Sources, Toxicological Effects and Removal Techniques of Nitrates in Groundwater: An Overview

摘要

Nitrate is a major pollutant in groundwater in many parts of the world. Concentration of nitrate above 45 mg/L as nitrate and 10 mg/L as nitrate-nitrogen is unsuitable for domestic use. Usually nitrate as such is not potentially harmful for human health but metabolic reactions in the human body convert nitrate to toxic compounds, like nitrite and nitrosoamines. Nitrate levels above the maximum permissible limit in the human body cause methemoglobinemia or blue baby syndrome, increased infant mortality, abortions, birth defects, cancer, histopathological changes, deterioration of immune system of the body, hypertension, etc. Infants are more prone to diseases due to high nitrate consumption through drinking water compared to adults. This also affects animal health and causes eutrophication of water bodies due to nutrient abundance. Sources of nitrate in groundwater and surface water includes agrochemicals, surface runoff from irrigated lands, septic tanks, leakage from drainage networks, livestock wastes, manure storage, landfills, urban fertilizer use, industrial wastewater, sludge disposal, etc. Over fertilisation leaves traces of nutrients in the soil even after harvesting and causes accumulation of nitrate in vegetables thus reaching the food chain. Though treatment options, like electrodialysis, ion exchange, reverse osmosis, chemical and catalytic denitrification and biological denitrification are available, they are not cost effective, time consuming and have their own disadvantages. Of these, ion exchange method is the least expensive and most widely opted removal method following which is the biological denitrification method for nitrate reduction from water. Non-treatment methods recommended are mixing or blending the water having high and low concentration of nitrate to arrive at permissible levels, use the required amount of fertilizers for crops considering the already available nitrate in soil and water used for irrigation, alternate use of animal waste as organic manure and storing the manure on lined surfaces to prevent seepage and avoid leakage from septic tanks by proper construction, operation and maintenance measures. Pollution prevention by adopting strong policy measures for fertilizer use and educating the farmers may extend great support in the process.