QUANTIFICATION OF POTENTIAL ARSENIC BIOAVAILABILITY IN SPATIALLY VARYING GEOLOGIC ENVIRONMENTS AT THE WATERSHED SCALE USING CHELATING RESINS
Abstract
Potential arsenic toxicity in different geologic environments is dependent on total arsenic
concentration and arsenic bioavailability. It is important to identify the geologic environments
that may sequester arsenic because these systems can act as long-term sources for arsenic as
well as retard transport and limit toxicity.
Bioavailability is defined as the readiness of a compound or element to be taken up by
organisms (Gregorich et al., 2001), while potential bioavailability is possible uptake of a
compound or element by organisms. The objective of this research is to quantify the potential
bioavailability of arsenic in laboratory microcosms and in different geologic environments in the
Nueces and San Antonio River Watersheds, Texas, using a chelating resin as an infinite sink.
To assess the applicability of chelating resins to estimate potential arsenic bioavailability in
the field, iron-loaded DOWEX M4195 resin was used to extract arsenic from solutions and
sediments (pond sediment, river sediment, and ephemeral stream sediment). The average
percentage of arsenic sorbed from solution was 66% ± 0.16. Competition studies between
arsenate, phosphate, and vanadate suggest there is moderate competition, reducing overall
arsenic sorption to the resin in the presence of competing ions. Iron-loaded resin was then
exposed to sediment samples spiked with increasing amounts of arsenic over 15, 30, 60 and 90
days. Results of the sediment study showed 1) increased arsenic sorption to the resin over time, 2) small variations of potential bioavailable arsenic among geologically different sediments, and
3) evidence of arsenic sequestration.
Field devices that housed iron-loaded resin were used to extract potentially bioavailable
arsenic from sediment in six different geologic environments (i.e. lake, river, perennial stream,
ephemeral stream, pond, and wetland) in the watersheds over a twenty-eight day period. The
wetland (15.7 mmol As/g wet resin) and perennial stream sediments (11.0 mmol As/g wet resin)
represented the maximal and minimal calculated potential bioavailability, respectively. However,
the potentially bioavailable index calculated from mmol As/g wet resin extracted from field
environments and mmol As/ g sediment in digested samples showed sequestration would be
high in the wetland environment and high bioavailability in the perennial stream and river
environments.
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Citation
LAKE, GRACIELA ESTHER (2002). QUANTIFICATION OF POTENTIAL ARSENIC BIOAVAILABILITY IN SPATIALLY VARYING GEOLOGIC ENVIRONMENTS AT THE WATERSHED SCALE USING CHELATING RESINS. Texas Water Resources Institute. Available electronically from https : / /hdl .handle .net /1969 .1 /6115.