Heavy metals pollution in riverine sediments: Distribution, source, and environmental implications

This research reports heavy metal pollution in riverine sediments from River Kabul, Pakistan, which could endanger human health and ecology via the food web. The results revealed a substantial special variation in the average contents (mg/kg) of chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), mercury (Hg), lead (Pb), iron (Fe), and aluminum (Al) in riverine sediments, in the order of Fe (20,234.51) > Al (17,550.86) > Mn (375.45) > Zn (149.08) > Ni (89.11) > Cr (83.36) > Pb (45.29) > Cu (19.86) > Cd (7.48) > Co (6.28) > Hg (0.81). Among the heavy metals, Cd exhibited the highest degree of pollution along the river, followed by Hg > Ni > Zn > Pb > Al > Cr > Mn > Fe > Cu > Co. The overall contamination factor (CF) values for the sum of heavy metals were highest at monitoring site S-9, followed by S-8 > S-10 > S-6 > S-5 > S-7 > S-1 > S-4 > S-12 > S-3 > S-2 > S-1 with pollution load index (PLI) > 1, whereas the geo-accumulation index (Igeo) values of Cd and Hg fluctuated between Levels 3, 4, and 6, suggesting moderate to extreme pollution in the river. The correlation statistics determined the fate and distribution of heavy metals by establishing significant positive correlations between the specific metals of bounded sediments. The cluster analysis separates the correlated metals into Groups A and B, and Groups 1 and 2. While the principal component analysis evaluates the qualitative behavior of clustering by discerning industrial, agrochemicals, mining, and domestic wastewater discharges, leakages of lubricants along with multiple geogenic inputs, erosion of mafic and ultramafic rocks, and minimal atmospheric deposition are all potential sources of Cr, Mn, Co, Ni, Cu, Zn, Cd, Hg, Pb, Fe, and Al contamination. In terms of risk, the contaminations of Mn, Co, Cu, Zn, and Pb in riverine sediments were 85, 100, 100, 17, and 11%, respectively, representing a rare biological influence because their value is less than their corresponding threshold effect concentrations (TECs), whereas the levels of Mn, Ni, Cd, and Hg were above their probable effect concentrations (PECs) of 100, 100, 81, and 52%, respectively, representing prominent adverse biological influence. Based on consensus-based TECs and PECs, the contamination levels of Cr, Mn, Zn, Cd, Hg, and Pb were 100, 85, 83, 19, 48, and 90%, respectively, indicating occasionally exhibited adverse biological effects on the riverine population. Besides, the overall potential ecological risk index (PERI) of Cd and Hg, in particular, exhibited the maximum pollution level ( $E_{\text{r}}^{\text{i}}$ ≥ 320), suggesting a very high potential ecological risk in the drainage that requires special attention from pollution control authorities.