Civil Engineering Reference
In-Depth Information
Common salt (NaCl)
•
Soda ash (Na
2
CO
3
)
•
Baking soda (NaHCO
3
)
•
Caustic soda (NaOH)
•
Sodium is a natural constituent of raw waters, but its concentration is increased by
pollution sources, such as rock salt treatment of road surfaces in freezing temperature,
precipitation runoff, soaps, and detergents.
Occurrence
Sodium is a major constituent in drinking water. A survey of 2,100
finished waters found concentrations ranging from 0.4 to 1900 mg / L, with 42 percent
having sodium greater than 20 mg / L and 5 percent having greater than 250 mg / L.
3
In another survey of 630 systems of finished waters, concentrations were found from
less than 1 to 402 mg / L, with 42 percent sampled with levels over 20 mg / L, and 3
percent with levels higher than 200 mg / L.
2
Health Effects
Sodium is associated with high blood pressure and heart disease in
the ''at-risk'' population, composed of persons genetically predisposed to essential
hypertension. In addition, certain diseases are aggravated by a high salt intake, in-
cluding congestive heart failure, cirrhosis, and renal disease. Harmful effects for the
population as a whole have not been conclusively shown.
Sulfate
Sources
Sulfates are found in natural waters in the final oxidized stage of sulfides,
sulfites, and thiosulfates, or in the oxidized state of organic matter in the sulfur cycle.
Sodium, potassium, and ammonium sulfate are highly soluble in water. The
SO
2
also occurs frequently in rainfall in or near metropolitan areas where sulfate is pro-
duced as a fossil fuel combustion by-product. Detergents add sulfate to sewage. In-
dustrial pollution from tanneries, steel mills, sulfate pulp mills, and textile plants may
contaminate raw water.
anion
Occurrence
A study of 969 supplies found sulfates in concentrations of 1 to 770
mg / L, with a median of 4.6 mg / L. Three percent had sulfate concentrations greater
than 250 mg / L.
Health Effects
High levels of sulfate cause diarrhea and dehydration. Sulfate salts
are absorbed by the intestine, excreted in the urine up to a cathartic dose of 1 or 2 g
(1,000 to 2,000 mg / L in a single liter). After a period of adjustment to unusually high
doses with diarrhea and gastroenteritis occurring, particularly in infants, a tolerance of
400 mg / L (an advisable maximum in certain situations) and greater have been noted.
In some cases, the local population apparently has not suffered from routine ingestion
of well waters with concentrations reported as high as 2,000 to 3,000 mg / L.
2
Sulfate is not known to be mutagenic, carcinogenic, or teratogenic in mammals.
