Chromium in Drinking Water
Feb 27, †Ј Chromium is present in many foods, including meats, grain products, fruits, vegetables, nuts, spices, brewerТs yeast, beer, and wine. However, chromium amounts in these foods vary widely depending on local soil and water conditions as well as agricultural and manufacturing processes used to produce them [ 4, 7, 12, ]. There are two forms of chromium: trivalent chromium and hexavalent chromium. The first is found in foods and supplements and is safe for humans. The second is a known toxin that can cause skin.
Chromium is a chemical element with the symbol Cr and atomic number It is the first element in group 6. It is a steely-grey, lustroushard, and brittle transition metal. Chromium is also highly valued as a metal that is able to how to drill a large hole in wood highly polished while resisting what is my sip number. What is chromium found in alloy is commercially produced from chromite by silicothermic or aluminothermic reactions and chromium metal by roasting and leaching processes followed by reduction with carbon and then aluminium.
Chromium metal is of high value for its high corrosion resistance and hardness. A major development in steel production was the discovery that steel could be made what is chromium found in resistant to corrosion and discoloration by adding metallic chromium to form stainless steel. In the United States, trivalent chromium Cr III ion is considered an essential nutrient in humans for insulinsugarand lipid metabolism. Abandoned chromium production sites often require environmental cleanup.
Chromium is the fourth transition metal found on the periodic table, and has an electron configuration of [ Ar ] what is chromium found in 5 4s 1. It is also the first element in the periodic table whose ground-state electron configuration violates the Aufbau principle.
This occurs again how to buy a new toilet seat in the periodic table with other elements and their electron configurations, such as copperniobiumand molybdenum. In the previous elements, the energetic cost of promoting an electron to the next higher energy level is too great to compensate for that released by lessening inter-electronic repulsion.
However, in the 3d transition metals, the energy gap between the 3d and the next-higher 4s vound is very small, and because the 3d subshell is more compact than chrpmium 4s subshell, inter-electron repulsion is smaller between 4s electrons than between 3d electrons.
This lowers the energetic cost what is chromium found in promotion and increases the energy released by it, so that the promotion becomes energetically feasible and one or even two electrons are always promoted to the how to get os7 on blackberry curve 8520 subshell.
Similar promotions happen for every transition metal atom but one, palladium. Chromium is the first element in the 3d series where the 3d electrons start to sink into the nucleus ; they thus contribute less to metallic bondingand what time is it now in vancouver b c canada the melting and boiling points and the enthalpy of atomisation of chromium are lower than those of the preceding element vanadium.
Chromium is extremely hardand is the third hardest element behind carbon diamond and boron. Its Mohs hardness is 8. Chromium is highly resistant to tarnishingwhich makes it useful as a metal that preserves its outermost layer from corrodingunlike other metals such as coppermagnesiumand aluminium.
Chromium has a high specular reflection in comparison to other transition metals. This is due to the magnetic moments at the cube's corners chhromium the unequal, but antiparallel, cube centers. Chromium metal left standing in air is passivated - it forms a ij, protective, surface layer of oxide. This layer has a ib structure a few atomic layers thick; it is very dense and inhibits the diffusion of oxygen into the underlying metal.
In contrast, iron forms a more porous oxide through which oxygen can migrate, causing continued rusting. Passivated chromium is stable against acids. Passivation can be removed with a strong reducing agent that destroys the protective oxide what is chromium found in on the metal.
Chromium metal treated in this way readily dissolves in weak acids. Chromium, unlike iron and nickel, si not suffer from hydrogen embrittlement. However, it does suffer from nitrogen embrittlementreacting with nitrogen cgromium air and forming brittle nitrides at the high temperatures necessary to work the metal parts.
Naturally occurring chromium is composed of three stable isotopes ; 52 Cr, 53 Cr and 54 Cr, with 52 Cr being the most abundant All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority less than 1 minute. Chromium also has two metastable nuclear isomers. This circumstance is useful in isotope geology.
Manganese-chromium isotope ratios reinforce the evidence from 26 Al and Pd concerning the early history of the Solar System. Hence 53 Cr provides what is chromium found in evidence for nucleosynthetic processes immediately before coalescence of the Solar System.
