IN SITU BIOASSAY CHAMBER FOR ASSESSMENT OF SEDIMENT TOXICITY AND BIOACCUMULATION USING BENTHIC INVERTEBRATES

Abstract

In this study, we describe the construction of a simple, inexpensive bioassay chamber for testing sediment toxicity (survival and growth) and bioaccumulation under field conditions using the midge Chironomus tentans and the oligochaete Lumbriculus variegatus, The test chamber is comprised of a Lexan® or Plexiglass core tube containing several screened ports to facilitate water exchange. A rubber stopper, equipped with a small plastic holding vessel to hold organisms, is secured on top of the test chamber before deploying the tube. Once the test chamber is pushed into the sediment to a depth of approximately 20 cm, the bioassay is initiated by releasing the test organisms from the holding chamber into the test chamber. We evaluated the performance of this in situ bioassay system by conducting 10-d exposures at two contaminated and two reference sites, and in a transplanted control sediment. Performance in the field test was compared to parallel 10-d laboratory tests. Survival of C. tentans was 68 and 72% at the two reference sites. Corresponding survival in these sediments in laboratory tests was 96 and 75%. Survival in the transplanted control sediment was 97%. Although significant differences between sediments in the absolute values of survival and growth were observed in both field and laboratory exposures to contaminated sediments, the relative pattern of response for these endpoints was comparable between the laboratory and the field. Variability (coefficient of variation) associated with both survival and growth was generally greater in field exposures (20-86%) than in laboratory exposures (5-72%). A portion of this variability seemed to reflect the occurrence of predatory species, because 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 contaminated 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 successfully to assess toxicity and bioaccumulation in contaminated sediments.