Evaluation of methods to determine causes of sediment toxicity in San Diego Bay, California, USA

Regulation of waterbodies impaired due to sediment toxicity may require development of Total Maximum Daily Load (TMDL) allocations to reduce chemicals of concern. A key step in this process is the identification of chemicals responsible for toxicity, and sediment toxicity identification evaluation procedures (TIEs) are the primary tools used to accomplish this. Several sites in San Diego Bay (CA, USA) are listed as impaired due to sediment toxicity associated with organic chemicals and metals, and due to degraded benthic macroinvertebrate communities. Sediment was collected from one of these sites, at the confluence of Switzer Creek in San Diego Harbor. The sediment was subjected to selected whole-sediment TIE treatments to evaluate the efficacy of these procedures for identifying the causes of toxicity at Switzer Creek. Toxicity was assessed using the estuarine amphipod Eohaustorius estuarius. The results indicated that toxicity of San Diego Bay sediment was likely partly due to mixtures of pyrethroid pesticides. These experiments showed that the effectiveness of the individual TIE procedures varied by treatment. Variability was mainly due to inconsistency between results of samples subjected to various Phase II TIE procedures, including chemical analyses of samples subjected to high-pressure liquid chromatography and direct analyses of acetone extractions of carbonaceous resin. The procedures require further refinement to ensure maximum sorption and complete elution and detection of sorbed chemicals. Despite these inconsistencies, the results indicate the utility of these procedures for identifying chemicals of concern in this system.