Assessment of Heavy Metal Contamination Using Geochemical Indices and Multivariate Statistical Techniques: A Study of the Neyyar River, Originating from Southern Western Ghats, India

The current study evaluated the extent of heavy metal concentrations in the bulk sediment samples of Neyyar River, a perennial river originating from the Western Ghats and flowing through the extreme south of Kerala State. In contrast to other rivers in India, Kerala rivers are very small and are severely degraded due to various types of human interventions. Mining for sand from river beds and banks, dumping of wastes, discharges from industrial and agricultural activities, etc., has imparted tremendous degradation in terms of weakening of river bank stability, modification of soil–water balance, pollution, structural loss of exposed riverine sediments, and change in normal river bed characteristics. The pollution status of the riverine systems can be well understood by analyzing the recent sediments. Hence, the evaluation of sediment pollution was conducted in Neyyar River using contaminant geochemical indices in the bulk sediment samples from 17 locations collected during Pre-Monsoon (PrMon), Monsoon (Mon), and Post-Monsoon (PoMon) seasons. The results suggested that the contamination factor (CNF) values for all metals except Cd were in low contamination category, whereas Cd values indicated moderate contamination (>1) at different sites. The PLI values obtained for the seventeen stations showed comparatively less status of sediment pollution in the riverine sediments. Although all metal concentrations in the sediment samples were below contamination and pollution levels, the mean EF values for Zn and Cd exhibited minor enrichment (2.08 and 2.77, respectively) suggesting the prevalence of these metals in the study area. Principal component analysis performed using eleven variables revealed both the geogenic and anthropogenic contribution of heavy metals into the riverine system.