Combining indices of soil pollution due to heavy metals

Abstract

Soil contamination indices based on a single heavy metal (HM) fail to satisfy the interests of regulatory authorities, landowners and researchers who are more interested in a comprehensive index by aggregating such measures, facilitating evaluation of the effectiveness of remedial actions. Existing indices suffer from methodological limitations. Avoiding limitations of existing indices, the paper suggests a composite index of soil contamination by HMs (by multiplicative aggregation of individual contaminant indices) defined as ratio of pooled average concentration of a HM and the Standard for the HM Logarithm of the index gives an additive model following a lognormal distribution. The index quantifies overall soil pollution status due to the concentration of different HMs, and satisfies desired properties like time reversal test, formation of chain indices and enables comparison across regions or time periods and undertaking parametric analysis. Novelty includes knowledge of the probability distribution of the index, assessment of progress or decline over the previous years and statistical inferences. The proposed approach with significant advantages can be computed for any finite number of HMs irrespective of sources of HMs and helps in better classification of regions with assessment of efficiency of classification. The proposed index with theoretical advantages is recommended.