Empirical assessment of an ambient toxicity risk ranking model's ability to differentiate clean and contaminated sites

Abstract

Abstract-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 1995 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.

Correlation of measures of ambient toxicity and fish community diversity in a Chesapeake Bay Tributary, Maryland, USA: A biological, chemical, and geological assessment

“…Statistical significance in this instance refers to typical sample versus control comparison tests, not a statistical test of the control-corrected response values. 3 Consistency ϭ ((N/2) Ϫ X) (1) where N equals the total number of endpoints and X equals the number of statistically nonsignificant endpoints. Each sample was ranked by the following scheme; percent response for each endpoint was multiplied by its respective coefficient of variation and the endpoint severity.…”

“…Dried samples were hand-ground with an agate mortar and pestle and powdered in a ball mill. Subsamples were transferred to Teflon digestion vessels with trace metal grade HNO 3 and HCl plus ultrapure water. Preparation blanks were made with high-purity water plus the acids.…”

“…A least-squares fit of the data was obtained using a Marquardt-type [20] algorithm. A strong correlation between metal concentrations and size fractions allowed prediction of metal levels at a given site (if the grain size composition is known) by substituting the correlation coefficients for the determined coefficients in Equation 3. Predicted values were then used to determine variations from the regional norm resulting from exposure of older, more metal-depleted sediments or from loadings from anthropogenic or other enriched sources.…”

“…Toxicity studies were coordinated with an independent fish community assessment program in an attempt to determine if quantitative links between the two approaches are possible. Previous studies in the program have demonstrated correlations between measures of ambient toxicity and fish community diversity indices in Chesapeake Bay tributaries [1][2][3]. This paper reports on the third year of field testing of the program, integrating ambient toxicity and fish community metrics.…”