The isotopes of chromium range in atomic mass from 43 u 43 Cr to 67 u 67 Cr. The primary decay mode before the most abundant stable isotope, 52 Cr, is electron capture and the primary mode after is beta decay. Chromium is a member of group 6of the transition metals. The resulting bright blue solution created from dissolving chromium II chloride is only stable at neutral pH. Many chromous carboxylates are chhromium as well, the most famous of these being the red chromium II acetate Cr 2 O 2 CCH 3 4 that features a quadruple bond.
Chromium III tends to form octahedral complexes. If anhydrous violet  chromium III chloride is dissolved in water, the violet solution turns green after some time as the chloride in the inner coordination sphere is replaced by water. This kind of reaction is also observed with solutions of chrome alum and other water-soluble chromium III salts.
It is dehydrated by heating chrmium form the green chromium III oxide Cr 2 O 3a stable oxide with a crystal structure identical to that of corundum. Chromium VI compounds are oxidants at low or neutral pH. They how to cook brinjal curry at an equilibrium, determined by pH:.
Sodium chromate is produced industrially by the oxidative roasting of chromite ore with sodium carbonate. The change in equilibrium is visible by a change from yellow chromate to orange dichromatesuch as when an acid is added to a neutral solution of potassium chromate. At yet lower pH values, further condensation to more complex what is chromium found in of chromium is possible. Both the chromate and dichromate anions are strong oxidizing reagents at low pH: .
Chromkum are, however, only moderately oxidizing at high pH: . Fohnd VI compounds in solution can be detected by adding an acidic hydrogen peroxide solution. Chromiuk acid has the hypothetical formula H 2 CrO 4. It is a vaguely described chemical, despite many well-defined chromates and dichromates being known.
The dark red chromium VI oxide CrO 3the acid anhydride of chromic acid, is sold industrially as "chromic acid". The only binary compound is the volatile chromium V fluoride CrF 5. Potassium peroxochromate K 3 [Cr O 2 4 ] is chdomium by reacting potassium chromate with hydrogen peroxide at low temperatures.
Compounds of chromium IV are slightly more common than those of chromium V. The tetrahalides, CrF 4CrCl 4and CrBr 4can be how to get rid of baggy eyes with makeup by treating the trihalides CrX 3 with the corresponding halogen at elevated temperatures.
Such compounds are susceptible to disproportionation reactions and are not stable in water. Most chromium I compounds are obtained solely by oxidation of electron-rich, octahedral chromium 0 complexes. Other chromium I complexes contain cyclopentadienyl ligands.
As verified by X-ray diffractiona Cr-Cr quintuple bond length Most chromium 0 compounds are derivatives of the compounds chromium hexacarbonyl or bis benzene chromium. Chromium is the 21st  most abundant element in Earth's crust with an average cjromium of ppm. Chromium compounds are found in the environment from the erosion of chromium-containing rocks, and can be redistributed by volcanic eruptions.
About two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan while IndiaRussiaand Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically chrpmium in Kazakhstan and southern Africa. This mine is a kimberlite pipe, rich in diamondsand the reducing environment helped produce both elemental chromium and diamonds. Chromium minerals as pigments came to the attention of the west in the eighteenth century.
After Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region. InLouis Nicolas Vauquelin received samples of crocoite ore. He produced chromium trioxide CrO 3 by mixing crocoite with hydrochloric acid. During the nineteenth century, chromium was primarily used not only as a component of paints, but in tanning salts as well.
Chromkum quite some time, the crocoite found in Russia was the main how to make a fern terrarium for such tanning materials.
Ina larger chromite deposit was discovered near BaltimoreUnited States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously.
Chromium is also famous for its reflective, what is chromium found in luster when polished. It is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by electroplating. Chromium was used for electroplating as early asbut this use only became widespread with the development of an improved process in Approximately Papp, writing for the USGS, "Ferrochromium is the leading end use of chromite ore, [and] stainless fouund is the leading end use of ferrochromium.
The two main products of chromium ore refining are ferrochromium and metallic chromium. For those products the ore smelter process differs considerably. For the production of how to make peppermint foot spray, the chromite ore FeCr 2 O 4 is reduced in what is chromium found in scale in electric arc furnace or in smaller smelters with either aluminium or silicon in an aluminothermic reaction.
