EMPIRICAL ASSESSMENT OF AN AMBIENT TOXICITY RISK RANKING MODEL'S ABILITY TO DIFFERENTIATE CLEAN AND CONTAMINATED SITES

摘要

Ambient toxicity results were used to investigate statistical implications of sampling design options for an existing toxicological risk ranking model. A battery of water column and sediment toxicity bioassays measuring lethal and sublethal endpoints was employed with fish, invertebrates, vascular plants, and bacteria. Bioassays were conducted monthly from July through September l995 with water from three stations in the South River estuary, Maryland, USA, and a reference station. Sediment bioassays were conducted in August with five discrete samples taken from each station. Water column assays indicated low-level contamination at the upstream stations. Sediment bioassays yielded greater toxic responses than water column assays. The toxicological risk ranking model identified a strong toxicity gradient from upstream to downstream in the South River. Toxicological risk scores for the downstream station in the South River were comparable to the reference station. Statistical analyses demonstrated that the risk ranking model does not require field sample replication for tributary-wide assessment. Characterization of an entire estuary does require broad coverage to assess the system as a whole, however. Threshold levels of toxic impact can be quantified with the model.