Ecotoxicological risks of metals in the subsistence food garden soils of Watut River floodplains, Papua New Guinea.

Exorbitant concentrations of toxic metals in the soil from anthropogenic activities are environmental hazards and key health risk concerns to humans. The subsistence food garden soils have minimum anthropogenic interventions. The ecotoxicological risk potentials of the metals in subsistence food garden settings are unexplored. The metals (Cr, Cu, Pb, and Ni) concentration were assessed in the surface soil fractions (2 mm and 0.2 mm) of food gardens (N = 20) on the floodplains of Watut River, Papua New Guinea. The threshold limits, index of geo-accumulation (Igeo), contamination factor (CF), pollution load index (PLI), and potential ecological risk index (PERI) served as potential risk indicators of metals. Regardless of soil particle size, the descending order of median metals concentration was Cr > Cu > Ni > Pb. The concentration of Cu and Ni in the soil particles exceeded the WHO threshold limits in 100% and 50% of the food garden soils, respectively. Metal enrichment led to severe pollution in 100% gardens (Igeo > 5). Cr, Cu, and Ni contamination factors were > 1 in 95% of the food gardens. The PERI values indicated a lower ecological risk of the metals (PERI < 100). The median concentration of Cu, Igeo, and CF values for Cu in the 2 mm soil particles were significantly greater than in 0.2 mm. The results suggested exposure of subsistence food gardens soils to geogenic metal contamination and the need to carefully choose appropriate soil particle size for the soil health assessments.

Assessment of heavy metal pollution risks in Yonki Reservoir environmental matrices affected by gold mining activity.

This study reports the heavy metal (Hg, Cd, Cr, Cu, and Pb) contamination risks to and safety of two species of fresh water fish (tilapia, Oreochromis mossambicus and carp, Cyprinus carpio) that are farmed in the Yonki Reservoir in the Eastern Highlands of Papua New Guinea (PNG). The upper reaches of the reservoir are affected by alluvial and large-scale gold mining activities. We also assessed heavy metal levels in the surface waters and sediments and in selected aquatic plant species from the reservoir and streams that intersect the gold mining areas. The water quality was acceptable, except for the Cr concentration, which exceeded the World Health Organization (WHO) standard for water contamination. The sediments were contaminated with Cd and Cu in most of the sampling stations along the upstream waters and the reservoir. The Cd concentration in the sediments exceeded the US Environmental Protection Agency's Sediment Quality Guideline (SQG) values, and the geoaccumulation index (Igeo) values indicated heavy to extreme pollution. In addition, the Cd, Cu, and Pb concentrations in aquatic plants exceeded the WHO guidelines for these contaminants. Between the fish species, tilapia accumulated significantly higher (P < 0.05) Cu in their organ tissues than carp, confirming the bioaccumulation of some metals in the aquatic fauna. The edible muscles of the fish specimens had metal concentrations below the maximum permissible levels established by statutory guidelines. In addition, a human health risk assessment, performed using the estimated weekly intake (EWI) values, indicated that farmed fish from the Yonki Reservoir are safe for human consumption.

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.