EJMP&EP





Evaluation of cleanup following loss of cyanide in flight to Tolukuma (Papua New Guinea) gold mine

B.N. Noller1* and G. Saulep2

1 National Research Centre for Environmental Toxicology, The University of Queensland, 39 Kessels Road, Coopers Plains, Qld 4108, Australia
2 Tolukuma Gold Mine Ltd., Tolukuma, Central Province, Papua New Guinea



Received 29 September 2002; accepted 15 April 2004




ABSTRACT

On 5 April 2000 the site of impact of a crate of sodium cyanide in mountainous terrain between Port Moresby and Tolukuma Gold Mine, Papua New Guinea, was visited to determine the extent of the impact of the incident and effectiveness of cleanup. Samples of soil, sediment and water were collected variously at the Impact Site Area, along Impact Creek (the creek below the point of impact); and downstream Inai and Yaloge Rivers to the first inhabited village (Inaina Village). The water samples were collected and processed at the mine assay laboratory to minimise losses of cyanide and its complexes before dispatch by air for analysis at an accredited laboratory in Australia. Apart from cyanide as weak acid dissociable (WAD) and as total and its species , water samples were also analysed for cyanide degradation products (thiocyanate, cyanate, total nitrogen, nitrite, nitrate and ammonia), other nutrients (phosphorus) and trace elements. Soil and sediment samples were analysed for WAD and total cyanide concentrations and (%)moisture.
The study showed the following:

  • That the impact site has been decontaminated. Although small cyanide residues were still present in soil and fire ash on 5 April 2000, continued removal of soil from the impact site had reduced soil cyanide to background levels,
  • The species of cyanide remaining in soil at the impact site included a significant proportion of soluble cyanide forms measured as WAD cyanide. Most of the total cyanide was present as WAD cyanide. Burning of vegetation concentrated cyanide in the fire ash giving levels which were similar to those in soil,
  • Levels of cyanide in Impact Creek sediment were present at much lower concentrations than those in soil at the impact. Transfer of the sediment in Impact Creek to at least the next major tributary removed the localised concentration of cyanide in sediment adjacent to the impact site, and
  • Although cyanide was present in the creek sediment, the results for cyanide in water showed that the WAD cyanide concentration in Impact Creek did not exceed drinking water criteria (0.08mg/l) and that there was no detectable WAD cyanide (which includes free cyanide) in river water at the first downstream village. There is no risk from cyanide to these people through drinking the river water, based on comparison with drinking water criteria. Evidence from trace element data for cobalt (Co) which forms a very strong cyanide complex shows that rapid dilution occurs for both surface runoff and seepage through soil to Impact Creek waters. There appears to be some cyanide present from natural sources, probably vegetation. Levels of cyanide species, thiocyanate and cyanate were at respective detection limits. The results for WAD and total cyanide concentrations in water were most useful. There was no ongoing impact observed to aquatic biota in the creek.

It was concluded that there was no long term impact from the loss of cyanide and that the site, where the lost cyanide had impacted, was effectively cleaned up.



Keywords: Cyanide; Cleanup; Degradation; Environmental impact; Health effect



* Corresponding author
   E-mail : b.noller@uq.edu.au