Hexavalent chromium compounds, toxicity

The primary routes of entry for animal exposure to chromium compounds are inhalation, ingestion, and, for hexavalent compounds, skin penetration. This last route is more important in industrial exposures. Most hexavalent chromium compounds are readily absorbed, are more soluble than trivalent chromium in the pH range 5 to 7, and react with cell membranes. Although hexavalent compounds are more toxic than those of Cr(III), an overexposure to compounds of either oxidation state may lead to inflammation and irritation of the eyes, skin, and the mucous membranes associated with the respiratory and gastrointestinal tracts. Skin ulcers and perforations of nasal septa have been observed in some industrial workers after prolonged exposure to certain hexavalent chromium compounds (108—110), ie, to chromic acid mist or sodium and potassium dichromate. 

Among warm-blooded organisms, hexavalent chromium was fatal to dogs in 3 months at 100 mg/kg in their food and killed most mammalian experimental animals at injected doses of 1 to 5 mg Cr/kg body weight, but it had no measurable effect on chickens at dietary levels of 100 mg/kg over a 32-day period. Trivalent chromium compounds were generally less toxic than hexavalent chromium compounds, but significant differences may occur in uptake of anionic and cationic CL3 species, and this difference may affect survival. 

Irritant.3 High pulmonary toxicity. Certain hexavalent chromium compounds have been listed as known human carcinogens.4 TLV-TWA 0.5 mg/m3.5... 

Hexavalent chromium compounds have no medical uses and are known as mutagens and carcinogens (19). In an in vitro study the coordination of chromium by picolinate ligands made chromium picolinate more toxic to cultured cells, leading to enhanced apoptosis (20). These observations support the hypothesis that chromium picolinate is a human carcinogen. 

Over time, increased quantities of chromium compounds have been used by man and introduced into the environment (Gauglhofer and Bianchi 1991). The danger of environmental contamination depends on the solubility and oxidation state of chromium [International Programme on Chemical Safety (I PCS) 1988], Chromium(III) compounds are generally poorly soluble and show little or no toxicity. Chromium in its hexavalent form is 100 to 1000 times more toxic than the most common trivalent compounds (Katz 1991 Katz and Salem 1993). Hexavalent chromium compounds can reduce plant growth and cause skin and respiratory irritation and ulceration and eventually lung cancer. Hexavalent chromium is recognized... 

Various agencies have investigated substances that may be present in the environment and cause adverse effects on the environment or on human health (IPCS 1988 O Flaherty 1994 Agency for Toxic Substances and Disease Registry 1998). Chromium was one of four metals include on the priority list for the Canadian Environmental Protection Act (Meek and Hughes 1995). Speci-ation was considered to be critical in evaluation of health effects, but there was little information on exposure to individual hexavalent chromium compounds (Hughes et al. 

After oral ingestion of hexavalent compounds, ascorbic acid has been suggested to assist the conversion of hexavalent to less toxic trivalent compounds. While no definitive studies exist, the treatment is benign and may be helpful. In animal studies the effective dose was 2-4 g of ascorbic acid orally per g of hexavalent chromium compound ingested. 

A buildup of Al + in the zinc phosphating baths will restrict the amount of coating formed unless these ions are ranoved by addition of fluoride or borate. An advantage of zinc phosphating, however, is that it avoids the use of toxic hexavalent chromium compounds. Some simple bath compositions for zinc and manganese phosphating of aluminium are... 

Chromium is a steel-gray, lustrous, hard metaL It is an essential trace element and has a role in glucose metabolism. Compounds of hexavalent chromium are toxic. Chromium is a very important alloying element for steel. More than 12% Cr makes steel stainless. 

Potassium dichromate (K2Cr207) This is a strong oxidizer, but it only contains 16% oxygen by weight. It has a corrosive effect on the mucous membranes, and its toxicity and suspected carcinogenicity suggest the use of alternate oxidizers. It is one of the family of hexavalent chromium compounds that have received considerable adverse publicity. 

Chromium is a controversial element with important essentiaUty and toxicity, depending on its different species. Chromium in the oxidation state 111 is an important essential element. In contrast, hexavalent chromium compounds (chromates and dichromates) are toxic and may be responsible for certain allergenic, mutagenic and carcinogenic effects. 

