Recipient Organization
NORTH CAROLINA STATE UNIV
(N/A)
RALEIGH,NC 27695
Performing Department
Soil Science
Non Technical Summary
Arsenic is a priority pollutant of local, regional, national, and international concern. High concentrations of arsenic in soils and water pose threats to agriculture, aquatic life, and public health; consumption of high quantities of arsenic, through drinking water or food, can lead to arsenicosis, a condition that may include skin lesions, paralysis, blindness, and bladder, lung, skin, kidney, liver, and prostate cancers. While considerable focus has been paid to arsenic concentrations related to mines, industrial wastes, and natural groundwater contamination, arsenic is also increasingly becoming a problem in agricultural settings, where it may be loaded onto soils via irrigation with arsenic-laden groundwater, pesticide spraying, and manure application. Once loaded to soils, arsenic may leach into porewater, degrading water quality and potentially entering the food chain. In the proposed work, field and laboratory experiments will be conducted to understand and quantify the processes that control the fate and transport of arsenic in soils and sediments. The results of this work will help improve arsenic management schemes that preserve environmental and public health.
Animal Health Component
(N/A)
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
While themes describing the causes of arsenic contamination of soils and groundwater are emerging, scientists and policy makers still lack the capacity to confidently predict arsenic-free areas, determine the susceptibility of environments to future arsenic contamination, and properly manage existing contaminated sites. The purpose of this research is to combine field, laboratory, and spectroscopic approaches in order to comparatively assess a multitude of processes that control arsenic in the sub-surface. Particular objectives of this work are: 1. determine the capacity for arsenic retention in soils and sediments following application of arsenic-bearing solids and solutions, 2. quantify the relative importance of key physicochemical processes that may stimulate arsenic release from soils and sediments to porewater in natural and agricultural systems, and 3. establish criteria for recognizing potential areas where arsenic may be released from soils to porewater in the future. By using natural samples and experimental parameters defined by field measurements, the results of this work will help improve arsenic management schemes that preserve environmental and public health. Following analysis of experiments, results will be disseminated through presentations at conferences and workshops, training materials, and academic publications. Students participating in research activities will graduate with an education in soil science, and research outcomes will be used as teaching materials for university courses and K-12 outreach activities.
Project Methods
For all objectives, research will involve iterative field and laboratory experiments that seek to evaluate the controls on arsenic cycling at various scales. Field sites will be identified on the existence of (or potential for) local arsenic contamination, and field measurements will be used to identify appropriate ranges of experimental parameters. Soil and sediment samples will be collected and characterized. Initial solid-phase arsenic concentrations will be measured following total digestion, mineralogy will be characterized by XRD, and chemical speciation of arsenic (and other elements) will be identified by XAS and sequential extractions. Soil pH, particle size distribution, organic carbon content, and BET surface area will also be assessed. Objective 1. Arsenic sorption envelopes will be conducted across a pH range of 3-10.5; initial arsenic loadings will be half, equal to, and twice the local dissolved arsenic concentrations, and parallel experiments will be performed using dissolved arsenate and arsenite species. Subsequently, arsenic adsorption isotherms will be conducted using pH values appropriate to the field areas. Because arsenic mobility is enhanced by flow, arsenic retention on soils and sediments will be further examined under dynamic conditions. Solids will be packed into columns and arsenic will be applied via pumped synthetic arsenic-laden groundwater or with an upstream arsenic-bearing solid source (e.g. poultry litter) and pumped synthetic arsenic-free groundwater. Columns will be run until arsenic breakthrough, and post-experiment solids will be analyzed as above. Finally, injection-withdrawal experiments will be conducted to examine arsenic retention by sediments under field conditions. Objective 2. Parallel, comparative column experiments will be used to elucidate the potential for arsenic release from soils and sediments due to reduction (lactate/acetate addition as a labile dissolved organic carbon source), ion displacement (phosphate addition), pH change (buffered solutions), and oxidation (oxygenated water addition). Baseline arsenic release studies will be performed by pumping buffered anaerobic deionized water through two sediment columns, one of which has been sterilized to exclude microbial activity. Input solute concentrations will be based on representative field measurements. Results of column studies will be used to inform injection-withdrawal experiments that seek to stimulate arsenic release in the field. Objective 3. A range of agricultural soils (not necessarily arsenic-impacted) under different management schemes will be selected for use in two sets of column experiments in order to understand how soil type, land use/soil management, and physicochemical environment may control arsenic retention and release. In the first set of experiments, dissolved arsenic solutions will be pumped through the columns until arsenic breakthrough, and retained arsenic will be calculated, as described above; in the second set of columns, soils will not be loaded with arsenic. A matrix of treatments (informed by previous results) will be utilized to examine arsenic release from both sets of columns.