Health Effects of Pesticides in Your Drinking Water

Jim Bauder, MSU, Jennifer Wintersteen, EPA, and Krista Pearson, MSU

Although most of us unknowingly encounter many toxic substances in our daily lives, in low enough concentrations they do not impair our health. Caffeine, for example, is regularly consumed in coffee, tea, chocolate, and soft drinks. The small amount of caffeine in these product impacts our nervous system acting as a stimulant. Excess amounts, however, can cause anxiety, high blood pressure and severe central nervous system stimulation. Although the amount of caffeine consumed in a normal diet does not cause illness, just 50 times this amount can kill a human. Similarly, oxalic acid found in rhubarb and spinach is harmless in low concentrations found in these foods, but oxalic acid will lead to kidney damage or death at higher doses. Gasoline, carbon monoxide, chlorine, household bleach and cleaners, and alcohol are just a few of the numerous other substances we interact with each day and which can be toxic in high concentrations or due to excessive exposure.

In the agriculture industry, pesticides are one of the most commonly dealt with substances with potential for adverse effects on humans. Health effects of pesticides depend upon their chemical characteristics. Many pesticides today are ‘organophosphorus' compounds. Although some organophosphorus compounds are highly toxic to humans, they generally break down rapidly in the environment and rarely have been found in groundwater. Another group are carbamate pesticides including aldicarb, carbofuran, and oxamyl. These compounds tend to be soluble in water and weakly adsorbed to soil. Consequently, if not degraded in the upper soil layers, they have a tendency to migrate to groundwater. The most significant occurrences of groundwater well contamination have been with carbamate pesticides. Aldicarb - one of the most common carbamate pesticides and one which has been detected in many wells - is used on potatoes. It is used only modestly in Montana.

Now days the agricultural community is constantly being reminded of potentially adverse effects of pesticides and other farm chemicals. Many recommendations are offered to deal with potentially toxic or harmful chemicals. The best approach to dealing with potentially toxic substances is to avoid contact with or exposure to these compounds. Avoidance and use of protective clothing, equipment, and safe practices are activities which can be easily adopted when the situation is known. Protection and prevention are a little more difficult when the problem is unknown or an individual is unaware - as in the possible case of water supplied from wells or springs. Today much attention is being given to water quality in agricultural communities.

Obviously, the first step to protection of human health after adoption of practices which protect the quality of the water supply is to regularly test your water. Results of water testing should serve as the basis for making necessary changes. In addition, safe chemical use and handling practices will help minimize local problems. However, because ground water supplies are "transient," i.e., they are moving, it is possible that a chemical which finds its way to ground water in one location can be detected or measured in a different location, some distance from the original source. Also, testing for pesticides can be very expensive - and sometimes frustrating. Initiating a testing program requires knowledge of the pesticides that could be in the water - rather than just random testing for all or any pesticides. Before undertaking sampling for pesticide testing, it probably is a good idea to contact one of the public service or natural resource protection agencies to determine if pesticide testing of ground water in your locale is currently underway or has been carried out in the past.

When pesticides are found in water supplies, they normally are not present in high enough concentrations to cause acute health effects such as chemical burns, nausea, or convulsions. Acute effects are those which show up soon after exposure and are likely to be relatively severe. Instead, pesticides typically occur in trace levels, and the concern is primarily for their potential for causing chronic health problems. These are the problems that show up due to long-term exposure to relatively low concentrations. An example of a herbicide which poses concern for chronic toxicity is atrazine, primarily a corn herbicide. The main reason this is of such concern is the potential for Atrazine to cause cancer in humans. Atrazine has been detected in many wells in the Midwest.

Evaluating The Potential For Pesticides and Agrichemicals in Well Water and Ground Water

One of the least expensive and most revealing steps a private well water user in an agricultural area can take is to evaluate the potential for pesticide and agrichemical contamination of ground water supplies.


Step 1. Evaluate the proximity of your well to areas of pesticide use. Determine if wells in your area have been sampled and if pesticide contamination was detected. Below is a list of agencies and phone numbers that might be able to advise you about pesticide testing in your area. Determine location of areas where pesticides of concern have been used. Determine general direction of groundwater movement from these areas. Groundwater flow generally follows surface contours, moving from higher areas toward lower discharge areas, such as rivers, lakes, marshes. One mile is considered a protected or safe wellhead zone for minimizing pesticide contamination where pesticides are used on coarse, permeable soils. Determine which pesticides are currently being used or have been used extensively in the past in the area where the recharge for your well water comes from.

