High Concentrations of Complexed Metals in the Guts of Deposit Feeders

Sediment particles passing through the guts of deposit feeders are subject to an environment unusually rich in dissolved organic material, especially proteinaceous materials, capable of binding metals. Concentrations of many heavy metals are high in gut fluids of various deposit feeders from pristine environments. Concentrations of Cu and Cd show strong correlations with total acid-hydrolyzed amino acids (TAHAA) in gut fluids in a cross-phyletic survey of 35 deposit feeder species. Similar correspondence with TAHAA obtains among individuals, along longitudinal gut sections, and among molecular weight fractions. Multiple incubations of sediments with a commercial protein solution having similar TAHAA concentration as gut fluid solubilized many metals, showing convergence toward similar composition as gut fluid. Adherence of gut-dissolved metal concentrations to the Irving-Williams order suggests that the rich milieu of soft ligands contained in gut fluids provides a mechanism for mobilization of softer metals in sediments.