Interactions of Cd and Cu in anaerobic estuarine sediments .1. Partitioning in geochemical fractions of sediments.

Partitioning of Cd and Cu between geochemical fractions of an anaerobic estuarine sediment was determined after equilibrating fine-sandy sediment with different combinations of added Cd (0, 2.5, 5 mg/kg) and Cu (0, 12.5, 25 mg/kg). Sediments were placed in aquaria with 20 ppt seawater where bioassay test organisms were exposed for 14 d. At the start and conclusion of the experimental period, sediments were sequentially extracted to determine the elemental content of the exchangeable CEP), easily reducible (ERP), organic-sulfide (OSP), moderately reducible (MRP), and acid exactable (AEP) phases. Partitioning of the metals in both the native and treated sediments was, for Cd: OSP much greater than ERP > AEP > EP (MRP was below detection) and for Cu: OSP much greater than AEP > ERP > MRP > EP. Cadmium extracted in all phases and Cu in the EP, ERP, and OSP were proportional to the respective treatments. The EP-Cd, ERP-Cd and OSP-Cd were affected by the Cu treatment and significant interactions occurred between Cd and Cu for the EP-Cd, ERP-Cd, OSP-Cd, EP-Cu, and ERP-Cu. Increasing levels of applied Cd and Cu resulted in greater amounts of EP-Cd and ERP-Cd, fractions that are the most bioavailable and the most readily available for desorption into the water column. A significant conclusion is that the input of nontoxic metals may affect the geochemical phase distribution, potential bioavailability, and toxicity of native sediment metals.