CONCURRENT EXPOSURE ASSESSMENTS OF ATRAZINE AND METOLACHLOR IN THE MAINSTEM, MAJOR TRIBUTARIES AND SMALL STREAMS OF THE CHESAPEAKE BAY WATERSHED: INDICATORS OF ECOLOGICAL RISK

摘要: The goals of this study were to: (1) measure atrazine and metolachlor concentrations during both high low use periods in the Chesapeake Bay's mainstem/major tributaries, smaller tributaries representative small agricultural streams 1995 1996; (2) compare these exposure data with toxicity benchmarks for each herbicide to predict ecological risk (3) in-stream fish community collected provide supportive characterization. Spatially, (<0.10–98 μg/L) (<0.10–68 highest streams, followed by (<0.10–11 μg/L atrazine; <0.10–8.6 metolachlor) lowest concentration mainstem Bay/larger (<0.10–0.22 <0.10–0.24 metolachlor). Temporally, herbicides greatest all three types habitats late spring early summer. Concentrations very or non-detectable sampled from August mid-April. Toxicity 20 based on an No Observed Effect Concentration (NOEC) microcosm/mesocosm studies acute 10th percentile 53 (protection ninety % species) laboratory selected assess annual seasonal risk. Both conservative estimates designed protect trophic group (plants) most sensitive herbicides. Based a comparison two years data, Bay/large agriculturally dominated was generally judged be low. During one 72-h stream rain event 1995, benchmark (20 exceeded part event. However, long-term permanent effects are not expected documented recovery potential (plant communities) reported transient nature pulses. Fish communities at sites receiving healthy Index Biotic Integrity (IBI) developed Maryland's coastal plain.