Trace Metal Distribution Coefficients in the Mersey Estuary, UK:  Evidence for Salting out of Metal Complexes

Abstract

An examination of partition data for trace metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) from a number of independent studies conducted in a highly contaminated, organic-rich estuary (Mersey, UK) indicates an increase in the sediment-water distribution coefficient, KD, with increasing salinity for all metals with the excepton of Cd. This behavior is not consistent with inorganic speciation calculations or empirical modeling studies in other estuaries, which predict an inverse relationship between KD and salinity due to competitive adsorption and complexation with seawater ions. The data are, however, well-defined by an empirical model based on the salting out of neutral organic chemicals and yield salting constants in the range 0.7-2.0 L mol(-1). It is suggested that trace metals are complexed by and, subsequently, neutralize organic ligands, and that the resulting neutral assemblages are salted out, possibly via electrostriction. Examination of sorption date from other environments suggests that the effect may be more general in highly contaminated or organic-rich estuaries, and that a specific pool of relatively large, but undefined ligands, is mainly responsible.

Speciation and partitioning of cadmium and zinc in two contrasting estuaries:The role of hydrophobic organic matter

“…4. The magnitude of these values is in broad agreement with the magnitude of K D s determined in previous adsorption studies employing radiotracers (Turner 1996). Cadmium displays a reduction in K D with increasing salinity that is characteristic of this metal and that is the combined result of competition for adsorption sites with divalent seawater cations (Ca 2ϩ and Mg 2ϩ ) and complexation of aqueous Cd by chloride ions (Paalman et al 1994).…”

“…To overcome these potential problems, we determined dissolved Hg(II) complexes in estuarine waters that were retained by reverse-phase C 18 ''Sep-Pak''-type columns, both before and after adsorption to sediment was effected (i.e., in the absence and presence of suspended sediment particles; Turner et al 2001). These columns consist of octadecyl carbon moieties chemically bonded to silica gel supports and are designed to separate hydrophobic organic species from hydrophilic (organic and inorganic) species in an aqueous medium.…”

Assessment of Metal Toxicity in Marine Ecosystems: Comparative Toxicity Potentials for Nine Cationic Metals in Coastal Seawater

“…primary producers, primary and secondary consumers), a free ion activity 225 HC 50-trophic was calculated as the geometric mean of the corresponding free ion EC 50 for all species 226 with available data. The geometric mean of the resulting three HC 50-trophic represents the free ion 227 activity HC 50 in saltwater for that specific metal . Then, for each combination of metal and LME, a 228 truly dissolved HC 50 was calculated using WHAM VII, based on the free ion activity HC 50 and 229 corresponding LME water chemistry.…”

“…The geometric mean of the resulting three HC 50-trophic represents the free ion 227 activity HC 50 in saltwater for that specific metal . Then, for each combination of metal and LME, a 228 truly dissolved HC 50 was calculated using WHAM VII, based on the free ion activity HC 50 and 229 corresponding LME water chemistry. Finally, EF was calculated as 0.5/truly dissolved HC 50 43 .…”

“…Increases in salinity leads to a higher ionic strength, which 329 results in lower free ion activity for a given free ion concentration, and thus a lower EF 65 . When 330 OM decreases, a fraction of metal may be released into truly dissolved forms, which leads to a 331 higher truly dissolved HC 50 , thus lower EF. 332…”