Step 2. Evaluate the construction of your well. Check with your local health department about having your well casing inspected for sanitary construction. Contact the well driller for a copy of the well log and construction details. Determine the depth of the well into the water table. (This is approximately equal to the depth of standing water in the well.) Shallow wells, such as those with less than 30 feet of casing or less than 10 feet of standing water in the well pipe have a greater potential for contamination.

Step 3. Test for general quality of your water and the levels of "basic health" indicators. Measure nitrate concentration, total dissolved solids, sodium levels, and pH. High nitrate levels often are found in wells with pesticide contamination, although low nitrate levels do not assure absence of pesticides. The leaching characteristics of nitrate often make it a good "model" for some pesticides. High total dissolved solids levels and high sodium levels usually do not coincide with the presence of pesticides. High pH water generally is characteristic of sites where pesticides will not readily leach to groundwater.

Testing for Pesticides: Where to Send a Sample for Pesticide Testing
Homeowners should understand that testing for pesticides is not an easy task, and it is usually pretty expensive. But, also be aware that public water supplies are required to test for specific contaminants on a regular basis. So, first thing to do is check with your local water supplier for the tests, the parameters, the protocols, and the frequency. Also keep in mind that not many labs routinely test for a broad spectrum of pesticides. A lot of labs will and can test for a particular pesticide, but few labs are equipped to do "general" testing or screening for pesticides. The best thing to do is to start by contacting either your state natural resources protection agency or specific testing labs for protocols and costs.

     Testing for pesticides is difficult because of several factors, those being:

  1. The uncertainty about just what pesticide to test for.
  2. The expense of testing or screening for the entire spectrum of possible pesticides.
  3. The actual expense involved in the testing procedures.
  4. The requirement to insure sample integrity - it's easy to contaminate a sample.

Few labs will take on the challenge of testing for pesticides that they don't know exist in a sample. By the same token, only with a great deal of effort and expense will a lab say ‘we can tell you what pesticides are present.' The general test procedure for any contaminant in a water sample is to know first of all what you are looking for. You then request that the lab test for that specific contaminant. The lab then sets up a test protocol for that contaminant. Each contaminant has a different test protocol.

One lab that offers a comprehensive pesticide ‘scan' is the Water Works Laboratories, which offers a wide range of very comprehensive tests. Also, you might contact your local Extension Agent (a branch of your state university system), the county sanitarian, or the public health department and inquire about pesticide testing. Many public labs do offer some degree of pesticide testing. In Montana, the two state-run labs that would be a good place to start are the Chemistry Analytical Lab, located at Montana State University, and the Montana Department of Public Health and Human Services Environmental Laboratory. Click here for a list of additional labs in Montana and the surrounding area.

Sometimes it may be less costly and more assuring to take the necessary steps to install a water treatment system or option, rather than constantly being concerned about the uncertainty of the quality of your water supply. Individuals with private water supplies have available to them several options for in-home water treatment.

Probably the most effective ‘immediate' solution to a contaminated water supply or one of questionable quality is installation of a POU - Point of Use Treatment, i.e., treating only the water at the tap or just before it is drawn for use. Water treatment can be defined as either mechanical or chemical filtration or disinfection. For these methods to be effective and to effectively treat for common water quality problems, it is necessary to treat first for turbidity, acidity, hardness, and iron. Your local water treatment specialist, public health official, or county Extension agent can help you identify the most effective and efficient POU treatment.

According to Dr. Michael P. Vogel, MSU Housing Specialist (EB102, 1991 "Household drinking water treatment and protection"), three common household drinking water treatments are typically used to treat water contaminated (or suspected of being contaminated) by pesticide and synthetic/volatile organic compounds: granular activated carbon filtration, reverse osmosis, and distillation. Each of these POU treatment methods has a different ability to remove pesticides. Granular activated carbon is rated "best" for removal of organic compounds, while distillation is rated as "best" for removal of inorganic compounds. Reverse osmosis is rated as "good for removal of both organic and inorganic compounds but not complete for either". The trade-off between complete removal by granular activated carbon or distillation and less-than-complete removal by reverse osmosis is the mechanics, cost, installation, and maintenance. Each system has beneficial and less-than-desirable features.

When it comes to water treatment systems, it's best to seek the assistance of a professional. He or she will know which system is most effective, once you've identified the need for treatment, based on repeated testing.