Heavy metal(loid) contamination remains a global concern as it continues to pollute the environment, and ultimately imposes negative consequences towards a myriad of ecosystems and human residents. For example, arsenic (As) is a prevalent metalloid naturally found in Southern California mine wastes with toxic, carcinogenic qualities that pose a potential human health risk. While arsenic concentrations and bioaccessibility can be readily measured from samples, the long-term effect of weathering on arsenic bioaccessibility in these materials is not well understood. Thus, it is equally important to understand significant natural factors that impact arsenic bioaccessibility, which include rainfall, temperature, humidity, and aging.<br/>Sedimentary samples were obtained from the Red Hill Mercury Mine in Tustin on a monthly basis for 2 years and sieved to ≤250 µm particle diameter. Selected samples, which had varying initial bioaccessibilities measured ranging from 5%-25%, underwent a simulated rain event to rinse off external soluble arsenic from the particle surfaces. Through the use of an environmental chamber, samples were then exposed to simulated diurnal temperature and humidity cycles based on weather data from that location (ranging from 61-82 degrees Fahrenheit and 16.1-27.8% humidity) at a 12x accelerated rate, such that 2 hours of real-time equated to 1 day of simulated time.<br/>After environmental chamber exposure times varying from 1-24 (simulated) months, samples underwent simulated gastric fluid (SGF) extraction followed by ICP-OES analysis to determine final As bioaccessibility levels. Arsenic bioaccessibility was observed to decline in the early stages of exposure, but eventually increase back up to and beyond its initial bioaccessibility levels after a few simulated months. This initial decline could be explained by the interactions between the samples and the humidity and temperature fluctuations in the chamber, causing the secondary formation of more stable As phases followed by the repeated dissolution and drawing of more internally-bound arsenic towards particle surfaces. While several samples did show this behavior, other samples with lower initial As bioaccessibility displayed a more consistent trend in bioaccessibility over time. These results suggest that initial As bioaccessibility levels can be utilized to predict changes in bioaccessibility over time, with lower levels inducing less change and higher levels producing more exaggerated trends.

Impacts of wetting/drying cycles on arsenic bioaccessibility in mine wastes

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.