Tuesday, February 22, 2011

Tap Water Contaminant: Chromium -6

Tap Water Contaminant: Chromium -6
Tap water has an average of 0.4 to 8 ppb of chromium.


What it is:

• Chromium is a metallic element that occurs naturally in association with iron.

• The odorless, tasteless, malleable metal takes a high polish and has a high melting point.

• Acting as a chemical cation, chromium freely surrenders its outer electrons to anions willing to receive them. This process leaves the chromium with three positive charges (Cr+3 or trivalent) or six positive charges (Cr+6 or hexavalent).

Occurrence:
• Trivalent chromium occurs naturally in the environment and can be found in rocks and soil as well as fruits, vegetables and meat.

• Hexavalent chromium is a by-product of industrial processes — forging stainless steel, chrome plating, manufacturing dyes and pigments, tanning leather, producing photographic materials and staining wood.

• Particles of Cr+6 are scattered through the air within and surrounding industrial plants, settling on land and water. While most of these particles cling to the soil, some sink into underground aquifers.

• Workers can be exposed to chromium dust in the air of industrial plants using dichromate salts by breathing in the materials or by skin contact.

• Persons living in the vicinity of such industrial facilities or uncontrolled waste sites may also be exposed via airborne dust and water contamination.

Health effects:
• Cr+3 is not considered a health risk. It is a mineral nutrient essential to cell membrane receptor sites stimulated by insulin. In the absence of trivalent chromium, tissues resist insulin's influence. Blood sugar cannot enter cells to be metabolized and signs of Type II diabetes may appear. The federal government has established a minimum daily requirement of 50 to 200 milligrams of chromium for dietary ingestion.

• Cr+6 is considered toxic. Exposure to hexavalent chromium may cause the following symptoms: Nausea; kidney and liver damage; thick muco-pus from respiratory membranes; punched-out, penetrating ulcers on mucous membranes; holes in the nasal septum and small bones defining the nasal and oral cavities; nosebleeds; reproductive problems; and body pains.

• Industrial workers exposed to chromate dust have a lung cancer rate 20 times that of the general population.

Regulation:
• The U.S. Environmental Protection Agency (EPA) has set a maximum contaminant level (MC.L) for total chromium of 0.1 ppm (100 ppb) in drinking water.

• Tap water has an average of 0.4 to 8 ppb of chromium.

Water treatment:
• Reverse osmosis and distillation will reduce all types of chromium found in water.

• Cr+3 can be removed from water with a strong acid cation ion exchange resin in the sodium form. An acid strip will normally be required periodically to strip Cr+3 from the resin, followed by a normal salt regenera.tion to convert the resin to the sodium form. A second regenera.tion may be necessary if the pH of the service cycle is too low.

• Reverse osmosis, deionization and distillation are considered effective in removing Cr+6.
Source: Water Technology

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