Detection of pesticides indicates that these chemicals are not being fully broken down or contained within the farm system. An ideal measure would address not simply the occurrence of pesticides, but also the frequency with which they are found over established threshold levels. However, such standards have been developed for only a fraction of the pesticides found in water samples, and not for mixtures of different compounds. Active research is ongoing in this area, and it will be monitored for possible reference in future reports Locations where pesticides are found frequently or at high concentrations , as a means of identifying areas where cropping practices, natural conditions, or other factors result in export of larger quantities of chemicals. In agricultural areas, about 45 percent of the groundwater and more than 80 percent of the streams and fish sampled have detectable amounts of at least one pesticide.
Many samples contain mixtures of pesticides.
About 10 percent of streams in all types of land uses have detectable amounts of 10 or more pesticides. Two currently used herbicides are found in more than half of the streams sampled in agricultural areas. No pesticide was found in more than one-third of ground water samples. The lines indicate that more samples contained one pesticide than had two pesticides, and so on. These graphs show the amounts detectable using current screening methods.