ENVIRONMENTAL STUDY ON A LONG HISTORY OF CU MINING IN HUBEI, CENTRAL CHINA

Abstract

High concentrations of As in windblown and vehicle-raised dust from historical gold mine tailings in Nova Scotia, Canada pose a potential health risk for residents who use these areas for recreational activities. Routes of exposure may include inhalation of dust, as well as oral ingestion of particles. It is important to understand the particle size, chemical composition, and speciation of As in the tailings-derived dust t6 evaluate the human health risk, and the need for management actions. In this study, electron microprobe, conventional and synchrotron-based X-ray diffraction, X-ray absorption near edge structure, and sequential extraction methods were applied to near-surface tailings samples from three sites. Primary minerals in the railings consist mainly of quartz, muscovite, clinochlore, and albite. Arsenic concentrations vary from 400x10 "6 to 28600x10 6 in the bulk samples, and from 3000x10 "6 to 105000x10 "6 in the <38 ktm fraction. These concentrations significantly exceed 12x10 6 As, the Canadian Soil Quality Guideline. Arsenic in the railings was originally in the form of arsenopyrite, but weathering reactions have oxidized most of the sulfide in near-surface samples. Scorodite (FeAsO4 ~ 2H20) was found to be the dominant secondary phase in some samples. On a microscopic scale, scorodite cements silicate grains; in the field, it forms hardpans which have been pulverized by vehicle activity at some sites. Arsenic is also hosted in amorphous Fe arsenates, Ca-Fe arsenates, and Fe oxyhydroxides containing up to 30 wt% As2Os. To evaluate how much of this As is potentially bioaccessible, the samples were subjected to an in-vitro two-part extraction method designed to mimic the human digestive system. The results indicate that the percent of bioaccessible As is significantly higher in samples where As is hosted by Fe oxyhydroxides and Ca-Fe arsenates, as compared to the scorodite-rich samples. However, because total As in the scorodite-rich samples is much higher, the actual concentration of As that is bioaccessible is also higher, Recognition of the potential human health impacts from abandoned railings sites led to the formation of a Provincial-Federal Historic Gold Mines Advisory Committee in 2005. Residents in several areas have been advised to avoid contact with gold mine railings, and signs have been posted at two sites warning of potential health risks