Site-Specific Water Quality Targets for Fish Contaminants: Application of Sediment, Water, and Tissue Targets based on Measured Partitioning Relationships
Abstract:For trace constituents such as dioxins and PCBs, §303(d) listings are often based on fish consumption advisories rather than actual water quality data. In developing TMDLs for these pollutants, a water-based concentration target is required to facilitate modeling, load allocations, and permitting. Yet these contaminants are exceedingly difficult and expensive to quantify directly in water. Also, the ultimate purpose of the TMDL is reduction of the fish tissue concentration, rather than the water concentration. Because sediment concentrations are easily measured, they can facilitate identification of contributing source areas, temporal trend analysis, and progress toward meeting the water quality target. Thus, it is advantageous, if not necessary, to establish quantitative relationships between water, fish, and sediment concentrations when developing TMDLs.
In development of a dioxin TMDL for the Houston Ship Channel in Houston, Texas, an extensive field effort quantified concentrations of dioxins and PCBs in sediments, fish and crab tissue, and the particulate and dissolved phases in water at 45 sites over several seasons. Concentrations of a number of other parameters, including tissue lipid, sediment organic carbon, total suspended solids and dissolved organic carbon, were also measured to assist in developing thermodynamic fluid phase equilibrium partitioning relationships.
Bioaccumulation factors (BAFs) are commonly expressed as the ratio of concentrations in tissue and water. Biota-sediment accumulation factors (BSAFs) are commonly expressed as the ratio of concentrations in tissue and sediment. The partition coefficient (Kp) expresses the ratio of the concentrations in bed or suspended sediments to those dissolved in water at equilibrium. In these relationships, tissue concentrations are often normalized by the lipid content of the tissue, and sediment concentrations are often normalized by the organic carbon content of the sediment. Also, because dissolved organic matter in water may provide a significant reservoir of colloidal contaminant not available for uptake into tissues or sediments, water dissolved concentrations are sometimes adjusted to reflect this unavailable colloidal pool based on the dissolved organic carbon concentration or other parameters. This paper presents and discusses the derivation and utility of various forms of BAFs, BSAFs, and Kps to link dioxin and PCB concentrations in sediment, tissue, and waters of the Houston Ship Channel system. The paper also discusses the utility of using water quality targets based on dioxin concentrations in water, tissue, and sediment in TMDL development and subsequent implementation plans.
Document Type: Research Article
Publication date: 2003-01-01
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