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

Brytne K Okuhata,Joseph K Fackrell,Henrietta Dulai,Christopher K Shuler,Aly I El-Kadi

doi:10.3390/w12082118

Brytne K Okuhata, Joseph K Fackrell + Show 3 more

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https://doi.org/10.3390/w12082118

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Abstract

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.

Highlights

Groundwater is the primary source of fresh drinking water for most oceanic islands [1]
Regular groundwater monitoring on Tutuila is limited to the U.S Environmental Protection Agency (EPA) safe drinking water testing standards, and is performed on an annual basis by the island’s sole water utility
This study explores the relationships and spatial distribution of geochemical parameters of groundwater in Tutuila and looks at possible biogeochemical effects of anthropogenic organic matter and NO3 − released into the aquifer

Summary

Introduction

Groundwater is the primary source of fresh drinking water for most oceanic islands [1]. On Tutuila, the main island in the U.S territory of American Samoa, groundwater supplies about 90% of the island’s fresh drinking water to approximately 55,000 people. Relative to the island’s less urbanized areas, the prevalence of residential units on the Tafuna–Leone Plain has the potential to cause a significant and measurable impact to groundwater quality, releases from on-site sewage disposal systems (OSDS), agricultural plantations, piggeries (small-scale pig farming operations), and a landfill [2]. Regular groundwater monitoring on Tutuila is limited to the U.S Environmental Protection Agency (EPA) safe drinking water testing standards, and is performed on an annual basis by the island’s sole water utility. Water quality parameters in multiple wells across the Tafuna–Leone Plain fail to meet regulatory limits and several districts are under a boil water notice [4]. It is important to better characterize the distribution and observable effects of groundwater contamination sources to

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