Overview

Environmental assessment and remediation programs can often include a sediment characterization component aimed at evaluating potential impacts on ecological and human health risk. The specific approach, goals, and data objectives can vary greatly depending on the type and purpose of the site evaluation, ranging from dredge material disposal, risk assessments for environmental and public health, habitat improvements, remedial goals, construction projects, and more. Analysis of samples in sediment, elutriate, and organism tissue provides information for understanding the presence and potential impact of different types of environmental contaminants.  Read on to learn more about each of these matrices.

Solid-Phase Sediment

Sediments can be a source or sink for contaminants of concern (COCs) over time and give us clues about current and historical trends. Chemical analysis of solid-phase or bulk sediment evaluates the presence and quantity of contaminants, which when paired with biological (toxicity) testing, translates direct effects of these COCs to organisms. Different contaminants have different binding affinities for sediment particles, which impacts their bioavailability to organisms living in the sediment. Physical sediment properties (such as grain size, organic content, etc.), can also influence contaminant binding and accessibility. Depending on the ultimate goal of the project, it can be advantageous to pair chemical analysis with biological testing

Elutriates

Elutriates or leachates are created from a mixture of solid-phase sediment and water. They can reveal the partitioning characteristics of COCs (i.e., how likely the COCs are to move into the aqueous fraction) and how organisms living in the water column are affected by water-soluble contaminants that migrate out of the sediment and impact water quality during activities like dredging or disposal.

Elutriate testing provides an estimation of the portion of contaminants that may become mobile and bioavailable.  Partitioning can also be explored in leaching and flux studies, and we encourage you to contact us to learn more about what method is most suitable for your project and goals. Results observed can depend on the variables inherent to the elutriate preparation method used, such as mixing intensity and duration as well as ratio of sediment to water.

Tissues

Tissue testing allows us to assess how contaminants may bioaccumulate in organisms over longer periods of time and be transferred through different tropic levels of the food web. Accumulation of the contaminant levels present in tissues can depend on the choice of species, type of organ tissue (e.g., liver, muscle, blood, or fat), and organism age, diet, and overall health. Tissue exposures can take place in-vivo, in-situ, or can be assessed as part of an ambient fish or animal tissue survey.

Tips for a Successful Sediment, Elutriate, and Tissue Analysis Program

With environmental testing for sediment, elutriate, and tissue matrices, here are a few best practices to keep in mind for achieving reliable results:

Engage with your laboratories early in the process. 

• The more information that the labs have about the study plan prior to sample collection, the better equipped they are to provide insight and advice about potential challenges, volumes of sample and site water needed, interference from confounding factors, cost considerations, and realistic project timelines.
• Note that the lab performing the biological exposure is not always the same lab that performs the sediment or tissue analysis. The analyte list for tissue analysis can dictate the number of organisms and replication needed for bioaccumulation exposures, which can ultimately influence the test cost.

Proper sampling techniques are critical.

• For all matrices, accurate results hinge on sample representativeness and good collection technique. Consider the depth, location, and mechanism of sample collection for the sediment and site water as well as which organisms and tissue types are most representative.

Work with an expert for accurate interpretation of the results.

• For example, just because high contaminant levels are present in the sediment doesn’t automatically mean that water quality and/or organism survival and health are impacted.

Know the applicable regulatory guidance.

• Comparison to regulatory standards can help in assessing compliance and environmental risk. Each project type, geographic region, or contaminant may have different thresholds for acceptable contaminant levels.

While it can be a complex undertaking, environmental analysis in sediment, elutriate, and tissue matrices contributes to a comprehensive assessment of COC loads, bioavailability, and ultimately, human health and ecological risk. Understanding the nuances of each matrix and method informs decisions for environmental management, remediation, and protection of public health.