For the production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process. The chromite ore is heated with chrimium mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms the stable Fe 2 O 3. The subsequent leaching at higher elevated temperatures dissolves the chromates and leaves the insoluble iron oxide. The chromate is converted by sulfuric acid into the dichromate.
The dichromate is converted to the chromium III oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium. The remainder of chromium is used in the chemical what is lanolin oil good for, refractoryand foundry industries. The strengthening effect of forming stable metal carbides at grain boundaries, and the strong increase in corrosion resistance made chromium an important alloying material for steel.
Also, nickel-based alloys have increased strength due to the formation of discrete, stable, metal, carbide particles at the grain boundaries. For example, Inconel contains Because of the excellent high-temperature properties of these nickel superalloysthey are used in jet engines and gas turbines in lieu of common structural materials.
The high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals. There are two deposition methods: thin, and thick. Thicker chromium layers are deposited if wear-resistant surfaces are needed.
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Chromium is a relatively abundant element in EarthТs crust; the free metal is never found in nature. Most ores consist of the mineral chromite, the ideal formula of which is FeCr 2 O 4. Chromium is an odorless and tasteless metallic element. Chromium is found naturally in rocks, plants, soil and volcanic dust, and animals. The most common forms of chromium that occur in natural waters in the environment are: Trivalent chromium (chromium-3). Apr 28, †Ј Chromium is the open source project that underpins Google's Chrome browser. Since the project is open-source, both Google and others are able to build on and use the Chromium source code. In fact, anyone can download, compile, and tinker with the source code for Chromium.
Get the latest public health information from CDC. Have a question? This fact sheet focuses entirely on trivalent chromium. Chromium might play a role in carbohydrate, lipid, and protein metabolism by potentiating insulin action [ ]. Although the precise mechanism for this activity has not been identified, scientists have proposed that chromium binds to an oligopeptide to form chromodulin, a low-molecular-weight, chromium-binding substance that binds to and activates the insulin receptor to promote insulin action [ 4 , ].
Chromium might also have antioxidant effects [ 1 ]. However, recent research has suggested that although chromium might have benefits at pharmacologic amounts e. The FNB has not evaluated chromium since However, in , the European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies concluded that no convincing evidence shows that chromium is an essential nutrient and, therefore, setting chromium intake recommendations would be inappropriate [ 5 ].
Chromium accumulates mainly in the liver, spleen, soft tissue, and bone [ 2 , 5 , 12 ]. Chromium is excreted mainly in the urine [ 1 , 12 , 13 ]. Urinary chromium levels are therefore a good indicator of chromium absorption.
However, because these levels are closely related to recent chromium intakes, they are not good indicators of chromium body stores [ 4 , 14 ]. Hair levels might reflect past chromium intakes [ 5 ], and some studies have measured chromium levels in hair, sweat, serum, and toenails [ 15 , 16 ]. However, no validated methods for determining chromium status and no clinically defined chromium deficiency state exist [ 6 , 8 ].
DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include:. The FNB therefore established AIs for all ages based on usual chromium intakes in healthy populations [ 2 ].
Table 1 lists the current AIs for chromium. However, chromium amounts in these foods vary widely depending on local soil and water conditions as well as agricultural and manufacturing processes used to produce them [ 4 , 7 , 12 , ]. For example, the amount of chromium can vary fold in samples of oatmeal because of growing and processing differences [ 21 ].
Some chromium can also be transferred to foods from stainless steel equipment during food processing and from pots and pans during cooking [ 3 , 4 , 10 , 17 , 20 , 22 , 23 ]. Most dairy products and foods high in sugar e. Human milk contains about 0. Small studies in Europe found chromium concentrations ranging from 0.
Dietary chromium absorption is low, ranging from about 0. Ascorbic acid and prostaglandin inhibitors, such as aspirin, increase chromium absorption, whereas oxalate and antacids inhibit it [ 1 , 22 , 25 ]. A variety of types of foods and their chromium levels per serving are listed in Table 2. Determining the chromium content of food is challenging because samples are easily contaminated by standard tools used for measurement and analysis [ 2 ]. Therefore, the values in Table 2 should only serve as a guide.
