I accept it.  The  Cr6+, in  Leather tanning,   as a primary standard, cleaning agent and oxidant in laboratories  is widely used.   I think researchers have to focus on it.

Cr6+ is more toxic and it is a very dangerous carcinogen as well. To avoid using Cr^+ you may consider 2% solution of nitric acid which is strong oxidant but also most of the nitrates are easily soluble in water so this approach should provide you satisfactory efficiency of washing laboratory glassware.

Dear Dr. Venkatathri,

The oxidation states of chromium ranging from -2 to +6 but only +3 and +6 are more stable in the environment. The Cr (VI) is more toxic due to carcinogenic and teratogenic effects. There are a number of technical and scientific literature about this element. Among many technical references I suggest purchasing the following books:

Seiler, H., Sigel, A., & Sigel, H. (Eds.). (1994). Handbook on metals in clinical and analytical chemistry. CRC Press.

Kaim, W., Schwederski, B., & Klein, A. (2013). Bioinorganic Chemistry--Inorganic Elements in the Chemistry of Life: An Introduction and Guide. John Wiley & Sons.

Best Regards and good job

Chromium can exist in oxidation state ranging from −2 to + 6, but is most frequently found in the environment in the trivalent (Cr+3) and hexavalent (Cr+6) form. The hexavalent state is a major part of chromium in waters. Hexavalent chromium easily penetrates biological membranes and for high oxidizing potential, is more toxic than the Cr+3 form.

Cr6+; within the 2017 in EU will be banned from galvanic industry for this reason.

Chromium (VI) is a well known carcinogen contrary to Cr(III) which is an essential nutrient that helps the body use sugar protein etc

Chromium 6+ is toxic

Chromium 3+ is considered to be not toxic and is needed for  life Of course in large enough quantities Chromium 3+, like anything can be toxic. But it is required for sugar metabolism in humans, and a deficiency of Chromium 3+ causes a disease called chromium deficiency. Trivalent chromium (Cr(III), or Cr3+) is required in trace amounts for sugar metabolism in humans (Glucose Tolerance Factor) and its deficiency may cause a disease called chromium deficiency. In contrast, hexavalent chromium is very toxic and mutagenic when inhaled as publicized by the film Erin Brockovich. Cr(VI) has not been established as a carcinogen when not inhaled but in solution it is well established as a cause of allergic contact dermatitis (ACD).

World Health Organization recommended maximum allowable concentration in drinking water for chromium (VI) is 0.05 milligrams per liter. Hexavalent chromium is also one of the substances whose use is restricted by the European Restriction of Hazardous Substances Directive.

Certain foods such as Brewer’s yeast were believed to contain intact glucose tolerance factor (GTF); in view of this consideration, these food products were considered as superior sources of chromium. However, recent attempts to identify the biological molecules(s) responsible for binding chromium (III) appear to have failed. The postulated complex, GTF, has remained elusive; it has not been possible to unequivocally identify this factor, and therefore its occurrence has been seriously questioned; it is thought that GTF arises as an artifact in process of chemical analysis. It has been recommended that the notion of GTF be abolished. Certain studies also indicate the strong possibility that chromium is not an essential trace element for humans.

Chromium is known to complex niacin, L-histidine, ascorbic acid, etc. Chromium (III) has been reported to act in conjunction with a very small protein, which has been designated as low molecular weight chromium-binding substance (LMWCr), which assists the action of insulin. LMWCr binding to chromium is not of a permanent nature. LMWCr does not appear to be a potential source of chromium in foods.

Evidence presented suggests that the consumption of high enough quantities of chromium results in the conversion of its original safe form (chromium III) into a known carcinogenic form, chromium 6.

Mulyani I, Levina A, Lay PA. Biomimetic oxidation of chromium(III): Does the antidiabetic activity of chromium(iii) involve carcinogenic chromium(vi)? Angew Chem Int Ed Engl. 2004;43:4504-4507.