Toxic effects of Cr + compounds are manifested only at extremely high doses. Much more toxic are hexavalent chromium compounds, which cause growth failure and liver and kidney damage. Chromate contact with the skin may cause dermatitis. Chronic exposure to dust containing chromates increases the risk of lung cancer development. 

Hexavalent chromium compounds are toxic and carcinogenic. For this reason, chromic acid oxidation is not used on an industrial scale. 

Reproductive Toxicity. No data are available that impHcate either hexavalent or trivalent chromium compounds as reproductive toxins, unless exposure is by way of injection. The observed teratogenic effects of sodium dichromate(VI), chromic acid, and chromium (HI) chloride, adininistered by injection, as measured by dose-response relationships are close to the amount that would be lethal to the embryo, a common trait of many compounds (111). Reported teratogenic studies on hamsters (117,118), the mouse (119—121), and rabbits (122) have shown increased incidence of cleft palate, no effect, and testicular degeneration, respectively. Although the exposures for these experiments were provided by injections, in the final study (122) oral, inhalation, and dermal routes were also tried, and no testicular degeneration was found by these paths. 

Metal Finishing and Corrosion Control. The exceptional corrosion protection provided by electroplated chromium and the protective film created by applying chromium surface conversion techniques to many active metals, has made chromium compounds valuable to the metal finishing industry. Cr(VI) compounds have dominated the formulas employed for electroplating (qv) and surface conversion, but the use of Cr(III) compounds is growing in both areas because of the health and safety problems associated with hexavalent chromium and the low toxicity of trivalent chromium (see... 

Chromium can exist as either trivalent or hexavalent compounds in raw wastewater streams. The chromium that passes through the POTW is discharged to ambient surface water. Chromium is toxic to aquatic organisms at levels observed in POTW effluents15 ... 

Hexavalent chromium is also a toxic compound (like lead, cadmium, mercury) and can be easily detected with UV spectrophotometry [20]. This system works for the quality control of electroplating treated wastewater with a detection limit of 5 pg It1. 

Chromium and certain chromium compounds are classified as substances known to be carcinogenic. ERA classifies chromium as a de minimis carcinogen, meaning that the minimum amount of the chemical set by the U.S. Occupational Safety and Health Administration (OSHA) is considered to be carcinogenic. Chromium compounds vary greatly in their toxic and carcinogenic effects. Trivalent chromium compounds are considerably less toxic than the hexavalent compounds and are neither irritating nor corrosive. 

Replacement of hexavalent chromium with trivalent chromium offers important environmental advantages. Trivalent chromium is considerably less toxic than hexavalent. Trivalent systems use chromium concentrations that are typically two orders of magnitude less than in hexavalent systems. Thus, far less chromium enters the waste stream. Trivalent systems also generate few toxic air emissions, while hexavalent systems involve a reaction that produces hydrogen bubbles which entrain chromium compounds and carry them out of the baths. Trivalent chromium is readily precipitated from wastewater, while hexavalent chromium solutions must go through an additional step in a treatment system in which the chromium is reduced to its trivalent form before precipitation. It has been shown that trivalent chromium systems can successfully replace hexavalent ones for decorative chrome applications. Trivalent chromium systems are not suitable for hard chrome applications. More information regarding trivalent chromium plating can be obtained from Roy (1984), Robison (1978), Chementator (1982), and Smart (1983). 

In general, chromium(VI) compounds are more toxic than chromium(III) compounds. The toxicity of hexavalent chromium is in part due to the generation of free radicals formed during reduction to chromium(III) in biological systems. 

California s Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65) restricts the use and disposal of antimony, arsenic, beryllium, cadmium, hexavalent chromium, lead, and nickel compounds, without specifying limits. 

Different metals and metal compounds have been in use since the beginning of human civilization. Metals include aluminum, antimony, cobalt, copper, chromium, iron, nickel, manganese, molybdenum, selenium, tin, vanadium, and zinc. The list of toxic metals includes but is not limited to arsenic, beryllium, cadmium, hexavalent chromium, lead, and mercury. Contamination of food, water, and the air by metals, particularly lead and cadmium, has caused global concern. Several studies have shown elevated levels of lead, nickel, chromium, and manganese in children s hair. 

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