Nitrate Contamination in Groundwater

Nearly half the water that is used for drinking and cooking worldwide comes from groundwater. There has been growing global concerns with regard to contamination of groundwater with nitrates brought about by intensive agricultural practices and lack of proper regulations. Nitrate contamination poses a serious threat to human health so this issue needs to be immediately addressed.

Factors that contribute to this problem include increasing use of synthetic or organic fertilizers, disposal of organic waste, and changes in landscape patterns. All of these have caused nitrate levels in the groundwater to rise to alarming proportions and this has prompted the World Health Organization (WHO) to take firm action. The WHO has established a maximum threshold of 10 mg/L nitrate‐N for drinking water to avoid problems such as hypoxemia especially in infants.

What are nitrates?

Nitrates are inorganic compounds that are found in the environment and are produced either naturally or synthetically. It is composed of one atom of nitrogen (N) bound with three atoms of oxygen (O) creating nitrate with the chemical designation of NO3. When one of the oxygen atoms is removed through a reduction process it produces a compound called nitrite (NO2). It is these nitrites that can cause health problems. When humans eat food with nitrates, oral bacteria converts the nitrates into the more dangerous nitrites form.

What health issues can come from nitrates?

Nitrates have been associated with causing a condition known as methemoglobinemia. Our red blood cells contain a compound called hemoglobin which is responsible for carrying oxygen to the tissues in the body. When nitrites are present, they convert the hemoglobin to a methemoglobin which is incapable of carrying oxygen which results in tissue hypoxia. In adults, enzymes can convert methemoglobin back to hemoglobin so methemoglobin levels normally should not exceed 1 percent. Infants however, do not have enough of these enzymes and this results in higher methemoglobin levels causing methemoglobinemia.

At high levels where the methemoglobin levels exceed 10 percent, symptoms like cyanosis occur. Babies will have bluish mucous membranes and may also have digestive and respiratory problems. At 20 – 30 percent, tissues will receive almost no oxygen creating a state known as anoxia. At 50 – 70 percent, brain damage or death can occur.

Methemoglobinemia can be easily remedied provided that the levels aren’t too high otherwise permanent damage may occur. Thus restricting exposure to nitrite and nitrates are important in preventing methemoglobinemia.

How do you restrict exposure to nitrates?

By adhering to the mandated nitrate levels of 10 mg/L as stipulated by the WHO, the levels of nitrates would be insufficient to increase the amount of methemoglobin in the body. Some individuals however, may experience increased susceptibility to methemoglobinemia because of exposure to antioxidant medications and chemicals or an existing medical condition that impairs the conversion of methemoglobin to hemoglobin (pregnancy or other rare diseases).

Conventional water treatment processes such as coagulation, sedimentation, filtration and chlorination are not very effective for nitrate removal. The key for the effective removal of nitrates from municipal water supplies include ion exchange, biological denitrification, reverse osmosis and electrodialysis.

It is important to test nitrate concentrations in the drinking water in your home. Households receiving water from sources that have consistently high levels of nitrates should consider installing a drinking water treatment device or finding an alternative drinking water source. Also remember that boiling water is not effective way of reducing nitrates.

Groundwater is a vital resource. Once these pollutants get into the groundwater, they can end up in rivers and lakes. All levels of government are beginning to take action to protect Canadian groundwater supplies. As individuals, Canadians must also do their part in safeguarding groundwater for future generations.

If you are a farmer in the Niagara Region and are interested in considering biosolids as a potential application to your fields, please call us on 1 (877) 479-1388.


Nitrate Contamination in Groundwater
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