Majid Jahangir
Srinagar, July 14 (UNI) Kashmir's lakes, including the famed Dal Lake, are becoming contaminated with heavy metals, and this pollution is finding its way into water chestnuts that people eat.
A new scientific study has raised concerns over heavy metal contamination in water chestnuts (Trapa natans), locally known as ‘Gaur’, harvested from some of Kashmir's major water bodies, with researchers identifying Dal Lake as the most polluted among the four water bodies examined.
Published in “Scientific Reports”, the study analysed water, sediments and different parts of water chestnut plants collected from Dal Lake, Hokersar Wetland, Manasbal Lake and Wular Lake to assess the accumulation of eight heavy metals, including cadmium (Cd), chromium (Cr), copper (Cu), cobalt (Co), iron (Fe), manganese (Mn), nickel (Ni) and zinc (Zn).
Dal Lake is a 22-square-kilometre urban water body fed by channels of the Jhelum River. Hokersar Wetland, a 13.75-square-kilometre Ramsar site nourished by the Doodhganga and Sukhnag streams, serves as a vital wintering ground for migratory birds. Manasbal Lake, spread over 2.81 square kilometres, is Kashmir's deepest lake and is renowned for its crystal-clear, spring-fed waters. According to the study, the roots of water chestnut plants accumulated the highest concentrations of heavy metals, indicating that the plants absorb contaminants primarily from polluted sediments.
The researchers found that contamination levels followed a clear spatial pattern, with Dal Lake recording the highest pollution load, followed by Hokersar Wetland, while Manasbal and Wular Lakes showed comparatively lower contamination.
According to the study, the roots of water chestnut plants accumulated the highest concentrations of heavy metals, indicating that the plant absorbs contaminants primarily from polluted sediments. Iron recorded the highest concentration in roots at 322.50 mg/kg, while zinc reached 82.45 mg/kg. Although fruits contained significantly lower concentrations than roots, researchers detected cadmium levels of up to 0.11 mg/kg in edible fruits collected from Dal Lake.
The study noted that cadmium concentrations in fruits from Dal Lake were approximately 5.5 times higher than the World Health Organization's recommended limit of 0.02 mg/kg. Zinc concentrations also exceeded guideline values, although the researchers observed that zinc and iron remain nutritionally important elements when consumed within safe limits.
Using internationally accepted health risk assessment methods, the researchers concluded that regular consumption of water chestnuts from Dal Lake could pose a non-carcinogenic health risk due to cadmium exposure. While the calculated Target Hazard Quotient (THQ) for most heavy metals remained below the threshold of concern, cadmium exceeded safe limits for samples collected from Dal Lake.
The scientists attributed the contamination primarily to untreated domestic sewage, agricultural runoff, urban waste, houseboat discharges and other human activities that have increasingly degraded Kashmir's freshwater ecosystems. They cited official figures showing that out of nearly 193 million litres of sewage generated daily in Srinagar, around 140 million litres remains untreated, with a substantial portion eventually reaching Dal Lake.
Besides analysing plant tissues, the researchers also examined water quality and bottom sediments. They reported elevated levels of biochemical oxygen demand (BOD), chemical oxygen demand (COD), nutrients and heavy metals in Dal Lake, indicating severe organic pollution and declining water quality. Sediments contained even higher concentrations of contaminants than the overlying water, highlighting their role as long-term reservoirs of pollution.
Despite the contamination concerns, the study also identified a positive aspect of the water chestnut plant. Researchers found that the plant possesses a strong ability to absorb and retain heavy metals, particularly in its roots, making it a promising candidate for phytoremediation—the use of plants to remove pollutants from contaminated environments.
Bioconcentration factor values greater than one for several metals indicated that Trapa natans acts as an efficient metal accumulator. However, low translocation factors showed that most contaminants remain trapped in the roots instead of moving into the edible fruits.
The authors cautioned that even though the plant can help reduce pollution levels in lakes, the presence of toxic metals in edible tissues raises concerns about their possible entry into the human food chain.
The study concluded that increasing anthropogenic pressure on Kashmir's freshwater ecosystems is directly influencing heavy metal availability in aquatic plants. It recommended continuous biomonitoring of lakes and routine screening of edible water chestnuts, particularly those harvested from highly polluted water bodies such as Dal Lake, to safeguard public health while supporting conservation of the region's freshwater ecosystems.
UNI MJR ARN