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Pesticides: Not Just Down on the Farm

by Kristine Bradof

This article originally appeared in the July 1992 issue of the Wellspring newsletter, published by the MTU Regional Groundwater Education in Michigan (GEM) Center, now the Center for Science and Environmental Outreach at Michigan Technological University.

The choice, after all, is ours to make. If, having endured much, we have at last asserted our "right to know," and if, knowing, we have concluded that we are being asked to take senseless and frightening risks, then we should no longer accept the counsel of those who tell us that we must fill our world with poisonous chemicals; we should look about and see what other course is open to us.

Rachel Carson, Silent Spring, 1962

Thirty years after Rachel Carsonís landmark call to action, and twenty years after DDT was banned, what we "know" about pesticides, their behavior in the environment, and their health effects is surprisingly limited. As of 1984, complete health effects data were available for only ten of more than 3,350 active and inert ingredients in pesticides (Stewart, 1990). Most pesticides in use today were registered before 1977, the year toxicity testing was required prior to Environmental Protection Agency (EPA) approval for use; some 600 active ingredients await evaluation and reregistration by the EPA (Stewart, 1990).

The word "pesticide" is associated mainly with farming, but more pesticides are used per acre in metropolitan areas than on farms, according to the National Academy of Sciences (Stewart, 1990). A survey by the U.S. EPA found that 91 percent of American households use pesticides; in 1986, 1.1 billion pounds of pesticides were used for nonagricultural purposes (Rudd and Engelking, 1988). About half of all pesticide use is nonagricultural: in parks, public buildings, hospitals, swimming pools, paper and textile mills; on golf courses; along highways and utility or railroad rights-of-way; and in homes (Stewart, 1990). Even contact lenses, Christmas trees, and hair wigs contain pesticides (Rudd and Engelking, 1988).

Widespread use of pesticides, as well as spills during manufacture, transport, or storage, can contribute to surface water and groundwater pollution. More than 700 synthetic organic compounds, including pesticides, were identified in U.S. drinking water supplies as of 1985 (Trautmann et al., 1985). Even inert ingredients, the carriers of the active compounds in pesticides, are potential contaminants. Of the 1,000-1,200 "inerts" used in pesticides listed by the EPA, 55 are known to be toxic (Stewart, 1990). They include compounds such as benzene, chloroform, formaldehyde, and vinyl chloride. Yet product labels are not required to list inert ingredients.

Factors that affect a pesticideís ability to seep into groundwater include soil characteristics, site conditions, properties of the pesticide itself, and management practices (Trautmann et al., 1989; Stewart, 1990). Fine soils with low permeability (ability to allow water to flow through) and high organic or clay content tend to attract, or adsorb, pesticides, preventing them from reaching groundwater. Sites where groundwater lies far below the surface, where clay layers separate surface deposits from groundwater, or where slope limits infiltration of water are less likely to suffer groundwater contamination (unless the contaminants migrated from elsewhere). Pesticides that are volatile, insoluble in water, readily adsorbed onto soil, and quick to degrade by exposure to sunlight, water, or microbes seldom reach groundwater. Careful application of recommended amounts and types of pesticides, in the absence of rainfall or irrigation, minimizes leaching to groundwater.

When research tells us that more pesticide usage occurs in cities than on farms, we must question the conventional wisdom of blaming only farmers for contamination of water by pesticides. Stewart (1990) and Rudd and Engelking (1988) point out that homeowners are often the only pesticide users not required to be trained to handle chemicals safely. A more-is-better attitude toward lawn and garden chemicals is all too common. Pesticides and fertilizers may be used "just in case" they are needed.

People may assume that if pesticides are registered by the EPA, they must be safe. Yet chronic health effects of low-level pesticide exposure are poorly understood because cause and effect is hard to prove (Hallberg, 1988; Stewart, 1990). As Hallberg notes, "While there are benefits, there are also debits, and the impact of agricultural chemicals on the environment can no longer be overlooked." Other options do exist, such as switching to organic gardening or changing our standards for the perfect lawn. The choice, after all, is still ours to make.

References:

Hallberg, G. R. 1988. When agrichemicals and groundwater meet: Understanding the connection. Journal of Freshwater, vol. 11, pp. 9-11.

Rudd, K. and P. Engelking. 1988. Urban agrichemical use: itís not just the farmerís problem. Journal of Freshwater, vol. 11, pp. 30-32.

Stewart, J.C. 1990. Drinking Water Hazards: How to Know if There Are Toxic Chemicals in Your Water and What to Do if There Are. Envirographics, Hiram, Ohio.
Trautmann, N.M., K.S. Porter, and R.H. Wagenet. 1985. Pesticides: Health effects in drinking water. Cornell Cooperative Extension Groundwater Fact Sheet.. 1989. Pesticides and groundwater: A guide for the pesticide user. Cornell Cooperative Extension Groundwater Fact Sheet.