[1] 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).
[1] 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.
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.
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.
While laboratory based experiments simplify a complex and dynamic environment, toxicity results allow the potential for field extrapolation.
[1] 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).
[2] 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.
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.
Application of the SQT is typically location-specific and can be used to compare differences in sediment quality temporally or across regions (Chapman, 1997).
In order to qualify for SQT assessment chemistry, toxicity, and in situ measurements must be collected synoptically using standardized methods of sediment quality.
An appropriate reference is a whole sediment sample (particles and associated pore water) collected near area of concern and is representative of background conditions in the absence of contaminants.
A chemical score index (CSI) of the contaminant describes the magnitude of exposure relative to benthic community disturbance.
Each component of the triad is assigned a response category: minimal, low, moderate, or high disturbance relative to background conditions.
Individual LOEs are ranked into categories by comparing test results of each component to established thresholds (Bay and Weisberg, 2012).
The SQT triad can also classify impact as inconclusive in cases when LOE between components are in disagreement or additional information is required (Bay and Weisberg, 2012).
[7] A decision matrix can be employed such that all three measures be analyzed simultaneously, and a deduction of possible ecological impacts be made (USEPA 1994)[6] Other advantages of the SQT include information on the potential bioaccumulation and biomagnifcation effects of contaminants, and its flexibility in application, resulting from its design as a framework rather than a formula or standard method.
As per state regulatory criteria, information on point and nonpoint source contamination, and its effects on sediment quality may be required for assessment of compliance.
The major limitations include: lack of statistical criteria development within the framework, large database requirements, difficulties in chemical mixture application, and data interpretation can be laboratory intensive (Chapman 1989).