Metal Mobilization As An Effect of Anthropogenic Contamination in Groundwater Aquifers in Tutuila, American Samoa

Groundwater is the primary drinking water source on most oceanic islands, including Tutuila, American Samoa. Drinking water quality on Tutuila is impacted by anthropogenic pollution sources such as on-site sewage disposal systems, piggeries, and agricultural leachate, particularly across the densely populated Tafuna-Leone Plain. The remineralization of anthropogenically sourced organic matter produces nitrate and dissolved inorganic carbon, which, according to previously published studies, have the potential to mobilize naturally occurring metals. This study provides further evidence that nutrients and dissolved inorganic carbon, along with naturally sourced metal concentrations, become elevated along pollution gradients and show correlation with each other. Across the Tafuna-Leone Plain, nitrate concentrations have a moderately positive correlation with uranium and vanadium. Dissolved inorganic carbon also positively correlate with nitrate, uranium, and vanadium. Similar studies elsewhere suggest that, in addition to nitrate, organic matter remineralization associated with carbonate create conditions to favor natural metal mobilization. Correlation analysis results imply that, while the surveyed trace metals are likely naturally sourced, some become soluble and more mobile in the presence of anthropogenically sourced nitrate and dissolved inorganic carbon, which alters redox conditions in the aquifer.