Research flags heavy metal contamination in vegetables across Bengaluru

Bengaluru: The use of wastewater to grow vegetables has led to a higher concentration of heavy metals in them, with researchers from EMPRI — who tested 400 samples of 10 vegetables — finding contamination above the permissible limits set by the Food and Agriculture Organisation (FAO).

Bengaluru, which hosts over a fifth of the state’s population, gets its vegetables from farmers’ networks in the outlying areas of Bengaluru Urban, Kolar, Chikkaballapur, Ramanagara and Bengaluru Rural. Hopcoms alone delivers 70 tonnes of vegetables while a majority of the population depends on private shops, ranging from pushcarts to supermarkets.

Researchers from Environment Management and Policy Research Institute (EMPRI) collected 400 samples from 20 stores across Bengaluru — five high-end supermarkets, five local markets, “organic stores” and Hopcoms. The samples of 10 vegetables — brinjal, tomato, capsicum, bean, carrot, green chilly, onion, potato, spinach and coriander — were examined to analyse the presence of heavy metals.

While the maximum permissible limit for iron is 425.5 mg/kg, beans bought from well-known organic shops had a concentration of 810.20 mg/kg, coriander 945.70 mg/kg and spinach 554.58 mg/kg. Among the vegetables from Hopcoms, onion had 592.18 mg/kg of iron.

Be it the supermarkets or small retail outlets, heavy metals exceeded permissible limits in most of the sampled vegetables. The FAO sets 0.2 mg/kg as the maximum limit for cadmium. But brinjal bought from a supermarket in BTM Layout had cadmium of 52.30 mg/kg. Coriander had 53.30/kg of cadmium, spinach 53.50 mg/kg and carrot 54.60 mg/kg.

Cadmium is a dangerous element that can cause toxicity in liver and lungs and impair the immune system. 

Lead, described as “purely toxic”, should not exceed 0.3 mg/kg. While it was below detectable levels in several

vegetables, beans from a supermarket had 12.20 mg/kg, raising concerns over the health of the people who consume the vegetable daily. The concentration of nickel was higher than the prescribed limit of 67.9 mg/kg in green chilly, carrot, potato, tomato and beans.

“It is clear from the present study that the edible portion of vegetables are hyper-accumulators of heavy metals. Taking into consideration the health risks associated with the consumption of these vegetables, it is suggested that cultivation should not use waste water as a source. Farmers should not resort to unethical farming practices such as irrigating crops with drainage and effluent waters,” the study said, adding a word of caution particularly about spinach.

The study flagged that leafy vegetables accumulate more heavy metals compared with others. This was due to the higher transpiration rate of plant to maintain growth and moisture, it said.

N Hema, the research scientist who led the one-year study, told DH that a wider study was required to look into three major issues. “First, the source of the vegetables needs to be traced to further ensure an evidenced-based approach. Second, we need to go deeper and prescribe maximum limits for each vegetable as well as exposure duration. Third, how the exposure affects children, adults and older people needs to be worked out. Lastly, a comprehensive study needs to be taken up to isolate the health impacts of vegetables on people,” she said.

Iron (permissible limit 425.5 mg/kg)

In samples tested:

Beans 810.20 mg/kg

Coriander 945.70 mg/kg

Spinach 554.58 mg/kg

Cadmium (permissible limit 0.2 mg/kg)

In samples tested:

Brinjal 52.30 mg/kg

Coriander 53.30/kg

Spinach 53.50 mg/kg

Carrot 54.60 mg/kg