The role of digestive surfactants in determining bioavailability of sediment-bound hydrophobic organic contaminants to 2 deposit-feeding polychaetes

Solubilization of sediment-bound hydrophobic contaminants (HOCs) by gut fluids of deposit-feeding polychaetes greatly exceeds solubilization by seawater. We present evidence that digestive surfactants exert a central role in HOC desorption, and that the degree of in vitro solubi- lization by gut fluids is an excellent predictor of HOC absorption efficiency (AE) by the respective worm species. We compared in vitro solubilization of sediment-bound 14 C-hexachlorobenzene (HCB) and 14 C-tetrachlorobiphenyl (TCBP) by gut fluids of 2 deposit-feeding polychaete species, Nereis (Neanthes) succinea and Pectinaria (Cistenides) gouldii, to AEs measured in live worms by pulse- chase methodology. N. succinea desorbed 72% HCB and 79% TCBP in vitro (during 6 h incubations), and absorbed both compounds with 73% efficiency, while P. gouldii desorbed only 37% HCB in 6 h, and analogously absorbed only 37% HCB. Higher desorption and absorption efficiencies of N. suc- cinea were accompanied by greater gut-fluid surfactancy and higher micelle concentration (deter- mined by drop contact angle) compared to P. gouldii. Calibration of desorption efficiencies with a synthetic surfactant, sodium dodecyl sulfate (SDS), showed that N. succinea gut fluid desorbed a sim- ilar amount of HOC as a 1% (ca 3.5 mM) SDS solution, whereas P. gouldii gut fluid was equivalent to a 0.25% (ca 0.9 mM) SDS solution. Detailed analysis of the kinetics of HOC desorption (after 1, 45 and 360 min) showed that gut fluids from both polychaetes desorbed more than two-thirds of the bioavail- able HOC within the first minute, suggesting that digestive desorption occurs rapidly and that gut- residence time has only minor influence on the degree of desorption or absorption of sediment-bound HOCs.