Chromium is a naturally occurring element. Out of all their compounds, the commonly occurring valence states are chromium metal Cr (0), trivalent chromium Cr (III) and hexavalent chromium Cr (IV). We need to dig out about 4 kg of chromium ore from earth to realize 1 kg usable chromium.
We use chromium compounds to fight corrosion, as tanning salts in leather industries and others, as an important constituent in metal alloys (metal alloys alone account for 85% of chromium usage), in wood preservation, cement manufacturing.
Abundantly used in today’s surface coating applications incl. chrome plating, paint and pigment applications (the brilliant yellow paint has to be made from high concentrations of chromium compounds) and in few anodizing process.
They were an essential compound in those infamous magnetic recording tapes and photography films: Progressive new technologies at least replaced these tapes and films with new mass storage devices and image sensors.
So, what is so special about these chemical compounds?
Hexavalent Chromium Cr (IV), a class I carcinogen, is one of the most celebrated chemical in recent times. Thanks to the sustainable status shift companies are aiming at. Even the ‘Erin Brokovich’ movie plot was built on Cr (IV) health effects based on a true story, where an industry’s waste water with high concentrations of Cr (IV) percolates in to ground water and lead to acute sufferings of people in and around that locality. In 1996, this company paid $333 million to the people living around its setup in a law suit.
Cr (IV) is readily reactive and soluble in water. It is still an essential alloy constituent in stainless steel and is/was used widely by those hundreds of leather tanneries of Kanpur and Vaniyambaadi in India (legally as well as illegally). People obviously love that shiny/silver finish of chrome plated products/parts. But researches say that their compounds are genotoxic even in small traces, exposure and inhalation can easily cause lung cancer and damages in kidneys and intestine. Occupational hazard is indefinitely high; certain leather tanneries no more employ young people and women, but still employ people.
Well, controversially, trivalent chromium Cr (III) is an essential mineral for human metabolism, a trace amount of it is necessary for maintenance of good health since it helps our body to utilize sugar, fat and protein. Cr (III) sounds necessary, isn’t it? Even then in many literatures, it is carefully denoted as ‘less toxic’ (than Cr (IV)), but not as ‘safe’ entirely. Continual exposure can lead to mentionable health effects and allergic situations.
Most of the literatures and research reports on Cr (III) never seem to take a firm stand on any side of good or bad affects and effects of it, hence concluded ‘less bad’ usually.
There are nearly about 20 different chromium compounds which have to be restricted / stopped in use. The new revised Hazardous waste act, 2008 enforced by Ministry of Environment and Forests, India limits hexavalent chromium only up to 50mg/kg in regulation. There are other better benchmarks which recommend complete avoidance of Cr (IV) usage until and unless it is highly necessary for technical performance in some cases, but it is essential to keep such products in closed loop of manufacture, use and recovery.
New environment regulations and measures led many to adopt Cr (III) as an effective alternative to Cr (IV) at least in surface coating applications (chrome plating etc).
# There are researches on, to discover possible absorption and removal of Cr (IV) through bacteria and other micro-organisms.
# EU norms (2006) prohibit marketing of new electrical and electronic equipments containing Cr (IV) at a concentration greater than 0.1% by weight.
# Arc welding of stainless steel is extremely dangerous.
# Trivalent chromium compounds are bluish-black.
# Hexavalent chromium compounds are yellow-orange-brown.