Commonwealth of Australia 2010
Sources of Environmental Exposure
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- 8.1.1Natural sources of cyanide
- 10.Cyanogenic glycosides in plants
- 14.1.1Anthropogenic sources of cyanide
- 14.1.2National emissions of cyanide (National Pollutant Inventory)
- 16.Release from diffuse sources
- 17.Release from industrial point sources
- Point source releases by industry type
8.Sources of Environmental ExposureThis chapter describes the sources of cyanide in the environment from the manufacture and use of sodium cyanide. Exposure to cyanide also occurs from natural sources and industrial uses of hydrogen cyanide. 8.1Environmental release of cyanides generallyCyanide is ubiquitous in nature, present mostly at low concentrations. Higher concentrations may occur in the environment due to anthropogenic sources. 8.1.1Natural sources of cyanide9.General commentsCyanides can occur naturally at low concentrations in ground and surface waters (Environment Australia, 1998), and the concentration of naturally occurring free cyanide in water supply systems is usually less than 0.01 mg/L (NHMRC, 2004). Low concentrations of cyanides may occur in tap waters, either derived from the source waters or from the distribution system (CalEPA, 1997); however, this is probably a rare occurrence. Natural sources of cyanide include degradation products from some micro-organisms and plants that synthesise cyanogenic glycoside compounds. There is a cyanide group in the molecule of vitamin B12 (cyanocobalamine), which is required at trace levels by many animals, including humans, in their diet. Cyanide-containing chemicals (all forms) are produced by many organisms (bacteria, fungi, algae, invertebrates and higher plants) as part of their normal metabolism (NSC, 2002; Irwin et al., 1997; Ciba Foundation, 1988; Vennesland et al., 1981; Ferris, 1970). 10.Cyanogenic glycosides in plantsCyanogenic glycosides are cyanide containing organic compounds that occur in at least 2000 species of plants (WHO, 1992; Knight and Walter, 2004). Examples of species containing cyanogenic glycosides include sorghums (Johnson grass Sorghum halepense, Sudan grass Sorghum almum), millet (Panicum millaceum; Poaceae), flax (Linum usitatissimum; Linaceae), elderberry (Sambucus canadensis; Caprifoliaceae), pits of Prunus spp. (plums, cherries, cherry laurel, pears, apricot, apple, peach, almond; Rosaceae) (CCWHC, 1999), sweet potatoes (Ipomoea batatas), corn (Zea mays), linseed (Linum sp.) (Irwin et al., 1997), spotted emu bush (Eremophila maculata), birdsfoot trefoil (Lotus australis), Lomatia silaifolia, milkweed (Asclepias curassavica; Asciepiadaceae), manna gum (Eucalyptus vimilalis; Myrtaceae) (McKenzie, 1997), Eucalyptus cladocalyx (Gleadow and Woodrow, 2000), cassava (Manihot esculentum; Euphorbiaceae), bamboo shoots (Bambusa vulgaris; Bambusaceae), lima beans (Phaseolus lunatus; Fabaceae) (Conn, 1979a-b), roses (Rosaceae) (MOH, 2000), and grasses such as button grass (Dactyloctenium radulans; Poaceae; Ballenger and Allan, 2001) and purple plume grass (Triraphis molis; Poaceae; Ballenger and Allan, 2002). Cyanogenic species also occur in other plants in the Leguminosae and in the Compositae and other plant families (Knowles, 1988). There are approximately 25 different types of cyanogenic glycosides known including amygdalin, dhurrin, linamarin, lotaustralin, prunasin and taxiphyllin (WHO, 1992). Another naturally occurring group of organic cyanides (nitriles) is the highly toxic pseudocyanogenic glycosides, especially cycasin (Cycadaceae), and these have been implicated in a variety of tropical diseases of the nervous system, and partial or total blindness. Other nitriles found in plants include the lathyrogenic compounds, glucosinolates, and the cyanopyridine alkaloids (Irwin et al., 1997). Cyanogenic glycosides are stored in plant cell vacuoles (Rothman, 1999). Consumption and masceration of plant parts by herbivores/omnivores leads to the release of the enzyme -glucosidase, which hydrolyses the cyanogenic glycosides to sugar and aglycone and subsequently to hydrogen cyanide (HCN), particularly in alkaline rumen conditions of ruminant herbivores. The HCN is subsequently detoxified in animals by metabolic processes (refer Chapter 31) or potentially excreted as a gas; however, adverse effects may occur if the capacity for detoxification is exhausted. In such instances, livestock losses may occur due to sublethal cyanide poisoning (cyanosis) (DPI, 2003). The release of HCN from endogenous cyanide-containing compounds in plants has been suggested as an effective herbivore deterrent (Gleadow and Woodrow, 1999). In addition to consumption and masceration, other damage to plants (e.g. wilting, drought, bruising, trampling, intense heat, frost, etc) may also result in contact between cyanogenic compounds and hydrolytic enzymes (Tsai, 2001; Rothman, 1999). 