Heavy Metals In Aquatic Environment Research Articles

Bioconcentration of heavy metals in aquatic environments: the importance of bioavailability

The importance of heavy metal bioavailability on the bioconcentration in aquatic biota is examined. To this purpose, mono- and multivariate statistical techniques are applied to develop correlations between heavy metal bioconcentration factor and sediment characteristics, that are expected to affect bioavailability, using a database of heavy metal concentrations in biota and sediment along with the available physicochemical characteristics. The statistical analysis shows that satisfactory correlations are obtained only when factors that affect bioavailability, such as metal oxides concentration and organic carbon content in the sediment, are taken into account.

Lead distribution in a simulated aquatic environment: Effects of bacterial biofilms and iron oxide

Biofilms influence the transport and fate of heavy metals in aquatic environments both directly by adsorption and complexation reactions and indirectly via interactions with oxides of iron and manganese. These reactions were investigated by introducing lead into a continuous-flow biofilm reactor that was designed to simulate conditions in a flowing freshwater aquatic environment. The reactor provided controlled conditions, and use of a chemically-defined growth medium allowed calculation of lead speciation with a chemical equilibrium program (MINEQL). Pseudomonas cepacia was employed as a test cell strain because of its ability to grow and form biofilms in the defined medium. This bacterium affected lead distribution in the reactor by adsorbing lead both to adherent and suspended cells. When the aqueous bulk lead concentration was 1.4 ± 0.1 μM and biofilm coverage (measured as chemical oxygen demand, COD) was 50 mequiv COD/m 2, lead adsorption was increased by about a factor of five relative to bare glass. Of the total lead in solution, only 1% was adsorbed to suspended cells (5 × 10 7 cells/ml). Lead adsorption to biofilms followed a Langmuir isotherm with a maximum adsorption ( Γ max) of 56 μmol Pb/equiv COD and an adsorption equilibrium constant ( K) of 0.64 liter/μmol Pb. Lead complexed with dissolved bacterial expopolymer was below detection limits. Pretreatment of glass slides with colloidal iron also significantly increased lead adsorption relative to bare glass. Lead adsorption to adsorbed iron fit a Langmuir isotherm with Γ max = 50 μmol Pb/mol fe, and K = 1.3 liter/μmol Pb. Lead binding to glass coated with both cells and iron was additive, and could be predicted by summing adsorption predicted using isotherms for each constituent. The presence of iron surface coatings increased initial biofilm formation rates, but after reaching steady state conditions, biofilm coverage was similar for slides treated with iron and untreated slides. A concentration of 1 μM lead produced a transient reduction in suspended cell counts. Cell counts recovered to the original cell density over the course of five to ten reactor retention times. With iron present, the magnitude of the reduction in cell concentration in response to the addition of lead was greatly reduced, suggesting that toxic effects of lead may be reduced by iron.

ES&T Books: Pollution Threat of Heavy Metals in Aquatic Environments

ES&T Books: Pollution Threat of Heavy Metals in Aquatic Environments

Book Reviews

Book reviewed in this article: Acidification of Freshwaters, by M. Cresser and A. Edwards. Published by Cambridge University Press. Sediment Transport in Gravel‐bed Rivers, edited by G. R. Thorne, J. C. Bathurst, and R. D. Hey. Published by John Wiley & Sons Ltd. Environmental Biotechnology, edited by C. F. Forster and D. A. John Wase. Published by John Wiley & Sons Ltd. Pollution Threat of Heavy Metals in Aquatic Environments, by G. Mance. Published by Elsevier, Applied Science Publishers Ltd.Coastline ‐ Britain's Threatened Heritage, by Greenpeace. Published by Kingfisher Books Ltd.