The State of Water in the US

The Council for Agricultural Science and Technology (CAST), a US science-policy think tank, has produced a paper Pesticides in Surface and Ground Water which provides a succinct overview of pesticide residues in the sources of human drinking water in the US. The report cites areas of the corn belt and the south-eastern coastal plain where intensive use of pesticides has led to the detection of atrazine, aldicarb, DBCP, EBD and dacthal. Until relatively recently, ground water was not widely analysed and it is not generally known how long these pesticides have been present.

Pesticides in excess
The Environmental Protection Agency (EPA) has developed a database on ground water analysis in which 65,865 wells were sampled, between 1971 and 1991. Of these, 14.4% (9,509) had concentrations of one or more pesticides in excess of health standards. Although indicative of problems, the high percentage reflects sampling bias as wells were sought for testing where pesticide leaching occurred. Recent US Geographical Survey results show that surface water, particularly lakes and rivers in the corn belt, contain residues of major pesticides used on corn and soybean. These include atrazine, alachlor and cyanazine which produce high levels in the two to three months in spring/early summer during application.
    It is clear that health standards are sometimes exceeded. Pesticide levels often range from 1 to 10 parts per billion (ppb) and sometime go up to 100 ppb. These may seem minuscule, however, maximum contamination levels (MCLs) [.i.e. lifetime exposure levels] for drinking water are often in the 1 to 1,000 ppb  range, depending on the active ingredient. Some species can show much greater sensitivity as there are insecticides which are toxic to aquatic invertebrates at less than 0.01 ppb.

Wildlife impact widespread
The EPA is also maintaining a database on incidents involving pesticide-related fish and bird kills. It suggests that these incidents are more widespread than was generally thought. Overall knowledge of the true extent of kills is sketchy and little is known about the toxicology and environmental fate of pesticide breakdown products, which may be more widespread than the original active ingredients.

Conclusion
The CAST report says that measures should be taken to minimise or eliminate exposure to pesticides. In effect this means widening safety margins. It was recommended that residues must be identified and fluctuations in concentrations established. “We must be vigilant for early warning signs of damage to ecological systems. We must seriously consider every claim on human illness. Finally, the science of pesticide safety, and the regulatory system based on that science, must continue to advance. Much improvement is needed” the clarion call of CAST concludes.

Pesticides in Surface and Ground Water, Council for Agricultural Science and Technology, Issue Paper No 2, April 1994.

[This article first appeared in Pesticides News No. 24, June 1994, page 15]