Pollution reconnaissance in stream sediments using non-residual trace metals

Abstract

Total non-residual (TNR) concentrations of Fe, Mn, Co, Ni, Cr, Cu, Pb, Zn and Cd have been determined in sediments from ten stream populations in North West England using a rapid 0·5 HCl leaching technique. It is shown that the technique can successfully be used as a first stage in a reconnaissance survey designed to identify trace metal pollution in stream sediments. The TNR trace metal concentrations are extremely variable in the sediments and a number of approaches are assessed in order to interpret the data in an environmentally useful manner. (i) Spatial variations in the distributions of the TNR trace metals in individual stream populations can be used to identify specific pollution sources, which often impose ‘man-made fingerprints’ on the sediments. (ii) In order to establish baseline concentrations for all the stream sediments, an artificial background sediment (ABS) is identified and sediments which have suffered pollution are identified as those whose TNR trace metal concentrations exceeds an $E{\overline{x}}_{ABS}$ + 2s parameter, in which $E{\overline{x}}_{ABS}$ is concentration of an element, E, in the ABS. The degree of pollution is assessed by an index of pollution (IP), which is related to the $E{\overline{x}}_{ABS}$ + 2s parameter. (iii) Partitioning of the trace metals in the non-residual sediment fractions is investigated using a five-stage sequential leaching technique. The application of the technique to a series of polluted and non-polluted stream sediments shows that the partitioning characteristics of a number of the TNR trace metals differ in respect to their host components. Further, the partitioning signatures of some of the TNR trace metals, especially that of Cd, are different in polluted and non-polluted samples.