 Parts of Varanasi are contaminated with industrial chemicals including toxic heavy metal . Studies of wastewater from Varanasi 's sewage treatment plants identify that water 's contamination with metals and the reuse of this water for irrigation as a way that the toxic metals come to be in the plants that people grow for food . One studied example is <unk> , a popular leafy vegetable which takes up heavy metal when it is in the soil , and which people then eat . Some of the <unk> sludge contains minerals which are fertiliser , which could make polluted water attractive to use . <unk> used in local farming are persistent enough to be spread through the water , to sewer treatment , then back to the farms as wastewater . 
