Toxic harvest from Bengaluru lakes

Scientists in Bengaluru have found several heavy metals in crops and vegetables grown on soil irrigated with water from six lakes in the city.

The three-year study, which was published in the journal Current Science, found that contamination in Margondanahalli, Yele Mallappa Chetty, Hoskote, Varthur, Byramangala and Jigani lakes was leading to heavy metal accumulation in agricultural soils in areas around them.

“In some cases, fertile land, whose yield was high years ago, are producing less,” said Professor N B Prakash of the Department of Soil Sciences and Agricultural Chemistry at the University of Agricultural Sciences in Bengaluru, one of the authors of the study.

The researchers said this was a result of farmers using lake sediments and silt in agricultural fields. “The heavy metals are absorbed by crops along with other essential plant nutrients,” Professor Prakash said.

The study found total chromium levels across the six areas ranging from 89.36 mg per kg to 145.21, as opposed to the 100 mg per kg limit set by India. Total cadmium levels ranged from 2.87 to 5.33 mg per kg as opposed to the limit of 3 set by India. Nickel levels ranged from 30.38 to 50.51 mg per kg, when the limit is 50.

Chromium levels exceeded the European of standard of 0.2 mg per kg in all crops. Particularly high concentrations were found in knol kohl (German turnip), spinach, tomato, amaranthus, paddy grain, beans and beetroot.

“This contamination build-up is due to decades of pollution,” Dr Prakash said.

Poor urban planning

The researchers said the problem is that unlike other Indian cities, lakes in Bengaluru have become part of the city’s drainage system where untreated and partially treated domestic sewage mixes with industrial effluents from a number of units like garment factories, electroplating industries and distilleries.

However, environment scientist Dr T V Ramachandra of the Indian Institute of Science who weighed in on the paper in an independent capacity, said the culprits are primarily industries.

“The findings are especially worrying because industrial contaminants are ending up in the meal plate,” he said. “This adds to the body of evidence that industries are continuing to pollute the landscape around them. According to environmental norms, they are supposed to have zero discharge. They need to be made answerable.”

Nutritionist and wellness consultant Sheela Krishnaswamy said the health implications are wide. “The ingestion of large quantities of heavy metals through vegetables could be potentially carcinogenic,” she said, adding that children are more at risk of neurotoxicity than adults.

She also clarified that cadmium is believed to cause oxidative stress in the body. “Damage from oxidative stress has been associated with various diseases like cancer, cardiovascular disease, insulin resistance and skin problems,” she said.