RESUMO
Pollution in Periyar River in Kerala is increasing rapidly and mercury is a major pollutant that is released by the industries situated on its banks. Mercury toxicity is difficult to diagnose and can eventually result in conditions such as Minimata disease if not controlled. An attempt has been made in this study to assess the extent of mercury contamination in the river by dithizone method and compare it with the maximum permissible level for river water. A comparison has also been attempted to assess the extent of mercury contamination of Periyar with that of other contaminated rivers of India. A total of 40 water samples each were collected from 10 different locations of Periyar river at surface level and at 1 metre depth. The samples were analysed by dithizone method of heavy metal extraction with the help of spectrophotometer. The mean mercury value obtained (at both levels) was 0.03 mg/L, which is 30 times more than the permissible level allowed in water (0.001 mg/L). The values obtained at 1m depth are slightly higher than at the surface. The mercury levels are comparable to that of polluted tributaries of other rivers such as Ganga and Yamuna in north India. It is imperative that the use of out-dated, inefficient methods of water treatment should be replaced with controlled release of mercury through separate sewer systems, and employing membrane cells, chitosan and granulated slag as adsorbents.