11.InvertebratesVarious invertebrate species, including some centipedes, millipedes, beetles, moths and butterflies produce and secrete cyanogenic glycosides for defensive purposes in repelling predators (Duffey, 1981; Nahrstedt, 1988). The cyanogenic system comprising cyanogenic glycosides, cyanohydrins, betaglucosidases, and nitrile lyases occurs in several species of arthropods, including the tiger beetle (Megacephala virginica), leaf beetle (Paropsis atomaria), zygaenid moths, and certain butterflies (e.g. Heliconius sara) (Nahrstedt, 1988; Engler, 2000). In Zygaena trifolii, cyanide compounds seem to function as protection against predators (Nahrstedt, 1988). Defensive secretions of cyanide have also been reported in polydesmid millipedes, and these organisms seem to be more tolerant than other species when exposed to HCN (Towill et al., 1978). In a millipede (Apheloria sp.), cyanide is generated in a two-compartment organ by hydrolysis of mandelonitrile; cyanide generation occurs outside the gland when the components of the two compartments are mixed during ejection (Towill et al., 1978). 12.Micro-organismsMany bacteria produce cyanogenic compounds (e.g. Chromobacterium violaceum and many strains of Pseudomonas aeruginosa and P. fluorescens; Knowles, 1988). Further details are provided in Section 1.6. 13.BushfiresBushfires can be a source of cyanide release into the atmosphere, especially on a local scale (CalEPA, 1997), and HCN can be detected in atmospheric plumes from large scale fires (wild fires or deliberately set for agricultural regeneration, clearing etc). HCN is mainly released upon the incomplete combustion of biomass, during low temperature smouldering (Barber et al., 2003). During bushfires, most cyanide compounds produced are emitted to the atmosphere, and a relatively small fraction resides in ash and may be leached by rain, potentially leading to cyanide in surface runoff waters (Barber et al., 2003). Biomass burning is considered to be the dominant source of HCN in the atmosphere (Section 23.3.3). 14.Other sourcesIn addition to producing nitrogen oxides (NOx), it has been suggested that lightning may also produce HCN in the atmosphere, but this is considered to be a negligible source in the earth today (Chameides and Walker, 1981; Cicerone and Zellner, 1983). This has been discussed as a possibility more recently by Lary (2004) but appears not to have been supported. Another possible source in the atmosphere is reaction of the gas acetonitrile (CH3CN – derived from various natural and anthropogenic sources) with hydroxyl radicals (Kleinböhl et al, 2006). Cicerone and Zellner (1983) also noted that thermodynamic equilibrium calculations indicate volcanoes can emit HCN, but that this source was difficult to quantify and is probably relatively small. 14.1.1Anthropogenic sources of cyanideCyanide releases to the environment may originate from a range of anthropogenic sources additional to the use of sodium cyanide for the mining and industrial purposes described in this review. Such sources include processes using other forms of cyanide, most notably HCN. HCN may be used as a fumigant, but more importantly is used as a precursor for the production of a wide range of products including plastics and synthetic fibres, herbicides, photographic development chemicals, anti-caking agents (i.e. sodium and potassium ferrocyanide), animal feed proteins (e.g. methionine) and explosive compounds (e.g. mercury and silver fulminate). HCN is released upon the incomplete combustion of several materials, including wool, silk, polyacrylonitrile, nylon, polyurethane, and paper (CalEPA, 1997) and coal (Wójtowicz et al., 1995). The amounts of cyanide released depend on the conditions of combustion (Pauluhn, 1992). Detonation of TNT also releases HCN, at a rate of 13 kg/tonne (Environment Australia, 