The significance of applying different factors for the evaluation of sediment contamination by toxic elements and estimation of the ecological risk

Abstract

The optimized three-step sequential extraction procedure for the fractionation of micro- and macroelements, was conductedto determine fractional characteristics of PTEs (potentially toxic elements) in surface sediments of rivers in the Vlasinawatershed. The sequential extraction results, which enable the evaluation of mobility of the studied elements, have indicatedthat Zn, Ni, Cu, Cr, and As can be considered slightly mobile, whereas Pb, Mn, Cd, and Co were regarded as possibly mobileelements. Lead was dominantly bounded (specifcally adsorbed or co-precipitated) to iron and manganese oxides (up to 80%)and may be released by reduction. Since the content of the exchangeable fraction (F1) is an indicator for anthropogenic impacton the aquatic environment, a low percentage (0–8%) of studied toxic elements in this fraction indicated that these elementshave lithogenic origin in most sampling locations in the area of study. Except for Pb, the substantial positive correlationsbetween Al and other elements showed that studied elements came primarily from terrigenous sources. Although the valuesobtained for the risk assessment code (RAC) indicated a slightly increased mobility of some elements (up to 22.44%), thevalues of the modifed risk assessment code (mRAC), which include toxic efects on the environment, showed there is nodanger of pollution by studied elements (all values were<1%). Our recommendation is to use mRAC instead of RAC inecochemical studies and assessment of the degree of sediment and soil pollution, because mRAC includes toxic efects ofelements. Based on ATI values, river sediments show no toxic to a low toxic degree. Even though obtained results indicatethat there was no considerable risk for river water contamination, the ecological risk for Fe and Pb should be monitored inthe future.