Environmental media quality guidelines for cyanide and products

81.3Environmental media quality guidelines for cyanide and products

Currently, Australia has no nationally accepted or consistent sediment, soil or air quality guidelines for environmental protection for cyanide compounds. Surface water quality guidelines for the protection of aquatic ecosystems (freshwater and marine) for free cyanide, ammonia and nitrate are established in Australia (ANZECC/ARMCANZ, 2000a; refer below). However, currently Australia has no nationally accepted or consistent surface water quality guidelines for cyanide products such as cyanate and thiocyanate for the protection of aquatic ecosystems.

This section describes water quality guidelines for cyanide for the protection of aquatic ecosystems. Water quality guidelines for the protection of wildlife are described in Section 86.1.1.

81.3.1Water quality guidelines for the protection of aquatic life

Table 11. provides a summary of Australian and international water quality guidelines for free and WAD cyanide species for the protection of aquatic ecosystems.

Table 11.. Water quality guidelines for cyanide for aquatic ecosystem protection

Environment	Trigger Value	Jurisdiction	Reference
Freshwater	7 g/L (protection of 95% of species)	Australia	ANZECC/ ARMCANZ (2000a)
	The one-hour average concentration should not exceed 22 µg/L more than once every 3 years on the average. The same value is listed by USEPA (2006b) as the ‘Criteria Maximum Concentration’ (CMC) for cyanide in freshwater. The CMC is described as ‘an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed briefly without resulting in an unacceptable effect.’	United States	USEPA (1985)
	The four-day average concentration should not exceed 5.2 µg/L more than once every 3 years on the average. The same value is listed by USEPA (2006b) as the ‘Criterion Continuous Concentration’ (CCC) for cyanide in freshwater. The CCC is described as ‘an estimate of the highest concentration of a material in surface water to which an aquatic community can be exposed indefinitely without resulting in an unacceptable effect’.
	5.0 g/L	Canada	Environment Canada (2002); CCREM (1987)
	3 g/L	Non-specific	Eisler et al. (1999)
	In a 30 day period the average concentration (based on a minimum of 5 weekly samples) of weak-acid dissociable cyanide (expressed as CN) in unfiltered samples should not exceed 5 g/L. The maximum concentration should not exceed 10 g/L at any time.	British Columbia	MWLAP (1986)
Marine and Estuarine	4 g/L (protection of 95% of species)	Australia	ANZECC/ ARMCANZ (2000a)
	Acute: The one-hour average concentration of cyanide should not exceed 1.0 µg/L more than once every three years on the average. Listed by USEPA (2006b) as the Criteria Maximum Concentration (CMC) for cyanide in saltwater.	United States	USEPA (1985)
	Chronic: The one-hour average concentration of cyanide should not exceed 1.0 µg/L more than once every three years on the average. Listed by USEPA (2006b) as the Criterion Continuous Concentration (CCC) for cyanide in saltwater.		USEPA (1985)
	Acute: The one-hour average concentration of cyanide should not exceed 9.2 µg/L more than once every three years on the average.	Puget Sound	Brix et al. (2000)
	Chronic: The one-hour average concentration of cyanide should not exceed 2.9 µg/L more than once every three years on the average.		Brix et al. (2000)
	The maximum concentration of weak-acid dissociable cyanide (expressed as CN) in unfiltered samples should not exceed 1 g/L at any time	British Columbia	MWLAP (1986)

The ICMC stipulated maximum concentration limit of 0.022 mg/L (22 µg/L) downstream of any established mixing zone and corresponding USEPA Criteria Maximum Concentration for freshwater are higher than the Australian water quality guideline trigger value of 7 µg CN/L for freshwater and 4 µg CN/L for saltwater for protection of 95% of species. However, as explained below, these guidelines are trigger values which enable further consideration of other site-specific factors.

Due to the range of possible forms of ecologically relevant cyanide in the environment (e.g. free and weakly complexed or rapidly dissociated under specific environmental conditions), site-specific ecotoxicological data may be required in order to derive accurate site-specific water quality guidelines for the protection of aquatic life. The Australian water quality guidelines for the protection of aquatic ecosystems (ANZECC/ARMCANZ, 2000a) are generic and widely applicable in Australia. However, they provide a hierarchical approach to water and sediment quality assessment that includes direct toxicity assessment (DTA) where investigation of site-specific ecotoxicological effects by testing site environmental media under laboratory or field conditions is one possible, more detailed, assessment option.

