Abstract

  An assessment using sediment quality triad methods (chemistry, toxicity and benthic macroinvertebrates) was conducted to determine the ecological significance of contaminants in the sediments of White Lake (Michigan). The assessment was augmented with 210Pb dating, detailed stratigraphy, and the measurement of organically bound chromium in the sediment to provide additional information related to contaminant flux and toxicity. The historic discharge of tannery wastes resulted in sediments that were highly contaminated with chromium (20,000 mg/kg), arsenic (174 mg/kg) and mercury (3.8 mg/kg). Elevated levels of arsenic and mercury were also measured. Total chromium was analyzed by ICP and organically bound chromium was determined in pyrophosphate extracts. Solid-Phase toxicity evaluations were performed with Hyalella azteca and Chironomus tentans and radiometric measurements were made using a low-background gamma counting.
   Total chromium concentrations at most locations exceeded sediment quality guidelines for probable adverse ecological effects. Statistically significant toxicity to Hyalella azteca was observed only at 40% of the stations. The concentration of organically bound chromium proved to be a better predictor of toxicity than total chromium. A similar trend was noted for the abundance and composition of the infaunal benthos. Total chromium stratigraphy in the effluent discharge region indicated that the top 15-20 cm of sediment were less contaminated (2,000-4,000 mg/kg) than sediment located at >30 cm (>5,000 mg/kg). Radionuclide results suggested that this surface sediment layer (0-20 cm) was well mixed, however, distinct from the deeper more highly contaminated sediments. This pattern demonstrated that mixing and re-suspension continue to be active in the former discharge zone. The recent deposition of chromium contaminated sediments exceeding 500 mg/kg in down gradient locations illustrated that export processes were responsible for the movement of contaminated sediments from the discharge area to main part of the lake.