Organophosphate Pesticides 

National Report on Human Exposure to Environmental Chemicals
Centers for Disease Control and Prevention
Atlanta, Georgia
Mar01

(pp.35-40 in report)

General Information

Organophosphate pesticides account for about half of the insecticides used in the United States. Approximately 60 million pounds of organophosphate pesticides are applied to about 60 million acres of U.S. agricultural crops annually; nonagricultural uses account for about 17 million pounds per year.¹ Organophosphate pesticides are active against a broad spectrum of insects and are used on food crops as well as in residential and commercial buildings and on ornamental plants and lawns. Exposure of the general population to these pesticides occurs primarily from ingestion of food products or from residential use.

About 75% of the registered pesticides metabolize to the dialkyl phosphate metabolites. ² This Report provides measurements in urine for the following six urinary metabolites of organophosphate pesticides: 

• Dimethylphosphate (DMP). 
• Dimethylthiophosphate (DMTP). 
• Dimethyldithiophosphate (DMDTP). 
• Diethylphosphate (DEP). 
• Diethylthiophosphate (DEPT). 
• Diethyldithiophosphate (DEDTP).

Table 17 shows the six urinary metabolites and their parent organophosphate pesticides. For example, chlorpyrifos metabolizes to diethylphosphate and diethythiophosphate. Measurement of these metabolites reflects exposure to organophosphate pesticides that has occurred predominantly in the last few days. Note that each of the six urinary metabolites can be produced from the metabolism of more than one organophosphate pesticide. In addition to reflecting exposure to the parent pesticides, the level of the metabolite in a person's urine may also reflect exposure to the metabolite itself if it was present in the person's environment.

The mechanism of toxicity of the organophosphate pesticides is inhibition of acetylcholinesterase, which catalyzes the deacetylation of acetylcholine. Acetylcholine helps transfer nerve impulses between nerve cells or from a nerve cell to other types of cells, such as muscle cells. Inhibition of the enzyme acetylcholinesterase leads to the build-up of acetylcholine, which then overstimulates muscles, causing symptoms such as weakness and sometimes paralysis.

Interpreting Organophosphate Metabolite Levels in the Tables

Urine levels of metabolites of organophosphate pesticides were measured in a subsample of NHANES participants 6 through 59 years of age who were selected to be representative of the U.S. population. As noted above, a particular metabolite may come from multiple parent organophosphate pesticides. Measuring these metabolites at these levels in urine is possible because of advances in analytical chemistry. Finding a measurable amount of one or more metabolites in urine does not mean that the level of the organophosphates causes an adverse health effect. Whether organophosphate pesticides at the levels of metabolites reported here are a cause for health concern is not known; more research is needed.

These data provide physicians with a reference range so that they can determine whether people have been exposed to higher levels of organophosphate pesticides than those experienced in the general population. Tables 18-23 summarize results of these tests. These data will help scientists plan and conduct research about exposure to organophosphate pesticides and health effects.

Table 17. Organophosphate pesticides and their metabolites

Dimethylphosphate (CAS No. 813-78-5)

Table 18. Geometric mean and selected percentiles of dimethylphosphate urine concentrations and creatinine-adjusted levels for the U.S. population aged 6-59 years, National Health and Nutrition Examination Survey, 1999.

Numbers in parentheses are 95% confidence intervals. 
*µg per gram of creatinine in urine. 
**Less than the limit of detection of 0.51 µg/L of urine. 
***Results that were below the limit of detection were not adjusted for creatinine. The lower confidence interval is not defined; the estimate is below the limit of detection.

Dimethylthiophosphate (CAS No. 1112-38-5)

Table 19. Geometric mean and selected percentiles of dimethylthiophosphate urine concentrations and creatinine-adjusted levels for the U.S. population aged 6-59 years, National Health and Nutrition Examination Survey, 1999.

Numbers in parentheses are 95% confidence intervals. 
*µg per gram of creatinine in urine. 
**Less than the limit of detection of 0.18 µg/L in urine. 
***Results that were below the limit of detection were not adjusted for creatinine. The lower end of the confidence interval is not defined; the estimate is below the limit of detection.

Dimethyl dithiophosphate (CAS No. 756-80-9)

Table 20. Geometric mean and selected percentiles of dimethyldithiophosphate urine concentrations and creatinine-adjusted levels for the U.S. population aged 6-59 years, National Health and Nutrition Examination Survey, 1999.

Numbers in parentheses are 95% confidence intervals. 
*µg per gram of creatinine in urine. 
**Less than the limit of detection of 0.08 µg/L in urine.

Diethylphosphate (CAS No. 598-02-7)

Table 21. Geometric mean and selected percentiles of diethylphosphate urine concentrations and creatinine-adjusted levels for the U.S. population aged 6-59 years, National Health and Nutrition Examination Survey, 1999.

Numbers in parentheses are 95% confidence intervals. 
*µg per gram of creatinine in urine. 
**Upper end of confidence interval cannot be reliably estimated.

Diethylthiophosphate (CAS No. 5871-17-0)

Table 22. Geometric mean and selected percentiles of diethylthiophosphate urine concentrations and creatinine-adjusted levels for the U.S. population aged 6-59 years, National Health and Nutrition Examination Survey, 1999.

Numbers in parentheses are 95% confidence intervals. 
*µg per gram of creatinine in urine.

Diethyldithiophosphate (CAS No. 298-06-6)

Table 23. Geometric mean and selected percentiles of diethyldithiophosphate urine concentrations and creatinine-adjusted levels for the U.S. population aged 6-59 years, National Health and Nutrition Examination Survey, 1999.

Numbers in parentheses are 95% confidence intervals. 
*µg per gram of creatinine in urine.

References

1. U.S. Environmental Protection Agency (EPA), Office of Pesticide Programs. Organophosphate pesticides in food: A primer on reassessment of residue limits [Online]. Available: www.epa.gov/pesticides/op/primer.htm  [2001, March 16]

2. U.S. Environmental Protection Agency (EPA), Office of Pesticide Programs. Status summary of the organophosphate review process [Online]. Available: www.epa.gov/pesticides/op/status.htm  [2001, March 16].

source: http://www.cdc.gov/nceh/dls/report/FAQs/default.htm 18sep01