It is noted that WAD CN methods are generally recommended for measuring CN for National Pollutant Discharge Elimination System (NPDES) Permits which address these criteria in the USA (Section 81.3.3). The Australian water quality guidelines (ANZECC/ARMCANZ, 2000a) note that the toxicity of cyanide to aquatic organisms is related to the pH, with un-ionised HCN having greater toxicity than CN^- (Section 50.1.4). The guidelines qualify what types of cyanide measurements are appropriate as follows:

For instance, if total cyanide is below the trigger value (TV) the risk is low and if above, users may proceed to ‘weak-acid-dissociable’ (WAD) cyanide measurement. Again, if WAD-CN is below the TV, the risk is low and if above, users may choose whether to accept this as exceeding the guideline and institute management action or to proceed to measurement of undissociated HCN for comparison with the TV. In waters of low ionic strength and low organic matter, total cyanide, WAD-CN and HCN will often be similar. However, in water with high content of complexing ions such as metals, it is likely that total cyanide > WAD-CN > HCN. Hence WAD-CN may overestimate the available cyanide concentration.

A further issue is the limit of detection of methods routinely used to measure WAD or free CN, which means that the above trigger values downstream of the discharge point are below concentrations which can be directly measured. Hence appropriate compliance limits at various measuring points need to be determined, allowing for subsequent dilution in the receiving waterbody.

81.3.2Guidelines for WAD CN or metallocyanide complexes

As discussed above, the ANZECC/ARMCANZ (2000a) guidelines are expressed in terms of free cyanide and some caution is required if relating WAD CN values with the relevant guideline trigger value, as the undissociated HCN concentration is considered the most toxic form. The guidelines do not provide trigger values in terms of WAD CN or specific metal-cyanide complexes.

Literature reviews have been undertaken on the toxicity of total and iron-complexed cyanides (Mudder, 1995) and WAD cyanide (Mudder, 1997). Mudder (1997) indicates that criteria based on free cyanide are not appropriate due to the presence of other potentially toxic forms of cyanide and the lack of accurate analytical techniques for free cyanide, and the use of total cyanide is too conservative and is subject to a variety of analytical interferences. A concentration of 100 g/L was used as the 'in-stream' site-specific aquatic life criterion for WAD forms of cyanide at the Golden Cross Mine, New Zealand (Mudder, 1997). In another instance, a site-specific final chronic value (FCV) for copper cyanide of ~80 g/L was derived by multiplying a final acute value (FAV) of 290 g/L by a corresponding acute to chronic ratio of 3.8 (Mudder, 1997). However, Mudder (1997) indicated that the FCV is conservative and not distinguishable analytically as there is inherent variability associated with the WAD cyanide analysis method. A method for the analysis of ‘available cyanide’ (USEPA, 1999) has been developed recently to improve the analysis of free and other forms of cyanide that may be dissociable and biologically available to wildlife.

The World Bank Group (1995) recommends target guidelines for free, WAD and total cyanide of 0.1, 1.0 and 5.0 mg/L for discharges below which there is expected to be no risk of significant adverse impact on aquatic biota. WBG (1995) indicates that in no case should the concentration in the receiving water outside of a designated mixing zone exceed 22 g CN/L (the US water quality criterion for cyanide). No ecotoxicity data were provided in support of these recommended WAD or total cyanide concentrations.

81.3.3Water quality monitoring

The Australian National Water Quality Management Strategy includes Australian Guidelines for Water Quality Monitoring and Reporting (ANZECC/ARMCANZ, 2000b). This provides guidance on appropriate sampling techniques.

Several state/territory agencies require water quality monitoring at sodium cyanide manufacturing facilities and mine sites that use sodium cyanide, and specify the types of sampling and analysis required.

The identification of diurnal changes to cyanide complexation and speciation in sunlight-exposed waters (Johnson et al., 2002) has implications for water quality monitoring programs. Factors such as sampling location (sunny, shaded), time of year (season) and weather patterns may influence the concentrations of free, WAD and iron-complexed cyanides obtained. For environmental monitoring, higher concentrations in surface water samples for free and WAD cyanide analysis may occur during daylight hours in solutions containing iron-cyanide complexes in sunlit locations due to photolysis (splitting) of the iron complexes to free cyanide.

Recent developments in the United States promote the monitoring of WAD cyanide species in surface waters rather than total or free cyanide, and the comparison of WAD cyanide concentrations to water quality criteria (trigger levels). Approximately 15 states in the United States adopt this approach, and approximately 345 National Pollutant Discharge Elimination System (NPDES) Permits use WAD cyanide for monitoring and/or discharge limits. The change to monitoring WAD cyanide species was instigated as total cyanide, which had previously been monitored, overestimates the amount of biologically available cyanide. Furthermore, analysis of WAD cyanide is considered a more accurate and reliable measurement of the free cyanide criteria and provides a scientifically rigorous basis for compliance and monitoring purposes while protecting aquatic life (Alaska Department of Environmental Conservation; ADEC, 2003). This approach has also been adopted in British Columbia (MWLAP, 1986).

Adequate precautions are needed to preserve samples, e.g. to avoid loss of HCN, or changes in total/WAD/free CN composition.

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