Factors influencing arsenic release into Canterbury groundwaters [article]

Ashlee Jane Dolamore, University Of Canterbury
2016
Arsenic is a toxic metalloid element which is naturally occurring in sediments, rocks, water and air. In some areas of the world, particularly Bangladesh, India, Pakistan, and Eastern Europe, elevated arsenic in groundwater causes health issues such as skin lesions, gastrointestinal disease, and cancer. Arsenic has been previously detected at concentrations exceeding the drinking water limit, 10 μg/L, in some groundwater wells in Canterbury. An investigation into the mechanism of arsenic
more » ... m of arsenic enrichment in groundwater was undertaken. Four possible mechanisms of arsenic release were investigated: the reductive dissolution of iron and magnesium species with adsorbed arsenic, competitive sorption with phosphate, pH-related release in arid conditions, and oxidation of arsenic-bearing sulfide minerals. The microbial transformation of arsenic to more mobile species was not investigated in detail as no microbial studies were undertaken. Initially an assessment of the existing groundwater monitoring data held by Environment Canterbury was carried out. In addition to this, nine wells with previously detected arsenic were selected and paired with nearby wells of a similar depth and with similar characteristics but lower historical arsenic. Samples were collected twice from each well in 2015; once in March or April (autumn), and once in July (winter). Each well was tested for conductivity, pH, temperature, and dissolved oxygen concentration and a full suite of chemicals including arsenic, manganese, iron, nitrate, phosphate, sulfate, cadmium, chromium, antimony and lead. Significant positive correlations were observed between arsenic and iron, manganese, and dissolved reactive phosphorus (DRP) in both the analysis of Environment Canterbury data and the analysis of sampling results. Mutually exclusive relationships were observed between arsenic, sulfate and dissolved oxygen. Elevated arsenic concentrations were found in lower-lying wells with a flood risk, less permeable sediments, and silt-sized soil particles. The Environment C [...]
doi:10.26021/7946 fatcat:rsprve53krbihgva3u4d22x7tu