Contaminant Transfer
Contaminants may be transferred into water through physical disturbance of the sediments, chemical diffusion, or biological activities. Sediment-dwelling organisms and bottom-feeding organisms, such as crabs and flatfish, can be directly exposed to sediment contaminants, which may accumulate in their tissues. Exposure may alter benthic (living in or on sediments) communities. When benthic organisms are preyed upon by other animals and humans, contaminants can be transferred up the food chain and may increase in concentration through the process of biomagnification.
Need for Sediment Quality Guidelines
In order to meet water quality goals, it is important to consider how much contamination is bound onto sediments and whether these contaminants are impacting organisms. Scientists use sediment quality guidelines (SQGs) to evaluate the biological significance of sediment contamination. SQGs usually consist of a set of chemical concentrations for which various types of adverse biological effects are expected to occur.
Evaluating Sediment Quality
Many monitoring programs assess sediment quality using a multiple lines of evidence (MLOE) approach. This approach, often referred to as the “sediment quality triad,” integrates information from three types of measurements: chemical analysis, toxicity tests and benthic community assessments. Integrating three types of evidence reduces the uncertainty associated with each separate measurement to provide a more robust measurement of sediment quality.