Bubbles and Dust: Experimental Results of Dissolution Rates of Metal Salts and Glasses From Volcanic Ash Deposits in Terms of Surface Area, Chemistry, and Human Health Impacts.

Explosive volcanic eruptions lead to ash deposition and subsequent leaching of contaminants into soils or surface water, impacting flora and fauna, including human health. This study determined the control of ash surface area and chemical composition on ash dissolution rates. Fresh, unhydrated ash samples from four contrasting volcanoes were analyzed in the laboratory. Column leachate tests were used to compare leaching rates over a range of basaltic to andesitic ashes as a function of time and surface area, to analyze the effects of ash deposition. It was found that surface area, measured both geometrically and by multipoint Brunauer-Emmett-Teller analysis, generally increases for a short time, gradually decreases, then increases over the rest of the leaching experiment, due to area to mass ratio fluctuations. After the column leachate tests, postleaching water analyses for elemental compositions were conducted by inductively coupled plasma-mass spectrometry and ion chromatography. Steady state dissolution rates initially decayed rapidly due to the smallest size fraction of ash (dust), which provides a large area of fresh leachable surfaces as well as the rapid dissolution of highly soluble metal salts. Some of the dissolved concentrations of elements relevant to human and ecosystem health such as F, Cd, Se, As, and Cr rose above World Health Organization (WHO) drinking water standards within an hour of experimental leaching. In nature, however, safe consumption standards are further dependent upon bioaccumulation and chronic exposure. As such, individual and recurring ash deposition events have applications to emergency response and preparedness in volcanic regions.