Nitrates in Water

What are Nitrates?

Nitrates occur naturally in soil and water. They are essential for plant growth, and consequently traces of nitrates are also found in vegetables that we eat. As nitrates enhance crop growth, they are often added to soils in the form of fertilizers to enrich the soil in an effort to yield better crops. Nitrates are highly mobile and are not naturally filtered out as they move through the soil. Consequently, nitrates from these fertilizers may leach through the soil or get washed into waterways by rainwater or irrigation runoff, where they can contaminate ground water and surface water systems. Other sources of nitrate as drinking water contaminants include: run off of animal manure from farmlands, municipal waste water and sludge, and septic tank seepage.

What are the Risks of Drinking Water High in Nitrates?

Risk to Humans

Nitrates are listed as drinking water contaminants that can cause health problems by the Environmental Protection Agency, who have set a maximum acceptable safety level of nitrates in drinking water at 10mg/L or 10 parts per 1000. While water with a higher level of nitrates may be harmless to most people, water above this safety limit poses a huge risk to infants under six months. Consuming water with a high level of nitrates can cause methemoglobinemia, commonly known as blue baby syndrome, which can be fatal if not treated immediately. Infants under six months do not have an adequately developed digestive system, and as a result have a larger amount of gut bacteria that are able to convert nitrates into nitrites. When nitrite is absorbed into the bloodstream, hemoglobin, which is responsible for carrying oxygen in the blood, is converted to methemoglobin. 

As methemoglobin does not not carry oxygen as effectively, this results in oxygen supply to vital organs, including the brain being reduced. While methemoglobin in the blood of adults usually changes back to hemoglobin, methomoglobin in infant blood does not. Consequently severe methemoglobinemia can develop, with the brain being starved of oxygen, resulting in brain damage or death. Others at risk from methomoglobinemia include pregnant women; people with reduced gastric acidity; and people who lack methomoglobin reductase, the enzyme responsible for turning methomoglobin back to hemoglobin.

Risk to animals

While animals can generally tolerate higher levels of drinking water contaminants, including nitrates, than humans, younger animals are more at risk from drinking water high in nitrates for the same reason as human infants. In infants this is whats known as "blue baby syndrome". Similarly, ruminants (sheep, goats, cows), which have a high presence of gut bacteria that are able to convert nitrates to nitrites, are also at risk. Horses are also vulnerable due to their large cecum and the role that bacteria play in digesting food in their gut.

Symptoms and Treatment

Symptoms of methemoglobinemia in humans usually include the skin turning blue (blue baby syndrome) as a result of reduced oxygen supply in the blood. Other symptoms include headache, dizziness, weakness and difficulty breathing. In animals the symptoms include stomach pain, diarrhea, weakness and poor motor coordination. If diagnosed in time, an injection of methylene blue will treat the symptoms and lead to a full recovery in both humans and animals.

Water Quality

Water from wells in rural areas, particularly agricultural areas, are more susceptible to nitrate contamination as a result of fertilizer runoff or runoff of animal manure into the groundwater. As nitrates are colorless and odorless, they can only be detected by chemical analysis of a water sample. If you draw drinking water from a private well it is advisable to have the water tested annually for drinking water contaminants, including nitrates.

Water Purification Treatment

Nitrates are not removed from water by boiling, adding softening agents, or by activated charcoal water purification filters. Water purification methods for nitrate contamination in drinking water include: distillation, reverse osmosis, ion-exchange, and blending. If you water has high levels of nitrates it is advisable to use one of the above recommended treatment methods, or to use water from an uncontaminated source until the problem is resolved. This is imperative if you have vulnerable members in the family. Water high in nitrates should under no circumstances be used for preparing formula for infants.

References

Environmental Protection Agency. Basic Information About Nitrate in Drinking Water. http://water.epa.gov/drink/contaminants/basicinformation/nitrate.cfm

Self, J.R. & R.M. Waskom. Nitrates in Drinking Water. Colorado State University Extension, Fact Sheet.
www.ext.colostate.edu/pubs/crops/00517.html

 
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