Elevated levels of arsenic and other uranium-associated elements have been observed in surface and ground waters of the Nueces and San Antonio River watersheds, Texas. These watersheds drain the Catahoula formation that includes the Gulf Coast U Province that is enriched in trace elements, including As, V, and U. These elements have been released from the U province through natural geochemical weathering over geologic time scales and intensive U mining from the 1960's to the 1980's. Mining activities have potentially impacted groundwater quality through infiltration and lateral migration of mineral-rich plumes generated by rainfall infiltration and leaching of ore bodies and spoil piles, recharge from contaminated rivers and streams, and infiltration from mine pits. Potential toxicity of arsenic in different geologic environments is dependent on the total concentration and bioavailability of arsenic. It is important to identify those geologic environments that sequester contaminants because these systems retard contaminant transport through the watershed, limit toxicity, and act as long-term sources for the contaminant.

The objective of this project was to quantify the bioavailability of arsenic in different geologic environments at the watershed scale using chelating resins as infinite sinks. Stripping voltammetry and Inductively Coupled Plasma Mass Spectrometry was used to quantify total arsenic, arsenic(III), and arsenic(V) sorbed by the pre-treated chelating resins. Loaded resins were placed in field sampling devices and exposed to individual soil and sediment layers. The laboratory technique was applied to the resins exposed to field environments to quantify the bioavailability of total arsenic, arsenic(III), and arsenic(V) over time. Such information has been identified as a critical need for protecting the agricultural and aquacultural resources, and the ecological quality of the Nueces Estuary system, a designated Estuary of National Significance by the U.S. Congress via the Water Quality Act in 1987.