National Emission Standards for Hazardous Air Pollutants: Mercury Emissions From Mercury Cell Chlor-Alkali Plants

This action promulgates national emission standards for hazardous air pollutants (NESHAP), specifically mercury emissions, from mercury cell chlor-alkali plants. The final rule will limit mercury air emissions from these plants. The final rule will implement section 112(d) of the Clean Air Act (CAA) which requires all categories and subcategories of major sources and area sources listed under section 112(c) to meet hazardous air pollutant emission standards reflecting the application of the maximum achievable control technology (MACT). Mercury cell chlor-alkali plants are a subcategory of the chlorine production source category listed under the authority of section 112(c)(1) of the CAA. The chlorine production source category was also identified as a source of mercury under section 112(c)(6) that must be subjected to standards. In addition, mercury cell chlor-alkali plants were listed as an area source category under section 112(c)(3) and (k)(3)(B) of the CAA. The final rule, which will satisfy our requirement to issue 112(d) regulations under each of these listings (for mercury), will reduce mercury emissions by about 3,068 kilograms per year from the levels allowed by the existing Mercury NESHAP. Mercury is a neurotoxicant that accumulates, primarily in the especially potent form of methylmercury, in aquatic food chains. The highest levels are reached in predator fish species. Mercury emitted to the air from various types of sources (usually in the elemental or inorganic forms) transports through the atmosphere and eventually deposits onto land or water bodies. When mercury is deposited to surface waters, natural processes (bacterial) can transform some of the mercury into methylmercury that accumulates in fish. Ingestion is the primary exposure route of interest for methylmercury. The health effect of greatest concern due to methylmercury is neurotoxicity, particularly with respect to fetuses and young children. In addition, in this final action, we are utilizing our authority under section 112(d)(4) of the CAA not to regulation chlorine and hydrochloric acid (HCl) emissions from the mercury cell chlor-alkali plant subcategory.