28 Nitrate pollution of groundwater and associated human health disorders Deepanjan Majumdar* and Navindu Gupta Division of Environmental Sciences Indian Agricultural Research Institute New Delhi *correspondence e-mail : joy_ensc@yahoo.com Telephone : +91-11-5781490/5786367; Fax : 91-11-5766420/5724273 Abstract Nitrate formed by the biochemical activities of microorganisms or added in chemically synthesized forms to lithosphere and biosphere enters hydrosphere with relative ease, as all these environmental components are dynamically interconnected. High solubility of nitrate in water and its low retention by soil particles make it a major component of groundwater in areas of high nitrate formation. Nitrate enters the human body through the use of groundwater for drinking and causes a number of health disorders, namely, methaemoglobinemia, gastric cancer, goitre, birth malformations, hypertension, etc., when present in high concentration in drinking water. With the increasing use of nitrogenous fertilizers in Indian agriculture and huge amount of organic waste generated by massive Indian population, groundwater nitrate pollution in many regions of India has assumed alarming proportions and may aggravate in the coming years. Introduction Groundwater has been used for drinking for a long time and its purity has made it a well-known source of potable water. Advancement of human civilization has put serious questions to the safe use of groundwater for drinking. Apart from its depletion due to excessive use, the quality has degraded due to the transport of various organic and inorganic pollutants to the groundwater. Nitrate (NO3 - ) is one of the several inorganic pollutants contributed by nitrogenous fertilizers, organic manures, human and animal wastes and industrial effluents through the biochemical activities of microorganisms. Excessive use of nitrogenous fertilizers in agriculture has been one of the primary sources of high nitrate in groundwater (De Roo, 1980; Schepers at al., 1984). Apart from nitrate, nitrogen is applied in ammonium (NH4 + ) and amide (NH2 - ) forms, which generates nitrate in soil system through mineralization, which is fairly rapid in tropical and subtropical soils. Due to its high solubility in water and low retention by soil particles, nitrate is prone to leaching to the subsoil layers and ultimately to the groundwater, if not taken up by plants or denitrified to N2O and N2. The rate of leaching is governed by the soil properties and amount of water present in the soil system. The arrival of nitrate to groundwater can be enhanced by shallow groundwater table; excessive application of nitrogenous fertilizers, manures and irrigation; and abundant rainfall. Livestock feeding, barnyards, septic tanks, animal and human contamination are the other important sources contributing high amounts of nitrate to groundwater (Stevenson, 1986). In and around areas of high urbanization and industrialization, municipal and industrial wastes may contribute high levels of nitrate to the groundwater (Handa, 1983). As and when the nitrate rich groundwater is pumped out and used for drinking, it causes a number of health disorders in humans. Different organizations and countries have set standards for NO3 in potable water (Table 1), to safeguard public health from the hazards associated with high concentration of nitrate. The anthropogenic element in the nitrate pollution of groundwater can well be perceived from the fact that terrestrial waters in uninhabited and less polluted regions like high altitude lakes, glaciers have negligible nitrate content. In Central Himalayan snow and ice, NO3 content is about 0.5 mg/l (Lunkad, 1994) while worlds average river water contains 1.0 mg/l NO3 and the ultimate sink of terrestrial waters, the oceans, on average, have 0.67 mg/l NO3 (Mason and Moore, 1985). Indian Journal of Environmental Health (2000), 42 (1): 28-39.