Heavy metals fractionation and multivariate statistical techniques to evaluate the environmental risk in soils of Huelva Township (SW Iberian Peninsula)

The city of Huelva and surrounding areas are affected by several sources of pollution such as acid mine drainage, industrial complexes, urban wastes and agriculture activities that could pose an important environmental risk. For this reason, the modified BCR (three steps) sequential extraction method was applied to evaluate the mobility and bioavailability of the trace elements in 25 representative samples of the study area. The operational scheme of the BCR was classified into three steps: water/acid soluble fraction, reducible and oxidisable fraction. The mobility sequence based on the sum of three first phases was: Cu (82.01%) > Zn (71.14%) > Cd (68.35%) > Ni (50.44%) > Pb (36.39%) > Cr (29.22%) > As (18.82%). Among metals, Cd poses a serious threat to human health and the environment due to the calculated high percentage of mobility. Additionally, multivariate statistical techniques (principal components and cluster analyses) were applied to the chemical results to evaluate the degree of metallic pollution and the levels of association between the variables (metal-metalloids) at the different steps of sequential extraction and to recognise possible sources of potential contamination. The PCA suggests that the study area is influenced by four sources of anthropogenic contributions: acid mine drainage, industrial activities, traffic, and agriculture, aside from the natural sources characteristic of the zone. Calculated environmental risk index reveal a considerable-high ecological risk in the saltmarshes of the Huelva estuary probably related to acid mine drainage and the industrial complexes located in these areas, while in the north sector of Huelva the metallic content is more closer to the natural sources values. The results obtained suggest the need for corrective remediation measures due to the higher accumulation of potentially dangerous metals, which in most cases exceed the limits established by certain legislation. (C) 2012 Elsevier B.V. All rights reserved.