In situ bioassay chamber for assessment of sediment toxicity and bioaccumulation using benthic invertebrates

In this study, we describe the construction of a simple, inexpensive bioass ay chamber for testing sediment toxicity (survival and growth) and bioaccum ulation under field conditions using the midge Chironomus tentans and the o ligochaete Lumbriculus variegatus. The test chamber is comprised of a Lexan (R) or Plexiglass(TM) core tube containing several screened ports to facili tate water exchange. A rubber stopper, equipped with a small plastic holdin g vessel to hold organisms, is secured on top of the test chamber before de ploying the tube. Once the test chamber is pushed into the sediment to a de pth of approximately 20 cm, the bioassay is initiated by releasing the test organisms from the holding chamber into the rest chamber. We evaluated the performance of this in situ bioassay system by conducting 10-d exposures a t two contaminated and two reference sites, and in a transplanted control s ediment. Performance in the field test was compared to parallel 10-d labora tory tests. Survival of C. tentans was 68 and 72% at the two reference site s. Corresponding survival in these sediments in laboratory tests was 96 and 75%. Survival in the transplanted control sediment was 97%. Although signi ficant differences between sediments in the absolute values of survival and growth were observed in both field and laboratory exposures to contaminate d sediments, the relative pattern of response for these endpoints was compa rable between the laboratory and the field. Variability (coefficient of var iation) associated with both survival and growth was generally greater in f ield exposures (20-86%) than in laboratory exposures (5-72%). A portion of this variability seemed to reflect the occurrence of predatory species, bec ause we observed a significant relationship between the number of predatory species and survival of C. tentans. In tests with L. variegatus, survival of worms was 85% in the reference sediment and 40 to 76% in two contaminate d sediments. At all sites, a sufficient tissue mass of worms was collected after 10 d to facilitate assessment of bioaccumulation. The results of this study demonstrate that the proposed in situ bioassay can be used successfu lly to assess toxicity and bioaccumulation in contaminated sediments.