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Water Pollution – Nitrates in Water

Written by Janice M on . Posted in Water & Environmental

What is Nitrate?

Nitrate is the most common dissolved form of Nitrogen to be found in water. It is also an important nutrient required by plants.

Human activities can greatly increase the amounts of nitrates found. There are often dangerous levels found in South Africa in groundwater (see Groundwater Nitrate Map below), according to recent research done by the CSIR. Sources of Nitrate include fertilizer, animal manure, discharge from sewage facilities, septic tank systems (these remove only half of the nitrate in wastewater, thus increasing groundwater nitrate concentrate). Thus, excessive Nitrate levels are common in rural areas.

Location of areas of high nitrate in groundwater in the Kalahari basin and different causes of high nitrate

Effects of High Nitrate Levels

  • Levels above 5 mg/l are undesirable in a water environment as this will disturb the ecosystem. Excessive plant growth will result, especially overgrowth of algae . This can clog streams and dams and use up too much oxygen, causing fish to die.
  • Water with nitrate contamination has the potential for other contaminants, such as bacteria and pesticides, to reach groundwater along with the contaminant.
  • Levels above 10 mg/l can be harmful to young babies and pregnant women. High concentrations can cause methoglobinemia, especially from drinking affected water in formula (blue baby syndrome). There are also links to longer-term human reproductive and cancer risks.
  • High nitrate levels are also harmful to ruminant animals. Concentrations over 100 mg/l are toxic.

Criteria in South Africa:

  • Fish Tanks: < 5 ppm is desirable
  • DWA Wastewater / effluent water: Nitrate as Nitrogen < 1.5 mg/l*
* DWA – Requirements for the Purification of waste water or effluent, Act No. 991 – 18 May 1984
  • SANS Drinking water class 1: < 11 mg/l**
** SANS 241-1: 2011 Drinking Water Standards 

What can you do?

  • Wells should be tested due to the high nitrates in groundwater
  • Kraal / barnyard runoff, nitrogen fertilisers and septic tanks should be situated further than 30 meters from streams / rivers / dams / wells
  • Water contaminated with nitrates can safely be used for washing and household purposes, but not for drinking or cooking
  • NOTE: boiling water or adding chlorine will not reduce nitrate levels
  • Water treatment methods such as anion exchange and reverse osmosis can be implemented
  • Check for other contaminants, as high nitrate levels allow bacteria and pesticides to enter the water, too

The Lovibond® MD 100 Photometer or the Lovibond® Checkit Comparator can be used to measure phosphates in water.

Read more about the CSIR Research on nitrates in groundwater in Southern Africa.

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