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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
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