Crops grown in Bangalore high on toxic heavy metals
Scientists in Bangalore, India have found toxic levels of four heavy metals, chromium, nickel, cadmium and lead, in crops and vegetables grown on soil irrigated with water from six lakes in the city, reports a study published December in Current Science.
According to the study, the 17 lakes in and around Bangalore, a bustling city of more than 12 million people, have become part of the city's drainage system, into which flow untreated sewage and industrial effluents from garment factories, electroplating industries, distilleries and other small-scale but polluting units. However, many farmers are now using water from these lakes to irrigate and water vegetable crops.
For the study, N.B. Prakash, a professor at the University of Agricultural Sciences, Bangalore and one of the authors of the study, analysed the soil and vegetable crops such as spinach, coriander greens, amaranth and kohlrabi, irrigated with water from six of these lakes—Margondanahalli, Yele Mallappa Shetty, Hoskote, Varthur, Byramangala and Jigani.
Soils irrigated by these lakes accumulate heavy metals to varying degrees depending on their concentration in the water and the frequency of irrigation, said the authors of the study. "The heavy metals are absorbed by the crops along with other essential plant nutrients."
Cadmium can be a carcinogen and an endocrine disruptor which can lead to fertility and reproductive issues in men and women while long-term exposure can lead to bone diseases, says Dharmanand.
Lead toxicity may result in anaemia, renal diseases and learning difficulties in children, excess chromium may lead to blood and gastrointestinal diseases and lung cancer while nickel is toxic to kidneys and reproductive organs, she adds.
The study found chromium content ranging from 7.93 to 56.15 milligrams per kilogram, exceeding the EU standard of 0.3 milligrams per kilogram, in all crops, but particularly high in coriander, spinach, radish, amaranth and kohlrab. Nickel exceeded permissible limits by 25 percent in all samples tested.
"If large water bodies turn toxic, it will become very difficult to purify them," says Prakash. "Farmers using contaminated lake water for farming end up contaminating the soil as well. There should be strict rules about the discharge of sewage water from residential apartments."
Remedial methods to remove heavy metals include physical excavation of contaminated soil, chemical treatment such as addition of lime, phosphates and silicon, biological methods including bioremediation and phytoremediation, says Prakash. "These would reduce the biomagnification of heavy metal toxicity."
C.A. Srinivasamurthy, former director of research at the Central Agricultural University, Imphal, Manipur, says: "This in-depth work on heavy metal contamination in soils and crops grown in peri-urban areas around Bangalore is very important as the lakes in and around Bangalore are being contaminated by indiscriminate discharge of untreated sewage and industrial effluents."
Can the situation be remedied? "The preliminary measure is to treat the wastewater (sewage and industrial effluents) at the source and well before it is allowed to reach large water bodies like Bangalore's lakes," says Prakash.
"Policymakers need to look into preventing heavy metal contamination of lakes, soils and crop plants. Stringent action must be taken by Bangalore Water Supply and Sewerage Board and Karnataka State Pollution Control Board in this regard," Prakash tells SciDev.Net.