KOCHI: The massive contamination of the Vembanad lake due to heavy metals and pesticide has reached alarming levels, posing a major health risk to humans through trophic transfer, it has emerged. It is a study by the Kerala State Pollution Control Board — to assess the lake’s contamination caused by heavy metals and pesticide content in water, sediment and organisms — which threw up the disturbing findings.
According to the research by CUSAT’s Marine Biology and Microbiology Department, long-term intake of high levels of heavy metals could well lead to a disruption of the body’s biological and biochemical processes. Vembanad Kol Wetland spread across 50,000 hectares is the largest wetland along the country’s south-west coast.
It is one of the most impacted zones —polluted by various organic and household waste, industrial activities and anthropogenic activities like agricultural disposal and land reclamation. The year-long study by Cusat researchers began in February 2017. And samples from 19 stations in the northern and southern parts of Thannermukkom barrage, Aroor in the north and Ranikayal on the southern side of the lake were analysed.
The study found there was drastic decline in the depth and transparency of Vembanad estuary. Higher alkalinity values were observed towards the northern stations. Southern stations recorded low dissolved oxygen level while the biochemical oxygen demand (BOD) was high.
Houseboat tourism, sewage discharge and spread of invasive plant species play a crucial role in the decline in dissolved oxygen level in the estuary’s southern parts. The phosphate, silicate and ammonia content was higher in the southern parts while nitrite and nitrate content was higher in the northern parts.
The highest sulphide concentration was detected at Punnamada, said S Bijoy Nandan, head of department, who coordinated the study. There was high concentration of zinc in the southern stretch and the Nehru Trophy Boat Race finishing point recorded the highest value of of 442 micrograms(mcg). In sediment, nickel concentration was found to be high in the southern stretch and Chithirakayal was found to be extremely contaminated. The Marthandam region showed higher values of heavy metals.
The study indicates that the southern part of the Vembanad backwaters suffers massive contamination from heavy metals. Waste dumping, rusted boats along the canals of Alappuzha and developmental activities are the main reasons for anthropogenic enrichment of heavy metals in the estuary, said Bijoy Nandan.