Chesapeake Bay watershed pesticide use declines but toxicity increases

Abstract

Large areas of the Chesapeake Bay, USA, watershed are in agricultural land use, but there is no baywide program to track application rates of current-use pesticides in any of the watershed jurisdictions. Watershed studies demonstrate that several pesticides are present in surface and groundwater throughout the region. Between 1985 and 2004, the Maryland Department of Agriculture conducted surveys to estimate pesticide application within the state. Application rates of the dominant insecticides and herbicides were compiled over the survey period. Toxicity of the pesticides was tabulated, and the toxic units (TU) of applied active ingredients were calculated for several animal and plant species. The total mass of pesticides being applied to the watershed declined during the survey period. Due to increasing potency of the chemicals, however, total TUs applied have remained static or have significantly increased depending on the species of bioassay test organism used to assess toxicity. Applying estimates of pesticide transport into rivers in the Mississippi River basin show that significant quantities of pesticides may be entering Chesapeake Bay. Environ. Toxicol. Chem. 2011; 30:1223–1231. © 2011 SETAC