Development and application of a 28-D chronic sublethal sediment bioassay using the estuarine amphipod Leptocheirus plumulosus

The need to develop sediment bioassays arises from the recognition that many sediments in freshwater and marine environments are contaminated to varying levels with inorganic and organic compounds. Bioassays are needed that not only interpret the significance of these contaminant levels via an effects based approach, but can account for differences in chemical bioavailability from site to site and physical and chemical site-specific sediment characteristics. Thus, biological tests protocols are necessary tools that may be employed to help make decisions about: (1) ecosystem and human health protection, (2) dredging and open water disposal of sediments, (3) contaminant source control, and (4) the need for the remediation of contaminated sites.; Based on the need for a test to evaluate chronic sublethal toxicity in estuarine sediments, a 28-day sediment bioassay with the estuarine amphipod Leptocheirus plumulosus (Shoemaker) was developed. The test is initiated with animals less than two weeks old (i.e., 425-600 {dollar}mu{dollar}m sieved size class). Test endpoints include survival, growth ({dollar}mu{dollar}g dry weight/day), and reproduction (number of neonates/surviving female). Factors with the potential to influence test animal performance (i.e., non-treatment factors) such as artificial sea salts, salinity, food ration, size at test initiation, intraspecific density, sediment grain size, and diet were evaluated. For example, intraspecific densities between 10 and 60 animals/beaker (i.e., 0.18 to 1.4 animals/cm{dollar}sp2){dollar} did not effect survival, growth, or reproduction. Similarly, L. plumulosus were tolerant of a wide range of sediment grain sizes with only extremely fine grained (e.g., {dollar}>{dollar}85% clay) or coarse grained (e.g., 100% sand) material significantly affecting survival, growth, and reproduction. Test performance criteria include control survival ({dollar}>{dollar}80%) and reproduction (production of offspring in all control replicates), and response to a reference toxicant test with cadmium chloride in a control chart format.; Traditionally, aquatic bioassays have been used to measure survival of sensitive species following acute exposure to high concentrations of contaminants. Currently, chronic bioassays are being developed to measure sublethal responses (i.e., growth and reproduction) in Leptocheirus plumulosus following 28 day environmental exposures to low-levels of contaminants. Since the exposure of aquatic organisms to low contaminant levels for long periods, more closely approximates field condition.; The purpose of this evaluation was to demonstrate the use of chronic sublethal sediment bioassay with Leptocheirus plumulosus and determine the spatial distribution of toxicity in the Gunpowder River and its tributaries. Two hundred sediment samples were collected covering an approximate 152 square mile area from 34 discreet zones in the Gunpowder River bordering the Aberdeen Proving Grounds, MD-Edgewood Area. Toxicity was determined following 28-d amphipod exposures to field replicated sediments (6 samples/area) in a one-way block design. The endpoints evaluated were survival, growth, and reproduction. Survival ranged from 55 to 92%, growth (mg individual dry weight/day) from 0.42 to 0.89, length (mm) from 5.8 to 7.8, and reproduction (number of neonates/surviving adult) from 0.34 to 2.6. Linear contrast analyses were used to detect toxicity gradients between the tested zones. Principal component analyses were done to show linear correlations between toxicity and sediment chemistry. Covariate analyses were used to evaluate the potential correlations between sediment grain size and toxicity.