TR(BR)-4/96-97 : Metal pollution assessment through aquatic sediments

Abstract

The introduction of metallic pollutants into a river, whether it is natural (erosion of its drainage basin) or artificial (anthropogenic), can occur in dissolved or particulate form. Depending on physico-chemical conditions, the pollutants in dissolved form can later precipitate as hydroxides, carbonates or other minerals. They can also be adsorbed by the iron or manganese oxides and hydroxides or coprecipitate with these, or form dissolved organic or organic complexes. In particulate form, associated with suspended matter, the pollutant can, under favourable hydraulic conditions, be deposited on the bottom sediments. Therefore, the study of metallic pollutant concentrations in sediments can be conveniently used to investigate possible pollution; the contents are generally well above detection limits which is not always the case in water. Furthermore, the analysis of sediments eliminates the problem of erratic fluctuations which are often observed in water.

The sediment existing at the bottom of the water body play a major role in the pollution schemes of the river and lake systems. They reflect the current quality of the water system and can be used to detect the presence of contamination that do not remain soluble after discharge into surface water. Moreover, sediments act as carriers and possible sources of pollution because heavy metals are not permanently fixed by them and can be released back to the water column by changes in environmental conditions. Therefore, the analysis of heavy metals in sediments permits us to detect pollution that could escape water analysis, and also provides information about the critical sites of the water system under consideration.

In the present report, an attempt has been made to compile and evaluate the present state of affairs with regard to metal pollution assessment through aquatic sediments in rivers and lakes.