Environmental Exposure Assessment

27.1Exposure at manufacturing facilities

At Orica’s plant near Gladstone, effluent containing cyanide is acidified to release HCN, which is then converted to NaCN by reaction with NaOH and fed back to the process stream (Orica, 2002). The effluent is then treated to convert any remaining cyanide residues to cyanate, transferred to the site batch effluent systems and mixed with other effluents, tested analytically and discharged offsite to a tradewaste facility operated by the local shire council. Tail gas from the HCN absorber is fed to a burner and combusted to produce oxides of nitrogen (NO_x), which are subsequently ‘denoxed’ prior to emission via a stack. Air from the drier system is scrubbed in a caustic scrubber (recovering HCN as NaCN) before emission via a stack. Air and water emissions are reported to and managed by Queensland EPA and Calliope Shire Council.

At AGR’s NaCN production plant at CSBP’s Kwinana facility, process water from the solution manufacture plants is recycled within the process (CSBP, 2009). Stormwater collected from the plant area is captured, treated and tested prior to discharge. Evaporated water from the solid sodium cyanide plant is purified by ammonia stripping, reverse osmosis and hydrogen peroxide treatment before being tested and discharged. Waste gases from the solution plants are incinerated, and the heat produced used to generate electricity. Gaseous emissions from the solids plant are combined and vented through a two stage wet scrubber stack incorporating demisters to ensure that air emissions comply with Western Australian Department of Environment & Conservation licence conditions.

Waste waters from the NaCN plant (CN^- concentration limit = 1 mg/L) initially flow to the CSBP containment pond, where they mix with other effluent from the site to allow further dilution and degradation of cyanide and other nitrogen-containing substances before release. Water from the pond then flows through a nutrient stripping wetland before discharge. Initially a single wetland cell was constructed as a pilot. In 2008-09 two additional cells were constructed which are designed to be filled on alternate days and feed the original cell. The wetland is designed to remove nitrogen from waste water using nitrification and denitrification biological processes. Low level concentrations of a number of metals are further reduced as water traverses the wetland. Marine discharge formerly occurred to Cockburn Sound, but discharge now goes to a common pipeline for ocean discharge from the Kwinana area, the Sepia Depression Ocean Outfall Landline (SDOOL). The Cockburn Sound discharge point is retained in case it is needed as an emergency outfall should SDOOL be unavailable. Daily concentration and load limits in effluent discharged from the site are specified in the Environmental Protection Act licence. The cyanide concentration limit is 0.1 mg free CN/L, and operation of the SDOOL occurs to a Monitoring and Management Plan which ensures that ANZECC/ARMCANZ (2000a) (Sections 9.8.2 and 11.9.1) 99% species protection guidelines for toxicants (with the exception of cobalt, for which the 95% species protection guideline will apply) will be met under both typical and ‘worst-case’ discharge concentrations at 100 m from the diffuser (Water Corporation, 2008).

27.2Exposure during transport

Wildlife should not normally be exposed to cyanide during the transport, delivery and storage of NaCN, either in solid or in liquid form. However, aquatic and terrestrial wildlife could potentially be exposed to cyanide as a consequence of an incident during transport by rail or road, such as a traffic accident, leakage, or other misadventure. The extent of exposure would depend on the nature of the accident, limited by the quantities transported at one time and clean-up action taken. Incidents that have occurred in Australia and overseas are discussed in Section 22.3.2. Three incidents in Australia have involved significant spillage of NaCN. In one case, NaCN in solution was spilt into a culvert from which wildlife drank and were killed, demonstrating the need for prompt action when a spill occurs. At the other two incidents, emergency response measures contained and recovered the spilt material, and in the more recent incident also removed contaminated soil and water, and no harmful effects on wildlife or aquatic organisms were reported. However, some overseas incidents where significant release of NaCN occurred to water led to downstream environmental contamination and harm to aquatic organisms. NICNAS has not investigated the regulatory control measures that were in place in the various overseas jurisdictions at the time of these overseas incidents.

Various legislation, National Standards and Codes of Practice are in place to ensure safety and protect the environment during the handling, storage and transport of sodium cyanide, which is considered a Dangerous Good, as discussed in Section 71.3. As discussed in Section 22.3.2, the number of transport incidents in recent years is small compared to the large number of journeys over long distances by road and rail. Significant release of sodium cyanide has only occurred in three of those incidents, and harm to wildlife or aquatic life only arose in one of those incidents. However, due to concerns that some improvements are needed following a recent road transport cyanide spillage incident, the NT Government initiated a review of the regulatory regime applying to dangerous goods transport in the NT. Possible considerations arising from the incident include whether there is a need to have greater controls on the size of loads and vehicles that may be used for road transport with different types of container, to reduce the risks of such significant incidents occurring. Completion of clean-up and recovery was prolonged in this incident, hence an important issue is whether improvements are needed to the planning and implementation of response measures, so that recovery and clean-up operations are not delayed or prolonged, as delayed recovery increases the risk of environmental contamination spreading before clean-up is complete.

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