APPENDIX A: PESTICIDES AND HEALTH

	Sorption is the partitioning of chemicals between soil and water phases. Pesticides vary greatly in their affinity for soil particles and their solubility in water. Pesticides can contaminate water supplies by moving with eroded soil particles that they are attached to.
	Degradation occurs when pesticides are broken down into smaller chemical components by sunlight, water, or microbes. Degradation of pesticides into daughter compounds alters their ability to control pests and can change their toxicity characteristics. The microbes that degrade atrazine require air. For that reason, atrazine degrades much more rapidly in unsaturated soil, where air is present, than in water, where air is lacking.
	Leaching occurs when pesticides move through the soil profile. Leaching can allow contaminants to reach groundwater, sources for well water, or it can allow contaminants to move laterally through the soil and then surface in seeps or streams.
	Runoff is the transport of contaminants in solution (dissolved) or suspension (undissolved). Runoff is the most common source of atrazine delivery to lakes and streams.
	Volatilization is the evaporation of pesticides into the air. Volatilization may cause some pesticides to move from the intended crop field to other locations. The discovery of DDT in Antarctica (Cramer, 1973) demonstrates the ability of volatilized persistent chemicals to travel to the most remote parts of the earth.

Pesticide losses depend primarily on the intensity and duration of rainfall, the time between herbicide application and the next runoff event, temperature, sunlight intensity, wind speed and duration, concentration of the pesticide in the soil, chemical properties of the pesticide, tillage practice, soil type, pH, organic matter, and slope. Most studies show that runoff losses are less than five percent of the amount applied, with the greatest losses (up to seven percent) occurring when intense rainfall occurred immediately after application (Johnson, et al., 1996).

Human Risk Assessment

EPA's Office of Drinking Water evaluates the health risks from contaminants in drinking water. The EPA has developed standard procedures for evaluating the health hazards associated with ingesting certain chemical contaminants found in drinking water (Whitford et al., 1995, Richards et al., 1995). If direct evidence of human health effects is not available, the evaluation relies upon tests conducted on laboratory animals. These tests and other information lead to the establishment of health advisory levels (HAL's) to aid the public in determining the health significance of chemicals in drinking water. The HAL is the concentration of a particular chemical in drinking water at which adverse health effects would not be expected to occur from a specified length of exposure time. HAL's are derived for exposure times of 1 day, 10 days, 7 years (10 percent of human life-expectancy), and 70 years (human life-expectancy).

To determine HAL'S, the EPA conducts tests on laboratory animals that consume the chemical in question through their drinking water or food. Tbrough these tests, two important dose levels are established. The No Observed Adverse Effect Level (NOAEL) is the maximum daily dose per unit body weight of animal of the chemical tested shown to produce no adverse health symptoms. The Lowest Observed Adverse Effect Level (LOAEL) is lowest daily dose per unit body weight of animal of the chemical tested confirmed to effect animals adversely. Doses are expressed on a body weight basis to facilitate comparisons between lab animals (rats, mice, dogs, rabbits, etc.) and larger species.

Typically, the NOAEL for the most sensitive response in the most sensitive animal is chosen as the basis for calculating the HAL. The NOAEL dose is divided by safety factors to account for the uncertainty in extrapolating from animals to humans and to account for varying sensitivities in the human population. If the LOAEL is used as the basis for calculation, much higher safety factors are used. For chemicals determined to be possible human carcinogens (Cancer Group C), an additional safety factor is applied. The dose calculated by applying all the applicable safety factors is called the reference dose (RfD) and is considered to reflect a dose that is safe for human consumption. The RfD is converted to Drinking Water Equivalent Levels (DWEL's) using assumptions of drinking water consumption and body weight. For the lifetime HAL it is assumed that 20 percent of the RfD comes from drinking water and 80 percent is set aside for exposure from other pathways resulting effectively in an additional 5-fold safety factor.

For atrazine the lifetime HAL is determined in the following way. The NOAEL lifetime dose has been determined by the EPA to be 0.48 mg/kg/day (milligrams of atrazine per kilogram of body weight per day). A 10-fold safety factor is applied to account for uncertainty in extrapolating from animals to humans. An additional 10-fold safety factor is applied to account for varying sensitivities in the human population. Since atrazine is a Class C (possible) Carcinogen, a further 10-fold safety factor is applied. The reference dose (RfD) for atrazine is then:

RfD = (0.48 mg/kg/day) / (10x10x10) = 0.0005 mg/kg/day

For lifetime consumption, only 20 percent of the RfD is assumed to come from drinking water resulting effectively in a further 5-fold safety factor for drinking water. Applying this factor and converting to the DWEL, assuming adults average 70 kg in weight and consume 2 L of drinking water per day, we get the lifetime adult HAL:

HAL = (0.0005 mg/kg/day) / (5X2L/day/70 kg) = 0.003 mg/L

The lifetime adult drinking water HAL for atrazine of 0.003 mg/L is equivalent to 0.003 parts per million (ppm) or 3ug/L which is equivalent to 3 parts per billion (ppb).

Pesticide Regulation

Pesticides are developed, registered with the EPA, and sold to the public with the assumption that users read, understand, and follow instructions found on the product label. Pesticide labels provide clear directions to allow maximum product benefits while minimizing risks to human health and the environment They also carry legal weight. Courts of law and regulators recognize the pesticide label as a legally binding contract which requires the person using the product to do so exactly as directed. Any departure from label requirements constitutes an illegal use of the pesticide (Whitford et al., undated).

The Safe Drinking Water Act (SDWA) was implemented in 1974 to protect public water supplies from contaminants. The SDWA directs the EPA to establish maximum contaminant levels (MCL's) for pesticides and other potential drinking water contaminants. MCL's are legally enforceable standards which may not be exceeded. Public water utilities are required by the SDWA to collect at least four samples per year from the finished water supply for contamination analysis. If the 12-month average contaminant concentration exceeds the MCL, consumer notification is required and utilities must take immediate steps to rectify the problem. The MCL for atrazine is equal to the HAL of 3 ppb.

TABLE A-1
DRINKING WATER STANDARDS AND HEALTH INFORMATION
FOR SELECTED PESTICIDES AS OF MAY 1993