Overview
Air quality remains a concern to governments, regulators, and the public because of the detrimental effect that air pollutants can have on human health and environmental sustainability. In particular, as the profile of metals as toxic air pollutants has grown in recent years, so the air quality infrastructure put in place to make measurements of these pollutants has similarly increased. The toxic effects of certain chromium (Cr) compounds in air have been recognized for a long time. The presence of Cr in the +6 oxidation state (Cr[VI]) is still observed in ambient air samples in California despite steps taken to reduce emissions from plating operations, welding and other types of ‘hot work’ on stainless steel and other metals that contain Cr, and spray paints and coatings. Hexavalent Cr or Cr(VI) is one of the oxidation states of the element Cr and is the toxic form that poses a health risk to workers exposed to it. The US Environmental Protection Agency has classified Cr(VI) compounds as ‘Group A carcinogens’, while the International Agency for Research on Cancer (IARC) as ‘known human carcinogens by inhalation (Group 1)’. The toxicity of hexavalent Cr arises from its ability to bind to cellular macromolecules. Chromium has oxidation states ranging from -2 to +6, of which the divalent (+2, chromous), trivalent (+3, Chromic) and hexavalent (+6) are the most important. Trivalent chromium, Cr(III), which is the most stable form of chromium, is found in trace amounts in the human body and is believed to be necessary for sugar metabolism. Studies have shown that Cr(III) is not toxic and non-carcinogenic. Hexavalent Cr compounds have varied uses in industry and are often used for their anti-corrosive properties in metal coatings, protective paints, dyes and pigments. Hexavalent chromium can also be formed when performing ‘hot work’ such as welding on stainless steel, melting chromium metal or heating refractory bricks in kilns. In these situations, the chromium is not originally in the hexavalent state but at sufficiently high temperatures undergoes oxidation (i.e., loses electrons) to yield the hexavalent form. The University of California Riverside’s Center for Environmental Research and Technology propose a three-phase study for the in-depth investigation of hexavalent chromium sources and formation mechanisms, as well as techniques for its emissions reduction from industrial operations. Preliminary tests from several furnace operations in the Paramont region conducted by AQMD indicate that heat treating chromium containing products such as stainless steel parts and parts racks, may lead to partial conversion of the solid chromium on the surface of the products under high temperatures. And result in high concentrations of hexavalent chromium in the air. This study will review the data collected to date, as well as a literature review, laboratory testing, and field testing to verify these findings and to identify the exact sources of the amount chromium in the +6 oxidation state released by industrial operations (welding and allied practices) in the South Coast Air Basin.
Lead Researcher: Dr. Georgios Karavalakis