Assessment of possible pollution risk using spatial distribution and temporal variation of heavy metals in river sediments

In the present study, an attempt was made to characterise bed sediments with respect to a river system, wherein sediment samples collected from May 2018 to June 2019 were subjected to bulk digestion and chemical partitioning. The concentrations of metals (Mn, Cu, Zn, Fe, Pb, Co, Cd) bound to five sedimentary phases or fractions were estimated using atomic absorption spectroscopy. On the basis of the five phases, the anthropogenic portion was estimated and are as follows: Mn (63%) > Zn (50%) > Cu (49%) > Cd (46%) > Fe (45%) > Pb (36%) > Co (34%). Then, anthropogenic contamination, as well as the ecological risk, was calculated using pollution load index (PLI), geoaccumulation index (I-geo), enrichment factor (EF), pollution index (I-POLL), potential risk of individual metal (E-r) and potential ecological risk (PERI). I-geo and PLI show a continuous anthropogenic impact on the sediments in the post-monsoon months. I-POLL shows Mn falls in the 'Moderately contaminate' category, Cu and Zn falls in the 'Uncontaminated to moderately contaminate' category and rest falls in the 'uncontaminated category'. From EF, Zn (7.98), Cd (6.40) and Pb (5.08) are significantly enriched in the river sediments indicating the source of metal as anthropogenic in origin. E-r value of Cd in September is greater than 80, indicating 'considerable ecological risk'. PERI value has the maximum for Cd (126.92), which belongs to the category 'Low ecological risk'. Even though PERI indicates 'low ecological risk' to the sediment contamination, continuous monitoring and management are needed in rivers to avoid significant pollution from domestic, commercial activities, agriculture and industrial activities as EF values are high for Zn, Cd, and Pb, which shows anthropogenic contamination.