Global evaluation of heavy metal content in surface water bodies: A meta-analysis using heavy metal pollution indices and multivariate statistical analyses.

Water is polluted by increasing activities of population and the necessity to provide them with goods and services that use water as a vital resource. The contamination of water due to heavy metals (HMs) is a big concern for humankind; however, global studies related to this topic are scarce. Thus, the current review assesses the content of HMs in surface water bodies throughout the world from 1994 to 2019. To achieve this goal, multivariate analyses were applied in order to determine the possible sources of HMs. Among the analyzed HMs in a total of 147 publications, the average content of Cr, Mn, Co, Ni, As and Cd exceeded the permissible limits suggested by WHO and USEPA. The results of the heavy metal pollution index, evaluation index, the degree of contamination, water pollution and toxicity load showed that the examined water bodies are highly polluted by HMs. The results of median lethal toxicity index showed maximum toxicity in As, Co, Cr and Ni in the surface water bodies. Results of ingestion and dermal pathways for adults and children in the current analyzed review showed that As is the major contaminant. Moreover, Cr, Ni, As and Cd showed values that could be considered as a high risk for cancer generation via the ingestion pathway as compared to the dermal route. It is recommended that remediation techniques such as the introduction of aquatic phytoremediation plant species and adsorbents should be included in land management plans in order to reduce human risks.