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Imbibing toxic/heavy metals through leafy vegetables

Long term and indiscriminate application of raw sewage effluent to agricultural field without prior treatment which contains heavy metals in association with suspended solids (sludge) particles may cause accumulation of toxic metals in soils (with subsequent transfer to food chain).

RESEARCH WAS conducted (during 2001) on heavy metal content of plant samples of sewage irrigated area of Coimbatore district. Leafy vegetables were found with very high levels of heavy metal contamination including Cd. Zn, Cu. Mn and Pb.

Various plant samples collected from sewage farms of Coimbatore (Tamil Nadu) and also from other taluks of Coimbatore district showed wide variation in the micronutrient content.

Alas, These leafy vegetables containing toxic metals are being supplied to the consumers. The analytical data of surveyed plant samples indicated that micronutrient (viz, Fe. Mn. Cu and Zn) content of the plant samples fell under safe range of concentration with few exception (classified based on standard critical limits).

The high Fe content followed by other micronutrient might be due to high content of micronutrient in the sewage water/sewage sludge.

The heavy metal content in amaranthus, paalak grown in Ukkadam sewage farm, at Coimbatore is being supplied to people of Coimbatore city.

The concentration of the heavy metals ranged from 16.4 to 21.4 mg Cd kg-1, 17.4 to 23.8 mg Ni kg-1 and 21.2 to 26.0 mg Pb kg-1 respectively. Among the heavy metals Cadmium and Nickel content were above the toxic limit in the amaranthus grown in Ukkadam sewage farm.

Fodder grasses such as the cumbu napier and water grass grown in this area were also supplied to the animals of Coimbatore city which was loaded with high content of heavy metals.

The content of heavy metals ranged from 17.2 to 22.0 mg Cd kg-1. 17.0 to 33.0 mg Ni Kg-1; 20.28 to 23.41 mg Pb kg-1. And the toxic levels of these metals fell under the toxic, excessive and below excessive levels respectively.

This study, indicated that long term and indiscriminate application of raw sewage effluent or letting of sewage water directly to agricultural field without prior treatment which contains heavy metals in association with suspended solids (sludge) particle may cause accumulation of toxic metals in surface and subsurface soils (with subsequent transfer to the food chain).

And build up of heavy metals in soil profile may prove harmful not only to plants and animals but also to consumers of the harvested crops.

A similar research conducted at Delhi (`Vegetables eating up vegetarians' published in The Hindu dated 27th march 2003) also found the presence of deadly heavy metals in vegetable samples collected from across the capital.

It is very disheartening to hear such a report across the various metropolitan cities.

If this continues further, human beings will to face a serious health hazards due to heavy metals toxicity.

J. Somasundaram

CSWCRTI, Research Centre Kota 324 002, Rajasthan

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