Guidelines for Metals and Metalloids in Ambient ... - ARCHIVE: Defra

Expert Panel on Air Quality Standards
58. At one time there was major use of arsenic in pesticides and this
continues in the form of copper chrome arsenate used as a timber
treatment. Other uses include incorporation in metal alloys. Because of
its presence in the earth’s crust, arsenic exists in a range of crustal
materials including coal and metal ores and consequently can be
released to the atmosphere during their combustion or processing.
2.1.2 Sources of arsenic in the UK atmosphere
59. Arsenic is primarily emitted into the atmosphere by high-temperature
processes such as coal-fired power generation, smelting, burning
vegetation and volcanoes (WHO, 2000). Natural low-temperature
biomethylation and microbial reduction also release arsenic into the
atmosphere; microorganisms can form volatile methylated derivatives
of arsenic under both aerobic and anaerobic conditions, and can
reduce arsenic compounds to release arsine gas (Cheng and Focht,
1979; Tamaki and Frankenberger, 1992).
60. Arsenic is released into the atmosphere primarily as arsenic trioxide
(As 2 O 3 ) or, less frequently, as one of several volatile compounds,
arsines. Arsenic released to air exists mainly in the form of particulate
matter (Coles et al., 1979). These particulate matter have a lifetime of
up to 10 days before removal by wet and dry deposition and readily
undergo long-range transboundary transport (USEPA, 1984). Arsines
that are released from microbial sources in soils or sediments undergo
oxidation in the air, reconverting the arsenic to less volatile forms that
are removed by wet and dry deposition (Parris and Brinckman, 1976).
61. Historically, the main source of arsenic emissions to the air in the UK
has been the combustion of coal in power stations, industry and for
domestic heating (Dore et al., 2006). The main sources reported in the
UK National Atmospheric Emissions Inventory for 2004 include
emissions from the combustion of treated wood and combustion of
coal in industry and power stations. Combustion of coal in power
stations, industry and for domestic heating contributed 10% of the
national total in that year. Combustion of fuel oil at refineries, in
industry and from shipping contributed 7%. Emissions from the
combustion of wood treated with copper-chromium-arsenic
preservatives were estimated to contribute up to 50%, although this
estimate is uncertain. Emission from metal industry sources make up a
relatively small percentage of total UK emissions (7%) but may
constitute the most important source in the vicinity of specific
industrial plants.
62. UK emissions of arsenic are estimated to have declined by 78%
between 1970 and 2004 as a result of reductions in the combustion of
coal in power stations, industry and for domestic heating.
18