Understanding Hexavalent Chromium (Chromium VI)
Chromium is a tasteless and odorless metallic element in two valence states: ‘Trivalent Chromium [Cr (III)] and Hexavalent Chromium [Cr(VI)].’ According to the National Institute of Environmental Health Sciences (NIEHS), “Hexavalent chromium is a form of the metallic element chromium. Chromium is a naturally occurring element found in rocks, animals, plants, vegetables, fruits, meats, soil, and volcanic dust and gasses. It comes in several different forms, including trivalent chromium and hexavalent chromium. Hexavalent chromium, or chromium (VI), is generally produced by industrial processes.” Also, the Occupational Safety and Health Administration (OSHA), the U.S. Department of Labor, states that “Hexavalent chromium [Cr(VI)]is usually produced by an industrial process.”
Sources of Hexavalent Chromium in Drinking Water
The sources of hexavalent chromium [Cr(VI)] in drinking water are discharges from metal plating operations, steel and pulp mills, boiler water corrosion control applications, and other industrial processes. In some areas, the chromium compounds get released into the environment due to poor storage, leakage, or improper disposal practices. According to the Department of Public Health and Environmental Protection Agency (EPA) of the United States, “Chromium compounds are very persistent in the aquatic environment, mostly bound to sediments and soil.”
Apart from these sources, it also occurs by the erosion of natural deposits of trivalent chromium that later on get oxidized to turn into chromium oxide (Cr2O3). In the Journal of Hazardous Materials, the Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to the natural environment has been published as “Results indicate that trivalent chromium in Cr2O3 could be readily converted to hexavalent chromium at a temperature range of 200–300 °C, with conversion rates of up to 50% in 12 h.” This way, it reaches anoxic environments or preciously in an aquatic environment or water sources like lakes, rivers, streams, oceans, estuaries, and wetlands.
Health Risks Associated with Hexavalent Chromium
Hexavalent Chromium [Cr(VI)] is more toxic in nature compared to its trivalent form. So far, there has been significantly less specific testing of Cr(VI) in drinking water at levels below 1 ppb as it has been believed to be inactive when ingested. Also, it was believed that hexavalent chromium is converted by stomach contents, such as organic material, into the less toxic form of chromium, which is trivalent chromium [Cr (III)]. According to the National Toxicology Program (NTP), “sodium dichromate dihydrate, a compound containing hexavalent chromium, causes cancer in laboratory animals following oral ingestion.” The Hexavalent Chromium [Cr(VI)] may be carcinogenic when ingested at high doses over a lifetime.
- Malignant tumors
- Benign tumors
- Allergic dermatitis
- Cancer
- Morphologically abnormal sperm
Regulatory Standards and Guidelines
No specific value for ingestion of hexavalent chromium (CrVI) in drinking water has been declared by federal (EPA) or state standards. The only standard is the amount of total chromium at 100 parts per billion (ppb) or 0.100 parts per million in drinking water. After the risk assessment study conducted by the California EPA and the US EPA, they suggested that the hexavalent chromium in drinking water of 0.06 ppb is the threshold level.
Detection and Testing for Hexavalent Chromium
Ion chromatography is the way to detect, test, and identify hexavalent chromium (CrVI) in water. There are two steps in this process: first is to determine the hexavalent chromium and later to determine the total chromium by potassium permanganate solution to oxidize the Cr (III) and find Cr (VI) after any conversion. Additionally, the conductivity detector is also used for CrVI detection with the oxidizing agent. It is a useful method for chromium speciation in water sources such as river and groundwater samples.
Treatment and Removal Methods
The treatment and removal of hexavalent chromium (CrVI) from water can be done using various methods, including reverse osmosis (RO) and nanofiltration (NF) membranes. According to the WHO, reverse osmosis (RO) and nanofiltration (NF) membranes both have a removal rate of 82–97% for chromium (both Cr[III] and Cr[VI]) from water. According to a pilot scale RO study, “a polyamide thin film composite membrane was capable of reducing a feed Cr(VI) concentration of 5.0 mg/L to 0.01 mg/L (10 µg/L), achieving greater than 99% rejection, at a permeate flux rate of 58.8 L/m²·h and a system recovery greater of 42.5%.’ Reverse osmosis (RO) is the most effective and affordable method for removing hexavalent chromium (CrVI) from drinking water in a home setup or domestic use. All Home Master RO systems are rated to remove Chromium.
Conclusion
Hexavalent chromium (Cr{VI]) is toxic and carcinogenic in nature yet has shown no significant health concern for humans. Hexavalent chromium in water occurs by both natural and industrial processes. If a water source or drinking water has hexavalent chromium (Cr{VI]) contamination, it is essential to treat and remove it. There are many ways to remove hexavalent chromium from water; however, for home or domestic uses, the reverse osmosis (RO) and nanofiltration (NF) membranes are capable of removing this toxic substance. Install a Home Master RO system to remove harmful contamination like hexavalent chromium and enjoy healthy, pure, and safe drinking water as advised.