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figure is based on the potential for nitrate poisoning of infants. Adults can to-
lerate higher levels, but high nitrate levels may cause irritation of the stomach
and bladder. The suggested maximum for livestock use is 100 mg/L.
Nitrate is converted to nitrite in the body. Nitrite causes asphyxiation by
entering the bloodstream and reacting with hemoglobin (the red, oxygen-
carrying pigment of the blood) to form methemoglobin, which is not able to
carry oxygen to the body's tissue. Nitrate in water is approximately 10 times
more soluble than in feed. Caution is needed to differentiate between nitrate
and nitrate-N or nitrate as N. Nitrate = Nitrate-N * 4.4
NO2 nitrogen (Nitrite) – has an element of toxicity. Nitrite is usually
an indicator of direct contamination by sewage or manure because nitrites are
unstable and quickly become nitrates.
pH – expresses the intensity of the acid or alkaline condition of a solu-
tion. A pH of 7 indicates neutral conditions on a scale of 0 (acidic) to 14 (al-
kaline). The generally accepted range for pH in water is 6.5 to 8.5 with an
upper limit of 9.5.
Sodium – is not considered a toxic metal. 5,000 to 10,000 milligrams
per day are consumed by normal healthy adults without adverse effects. The
average intake of sodium from water is only a small fraction of that con-
sumed in a normal diet.
People suffering from certain medical conditions such as hypertension
may require a sodium restricted diet, in which case the intake of sodium from
drinking water could become significant.
Sodium is a significant factor in assessing water for irrigation and plant
watering. High sodium levels affect soil structure and a plant's ability to take
up water.
Sulphate (SO4) – concentrations over 500 mg/L can be a laxative to
some humans and livestock. Sulphate levels over 500 mg/L may be a concern
for livestock receiving marginal intakes of certain trace minerals. Very high
levels of sulphates have been associated with some brain disorders in cattle
and pigs.
Total Dissolved Solids (TDS) – comprise inorganic salts and small
amounts of organic matter that are dissolved in water. The principal constitu-
ents are usually the cations calcium, magnesium, sodium and potassium and
the anions carbonate, bicarbonate, chloride, sulphate and, particularly in
groundwater, nitrate (from agricultural use).
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