Pesticides in Drinking Water

Traces of pesticides detected in some Wisconsin privately-owned wells occasionally have been at levels high enough to make the water unfit for human use. The state's drinking water is relatively healthy, but this warning of potential deterioration of groundwater quality requires preventive and corrective action by all concerned. The DNR is conducting a groundwater monitoring program to sample a representative portion of private wells and some community wells for pesticides. This program targets water supplies considered most vulnerable to contamination. One segment of the program tests for about 30 different pesticides, and the other segment tests specifically for the pesticide aldicarb. As of mid-1985, the first segment had detected pesticides in about 10% of homes and facilities sampled in 50 counties; about 3 % show concentrations above health advisory levels. Aldicarb testing had revealed traces in about 20% of sampled wells in 21 counties, with about 10% above the advisory levels.Well owners are notified when even small amounts of one or are pesticides are detected. The DNR offers guidance for owners whose wells show levels high enough to warrant obtaining alternate water supplies or beginning treatment of existing supplies. A state well compensation program helps such owners bear related costs. Corrective efforts must also include preventing further contamination, which requires safe and sparing use of pesticides as well as improved storage and handling methods. This brochure addresses frequently asked questions on the causes of pesticides in water supplies, regulation, health effects, and options to remedy this problem. You may also wish to consult the DNR brochure "VOCs in Water Supplies" for information on a related concern.

How do pesticides get into water supplies?

Pesticides not taken up by plants, adsorbed by soils or broken down by sunlight, soil organisms or chemical reactions may ultimately reach groundwater sources of drinking water. This will depend upon the nature of the soil, depth to groundwater, chemical properties of the pesticide, and the amount and timing of precipitation or irrigation in an area. Usually the faster a pesticide moves through the ground, as with sandy soils and heavy rainfall or irrigation, the less filtration or breakdown. Heavier soils, combined with lower moisture levels and warmer temperatures, provide a greater opportunity for pesticides to break down before reaching groundwater.

The amount of a pesticide detected in well samples also relates to the kind of pesticide and the amount originally applied. Contamination problems can result from using high concentrations of water-soluble pesticides for a specific crop in a vulnerable area.

Pesticides are, of course, designed to be toxic for certain insects, animals, plants or fungi. But when used without regard to site characteristics, such as adsorption capacity of the soil ("stickability"), solubility, climatic conditions, and irrigation patterns, a given pesticide can cause greater environmental problems than the damage the pest could cause. Aldicarb is an especially problematic pesticide due to its toxicity, slow breakdown rate, poor soil adsorption capacity and water solubility.

Once in groundwater, pesticides continue to break down, but usually much slower than in surface layers of soil. Groundwater carrying pesticides away from the original point of application can lead to contaminated well samples years later in a different location.

What are patterns of pesticide contamination in Wisconsin?

Generally pesticides are a problem with private rather than community wells because private wells are shallower and often located near areas of pesticide use. This means that some of the pesticides' toxic qualities may still be present when the water is drawn for human use. Parts of central Wisconsin are especially vulnerable because of porous sandy soil and relatively heavy irrigation. Aldicarb has been used extensively in the Central Sands to control insects that attack potatoes.

Pesticide contamination, however, has been found in locations ranging from Waukesha County in the southeast to Barton County in the northwest. Atrazine, a common herbicide widely used to control weeds in corn, is the second most commonly detected pesticide. Most detections are in rural areas, although property where pesticides are stored and handled have also proven vulnerable to contamination. Leaks or spills around storage facilities may be primary causes of this problem.

The aldicarb testing began in 1981, with Union Carbide analyzing samples collected by the DNR. By mid-1985, over 1,000 wells had been sampled. The testing for about 30 other pesticides started in 1983 and is continuing. Wells showing traces of one or more pesticides are resampled for verification and any changes. Anyone suspecting their well is contaminated by pesticides should contact the DNR about the possibility of being sampled. Well owners may also have their wells tested by a private laboratory.

The list below shows pesticides that have been found in Wisconsin water supplies.

What health risks are involved?

State health advisory levels have been established for pesticides found in Wisconsin wells. They are calculated from available toxicological studies. These advisory levels are set to protect exposed populations. Further studies continue to resolve uncertainties. For example, the U.S. Environmental Protection Agency suggests a level of 10 ppb for aldicarb, while the manufacturer Union Carbide maintains 30 ppb is a more accurate figure. Wisconsin continues to use the EPA levels.

Pesticides can be absorbed through the skin and lungs as well as by drinking water. Adverse health effects are not expected from consuming water with pesticides below the health advisory levels. Potential health effects in people consuming pesticides above the health advisory levels depend upon the kind and amount of pesticide, how long the person has been consuming the water, and the person's overall health. Acute pesticide poisoning symptoms may include headaches, dizziness, stomach and intestinal upset, numbness f extremities, spasms, convulsions, and heart attacks; however, no reported acute symptoms have to date been confirmed in Wisconsin as caused by pesticide-contaminated water.

 While the long-term, chronic effects of pesticides in humans are not completely understood, some pesticides are suspected of causing cancer. Additionally, the well sampling program must consider possible additive effects when more than one pesticide is present. Citizens will be informed as new information becomes available on pesticides and human health. Concerned readers should contact local health officials before assuming any specific health problem is related to pesticides in drinking water.

How can pesticide levels be reduced?

It is obviously preferable to keep groundwater free of pesticides, since removing the contamination is difficult. There are, however, both temporary and long-range corrective options for owners of wells with pesticide contamination. Temporary arrangements include using bottle water, connecting to a neighboring well, or using a home water treatment unit. The Wisconsin Department of Workforce Development must approve the make and model of home units. DNR approval is required for installation of the treatment device. Well owners should be wary of high-pressure sales claims for such water treatment systems.

The preferable option is obtaining a natural water supply through reconstruction of the well, construction of a new well, or connection to a community water supply. Where clean groundwater is available, a long-term water supply may be acquired without the continued monitoring and maintenance necessary with treatment units.

Under a new program, owners of contaminated private residential wells may receive well compensation grants. These grants pay 75 % of costs for testing, temporary water supplies, well construction or reconstruction, or water treatment. To be eligible, DNR must advise owners that their water supply poses a health risk. Grant application procedures are available from district DNR offices.

To avoid further pesticide contamination, informed and careful pest control is necessary. Over-application is a possible cause of pesticides in water supplies. Pesticides should not be viewed as the only answer to a pest problem; other methods may be appropriate. Integrated Pest Management (IPM) may include crop rotation, biological control, and soil analysis and conditioning. IPM is augmented by "scouting" for early signs of pests.

Follow label instructions exactly when using pesticides This includes instructions for storage and handling, and disposal of empty containers. If you are aware of a pesticide spill, or note any questionable activity by others involving pesticides, please contact the nearest DNR or Department of Agriculture, Trade and Consumer Protection (DATCP) office. You may use the 24-hour emergency hotline 1-800-943-0003. Demonstrating careful pesticide use for young people and spreading awareness of pesticide concerns to neighbors will also help safeguard our groundwater.

In addition to the well sampling programs, federal and state efforts will continue to provide better storage and handling guidance, assure proper label instructions, and increase knowledge of factors such as well depth and location if groundwater is contaminated by a pesticide. We live in a society accustomed to quick repair or replacement of damaged goods, but our air, soil and water cannot be replaced. Remedying the problem of pesticides in water supplies requires public concern for natural resources and for those who must use them in years to come.

For further information, contact your regional DNR offices or the Bureau of Water Supply, Box 7921, Madison, Wisconsin 53707-7921.