types of toxic chemicals in rivers
Tanneries are responsible for the most harmful type of toxins and when concentrated in clusters in a small area like Unnao, where more than 790 times the accepted standard of chromium is dumped into the river (nearly 1,125 tons) entire farms burn up. More details about the issues with chromium in point 7.
The toxicity of substances can be observed by (a) studying the accidental exposures to a substance (b) in vitro studies using cells/ cell lines (c) in vivo exposure on experimental animals. Chemical toxicants include inorganic substances such as, lead, mercury, hydrofluoric acid, and chlorine gas, and organic compounds such as methyl alcohol, most medications, and poisons from living things.