Water and Sediment Criteria Development

Bioavailability is a fundamental consideration in the evaluation of the toxicity and bioaccumulation potential of chemicals in water, sediments and soils. The reason is that varying degrees of toxicity and bioaccumulation are often associated with environmental media having the same total chemical concentrations, and much of this variability can be accounted for by understanding how the characteristics of the media interact with the chemical of interest to alter its biological availability and toxicity to the exposed biota. For example, in the case of metals’ toxicity in the sediment, a significant portion of the total metal may be chemically bound to sulfides that are present in the sediment, thereby removing that portion for uptake by benthic organisms. Bioavailability has, therefore. become a fundamental consideration by the EPA, the European Union and elsewhere, as part of their ongoing efforts to develop modern water quality criteria (or their equivalents) for metals and equilibrium partitioning-based sediment quality guidelines (ESGs) for both metals and organic chemicals.

HydroQual staff, working for EPA and municipal and industrial research groups, have served in a leadership capacity in the development of these methods. They have presented the results to the EPA Science Advisory Board and worked to resolve remaining questions as a way to enhance the technical defensibility of the methods that have been proposed. The recent release of an updated draft water quality criterion (WQC) for copper (Cu) is the first of a number of biotic ligand model (BLM)-based metal WQC updates that are planned and serves as evidence of the increasing acceptance of these methods by regulatory and industry groups alike. A further demonstration of acceptance in criteria development is that EPA has also published several guidance documents that describe the implementation of ESG methods for sediments.

A fixed sediment metal concentration can be associated with a wide range of effects.

Consideration of SEM and AVS serves as a first step in refining an assessment of ecologically safe (SEM/AVS < 1) versus potentially impacted areas (SEM/AVS > 1).