1999f). Cyanide is found in association with spent pot linings (SPL) that are derived from aluminium smelting. Typically, SPL wastes have historically been sent to landfill for disposal under license; however, treatment procedures have been developed to detoxify the cyanide present in these wastes to minimise environmental releases. Residues resulting from previously used practices are also found at coal gasification/gasworks sites (Kunze and Isenbeck-Schröter, 2000; Hathaway, 2000; Meehan, 2000; Kjeldsen, 1999; Kaminski, 2003). Coal contains about 0.5% to 1.5% by weight of nitrogen bound into the organic structure of the coal. When coal is heated, much of the nitrogen is released during the devolatilisation stage as HCN, other cyano species, and as ammonia (NH3). These species are rapidly converted into NOx or N2, and thus are generally not emitted directly from coal combustors associated with power plants. Emissions may occur at metal manufacturing facilities in association with coke oven facilities, where cyanide may be generated under sub-optimal conditions. In the United States, of the total cyanide released to air (then estimated at 20 000 tpa), which accounts for about 60% of the environmental load of total cyanide, about 90% is due to the fuel combustion emissions from vehicles (Hagelstein and Mudder, 1997a). The second largest source of release of cyanide to air in the US is from facilities that manufacture organic chemicals (i.e. methylmethacrylate and acrylonitrile) and HCN (USEPA, 1981). Releases of cyanide to land in the United States are mainly through landfill disposal and the use of cyanide-containing road salts. Releases of cyanide to waters in the United States are derived mainly from anthropogenic sources, with most originating from discharges from wastewater treatment plants (WWTPs). Electroplating and heat treatment facilities account for the majority of influent into WWTPs. Non-point sources of cyanide are derived from agricultural and road run-off, due to the use of ferrocyanide-containing anti-caking ingredients in road salts (not used in Australia). Data for anthropogenic cyanide release in Australia is discussed in the following section. 14.1.2National emissions of cyanide (National Pollutant Inventory)15.General commentsThe National Pollutant Inventory (NPI) is a database administered by the Department of the Environment, Water, Heritage and the Arts, to provide information on the types and amounts of certain substances being emitted into the Australian environment (DEWHA, 2009a; EPHC, 2007b). The NPI data for environmental emissions of ‘inorganic cyanides’ (including all forms encompassed under the definition of total cyanide – Section 3.3.1) for the period 2007-08 have been summarised in the following sections. For the purpose of reporting to the NPI, ‘emission’ means emission of a substance to the environment whether in pure form or contained in other matter, and whether in solid, liquid or gaseous form. Individual facilities are required to report emissions of NaCN (listed by the NPI as a ‘Category 1’ substance) when their use totals ≥ 10 tonnes of the substance per year. ‘Emissions’ do not necessarily reflect the extent to which different uses occur– there are limitations in the data due to factors such as the scale for reporting individual sites, and different processes may result in widely different proportions of reportable emissions (e.g. total emissions recorded for the gold industry are of the order of 1500 tonnes, compared to ~50,000 tonnes used). ‘Emissions’ data does not included deposit of a substance to landfill; or discharge of a substance to a sewer or a tailings dam; or removal of a substance from a facility for destruction, treatment, recycling, reprocessing, recovery or purification. These activities are classed as transfers and in the past have not reported under the NPI. Procedures for reporting transfers of NPI substances in waste to their final destination have now been developed and data for transfers are currently being collected and will be published alongside the 2008-09 emissions data. It should also be noted that the NPI data do not distinguish between inorganic cyanide emissions derived from sodium cyanide and those emissions derived from other cyanide compounds (e.g. HCN, KCN). There is insufficient information available to evaluate the relative contribution that