researchers from the University of Calcutta and the National Bureau of Soil Survey and Land Use Planning have found high levels of toxic heavy metals in an aquatic plant species in Tiljala wetlands on the eastern fringes of Kolkata.

"A rise in the levels of heavy metals has caused genetic changes in a duckweed species scientifically known as Lemna minor,' says Ashish Kumar Duttagupta, the lead researcher. The gene affected codes for the enzyme esterase, which is crucial to the detoxification process. The findings of the study were published recently in Environment International (Vol 30, No 6).

Spread over 250 square km, the Tiljala wetlands have become a virtual sink for urban and industrial wastes. The top layers of the waterbodies harbour large numbers of surface-active molecules that trap heavy metals. As duckweed is a floating plant, it is especially prone to contamination with heavy metals.

The study was based on about 50 samples of duckweed and water collected from the Tiljala wetlands. Nitric and hydrochloric acids were added to the samples to disintegrate and dissolve the plants. Each sample was then filtered and the concentration of heavy metals