PARENT SESSION
WA5a Bioavailability of Organic Chemicals: Concepts, tools and consequences
9:00 AM to 11:00 AM, Wednesday, 09 May 2001
Session Chair: J.J. Ortega
Room 5

(322) Influence of sediment organic carbon quality on bioavailability of Hexachlorobiphenyl and Nonylphenol to estuarine benthic amphipods.

Gunnarsson, Jonas¹, Hecht, Scott², Boese, Bruce³, Lamberson, Janet³, Weston, Donald¹, Giger, Walter⁴, ^{1 2 3 4}

ABSTRACT- The objective of this study was to evaluate the role of the quantity and nutritional quality of total organic carbon (TOC) on bioavailability of sediment-associated hydrophobic organic contaminants to benthic amphipods. Using standard 16-day laboratory bioassays, two amphipods Eohaustorius estuarius and Grandidierella japonica, having different feeding strategies, were exposed to sediments spiked with ¹⁴C-2,2',3,3',5,5'-Hexachlorobiphenyl (HCBP) or ¹⁴C-4-Nonylphenol (NP). Sediment was enriched 1.5 times its initial TOC content with refractory (pulp mill lignin) or labile (algae Ulva sp.) organic matter. Nutritional quality was measured with a biomimetic method, using bacterial proteolytic enzymes, to obtain bioavailable (EHAA) and total (TAA) amino acid concentrations. For NP, highest accumulation rate and steady state concentrations were obtained in the controls (no additional TOC) in both ampiphod species. There was no significant difference between the two TOC qualities. For HCBP there was a significant treatment effect both for TOC quantity and quality, and a different accumulation pattern in the two species. Our results suggest that for moderately hydrophobic compounds such as NP (Log K_OW 4.5), pore-water is the main exposure route and the Equilibrium Partitioning Theory can be applied to predict bioaccumulation. However, for more hydrophobic compounds such as HCBP (Log K_OW 6.3), diet is a major exposure route and bioaccumulation is a function of TOC's nutritional quality and of the organisms' feeding strategy. In vitro digestion of sediment in gut fluids from the polychaete Arenicola brasiliensis showed that 69 % of NP and 59 % of HCBP was extracted through gut juice solubilization and hence through sediment ingestion. TOC quantity or quality did not affect solubilization. EHAA and TAA were excellent measurements of TOC's nutritional quality. Correction of Biota Sediment Accumulation Factors (BSAFs) for TOC quality, using amino acid concentrations, reduced the treatment effects and corrected BSAFs came closer to the theoretical value of 1.7.

Key words: Bioavailability, TOC quality, Amino acids, BSAF