Contamination of ground and surface water with agricultural pesticides is well documented, often at levels harmful to birds, fish, amphibians and aquatic organisms. These chemicals also contaminate drinking water. Herbicides, insecticides and soil fumigants have all been measured in various water sources at levels that are known to have negative impacts on human health.
Pesticide contamination of waterways is widespread. In the agriculturally-intensive Central Valley region of California, more than 635 miles of rivers and streams have been designated “impaired waterbodies” by EPA. The pesticide contamination levels is so high, the water is unsafe for fishing, swimming or drinking. In Midwestern states, the widely used herbicide glyphosate was recently found in 66 of 70 streams sampled by the US Geological Survey (USGS).
The following are just a few specific examples illustrating the significant and pervasive problem of pesticide water contamination.
Atrazine: Water sampling across four Midwestern states in the U.S. in 2012 – Illinois, Nebraska, Iowa and Minnesota – found the endocrine disrupting pesticide atrazine in drinking water sampled from homes and farms in those states.. The results, on average, showed five times the levels of atrazine associated with adverse human health effects, including cancer, birth defects and low birth-weight in babies. Atrazine is also found more often than any other pesticide in groundwater, and nearly all of the drinking water tested by USDA contains the chemical. The herbicide also contaminates water supplies throughout the Midwest at levels above those found to turn male tadpoles into female frogs in laboratory experiments.
1,2,3-trichloropropane (TCP): A known carcinogen, TCP is a by-product of the plastics manufacturing process. Shell Oil and Dow Chemical included it with mixtures of fumigant pesticides applied in agriculture for many years as a way to avoid disposal costs. Most of the TCP contamination found in drinking water today stems from extensive application of pesticides manufactured prior to the 1990s. According to the State Water Resources Control Board, TCP has been found in about a hundred public water systems across California, mostly in agricultural counties in Central Valley.
Chlorpyrifos: The organophosphate insecticide chlorpyrifos has been found in waterways around the globe. In 2013, a New Zealand study found chlorpyrifos in 87% of the streams tested, and the California Department of Pesticide Regulation has reported frequent detections of unacceptable levels of chlorpyrifos in streams and rivers. The chemical has been documented far from where it is applied: residues of chlorpyrifos have been measured in the Arctic and in the air above the Southern Alps. For three consecutive years (2010-2012), chlorpyrifos was found in surface water testing in Minnesota lakes above acceptable levels for aquatic life.
Organized public pressure has, in some cases, prompt steps that protect waterways from pesticide contamination. California officials, for example, took action to force cleanup of TCP by setting a stringent “maximum contamination level” (MCL) for this cancer-causing chemical in the state’s drinking water. Officials in the state of New Jersey announced a similar plan to eradicate TCP from that state’s waterways.
Minnesota enacted “Best Management Practices” in 2013 focused on reducing chlorpyrifos contamination, and several U.S. states and Europe have now implemented full bans of the chemical. Switzerland, home of atrazine’s producer Syngenta, recently pledged to stop exporting the chemical, which has been banned for use on Swiss farms since 2012.
PAN Groundwater Contaminant Rating
The PAN groundwater contaminant rating can be either Known, Potential or Insufficient data.
This ranking is based primarily on data from California, which is the only U.S. state with comprehensive pesticide use reporting data (collected annually since 1991) and significant environmental monitoring. A number of pesticides, primarily herbicides and soil fumigants, have been found repeatedly in California groundwater. These compounds are on a list maintained by the California Department of Pesticide Regulation (DPR) and are labeled as Known groundwater contaminants in Pesticide Info.
Pesticides may also be designated as Known contaminants if they meet DPR’s criteria but were banned from use in California before they were evaluated for their potential to contaminate groundwater. Other pesticides will be designated as Known contaminants if the chemical has been found repeatedly in groundwater in locations other than California, drawing this information from other reliable data sources.
Potential groundwater contaminants are pesticides that meet DPR’s criteria for water solubility, ability to bind to soil, and half life. If the rating is Insufficient data, we do not yet have the data to make an assessment of whether a pesticide is likely to contaminate groundwater.
Compounds classified as PAN Known groundwater contaminants may not be classified by DPR as Known groundwater contaminants for the following reasons:
- The pesticide in question is no longer registered for use in California. This is the case for older pesticides such as dibromochloropropane (DBCP), 1,2-dichloropropane (1,2-D), and ethylene dibromide.
- The pesticide in question is not used in large amounts in California, so has not been detected in groundwater; however, data from other states or countries provides ample evidence of groundwater contamination when substantial amounts of the pesticide are used.
- DPR uses a method of verifying detections of pesticides in groundwater samples that requires “verification” procedures that overlook real-world barriers to sampling (e.g., landowner denied access to well, only single sample collected, etc).
Previous versions of Pesticide Info included a Water & Pesticides Information Center (WaterPIC) tool to explore information about the relationships between reported pesticide use in California and measured surface water concentrations in the environment. This tool was eliminated in the 2020 update of Pesticide Info, and we encourage users to explore the US Geological Survey (USGS) Pesticides and Water Quality information and mapping tools.
California Proposition 65
The Safe Drinking Water and Toxic Enforcement Act of 1986, better known as Proposition 65, was adopted by the voters of California 1986. Proposition 65 requires California EPA’s Office of Environmental Health Hazard Assessment (OEHHA) to develop and regularly update a list of chemicals that are known to cause cancer, birth defects or other reproductive harm.
Prop 65 contains a prohibition on the discharge, above specified risk levels, of listed compounds into any waterway that could be a source of drinking water.
More than 800 chemicals and related compounds are currently on the Proposition 65 list, which is updated annually by OEHHA. Pesticides listed as Prop 65 chemicals are designated as such in Pesticide Info. The absence of a chemical on this list does not necessarily mean it is not toxic. It may mean that it has not yet been evaluated.
Resources
USGS: Pesticides and Water Quality
USGS: Glyphosate Prevalent in US Streams and Rivers
CA Department of Pesticide Regulation: Potential Pesticide Contaminants
Proposition 65 in Plain Language
Toxics on Tap: Pesticides in California Drinking Water Sources
PAN Press Release: Atrazine Found in Water of Dozens of Midwest Communities
PAN GroundTruth Blogs: