What are Nitrate and Nitrite?
Nitrate and nitrite are naturally occurring chemicals that are part of the nitrogen cycle. Nitrate is used widely in inorganic fertilizers, in explosives, as a food preservative and as a raw chemical in industrial processes. Nitrite is used predominately as a food preservative, especially in cured meats. Nitrate is the more stable of the two forms of nitrogen but can be reduced by microbial action to nitrite, which is the more toxic form.

How do Nitrate and Nitrite enter our water?
Nitrate and nitrite are naturally occurring and are widespread in the environment. Both are products of the oxidation of nitrogen (which comprises roughly 78% of the atmosphere) by micro-organisms in plants, soil or water and, to a lesser extent, by electrical discharges such as lightning. Nitrate is more stable and can be transformed into nitrite. Nitrite levels in most water supplies are very low.

All sources of nitrogen are potential sources of nitrate. In water, especially groundwater, these sources include decaying plant or animal material, agricultural fertilizers, manure, domestic sewage, industrial wastewaters, precipitation, or geological formations containing soluble nitrogen compounds. The nitrate concentration in groundwater and surface water is normally low, but can reach high levels from agricultural runoff, or from contamination by human or animal wastes. Nitrate levels in Canadian municipal water supplies are generally less than 5 milligrams per litre of water though groundwater levels are often higher than surface water.

How do Nitrate and Nitrite affect human health?
Excessive levels of nitrate in drinking water have caused serious illness and sometimes death, especially in young infants. The harmful effect in adults and infants occurs when nitrate is converted in the body to nitrite. This interferes with the oxygen-carrying capacity of the blood, resulting in a condition called "methaemoglobinaemia". This condition is also known as "blue baby syndrome", because the symptoms include shortness of breath and blueness of the skin. Infants less than 3 months of age are particularly susceptible.

Nitrate and nitrite have not been found to directly cause cancer in animal studies. However, nitrate, after conversion to nitrite in the body, may react with certain foods containing nitrosamines (such as cheese) to form N-nitroso compounds. Some N-nitroso compounds are potent carcinogens in animal species and could be cancer-causing in humans.

How do Nitrate and Nitrite affect the aquatic environment?
Nitrate is less toxic than the other forms of nitrogen in the aquatic environment, such as nitrite and ammonia. There is growing evidence, though, that nitrate can have a harmful impact on the development of early life stages in aquatic organisms, by reducing the oxygen-carrying capacity of the blood, or by disrupting an ability to maintain proper balance of salts. Although not usually lethal to the organism at background levels, nitrate could cause stunted growth or limit survival by causing organisms to become lethargic.

Increased levels of nitrogen in the water, combined with phosphorus, can cause excessive plant and algal growth that depletes oxygen levels, possibly to lethal levels. Some algal blooms also produce toxins that can affect aquatic life or humans that consume them.

What are the Nitrate and Nitrite guidelines?
The Federal-Provincial-Territorial Committee on Drinking Water has established a guideline for nitrate of 45 milligrams per litre of drinking water. The guideline also states that in cases where nitrite is measured separately from nitrate, the concentration of nitrite should not exceed 3.2 milligrams per litre .

• Drinking Water Guidelines

Currently, there are no national guidelines for the protection of aquatic life for nitrate, although they are being developed. Canadian Water Quality Guidelines for the protection of aquatic life for nitrite are set at 60 micrograms per litre.

• Canadian Water Quality Guidelines for the Protection of Aquatic Life

What can individuals do to help?
To limit nitrate in the water supply:

• Limit fertilizer use and apply only at appropriate times. Nutrients in chemical fertilizers can run off into local waterways, and could enter sources of drinking water. If you must fertilize, always follow the application instructions. Never over fertilize.
• Control runoff and soil erosion. Reducing erosion and preventing runoff will reduce the amount of sediments and nutrients entering the watershed.
• Start a compost pile and recycle yard waste. This both reduces waste and creates a natural fertilizer for your lawn.
• Plant trees and shrubs. Both filter and control polluted runoff, take up nutrients, and reduce soil erosion.