nitrates in water
Concentrations of nitrates in water of rain of up to 5 mg/l have been observed in industrial areas . In rural areas, concentrations are somewhat lower. The nitrate concentration in surface water is normally low (0–18 mg/l) but can reach
high levels as a result of agricultural runoff, refuse dump runoff or contamination or animal wastes. The concentration often fluctuates with the season and may increase when the river is fed by nitrate-rich aquifers. Nitrate concentrations have
gradually increased in many European countries in the last few decades and have sometimes doubled over the past 20 years. In the United Kingdom, for example, an average annual increase of 0.7 mg/l has been observed in some rivers.
concentration of nitrates in water is analysed in abram laboratory
The natural concentration nitrates in water groundwater under aerobic conditions is a few milligrams per litre and depends strongly on soil type and on the geological situation. In the United States of America (USA), naturally occurring levels do not exceed 4–9 mg/l for nitrate and 0.3 mg/l for nitrite . As a result of agricultural activities, the nitrate concentration can easily reach several hundred milligrams per litre. For example, concentrations of up to 1500 mg/l were found in groundwater in an agricultural area of India.
In the USA, nitrates are present in most surface water and groundwater supplies at levels below 4 mg/l, with levels exceeding 20 mg/l in about 3% of surface waters and 6% of groundwaters. In 1986, a nitrate concentration of 44 mg/l (10 mg of nitratenitrogen per litre) was exceeded in 40 surface water and 568 groundwater supplies. Nitrite levels were not surveyed but are expected to be much lower than 3.3 mg/l.
The increasing use of artificial fertilizers, the disposal of wastes (particularly from animal farming) and changes in land use are the main factors responsible for the progressive increase in nitrate levels in groundwater supplies over the last 20 years. In
Denmark and the Netherlands, for example,nitrates in water are increasing by 0.2–1.3 mg/l per year in some areas.Because of the delay in the response of groundwater to changes in soil, some endangered aquifers have not yet shown the increase expected from the increased use of nitrogen fertilizer or manure. Once the nitrate reaches these aquifers, the aquifers will remain contaminated for decades, even if there is a substantial reduction in the nitrate loading of the surface.
In most countries, nitrate levels in drinking-water derived from surface water do not exceed 10 mg/l. In some areas, however, concentrations are higher as a result of runoff and the discharge of sewage effluent and certain industrial wastes. In 15
European countries, the percentage of the population exposed to nitrates in waterabove 50 mg/l ranged from 0.5% to 10%
this corresponds to nearly 10 million people. Individual wells in agricultural areas throughout the world especially contribute to nitrate-related toxicity problems, and nitrate levels in the well water often exceed 50 mg/l.
Chloramination may give rise to the formation of nitrite within the distribution system, and the concentration of nitrite may increase as the water moves towards the extremities of the system. Nitrification in distribution systems can increase nitrite
levels, usually by 0.2–1.5 mg of nitrite per litre, but potentially by more than 3 mg of nitrite per litre