Total Nitrogen: Health effects
Description
There are no specific health effects directly associated with total nitrogen as such - nitrogen is in fact an essential nutrient for life and integral constituent of protein.
The main health effects associated with nitrate and nitrite is methaemoglobinaemia (often referred to as 'blue-baby syndrome'). Infants and pregnant mothers are particularly susceptible to this condition. Nitrite oxidises haemoglobin to methaemoglobin a form which is unable to transport oxygen to body tissue. Although nitrite is the direct cause of methaemoglobinaemia, the toxicity of nitrate is the result of its reduction to nitrite within the body after ingestion.
Although nitrate and nitrite have not been demonstrated to be carcinogenic, nitrite does react with some compounds in the human stomach to form 'N-nitroso' compounds. Most N-nitroso compounds have been found to be carcinogenic to all animal species tested and consequently are also likely to be carcinogenic to humans. Data from a number of epidemiological studies have nevertheless only been suggestive in relation to this issue. Some geographical correlation studies have also suggested associations between nitrate levels in water supplies and some forms of gastric cancer, however, follow up studies have been equivocal. This could be the result of the intake of dietary components of vegetables, such as vitamins C and E, which decrease the risk of gastric cancer, may well mask or antagonise the effects of high nitrate intake in such correlation studies.
A more general concern in relation to the inorganic component of Total Nitrogen is its environmental effects, where elevated levels of nitrogen (and phosphorus) often cause enhanced algal growth. This may ultimately manifest itself as cyanobacterial (blue-green algal) blooms which can produce hepatotoxins, neurotoxins and endotoxins and affect human health through contact or consumption.
Entering the body
The main pathway of nitrate into the human body is through eating, where nitrate levels in drinking water are below 10 mg-nitrate/L (0.01 g-nitrate/L). Where nitrate levels in drinking water exceed 50 mg-nitrate/L (0.05 g-nitrate/L) drinking becomes the main pathway. Nitrite is usually found at low levels in water supplies, consequently food, particularly cured meats, provides the dominant source for the human body. Inhalation of oxidised forms of nitrogen as a result of air pollution is only a minor source. Note of course that nitrogen gas (N2) represents about 80% of the air we breath, although it is unreactive.
Exposure
Through eating food containing nitrates and/or nitrites, or by drinking water containing nitrates and/or nitrites in solution.
Health guidelines
NHMRC & ARMCANZ 1996 Australian Drinking Water Guidelines:
Nitrate: 50 mg-nitrate/L (i.e. 0.05 g/L). Levels of up to 100 mg-nitrate/L (i.e. 0.1 g/L) can be safely consumed by adults and children over 3 months of age. Where a water supply has between 50-100 mg-nitrate/L (i.e. 0.05 to 0.1 g/L) alternative water sources are needed for bottle-fed infants under 3 months of age. Although nitrite levels are generally not high in natural waters a standard of 3 mg-nitrite/L (i.e. 0.003 g/L) has been set. (NHMRC and ARMCANZ , 1996). In major Australian water supplies nitrate concentrations may range up to 18 mg-nitrate/L, (0.018 g/L) but is typically less than 0.15 mg-nitrate/L (0.00015 g/L). High concentrations of nitrate have been recorded in some groundwaters. Nitrite is generally not present in significant levels.
Key
Links to an another web site
Opens a pop-up window
