Bioavailability Of Metals In Sediments Research Articles

Acid‐volatile sulfide as a factor mediating cadmium and nickel bioavailability in contaminated sediments

AbstractWe investigated the influence of sulfide, measured as acid‐volatile sulfide (AVS), on the bioavailability of cadmium and nickel in sediments. Seventeen samples from an estuarine system heavily contaminated with cadmium and nickel were analyzed for AVS and simultaneously extracted metals (SEM) and tested in 10‐d exposures with the amphipod Hyalella azteca and the oligochaete Lumbriculus vanegatus. Molar SEM (cadmium + nickel)/AVS ratios in the sediments ranged from less than one to greater than 200, with several in the range of 1 to 10. Samples with SEM/AVS ratios greater than one were consistently toxic to Hyalella azteca, whereas sediments with ratios less than one were not. Lumbriculus variegatus was less sensitive to the test sediments than Hyalella azteca, which was consistent with their relative sensitivity to cadmium and nickel in water‐only exposures. SEM/AVS ratios in the sediments also appeared to be important in determining bioaccumulation of metals by Lumbriculus variegatus. These results support other studies with metal‐spiked samples in demonstrating the importance of AVS in determining metal bioavailability in sediments and suggest that AVS normalization is a reasonable means for assessing the hazard of some sediment‐associated metals to aquatic ecosystems.

An integrated chemical and biological study of the bioavailability of metals in sediments from two contaminated harbours in New Brunswick, Canada

Dalhousie and Belledune, New Brunswick, Harbour sediments are known to be contaminated with copper, zinc, lead and cadmium. Relatively high concentrations of these metals in the resident organisms were reported from previous surveys. Experiments were conducted in the laboratory to study the partitioning and bioavailability of heavy metals present in the contaminated sediments. A procedure to extract metals sequentially from sediments was used to determine their distribution in various geochemical fractions. A companion experiment was also set up to determine the bioavailability of trace metals from these sediments. Experimental data indicated that the metals associated with hydrous oxides of iron and manganese and the residual fraction carried the major burden of heavy metals in the sediment. Appreciable uptake of metals was observed to occur only from the Belledune sediment. Biota accumulated lead and cadmium to the greatest extent, with strontium, cobalt and zinc taken up to a lesser degree as compared with control animals in uncontaminated sediments. Concern is directed to heavy metals associated with hydrous oxides of iron and managenese because changing environmental conditions can transfer these elements from the sediments into the aqueous phase.

Can we determine the biological availability of sediment-bound trace elements?

It is clear from available data that the susceptibility of biological communities to trace element contamination differs among aquatic environments. One important reason is that the bioavailability of metals in sediments appears to be altered by variations in sediment geochemistry. However, methods for explaining or predicting the effect of sediment geochemistry upon metal bioavailability are poorly developed. Experimental studies demonstrate that ingestion of sediments and uptake from solution may both be important pathways of metal bioaccumulation in deposit/detritus feeding species. Relative importance between the two is geochemistry dependent. Geochemical characteristics of sediments also affect metal concentrations in the tissues of organisms collected from nature, but the specific mechanisms by which these characteristics influence metal bioavailability have not been rigorously demonstrated. Several prerequisites are necessary to better understand the processes that control metal bioavailability from sediments. 1) improved computational or analytical methods for analyzing distribution of metals among components of the sediments; 2) improved computational methods for assessing the influences of metal form in sediments on sediment-water metal exchange; and 3) a better understanding of the processes controlling bioaccumulation of metals from solution and food by metazoan species directly exposed to the sediments. Such capabilities would allow mechanistic explanations essential to the development of practical tools sought for determining sediment quality criteria for metals.