Alternative to potassium dichromate in water analysis
Potassium dichromate is used in standardized method to determine the chemical oxygen demand (COD), an indicator of the content of oxidizable chemicals in waters. Alternatives to the hazardous potassium dichromate are available, but there are limitations to some of them, like the range of applicability and/or the content of equally hazardous substances.
IR detection method
Potassium permanganate has some of the hazards of the potassium dichromate that it substitutes but unlike the chromate, it is not classified as EU carcinogenic 1B, mutagenic 1B and skin sensitizer.
In France a required standardised method for COD measurement uses potassium dichromate, a CMR 1B and a respiratory and skin sensitizer. Conditions of use include direct manipulation and 2 hour boiling of the sample.
Alternative methods exist, but have their limitations.
The use of potassium permanganate is also part of a standardised method and is a safer option. It is however applicable to levels of COD specific to water for human consumption, below 10mg/l, generally much lower than the level in polluted waters.
Another alternative is determination of COD by vaporising minute quantities of sample under conditions that transform organic matter in carbon oxide, measured by infrared (IR)) adsorption. This method is applicable to broad range of organic matter content in the sample as well as for samples containing high levels of chlorine. This method needs more expensive devices than the one it substitutes.
Replacement of potassium dichromate in COD measurement is possible if the limitations of the alternatives , like lower measuring range or higher price,s are not a major inconvenient. The problem is of interest not only in France since many other countries have standardised methods using hazardous potassium dichromate.
Original document only in French
Type of information supplier
INSTITUT NATIONAL DE RECHERCHE ET DE SÉCURITÉ pour la prévention des accidents du travail et des maladies professionnelle ), France, email@example.com, www.inrs.fr
The Fact sheet was developed by CNAMTS and INRS , France and published by INRS on its website in 20o7.Type of publication and availability
Fact shhet freely available on internet, in French
Publication or last update: 30.03.2012