA will review this assessment and make further changes as appropriate.

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Summary of the Revised OP Cumulative Risk Assessment

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