Guilty by association: Assessment of environmental loadings on arsenic distribution in two Pacific Island rivers

This work evaluates the immediate risk of arsenic toxicity in two major river systems located in Western Viti Levu, Fiji and Guadalcanal, the Solomon Islands. Using principal component analysis, the associations between the major inorganic arsenic species, As (V) and As(III) and those of the controlling parameters, pH, dissolved oxygen and temperature were investigated in these aquatic systems. As(III) was found to be the dominant form of total inorganic As concentrations in five of the thirteen sites studied. There remains a high risk of As(III) exposure from these sites in the rivers. The study also examined the potential role of mine adits in influencing the distinct water chemistry at the sites. Over 50% of As was found to exist as the more toxic As(III) species at some sites (with higher levels near the gold mines) in both river systems. This finding implies that there may be health risk to populations relying on the river waters for agriculture. As(V) at most sites across both rivers exceeded 13 μg/L, defined as a trigger value for aquatic ecosystems by Australia and New Zealand standards. The PCA indicated that spatial variations play a significant role in water chemistries between sites further from the mine adit location in the Metapona River. In the Sabeto River system, there was also considerable intra-variability in the water chemistries between sites. Further detailed studies are necessary to determine a complete profile of As species and associated biogeochemical processes in these rivers which could lead on to identify appropriate containment or mitigation measures.