What is the relation between pesticide use and pesticide occurrence?
Pesticide use is a major determining factor in pesticide occurrence, particularly in streams. For example, concentrations of atrazine, metolachlor, simazine, acetochlor, 2,4-D, chlorpyrifos, and diazinon in stream samples directly correlate with where they are used on crops. Some of the highest concentrations of atrazine were observed in streams within the Corn Belt and other areas where corn is a primary crop and where the herbicide is most heavily used. The NAWQA study clearly indicates that as pesticide use changes, such as in response to such factors as regulations and market forces, levels of pesticides in water samples change. Findings therefore must be evaluated in context of chemical use, during and after the study. For example, levels of the herbicide alachlor declined in streams in the Corn Belt (generally including Illinois, Indiana, Iowa, Nebraska, and Ohio, as well as parts of adjoining States) throughout the study period as its use on corn and soybeans declined, with no l
