From the fields…Pesticide Testing continues
By Jim Morrison
As discussed during private pesticide applicator training sessions, how hazardous a pesticide is relates to its toxicity and exposure. Wearing the appropriate personal protective equipment can minimize an applicators exposure to a pesticide. Toxicity is determined by exposing mammals, such as mice and rats, to a pesticide and observing the toxic effects. The dosages are measured in milligrams of pesticide per kilogram of test animal body weight. This measurement is the same as parts of pesticide per million parts of test animal body weight, or parts per million (ppm).
The ppm methodology allows data obtained by using small mammals to be more meaningful when applied to large mammals such as humans. Determining how likely a person is to be harmed by a pesticide is called risk assessment.
Phil Nixon, University of Illinois Extension specialist, commented on pesticide risk assessment in the recent Illinois Pesticide Review newsletter. The highest dose that will cause adverse effects, but not death, is called the Maximum Tolerated Dose (MTD). The highest pesticide dose that does not cause any observable harm or side effects to experimental animals is called the No Observable Effect Level (NOEL). This NOEL is typically divided by a safety factor of 100 or more to obtain the Reference Dose (RFD). The RFD is the toxicity level normally used in estimating the human toxicity of a pesticide. The RFD is the amount of a pesticide residue that could be ingested daily over a 70-year lifetime without any ill effects.
Nixon further notes that once a pesticide is on the market, the U.S. Environmental Protection Agency continues monitoring health effects from pesticide use to validate the chronic exposure (low-level exposure over a long period of time) studies conducted before the pesticide was registered. The health records of pesticide applicators, as well as those working in pesticide production facilities, are monitored. However, most of the pesticides used today were developed after World War II, with many developed during the last 20 years. Thus, a 70-year lifetime exposure to these pesticides has yet to occur, making complete validation of the risk-assessment model incomplete in some peoples minds.
Nixon concludes that although risk assessment is based on scientific principles, and the uncertainties are protected with safety factors, it is one of the most debated principles of pesticide use.-