Heavy metal pollution in the Sabarmati river

The bathing standards for water bodies do not include heavy metals. Since the Sabarmati river receives the treated/un-treated industrial effluents, it becomes important to study the extent of heavy metals present in the river, especially downstream of Ahmedabad as the river is the only source of water for the villages downstream. The Bureau of Indian Standards has defined standards for heavy metals in the water used for drinking purposes, as well as for the water to be used for irrigation. Some heavy metals such as copper and zinc are essential as trace elements to maintain the metabolism of the human body, but at higher concentrations they may have toxic effects. Many other metals (e.g. mercury, cadmium and lead) have direct toxic effects on human health. Heavy metals are non-biodegradable and tend to bio-accumulate and bio-magnify in the food chain. Even if heavy metals are present in an undetectable concentration, their biomagnification may lead to a concentration which becomes toxic. Long-term exposure to these may cause damage to the nervous system, lungs, kidneys, liver and other vital organs.

The analysis of heavy metals in the Sabarmati at Miroli (monitoring point downstream of the city) is presented in the Table 7.2. There are 23 samples taken during the period April 2014 to March 2017, for which details are summarised.

It is observed that a large number of samples do not meet the drinking quality standards for heavy metals such as chromium, copper, iron, lead and nickel. The only heavy metal which meets the standards is zinc. Even if we consider the standard for water to be that which is used for irrigation, a large number of samples fail to meet the desired norms for iron and lead.

It can be summarised that the Sabarmati river undergoes a complete degradation as it leaves the city, though the water quality meets the norms when the

TABLE 7.2 Heavy metal pollution in the River Sabarmati

Source: Unpublished data from GPCB.

river enters the city. When it leaves the city, after receiving the sewage discharge from the STPs and the industrial effluents, the river becomes ‘dead,’ i.e. dissolved oxygen becomes zero. The impact of seasonal variations on the river quality is not much. The quality is bad throughout the analysis period—for all the six years for which monthly data has been analysed.