Submitted to: Water Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 1996
Publication Date: N/A
Interpretive Summary: Pesticides have been used for many years to control harmful insects and to maintain good crop production. Some pesticides, especially the older, "persistent" pesticides tend to build up in the environment. Since this build up can be harmful it is important to discover where these build ups may occur. It is also important to know how long the newer "current-use" pesticides last in the environment. This paper shows where both new and old pesticides accumulate in agricultural watersheds, how abundant they are and how they affect water resources. This study showed that insecticides were usually higher in fish, but the highest concentrations of metals were found in soil and sediments. This study also demonstrated that contamination of water only occurred during storm runoff and that newer, current use, insecticides were only found seasonally and in extremely low concentrations This information is important to scientists studying pesticide movements in watersheds, and extension service representatives who help farmers choose the right pesticide for their needs.
Technical Abstract: Sampling of major watershed features of Otoucalofa Creek was conducted to study the distribution and concentration of residual and current use insecticides and metals in a mixed cover agricultural watershed. Samples of water, soil, sediment and fishes were taken from Otoucalofa Creek watershed and tested for 23 contaminants, including persistent organochlorine and current-use insecticides, PCB's and metals The greatest concentrations of insecticides were found in fish, but the highest concentrations of metals were found in soil and sediments. Six of seven metals and 11 of 15 insecticides tested were present in fish samples. Arsenic and mercury averaged 0.67 ug/g and 0.31 ug/g, respectively, in soil samples and 0.25 ug/g and 0.03 ug/g in sediment samples, but were in lower concentrations in fish tissue. Relatively high concentrations of zinc were found in soil and sediment. DDT and its metabolites averaged 118 ng/g in fish, averaged only 1.90 ng/g in sediments and were undetectable in soil. Contamination of water was dependent upon storm related discharge and is therefore a transient phenomenon. Water samples taken during normal flow had the lowest concentrations of both metals and insecticides. Storm flow (High Stage) samples had significantly higher concentrations of insecticides and metals than did normal flow. Current use insecticides were only detected seasonally and in extremely low concentrations. Since arsenic is the only persistent contaminant still being applied to agricultural land, concentrations of residual insecticides should steadily decline.