THE EFFECT OF SOIL TEMPERATURE ON ARSENIC DE-SORPTION IN CARBONATE-RICH ENVIRONMENTS

Arsenic is a known human carcinogen and has been reported in dangerously high levels in groundwater in certain parts of the world. The reason for the accumulation of arsenic in these regions is not completely understood, but much of the arsenic is believed to exist as aqueous As(V) and As(III) species sorbed to iron (hydr)oxide minerals. In this research, I investigate the effect of aqueous carbonate concentrations on de-sorption of arsenic from soil samples. Calcium carbonate has atypical solubility, meaning it is more soluble at cooler temperatures. I will complete batch de-sorption experiments at three different temperatures (4^oC, 10^oC, ambient bath) to examine the effect of temperature on the release of carbonate and its competitive effect on arsenic sorption.

Sediment samples used in these experiments are saprolitic soils from the Oak Ridge National Laboratory in Tennessee with no measurable arsenic content. Soil samples have been pre-treated with known concentrations of arsenic for these experiments. Pre-treated sediment samples will be cooled to 4^oC, 10^oC and ambient bath and the amount of arsenic desorbed from the soils will be measured by a molybdenum blue colorimetric method using a ultraviolet-visible spectroscopy. Supernatant aqueous carbonate concentration will be measured titrimetrically and soil pH will be monitored in all experiments.

The objective of this research is to determine the effect of soil temperature on arsenic de-sorption in carbonate rich environments. The outcome of the study will aid in understanding why arsenic levels are more concentrated in certain parts of the world. Feasibly, leading to procedures to inhibit arsenic transport and preserve areas from reaching elevated groundwater arsenic concentrations.