Summary

Description

As part of the Chesapeake Bay Agreement, the Maryland Toxics Reduction Strategy for the Chesapeake Bay and its Tributaries committed the State to identify the most extensively used pesticides and to select those to be included in any monitoring program. As a first step toward implementing a monitoring program, this reconnaissance level survey analyzed water from streams throughout the state for seven priority pesticides: atrazine, alachlor, carbofuran, chlorpyrifos, cyanazine, metolachlor, and simazine. Water samples were collected from 21 sites on 12 streams, ranging in size from small drainage ditches between agricultural fields to major rivers such as the Monocacy River. All but one of the seven pesticides were detected. Metolachlor was detected most frequently in 14 of 21 sampling sites, followed by atrazine and cyanazine both occurring in 6 of 21 sites. Chlorpyrifos was detected in only one stream which was surrounded by urban and industrial development. Carbofuran was not detected in any sample, however laboratory tests showed degradation may have occurred during storage. The largest stream sampled, the Monocacy River, contained the highest number of pesticides. Only one stream, excluding control streams, contained no detectable levels of the seven pesticides. Chlorpyrifos was the only pesticide analyzed for with established U.S. Environmental Protection Agency water quality criteria. Levels found in samples from the single stream were at or above acute and chronic criteria levels for the protection of freshwater aquatic organisms. All other pesticides detected were herbicides, and occurred at concentrations several orders of magnitude below those expected to cause toxicity to vertebrates and invertebrates. Atrazine was measured in samples from some streams at levels ranging from below detection to 2.88 ugL. Results of other studies have indicated toxicity to photosynthetic organisms at these levels. Recommendations for future monitoring and further research are provided.