The U. Food and Drug Administration FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for chromium is 35 mcg for adults and children aged 4 and older [ 26 ]. FDA does not require food labels to list chromium content unless chromium has been added to the food.
Supplements containing only chromium are also available, and they commonly provide mcg to mcg chromium, although some contain up to 1, mcg [ 16 , 27 ]. Dietary supplements contain many forms of chromium, including chromium picolinate, chromium nicotinate, chromium polynicotinate, chromium chloride, and chromium histidinate [ 18 , 27 ]. The absorption of various forms of chromium is similar [ 6 , 9 ].
For example, research suggests that the proportion of chromium absorbed from chromium picolinate is about 1. These values are similar to the proportion of chromium absorbed from food [ 5 ]. Chromium compounds contain various percentages of elemental chromium. For example, elemental chromium accounts for The Supplement Facts label on a dietary supplement product declares the amount of elemental chromium, not the weight of the entire chromium compound, in the product.
Therefore, data on chromium intakes in the United States are limited. In another study, the mean chromium content per 2, kcal of 22 well-balanced diets designed by nutritionists was about 27 mcg and ranged from about 17 to 47 mcg [ 17 ]. These findings suggest that most people in the United States have chromium intakes similar to the AIs. Data on chromium intakes from dietary supplements are also very limited. Chromium deficiency has not been reported in healthy populations, and no definitive deficiency symptoms have been established [ 3 , 4 ].
These effects were alleviated with pharmacologic amounts of chromium. Although these adverse effects were presumed to be caused by chromium deficiency, the studies did not adequately evaluate the chromium concentrations in the TPN solutions [ 5 ]. Scientists have concluded, based on recent evaluations, that these studies do not provide evidence that the patients had chromium deficiency and thus do not demonstrate that heathy people can develop chromium deficiency [ 3 , 5 , 6 , 10 , 13 ].
Currently, chromium is routinely added to TPN solutions to provide 10Ч15 mcg chromium per day, a much higher daily amount than the approximately 0. Thus, the American Society for Parenteral and Enteral Nutrition and other experts recommend research on parenteral chromium requirements to determine whether chromium levels in TPN solutions should be lowered [ 9 , 13 , 35 , 36 ].
This section focuses on five conditions in which chromium might have beneficial effects: impaired glucose tolerance and diabetes, metabolic syndrome, polycystic ovary syndrome, dyslipidemia, and weight and lean body mass.
Impaired glucose tolerance and diabetes Because chromium might potentiate the action of insulin, studies have examined whether increasing chromium intakes might reduce the risk of impaired glucose tolerance. Numerous randomized controlled trials have assessed the effects of chromium supplementsЧЧoften at pharmacological doses e. One of the most commonly cited intervention studies of the effects of chromium supplementation for type 2 diabetes was a randomized controlled trial [ 37 ].
The trial assigned adults aged 35Ч65 years with type 2 diabetes to receive mcg chromium as chromium picolinate , mcg chromium, or placebo twice daily for four months. At 4 months, for example, mean fasting serum glucose levels were 7. HbA1c is a robust measure of blood glucose control because it reflects long-term changes in blood glucose levels [ 38 ]. Several subsequent studies that used various doses of chromium had inconsistent findings.
A review of chromium and glycemic control included 8 meta-analyses and systematic reviews of a total of 58 clinical trials [ 16 ]. The trials lasted from 3 weeks to 6 months and administered 1. The most frequently used form was chromium picolinate, followed by yeasts containing chromium and chromium chloride.
Overall, when used as an adjuvant treatment, chromium lowered fasting plasma glucose and HbA1c levels slightly in people with diabetes. However, the clinical significance of these findings is unclear. The authors of a review of chromium supplementation in people with type 2 diabetes drew similar conclusions, noting the insufficient rationale to recommend chromium supplements for people with type 2 diabetes and that chromium supplements do not help moderate glucose levels in healthy individuals [ 39 ].
Some research suggests that responses to chromium supplementation may vary, and supplements might be more likely to benefit people with more severe insulin resistance and poorer glycemic control [ 18 , 40 ]. In a randomized trial in participants aged 30Ч70 years with type 2 diabetes, daily supplementation with 1, mcg chromium as chromium picolinate for 24 weeks did not significantly affect insulin sensitivity, fasting glucose levels, or HbA1c values in comparison with placebo [ 40 ].
