Commonwealth of Australia 2010
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- 3.3.2Atmospheric monitoring
- 3.3.3Biological monitoring
3.3Methods of analysis3.3.1Analysis of cyanide compoundsMethods of sample preservation, handling and analysis of environmental media containing cyanide compounds have been described by Zheng et al. (2003), Schulz (2002), USEPA (1999), APHA (1998), Noller (1997), Smith and Mudder (1993) and Noller and Schulz (1997, 1995). The cyanide content of a sample of environmental media (water, slurry, soil, sediment etc) can be composed of many different cyanide compounds and there are several methods available for their extraction and analysis. In general, most analytical methods contain an analogue separation procedure whereby the cyanide content to be measured is obtained as a gas (i.e. HCN; Kjeldsen, 1999). The content and composition of cyanide present varies with when and where samples are taken and with subsequent treatment and handling, the appropriate preservation methods vary with the type of analysis to be performed, and the type/s and accuracy of analysis needed vary with the purpose for which the information is required. Hence decisions regarding where and how to sample, how to prepare the sample and what and how to analyse are all important to the subsequent interpretation of the data and addressing the purpose for which the samples are taken (Schulz, 2005) Cyanide analyses have historically been identified in one of three commonly used categories: free cyanide, weak acid-dissociable (WAD) complexes of cyanide and total cyanide.
Analyses of free, WAD and total cyanides do not include the CN-containing forms cyanate (OCN-), thiocyanate (SCN-), cyanogen ((CN)2) or cyanogen chloride (CNCl), which are potential chlorination/oxidation products of different cyanide forms. Each of these requires specific analytical determination. As noted above, SCN may cause interference to some total cyanide determination methods and the result then needs to be corrected accordingly. Strong complexes of cyanide (e.g. cobalt) may not be determined through total cyanide analysis. However, with the advancement of analytical methods, categorisation is defined not only by the specific chemical speciation in each group, but by the technical definition based on the type of analysis performed. This is particularly relevant for WAD forms of cyanide due to the various analytical methods available and the variations in the analytes included in each analysis. However, overestimation of free cyanide may occur with some methods, and inclusion of thiocyanate with some total cyanide methods may lead to an overestimate in total cyanide. Appendix 1 provides a list of analytical methods and description for commonly analysed cyanide compounds in various environmental media. As indicated in Appendix 1, there are several methods available for cyanide extraction and determination of cyanide concentration. Each method is subject to positive and negative interferences, and these are typically described in the method protocol. Improper choice of sampling technique, sample preservation and analysis method may produce significantly erroneous analytical results. To minimise errors, the choice of method used should be aligned to particular sample requirements, and multiple analyses using several methods may be undertaken to minimise analytical uncertainties. Furthermore, the specific method of analysis, pH and type of extractant used should be reported along with the analytical results. WAD CN is widely used in an attempt to measure ‘biologically available’ cyanide because it includes free cyanide and various forms of cyanide which may release free cyanide once consumed by an animal, but not forms of cyanide that are unlikely to release free cyanide to an animal. Therefore WAD CN is considered the most appropriate general measure on which to base environmental monitoring for cyanide toxicity, and the term is referred to extensively in this report and its recommendations. Some further discussion of the adequacy of WAD CN as an indicator of biological availability is provided below. Methods for WAD CN analysis include distillation methods APHA 4500 CN-I and ASTM Method D and the Picric Acid Method (colorimetric; Smith and Mudder, 1993). Kjeldsen (1999) indicates that there are at least two extraction methods available for analysis of WAD cyanide compounds based on different pH. The choice of method used will depend on the objective of the analyses, suggesting that the lower pH be used when attempting to simulate gastro-intestinal bioavailability. The methods include:
Henny et al. (1994) suggest that total reliance on conventional WAD cyanide analysis may not account for all of the cyanide potentially available to wildlife ingesting cyanide solutions. Only cyanide that dissociates at pH 4.5 is represented by the conventional WAD cyanide analysis. Some common metal-cyanide complexes dissociate below pH 4.0, as likely occurs when exposed to gastric juices of some aquatic birds (pH 1.0-2.0; Duke, 1986) and some raptorial species (as low as pH 1.3; Duke et al., 1975) and other animals (Kjeldsen, 1999). Henny et al. (1994) indicated that the effects might be counteracted by a potentially slower rate and degree of dissociation of the metal-cyanide complexes and by the alkalinity of the ingested solution. Henny et al. (1994) indicated that the presence of cyanide in weakly complexed forms in waters, as often found in association with ore processing wastes, may potentially have the effect of increasing the dose required to promote the onset of acute lethal effects due to the slower rate of dissolution and gastrointestinal absorption, but may lengthen the duration of sublethal effects. Thus, delayed or prolonged sublethal effects may be evident when WAD cyanide concentrations, measured using