Assessment of trace metals and its pollution load indicators in water and sediments between Upper and Grand Anicuts in the Cauvery

Abstract

This study focuses on the contamination level of trace metals in river water, its sediments, the surrounding groundwater and its soil sediments. The region stretching between Upper Anicut and Grand Anicut in the Cauvery delta in Trichy District, Tamil Nadu, India, was chosen for study. This stretch of the river Cauvery experiences maximum quantum of water flow during the monsoon season. Once a perennial river, in recent decades, it experiences only seasonal flow. The Cauvery is the lifeline of millions of people and various flora and fauna. The Cauvery irrigates thousands of hectares of cultivable land, and its delta has sustained the enviable name—the ‘Granary of the South.’ However, the contamination of water and sediments poses grave threat to all life forms. In this study, by using atomic absorption spectrophotometer (AAS) the presence of seven trace metals Cd, Cr, Cu, Ni, Fe, Pb and Zn in water and sediments was ascertained. The trace metal contamination level in sediments was predicted by pollution load indicators such as pollution load index (PLI), geo-accumulation index (I_geo), enrichment factor (EF) and contamination factor (CF).The concentration level of trace metals in water and sediments was determined for four different seasons of a year, at 11 locations (five from river sites and six from land sites) along the Cauvery. A higher-level concentration of Fe 2.18 mg/l and 2.95 mg/kg was found in water and sediments, respectively, during the four different seasons. It was also found to have a low-level concentration of Ni with a range of 0.09 mg/l and 0.24 mg/kg in water and sediments, respectively, for four different seasons. Based on pollution load indicators, the PLI values of trace metals in sediment samples in all four seasons were less than zero; the I_geo values of trace metals in sediment in all four seasons were less than zero; the contamination factor (CF) values of all heavy metals except cadmium in sediments samples in all seasons were less than zero; the enrichment factor (EF) value of trace metals in all sediment in all four seasons was higher than 40. Eventually, it was disclosed that the study area was lightly contaminated by the presence of the trace metals Fe and Cd than other trace metals. It is a known fact that all living organisms need some trace metals including cobalt, copper, iron, manganese, molybdenum, vanadium, strontium and zinc. When the levels of essential metals exceed the desirable limit, they prove to be detrimental to the organisms. Similarly, the presence of nonessential metals like cadmium, chromium, mercury, lead, arsenic and antimony in water bodies causes undesirable effects on human and aquatic life. Once these metals enter into the system, they are capable of reacting with a variety of binding sites in the human body. Thus, this study assumes significance.