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Over the last 10 years a great deal of research effort has concentrated on determining the effects of contaminated sediments on aquatic organisms. For marine systems, this effort has emphasized acute sediment toxicity tests using amphipods, although a variety of other end points and species have been used. Another candidate species for marine, solid-phase, sublethal sediment toxicity testing is the bivalve Mulinia lateralis. Useful attributes of this euryhaline bivalve include a wide geographic distribution (along the North American Atlantic coast from Prince Edward Island to the Gulf of Mexico), easy lab culture, and amenability to toxicity testing applications (end points are mortality and growth [milligrams per organism dry weight]). Detailed in this paper are organism selection and culture, establishment of statistical design, and an estimate of organism mortality and sublethal response variability. Results of Mulinia lateralis toxicity tests with 65 contaminated sediments from eight sites are reported, as well as results of comparative toxicity tests using two amphipod species, Ampeliscu abdita and Eohaustorius estuarius. Analysis of statistical power indicates treatment weight and survival responses that are 25% different from the site control responses can be detected with a probability of 95%. Results of comparative toxicity tests illustrate that although Mulinia iateralis and amphipod acute end points are relatively similar in sensitivity, utilization of the Mulinia lateralis sublethal growth end point greatly increases test sensitivity. This paper describes a new marine sediment toxicity test that complements the existing suite of marine sediment toxicity assessment techniques.

This study tested the influence of system complexity on the environmental assessment of a chemical. Marine microcosms were perturbed with a phthalate ester, di(2-ethylhexyl) phthalate (DEHP). Concentrations of 1, 10, and 100 µg of DEHP per litre were added to the water-column subsystem of marine microcosms for 30 days during the summer (18°C) and winter (1°C) seasons. Significant portions of the DEHP losses from the water-column subsystem during the experiments were due to the complete breakdown of the parent compound to carbon dioxide (CO2). In the benthic subsystem, DEHP concentrations in the sediment were increased by more than 50 and 250 times the concentration in the water column during the winter and summer seasons, respectively. Statistically significant (α = 0.05) reductions in the fluxes of ammonia (NH3) from the benthic subsystem were observed in microcosms receiving 100 µg of DEHP per litre during the summer. Concentrations of DEHP in selected bivalves ranged from 174 to 229 000 µg of DEHP per wet kilogram, depending upon the water column exposure concentrations and the season of the year.