In aquatic toxicology, the sediment quality triad (SQT) approach has been used as an assessment tool to evaluate the extent of sediment degradation resulting from contaminants released due to human activity present in aquatic environments (Chapman, 1990). This evaluation focuses on three main components: 1.) sediment chemistry, 2.) sediment toxicity tests using aquatic organisms, and 3.) the field effects on the benthic organisms (Chapman, 1990). Often used in risk assessment, the combination of three lines of evidence can lead to a comprehensive understanding of the possible effects to the aquatic community (Chapman, 1997). Although the SQT approach does not provide a cause-and-effect relationship linking concentrations of individual chemicals to adverse biological effects, it does provide an assessment of sediment quality commonly used to explain sediment characteristics quantitatively. The information provided by each portion of the SQT is unique and complementary, and the combination of these portions is necessary because no single characteristic provides comprehensive information regarding a specific site (Chapman, 1997)
Components
Sediment chemistry Sediment chemistry provides information on contamination, however it does not provide information of biological effects (Chapman, 1990). Sediment chemistry is used as a screening tool to determine the contaminants that are most likely to be destructive to organisms present in the benthic community at a specific site. During analysis, sediment chemistry data does not depend strictly on comparisons to sediment quality guidelines when utilizing the triad approach. Rather, sediment chemistry data, once collected for the specific site, is compared to the most relevant guide values, based on site characteristics, to assess which chemicals are of the greatest concern. This technique is used because no one set of data is adequate for all situations. This allows you to identify the chemicals of concern, which most frequently exceed effects-based guidelines. Once the chemical composition of the sediment is determined and the most concerning contaminants have been identified, toxicity tests are conducted to link environmental concentrations to potential adverse effects.
Sediment toxicity 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.
Field effects on benthic organisms The analysis of field effects on benthic organisms functions to assess the potential for community based effects resulting from the identified contaminants. This is done because benthic organisms are sessile and location specific, allowing them to be used as accurate markers of contaminant effect (Chapman, 1990). This is done through conducting field-based tests, which analyze changes in benthic community structures focusing on changes in number of species, abundance, and percentage of major taxonomic groups (Chapman, 1997). Changes in benthic communities are typically quantified using a principal component analysis and classification (Chapman, 1997). There is no one specifically defined method for conducting these field assessments, however the different multivariate analysis typically produces results identifying relationships between variables when a robust correlation exists. Knowledge of the site-specific ecosystem and the ecological roles of dominant species within that ecosystem are critical to producing biological evidence of alteration in benthic community resultant of contaminant exposure. When possible, it is recommended to observe changes in community structure that directly relate to the test species used during the sediment toxicity portion of the triad approach in order to produce the most reliable evidence.
Bioaccumulation Bioaccumulation should be considered during the utilization of the triad approach depending on the study goals. It preparation for measuring bioaccumulation, it must be specified if the test will serve to assess secondary poisoning or biomagnification (Chapman, 1997). Bioaccumulation analysis should be conducted appropriately based on the contaminants of concern (for example, metals do not biomagnify). This can be done with field-collected, caged organisms, or laboratory exposed organisms (Chapman, 1997). While the bioaccumulation portion is recommended, it is not required. However, it serves an important role with the purpose of quantifying effects due to trophic transfer of contaminants through consumption of contaminated prey.
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