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

Abstract

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 solubilization 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 14C-hexachlorobenzene (HCB) and 14C-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. succinea were accompanied by greater gut-fluid surfactancy and higher micelle concentration (determined 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 similar 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 bioavailable 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.