Heavy metals poison Veeranam lake in Tamil Nadu

Wetlands in India, under threat!

Inland wetlands that include freshwater habitats such as lakes and ponds are valuable and not only support aquatic organisms, but also provide water for agriculture, drinking and support livelihoods of large sections of the population in India.

However, they are increasingly under threat due to contamination from diverse sources, with heavy metals being one of the important sources of water pollution. Heavy metals are harmful as they alter the physiology and behaviour of large and small animals living in the water and consequently affect the health of human populations who depend on the wetlands for their food and water.  

Waterbirds as bioindicators to assess health of wetland ecosystems 

A large number of animals - large and small live in and around lakes and ponds and are affected by changes in the water quality of the wetlands. Many of them can be useful as indicators to understand the state of the wetlands. 

Heavy metal pollution of the Veeranam lake in Tamil Nadu

The study aims at determining the level of heavy metals in the tissues, liver, kidney, and feathers of waterbirds mainly herons and their prey species, such as crabs, prawns, snails, slugs and fish in the Veeranam Lake in Tamil Nadu, which is one of the largest lakes in Southeast Asia and provides drinking water as well as seasonal feeding and breeding grounds for numerous species of waterbirds.

Veeranam Lake is about 30 km from the Bay of Bengal and was dug by the Chola King, “King Paranthaga” during the 19th century. The lake area is about 25 km² and has the capacity to store 930 Mcf of water. The lake’s 34 sluices provide water to 40,000 acres of agricultural farmland every year. Vadavar and Sengal rivers take water from the Keealani (Lower Anaicut) of the Cauvery and discharge into the Veeranam Lake. Every day, 7000 ft³ of water is discharged for agricultural use in the nearby areas of the lake.

Besides being an important water reservoir supplying drinking water to the capital of Tamil Nadu, the lake is also a biodiversity hotspot and a home to various seasonal and migratory waterbirds and their prey species.

The presence of seven different metals, such as arsenic (As), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), and zinc (Zn), was evaluated from the tissues, liver, kidney, and feathers of dead carcasses of the Indian pond heron and black-crowned night heron and their prey species such as freshwater crab and prawns and different kinds of fish found in the waters.

The study found that:

Large amounts of heavy metals were found in the tissues, organs and feathers of waterbirds, and crab and fish in the lake.

Lead concentrations in fish, snails, crabs, prawns etc was much higher than in other species. Studies show that the mating success of waterbirds is negatively affected and there is an increase in cellular stress and memory loss due to excess deposition of lead in the bodies of waterbirds. 

Higher levels of chromium were found in fish which got deposited into the birds as birds ate fish, which was much higher than the threshold level at 2.8 lg/g. 

High levels of nickel were found in the feathers and liver of both bird species. The highest concentration of nickel was obtained from a fish species (C. batrachus), a primary food source for the Indian pond heron and the black-crowned night heron. Nickel was also found to be higher in the lake dwelling animals in the food chain and food web like fish and crabs. Nickel levels in two species of waterbirds and their prey were above the threshold limits. The buildup of nickel in birds can impair their cellular communication, flying mechanics, and lead to tumor development and death.

The feathers of the Indian pond heron and liver of the black-crowned night heron were found to have a higher zinc concentration. The study found that prey animals had the highest levels of zinc, particularly crabs and fishes.

The liver of the Indian pond heron, the kidney of the black crowned night heron, and their prey such as crabs and fish had high levels of arsenic. The amount of arsenic among bird species and fish was much higher than that found in earlier studies. The concentrations of copper and mercury were relatively lower in the waterbirds as comapred to other metals.

Metal pollution was due to discharge of effluents from industries, agricultural wastes and sewage from cities into the lake

The Veeranam lake supplies drinking water to the surrounding areas as well as to Chennai and irrigates hundreds of hectares of agricultural land with water. The primary source of pollution of the lake due to metals is because of the small, medium, and large-scale industries that include tanneries, battery factories, and distilleries that are transferred to the lake through the Cauvery river.

In addition, the river also collects wastewater from the river basin communities that gets deposited in the lake. The river also carries sewage from the local panchayat, cities, and municipalities and is contaminated with pesticides, fertilizers, and chemicals used for cultivation of crops in the region.

Protection of wetlands such as the Veeranam lake is crucial

This highly contaminated water can harm both animal and human health, since the lake serves as a source of potable water for a large section of the population.  The study highlights the urgent need:

• To manage, protect and maintain the ecological balance of the lake and protect the health of humans who depend on the lake for their livelihood and survival. 
• To monitor the health of wetlands such as lakes as they provide clean drinking water, support livelihoods and serve as a habitat for many types of animals and birds.