conventional analytical methods, would suggest otherwise. The various methods for analysing WAD cyanide compounds all attempt to measure ‘biologically available’ cyanide, and each measures nearly the same species of cyanide. The cyanide amenable to chlorination (CATC) method has been largely replaced by the WAD cyanide method, which is essentially the same, but more rapidly performed. CATC is reportedly highly susceptible to poor accuracy and precision due to interferences (Smith and Mudder, 1993). USEPA Method OIA-1677 was recently developed to analyse ‘available cyanide’ in water and wastewater by flow injection, ligand exchange and amperometric titration. It is considered a more robust and accurate method for determining available cyanide (USEPA, 1999; Milosavljevic et al., 1995). Method OIA-1677 may be undertaken under field conditions using a Perstop 3202 CN analyser with results available 1-2 hours after sampling (Evans et al., 2003), which is advantageous for field-based operations. Evan et al. (2003) indicate that Method OIA-1677 (modified) is superior to APHA Method 4500 CN-I when using a Perstop analyser due to lower interferences (sulphides, metals) and more precise and accurate results. The traditional WAD CN method (4500 CN-I) uses a weak acid distillation method to release cyanide from the defined metal complexes for subsequent distillation and analysis. With Method OIA-1677, using a Perstop analyser, a proprietary ligand exchange reagent is used to chemically bind WAD metals thus releasing free cyanide for flow injection analysis. Evans et al. (2003) indicate that Method 4500 CN-I (WAD CN) has the potential to underestimate WAD CN concentrations, particularly when high metals concentrations are present, due to the inability (periodically and randomly) of the weak acid to break down some of the metal cyanide bonds in order to free the cyanide for analysis, a problem that was not evident with the proprietary reagent. USEPA (1999) indicate that method OIA-1677 is less subject to interference by sulphide, relative to CATC methods. However, Evans et al. (2003) indicate that there are several minor but critical amendments that should be made to Method OIA-1677 when using a Perstop analyser in order to minimise interferences from sulphides and high metals concentrations. These amendments include always assuming there are sulphides in the sample and pretreating accordingly, even when screening test results show otherwise, substitution of lead acetate for lead carbonate to precipitate sulphide, and use of a limited amount (i.e. 1%) of lead acetate, otherwise the ligand reacted only with the lead acetate and not the metals from metal cyanide complexes. Zheng et al. (2003) evaluated seven alternative methods for the analysis of cyanide species or groups of species in reagent water and five different contaminated water matrices, including five species-specific methods (weak acid dissociable (WAD) cyanide, free cyanide by micro diffusion, Available Cyanide, automated WAD cyanide by thin film distillation, metal cyanides by ion chromatography), and two automated techniques for total cyanide (total cyanide by thin film distillation and total cyanide by low-power UV digestion). All seven methods evaluated achieved low, ppb-level, detection limits and exhibited satisfactory accuracy and precision for most contaminated waters tested. Analysis of low concentrations of cyanide species in raw wastewater was problematic for Available Cyanide and Ion Chromatography Methods, which experienced significant interference problems and/or low recoveries. Sulphide interference in the Available Cyanide method when using sewage treatment plant clarifier effluent may be corrected using the amended method described above (Evans et al., 2003). There was recovery of significant diffusible cyanide in the Micro diffusion tests with nickel-cyanide-spiked samples, reflecting dissociation of this weak metal-cyanide complex during the test and demonstrating that the test can recover some WAD cyanide in addition to free cyanide. The automated Total Cyanide methods, which involved UV digestion, achieved low detection limits for most waters tested, but exhibited low recoveries for some waters tested. The conventional WAD cyanide method, along with its automated version (WAD-TFD), performed well, yielding acceptable cyanide recoveries in all water matrices tested and excellent accuracy for the performance evaluation samples. The Available Cyanide method was also satisfactory when interferences are accounted for. The CATC method was problematic for measurement of weak acid dissociable cyanide in contaminated waters. 3.3.2Atmospheric monitoringSampling of hydrogen cyanide gas can be either continuous, using electronic detection equipment, or semi-batch, using air pumps and sampling tubes. The former gives a faster response and allows more time for action in emergency situations (Environment Australia, 1998). Several types of portable and stationary air HCN sampling devices are available. According to IPCS (2004), detection limits for the different methods for hydrogen cyanide in air samples range from 0.8 to 400 mg/m3. 3.3.3Biological monitoringThe rapid metabolic processes that degrade cyanide to thiocyanate complicate biological monitoring for cyanide (Ramey et al., 1994). Monitoring for cyanide may involve measuring cyanide (HCN) in whole blood or selected target organs (Troup and Ballantyne, 1987; Lundquist et al., 1985; Logan, 1996; Calafat and Stanfill, 2002) or monitoring analytes that indicate exposure to cyanide (e.g. urinary thiocyanate, rhodanese enzyme; Schulz, 1984); however, these indicator analytes may be non-specific (Sittig, 1985). Thiocyanate and 2-aminothiazoline-4-carboxylic acid may also be measured in urine (Lundquist et al., 1995). 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