However, some participants did respond to chromium supplementation, and these people had significantly lower insulin sensitivity 3. Manufacturers market chromium supplements widely in the United States for people with type 2 diabetes, and many adults use them in the hope that the supplements will reduce their risk of diabetes or improve their glycemic control [ 6 , 8 , 18 , 39 ].
However, FDA allows only the following qualified health claim for chromium picolinate dietary supplements:. In its diabetes guidelines, the American Diabetes Association concluded that because studies have not definitively shown that chromium supplementation benefits people with diabetes or obesity, the association cannot recommend such supplementation [ 43 ].
This determination was based on conflicting evidence from poorly controlled or uncontrolled studies. Similarly, the association concluded in its position statement that evidence is insufficient to support the routine use of supplements containing chromium and other micronutrients for glycemic control in people with diabetes [ 44 ].
Additional research is needed to determine whether specific populations e. Insulin resistance is an integral component of this condition and is a potential therapeutic target for dietary interventions for metabolic syndrome [ 46 ]. A prospective study of 3, adults aged 20Ч32 years found that baseline toenail chromium concentrations were inversely associated with the incidence of metabolic syndrome over 23 years of follow-up [ 47 ]. For these reasons, some scientists have hypothesized that chromium supplements might benefit people with metabolic syndrome.
Only a few clinical trials of chromium supplementation for metabolic syndrome have been conducted [ 46 , ]. One of these trials included 63 adults aged 18 to 75 years with metabolic syndrome who received either mcg chromium picolinate or placebo twice daily for 16 weeks [ 46 ]. In comparison with placebo, chromium supplementation significantly increased acute insulin response to glucose but did not affect HbA1c levels, insulin sensitivity, or other measures of glucose metabolism.
Chromium supplementation also had no effect on body weight or serum lipids. Similarly, in a clinical trial of 70 adults mean age 58 years with metabolic syndrome and impaired glucose tolerance, daily supplementation with mcg chromium mcg with breakfast and mcg with dinner, as chromium yeast for 24 weeks did not affect fasting glucose levels, HbA1c, waist circumference, blood pressure, or lipid levels [ 49 ].
Overall, limited research suggests that chromium supplements do not significantly benefit people with metabolic syndrome. It is characterized by infertility, obesity, dyslipidemia, hyperandrogenism, and elevated risks of type 2 diabetes and cardiovascular disease [ 51 , 52 ]. Because insulin resistance is often a central component of PCOS, studies have investigated the use of chromium supplements in people with PCOS to help maintain glycemic control and reduce lipid levels [ 16 , 53 ].
Four recent systematic reviews and meta-analyses of randomized clinical trials have examined the effects of chromium supplements on signs and symptoms of PCOS [ 52 , ]. One analysis included 7 trials with a total of participants that administered chromium as chromium picolinate at mcg to 1, mcg daily for 8 to 24 weeks [ 52 ].
Chromium supplementation had no effect on fasting blood glucose, total testosterone, dehydroepiandrosterone, follicle-stimulating hormone, or luteinizing hormone levels. However, chromium did significantly reduce body mass index BMI by 2. Chromium supplementation had no significant effect on fasting insulin levels or insulin sensitivity, but data from two trials showed that it did significantly lower a measure of insulin resistance.
In addition, one trial included in the review found that chromium supplementation significantly improved a measure of beta-cell function. Similarly, another meta-analysis and a systematic review had mixed findings [ 54 , 56 ]. Overall, the evidence on whether chromium supplementation reduces the risk of PCOS or is beneficial for women with this condition is mixed, making it difficult to draw firm conclusions [ 16 ].
Additional studies with sufficient samples sizes and duration in well-defined populations are needed [ 53 ]. Dyslipidemia Numerous studies show associations between poor chromium status and elevated blood cholesterol levels [ 7 ].
Therefore, scientists hypothesize that chromium supplementation might improve blood lipid levels. Studies have examined this possibility in various populations, including people with impaired glucose tolerance, diabetes, or PCOS. In a randomized clinical trial in 71 participants mean age