sodium cyanide-derived cyanide contributes to the total amount of environmental releases of cyanide relative to all other natural and anthropogenic sources of cyanide compounds. However, information is available on the quantity of sodium cyanide manufactured and used in Australia (Section 4). In addition, knowledge of the cyanide product used by various industries provides an indication of the parent compound used and thus the origin of the cyanide compounds released into the environment by that industry (Section 4.4). For example, the Australian gold mining industry is a major user of sodium cyanide for ore beneficiation and cyanide emissions from this industry are largely derived from this use, while electroplating industries use heavy metal cyanides in addition to sodium cyanide or potassium cyanide (Sections 5.2.2 and 19.1.2). 16.Release from diffuse sourcesIn addition to reporting emissions from industrial point sources, the NPI reports estimated releases from diffuse sources. For total inorganic cyanide, the estimated total annual emission of inorganic cyanides from diffuse sources in 2007-2008 was 610 tonnes, primarily from motor vehicles, and all considered to go to air (Figure 5.). These sources involve releases of cyanide through processes such as combustion, rather than the use of cyanide salts such as sodium cyanide. The estimated release from these sources is approximately 45% of that estimated from industrial point sources in Australia. However, this and the relative contribution from different NPI diffuse emission categories appear to contrast markedly with estimates of HCN emission to the atmosphere on a worldwide scale, where biomass burning is considered the major source and HCN has been proposed as a sensitive tracer of biomass burning on a large scale for observations from space (Rinsland et al, 2001, 2005; Li et al, 2003; Singh et al, 2003). Figure 5.. Contribution of major diffuse sources of emissions of inorganic cyanide to air in Australia reported by the National Pollutant Inventory (2007-2008). The NPI indicates that reporting facilities (i.e. major Australian industrial facilities) estimated that they emitted a total of 1426 tonnes of inorganic cyanides into the environment in 2007-08 (DEWHA, 2009a). These emissions correspond to approximately 1%-2% of the total quantity of sodium cyanide manufactured in and imported into Australia each year (Sections 4.2 and 4.3). Emissions from TSFs to the atmosphere and land, including groundwater, are included in the overall figure. Some cyanide is also consumed during processes for which it is used or destroyed before release. However, it is clear that a major reason for the large difference between emissions and use is that much of the sodium cyanide used in Australia is transferred to tailings storage facilities at mine sites, where much of the material transferred is stored indefinitely as stable cyanide products or as cyanide breakdown products, or broken down and emitted as simple substances such as ammonia and carbon dioxide, rather than as cyanide. As agreed in a variation to the NPI NEPM (June 2007), facilities will be required to report transfers of NPI substances in waste to final destination – including tailings storage facility, sewerage system, underground injection or for destruction. The reporting of transfer of NPI substances to a destination for re-use, recycling, reprocessing and other similar practices is to be voluntary. The current NPI Guide, which assists facilities in estimating their emissions, has been amended to include information on calculating transfers. In addition, a transfers booklet has also been published (DEWHA, 2009b). The following sections provide an analysis of the relative percentages of emissions in 2007-08 by location and industry type. Taking into account the data quality limitations mentioned above, the estimates provided below should be interpreted as indicative.
According to the NPI, the majority (88.4%) of inorganic cyanide releases from reporting facilities in 2007-08 were to the atmosphere, principally as HCN, with 11.2% to land and only 0.4% to water. Figure 5.. Contribution of industry types to inorganic cyanide emissions reported by the National Pollutant Inventory for 2007-2008.
Differences in releases from point sources between states/territories
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