Monitoring of river water for free cyanide pollution from mining activity in Papua New Guinea and attenuation of cyanide by biochar.

Cyanide (CN) pollution was reported in the downstream areas of Watut and Markham Rivers due to effluent discharges from gold mining and processing activities of Hidden Valley mines in Morobe province of Papua New Guinea. We monitored free cyanide levels in Watut and Markham River waters randomly three times in years for 2 years (2012 and 2013). Besides, a short-term static laboratory study was conducted to evaluate the potential of river sediment to attenuate externally added cyanide, with and without the presence of biochar material. Results indicated that the free cyanide content ranged between 0.17 and 1.32 µg L(-1) in the river waters. The free cyanide content were found to be significantly (p < 0.05) greater in June (0.87 µg L(-1)) and May (0.77 µg L(-1)) months of 2012 and 2013, respectively, than the rest of the months. However, free cyanide levels in all four monitoring sites across three sampling intervals were lower than 0.20 mg L(-1) which is the maximum contaminant level (MCL) permitted according to US Environmental Protection Agency. Under laboratory conditions, the biochar-impregnated sediment showed ∼3 times more attenuation capacity for cyanide than non-amended sediment, thus indicating possibility of using biochar to cleanse cyanide from spills or other sources of pollution.