Thursday, February 18, 2010

Agricultural Run Off and Nonpoint Source Pollution

National Water Quality Inventory Report to Congress was intended to identify widespread water quality problems of national significance. This has served as a proxy for the quality of the waters of the nation despite a non systematic approach to identifying water quality by the states. Many states target their limited monitoring resources to waters they suspect are impaired and, therefore, assess only a small percentage of their waters. These may not reflect conditions in state waters as a whole and tend to reflect areas of concern in the “water community.” The US-EPA in its report to Congress in 1994 identified agriculture as the leading cause of water quality impairment of rivers and lakes in the United States. Agriculture is also cited as a leading cause of groundwater pollution in the United States. In 1992, forty-nine of fifty states had identified that nitrate was the principal groundwater contaminant, followed closely by the pesticides in the samples taken. The US-EPA (1994) concluded that: "more than 75% of the states reported that agricultural practices posed a significant threat to groundwater quality." The way to reduce impact of these non point source pollution on the environment is to implement what has been called “best management practices.”

Agriculture contributes significantly to water pollution problems in many areas of the United States. Many synthetic pesticides (organic chemicals) behave largely in an unknown fashion in nature; their persistence, transport through food chains, and degradation patterns are often not well-understood. Pesticide runoff is a large contributor of known pollutants to the watershed. In April of 2009 the US EPA issued the Final List of Initial Pesticide Active Ingredients and Pesticide Inert Ingredients to be Screened Under the Federal Food, Drug, and Cosmetic Act as potential endocrine disruptors.

The current generation of herbicides and pesticides were developed with the encouragement of the US EPA. These newer herbicides were encouraged by the US EPA because they are applied at much lower levels, were broken down more quickly in the environment and were less toxic to animals. The new generation of herbicides was based on sulfonylurea and imidazolinone, but unintended consequences have come to light. Now it seems that the degradation products of these new herbicides are far more persistent in the environment that originally believed or hoped. Pesticide runoff may be carrying undesirable nutrients and endocrine disruptors to the waters of the nation and now we should again examine older, natural pest solutions.

Some of the more natural pesticides were introduced in the 19th century, and are based on, pyrethrum which is derived from chrysanthemums, and rotenone which is derived from the roots of tropical vegetables. Others like boric acid (used to kill amongst other pests termite colony invasion inside homes and ant hills) and soap salts are just older and though modesty less effective are believed to be far less toxic. These older, naturally occurring pesticides based on, pyrethrum and rotenone both derived from plants are not as effective, but believed to be safer than the new generation of herbicides developed during last quarter century.

The state of Washington has performed private well testing in various regions of the state over the years. In the 1980’s their sampling program in Yakima, Franklin, and Whatcom Counties, which are strongly agricultural tested 81 wells for 46 pesticides and nitrate contamination. Of the 81 wells tested, 23 tested positive for at least one of the pesticides and seven exceeded drinking water standards. Sixty-one of the wells tested positive for nitrates, at concentrations ranging from .10 to 24.4 mg/L, and 18 exceeded the 10 mg/L standard for drinking water. Additional testing in the 1990’s found ethylene dibromide at 62% of the sites and nitrate plus nitrite-nitrogen in all tested wells though only a few of the wells tested exceeded drinking water standards. None of the wells were tested for endocrine disruptors because at the time even proxy testing was not done for these things. The point is that the agricultural and routine use of pesticides needs to be reexamined in the light of increasing use of groundwater and growing populations. The risks involved with biocides and toxics impacting our water may be large and are uncertain, but could impact current and future generations.

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