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Rapid regeneration of ‘OgCd and 65Zn from their picoplankton prey into the dissolved phase by microzooplankton was observed in water sampled from the pelagic surface waters of Lake Erie (summer 1994 and 1995). Trace metals were added to grazing (lake water < 2’10 brn) and control (lake water CO.2 pm) treatments in the form of radiolabeled Synechococcus, Picoplankton (0.2-3 pm) were grazed heavily by consumers in the nanoplankton (3-20 pm) and microplankton (20-2 10 pm) size classes (collectively referred to as microzooplankton) as confirmed by dilution assays used to independently measure grazing activity. Most consumed trace metals were regenerated into the dissolved phase (x0.2 pm), but some trophic transfer of ‘OgCd and 65Zn from radiolabeled prey into the nanoplankton and microplankton did occur: 65Zn was transferred 2.5 times more efficiently into the microplankton and 2.9 times more efficiently into the nanoplankton than was logCd. Recycling of regenerated logCd back into plankton biomass was greater than that for 65Zn. Grazing by microzooplankton influenced the molecular size distribution of regenerated trace metal in the dissolved phase (77 + 6% log Cd

The presence of high concentrations of heavy metals in wastewater sludge is one of the most important factors that limit the application of sludge on agricultural land. In the last few years, the microbiological process of heavy metals removal from wastewater sludge has been studied in a batch mode. In the present study, the effects of metals, solids concentration, and initial pH on indigenous sulfur-oxidizing thiobacilli growth and metal solubilization were examined. The results obtained indicate that metals removal is possible even in high sludge solids concentration (70 g/L). The rate of sulfuric acid production through the oxidation of added elemental sulfur is increased by the increased sludge solids concentration.

Cadmium concentrations were measured at 49 littoral sites in 38 lakes distributed over 350,000 km2 in the provinces of Quebec and Ontario, both in the abiotic environment (oxic sediments and overlying water, diagenetic iron oxyhydroxide deposits on Teflon collectors) and in the soft tissues of the freshwater bivalve Anodonta grandis collected along a Cd contamination gradient. Concentrations of dissolved Cd above the water-sediment interface were highly undersaturated with respect to CdCO,(s). The partitioning of Cd between water and surficial oxic sediments is interpreted in terms of sorption of this metal to sedimentary organic matter and Fe oxyhydroxides, by means of surface complexation concepts. Binding intensity values for the sorption of Cd to Fe oxyhydroxides (&-& and organic matter (J&& are estimated from field data (i.e. Cd concentrations in diagenetic Fe deposits, in the sediments, and in the water). The following empirical relationships between binding intensities and lake pH are found: log K Fe-Cd = 0.82 pH - 1.30 (r2 = 0.89) and log Kc,M-Cd = 0.97 pH - 2.45 (r2 = 0.78). Calculated Cd partitioning with these binding intensities indicates that Cd is bound mainly to organic matter in these sediments. Linear regression analysis indicates that Cd concentrations in the soft tissues of the bivalves, [Cd(Org)] (pg g-l dry wt), are related to dissolved Cd concentrations: [Cd(Org)] = 44[Cd2+] + 10 (r2 = 0.81) for [Cd2 + ] expressed in nmol liter- I. In these lakes, simple normalization of sedimentary extractable Cd with respect to sedimentary Fe oxyhydroxide or organic C concentrations proved inadequate for predicting Cd concentrations in A. grandis. Combining surface complexation concepts with the free-metal ion model of trace metal-organism interactions, we show that Cd concentrations in the soft tissues of A. grandis can be predicted with similar success as with the dissolved Cd concentration from water pH and sediment chemistry (total sedimentary Cd, Fe oxyhydroxides, and organic C concentrations).