Sediment toxicity is evaluated based on bioassay analysis. Standard bioassay toxicity tests are utilized and are not organism restricted (Chapman, 1997). Differences in mechanisms of exposure and organism physiology must be taken into account when selecting your test organisms, and you must be able to adequately justify the use of that organism. These bioassay tests evaluate effects based on different toxicological endpoints. The toxicity tests are conducted with respect to the chemicals of concern at environmentally relevant concentrations identified by the sediment chemistry portion of the triad approach. Chapman (1990) lists typically used endpoints, which include lethal endpoints such as mortality, and sublethal endpoints such as growth, behavior, reproduction, cytotoxicity and optionally bioaccumulation. Often pilot studies are utilized to assist in the selection of the appropriate test organism and end points. Multiple endpoints are recommended and each of the selected endpoints must adequately complement each of the others (Chapman, 1997). Effects are evaluated using statistical methods that allow for the distinction between responses that are significantly different than negative controls. If sufficient data is generated, minimum significant differences (MSDs) are calculated using power analyses and applied to toxicity tests to determine the difference between statistical difference and ecological relevance.
The function of the toxicity portion of the triad approach is to allow you to estimate the effects in the field. While laboratory based experiments simplify a complex and dynamic environment, toxicity results allow the potential for field extrapolation. This creates a link of exposure and effect and allows the determination of an exposure-response relationship. When combined with the other two components of the Sediment Quality Triad it allows for a holistic understanding between cause and effect.