An investigation of arsenic sources, speciation and mobilization processes in selected Irish aquifers
PhD Candidate: Alex Russell
Supervisors: Professor Frank McDermott (UCD), Dr Liam Morrison (NUIG), Dr Tiernan Henry (NUIG)
Funded by: Science Foundation Ireland through iCRAG
Global compilations of naturally occurring arsenic (As) in groundwater (Nordstrom, 2002; Ravenscroft et al., 2009) have revealed that at least 33 million people in 20 countries are exposed to chronic arsenic poisoning. Dissolved inorganic arsenic is known to be a powerful carcinogen, with an epidemiological association with cancers of the lung and urinary tract. For this reason, the U.S. Environmental Protection Agency (EPA) lowered the maximum contaminant level (MCL) in drinking water from 50 to 10 ?g/litre in recent years. At the new lower MCL, >80 million people are exposed globally, underlining the need for a much better scientific understanding of As mobilisation processes, coupled with an improved public awareness of the problem in Ireland and elsewhere. This PhD project will investigate the occurrence, speciation and geochemical processes responsible for the mobilisation of geogenic arsenic in selected Irish groundwaters. Geological environments similar to those in which high levels of dissolved arsenic occur elsewhere (e.g. sulphide bearing volcano-sedimentary sequences, unconsolidated glacial, fluvioglacial and alluvial deposits) are common in Ireland, yet reliable ppb-level As data for Irish groundwaters are sparse. Reconnaissance studies of groundwaters from Ordovician volcanics, glacial tills, fluvioglacial sediments, the Longford-Down massif and the Dalradian Supergroup have revealed elevated arsenic concentrations that locally exceed WHO limits. Analysis of wells within the Dalradian rocks of Mayo and Donegal will test the hypothesis that As is mobilised through oxidation of sulphide-bearing quartz veins. Within the Dalradian, the available Tellus Border data point to elevated As levels in top-soils and streams on the Argyll Group rocks in particular, suggesting perhaps a more fundamental regional scale bedrock-related control that remains to be investigated. Initial work in north County Louth (in the Longford-Down massif) completed by NUIG will be extended. Laboratory scale leaching experiments will be performed on a range of selected lithologies and unconsolidated deposits in order to test particular leaching hypotheses (e.g. alkali desorption). Data generated in this PhD project will offer new scientific insights into the ‘arsenic problem’ that are applicable globally.
Nordstrom, K. (2002) Worldwide occurrences of Arsenic in Groundwater. Science 296, 2143-2145.
Ravenscroft, P., Brammer, H. and Richards, K. (2009) Arsenic Pollution: A Global Synthesis