沒想到， 水裏可能有至癌物質。ZT

ZT: US water has large amounts of likely carcinogen

沒想到， 水裏可能有至癌物質。
提示化學反應： hexavalent chromium + H2O2 >> hydroxyl radicals >> somatic cell chromosome DNA damage >> mutations >> some mutations if not repaired can cause cancers

 
 WASHINGTON (AFP) – A US environmental group has found that drinking water in 35 American cities contains hexavalent chromium, a probable carcinogen, The Washington Post reported Sunday.

The study by the Environmental Working Group -- the first nationwide analysis measuring the presence of the chemical in US water systems -- is to be made public on Monday, the daily reported.

The group found hexavalent chromium in the tap water of 31 out of 35 cities sampled. Of those, 25 had levels that exceeded the goal proposed in California, which has been trying aggressively to reduce the chemical in its water supply.

The federal Environmental Protection Agency is considering whether to set a limit for hexavalent chromium in tap water. The agency is reviewing the chemical after the National Institutes of Health, deemed it a "probable carcinogen" in 2008.

Hexavalent chromium has long been known to cause lung cancer when inhaled, and scientists recently found evidence that it causes cancer in laboratory animals when ingested. It has been linked in animals to liver and kidney damage as well as leukemia, stomach cancer and other cancers.

A widely used industrial chemical until the early 1990s, hexavalent chromium still used in some industries, such as in chrome plating and the manufacturing of plastics and dyes. The chemical can also leach into groundwater from natural ores.

The chemical compound was first made famous in the hit 2000 Hollywood movie "Erin Brockovich" about the eponymous environmental crusader who also commented on the EWG's alarming finding.

"This chemical has been so widely used by so many industries across the US that this doesn't surprise me," said Brockovich, known for her fight on behalf of the residents of Hinkley, California against Pacific Gas & Electric.

In that case, PG&E was accused of leaking hexavalent chromium into the town's groundwater for more than 30 years, and ultimately was made to pay 333 million dollars in damages to more than 600 inhabitants of the town, which it was required to clean up.

"Our municipal water supplies are in danger all over the US," Brockovich told The Post. "This is a chemical that should be regulated."



From Wikipedia, the free encyclopedia
"Hex chrome" redirects here. For the color printing process, see Hexachrome.
An example of a chromium(VI) compound: chromium trioxide

Hexavalent chromium (chromium VI) refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate. Approximately 136,000,000 kilograms (300,000,000 lb) of hexavalent chromium were produced in 1985.[1] Other hexavalent chromium compounds are chromium trioxide and various salts of chromate and dichromate. Hexavalent chromium is used for the production of stainless steel, textile dyes, wood preservation, leather tanning, and as anti-corrosion and conversion coatings as well as a variety of niche uses.

Hexavalent chromium is recognized as a human carcinogen via inhalation.[2] Workers in many different occupations are exposed to hexavalent chromium. Problematic exposure is known to occur among workers who handle chromate-containing products as well as those who arc weld stainless steel.[2] Within the European Union, the use of hexavalent chromium in electronic equipment is largely prohibited by the Restriction of Hazardous Substances Directive.

Toxicity

Hexavalent chromium is transported into cells via the sulfate transport mechanisms, taking advantage of the similarity of sulfate and chromate with respect to their structure and charge. Trivalent chromium, which is the more common variety of chromium compounds, is not transported into cells.

Inside the cell, Cr(VI) is reduced first to metastable pentavalent chromium (Cr(V)), then to trivalent chromium (Cr(III)). Chromate-dyed textiles or chromate-tanned leather shoes can cause or exacerbate contact dermatitis. Vitamin C and other reducing agents combine with chromate to give Cr(III) products inside the cell.[3]

Hexavalent chromium compounds are genotoxic carcinogens. Chronic inhalation of hexavalent chromium compounds increases risk of lung cancer (lungs are especially vulnerable, followed by fine capillaries in kidneys and intestine). According to some researchers, the damage is caused by hydroxyl radicals, produced during reoxidation of pentavalent chromium by hydrogen peroxide molecules present in the cell. Strontium chromate is the strongest carcinogen of the chromates used in industry. Soluble compounds, like chromic acid, are much weaker carcinogens.[3]

In the U.S., the OSHA PEL for airborne exposures to hexavalent chromium is 5 µg/m3 (0.005 mg/m3).[4][5]