Definitely, hexavalent Cr is much more dangerous and toxic for both acute and chronic exposures. It is carcinogenic and can be transported to cells whereas trivalent cannot. For humans, the respiratory tract is the major target organ for hexavalent chromium

Cr(VI) is much more toxic.  Check the Material Safety Data Sheets for Cr+6 and Cr+3 compounds.  The EPA classifies Cr(VI) as a known human carcinogen, and epidemiological studies of people who work with Cr(VI) have clearly established that inhaled chromium (VI) results in an increased risk of lung cancer.  The EPA states that Cr(III) is not classifiable as to carcinogenicity in humans, but suggests it might have carcinogenic potential, I.e., via conversion to Cr(VI). 

Simple experiment for chemistry Practical is Titration between Ferrous Ammonium Sulphate and Potassium Dichromate  using N-Phenyl Anthranilic Acid /Diphenyl Amine  as Indicator.

In this  case Chromium (VI) is converted into Chromium(III) and Ferrous is converted into Ferric ions.

whether this experiment is continued ...

As per Chromium also used in Tanneries and more useful as pigments in various product , where yellow -orange colour appers 

Chromium a toxic ,specially of Cr(VI) .

Dr. Venkatathri, 

Pot. dichromate is highly useful reagent in redox titrations and many other oxidation reactions, generally carried out in laboratories. I will not suggest replacing it with any other oxidant owing to excellent oxidizing properties. In my opinion, Cr(VI) should be converted to less toxic Cr(III) using FAS or other chemicals before discarding Cr(VI) effluents/solution to avoid contamination to water bodies.

Dr.randhava,

I agree with your informations on Cr(VI)

However the problem in our life ,is with Cr(VI) is because of so many Colouring Pigments are related with this.

How we can combat the problems appeared in our life 

Chromium 3+ is  not toxic and essentially need for life in traces.These are oxidizing properties of chromium which makes it toxic that depends on valance. hexavalent Cr is highly dangerous and toxic for both acute and chronic exposures  to man.

In aqueous systems, chromium can exist in both trivalent and hexavalent oxidation states. Because of its great toxicity Cr(VI) must be removed from wastewater before being discharged.

Please examine MSDS (material safety data sheet) for avoiding. 

Chromium VI is more toxic to Cr(III)

1.      Metabolically reduced species of Cr (VI) [formed during the reduction of Cr (VI) to Cr(III)] are considered to play causative roles in inducing DNA damage and mutations. The trace element, Cr(III), has been considered to be an essential nutrient (although this issue has recently been debated), and is a common nutritional supplement.

2.      Hexavalent chromium [Cr(VI)], a heavy metal, has been classified as a group 1 carcinogen (carcinogenic to humans), with a clear link to lung carcinogenesis (International Agency for Research on Cancer [IARC], 2012). Evidence accrued from epidemiologic studies substantiates the hypothesis the contention that occupational inhalation of  Cr(VI) is associated with human stomach cancer. In cells, Cr(VI) undergoes reduction  to intermediate oxidation states, such as Cr(V) and Cr(IV), before forming stable Cr(III) forms. Following ingestion, Cr(VI) undergoes reduction to Cr(III) in the stomach.

3.      Entry of Cr(VI) into the cell occurs through non-specific anion channels.  Ascorbate, glutathione, and cysteine metabolically reduce Cr(VI) to Cr(V), Cr(IV), and Cr(III).  Very low membrane permeability capacity of Cr(III) impedes the crossing of  the cell membrane by Cr(III); as a result it is confined within the cell where it can bind to DNA and manifest genetic damage (occurrence of DNA adducts, DNA-strand breaks, oxidized bases, etc.).

4.      The above (see #2 above) intermediate (reduced) forms of chromium seem to directly interact with cellular constituents to generate reactive oxygen species (ROS), which have been implicated as causative agents in major proportions of DNA damage and mutations induced by Cr(VI).  By scavenging ROS through its cysteine residues, the heavy metal-binding protein, metallothionein (MT), which cannot bind chromium, may act as a protective factor against Cr(VI)-induced DNA lesions. 

Cr hexavalent is toxic

Very good and highly useful discussion on Cr(VI) and Cr(III).

Hexa valent Cr is several times more toxic than Cr III.

Naturally chromium ions exist predominantly in two different oxidation states, trivalent Cr3+ ions and hexavalent Cr6+ ions. Trivalent chromium is a thousand times less toxic than Cr6+ and is an essential micronutrient for several organisms.

Cr6+ is mutagenic and carcinogenic