Long term exposure to respirable volcanic ash on Montserrat: a time series simulation

Abstract

Frequent ash fallout from long-lived eruptions (with active phases greater than 5 years) may lead to local populations experiencing unacceptably high cumulative exposures to respirable particulate matter. Ash from Montserrat has been shown to contain significant levels of cristobalite and other reactive agents that are associated with an increased risk of developing pneumoconiosis (including silicosis) and other long-term health problems. There are a number of difficulties associated with estimating risks in populations due to uncertain and wide ranging individual exposures, change in behaviour with time and the natural variation in individual response. Present estimates of risk in workers and other population groups are simplifications based on a limited number of exposure measurements taken on Montserrat (1996Montserrat ( -1999, and exposure−response Editorial responsibility: J Stix curves from epidemiological studies of coal workers exposed to siliceous dust. In this paper we present a method for calculating the long-term cumulative exposure to cristobalite from volcanic ash by Monte Carlo simulation. Code has been written to generate synthetic time series for volcanic activity, rainfall, ash deposition and erosion to give daily ash deposit values and cristobalite fraction at a range of locations. The daily mean personal exposure for PM 10 and cristobalite is obtained by sampling from a probability distribution, with distribution parameters dependent on occupation, ground deposit depth and daily weather conditions. Output from multiple runs is processed to calculate the exceedance probability for cumulative exposure over a range of occupation types, locations and exposure periods. Results are interpreted in terms of current occupational standards, and epidemiological exposure−response functions for silicosis are applied to quantify the long-term health risk. Assuming continuing volcanic activity, median risk of silicosis (profusion 1/0 or higher) for an average adult after 20 years continuous exposure is estimated to be approximately 0.5% in northern Montserrat to 1.6% in Cork Hill. The occupational group with the highest exposure to ash are gardeners, with a corresponding 2% to 4% risk of silicosis. In situations where opportunities for in-depth exposure studies are limited, computer simulations provide a good indication of risk based on current expert knowledge. By running the code for a range of input scenarios, the cost-benefit of mitigation measures (such as a programme of active ash clearance) can be estimated. Results also may be used to identify situations where full exposure studies or fieldwork would be beneficial.

Modeling volcanic ash resuspension – application to the 14–18 October 2011 outbreak episode in central Patagonia, Argentina

“…fresh deposits of Mount St. Helens in the US (Hobbs et al, 1983), Soufriere Hills in Montserrat (Hincks et al, 2006), Mount Hudson in the southern Argentinean Patagonia , Eyjafjallajökull in Iceland (Thorsteinsson et al, 2012;Leadbetter et al, 2012), and Cordón Caulle in the central Argentinean Patagonia, which is addressed in this paper.…”

PM<sub>10</sub> measurements in urban settlements after lava fountain episodes at Mt. Etna, Italy: pilot test to assess volcanic ash hazard to human health

“…Studies by Hincks et al (2006) and Barsotti et al (2010) also linked the resuspension to the amount of tephra cover and showed the direct correlation between the thickness of tephra deposit to the higher concentrations of PM 10 and 10 µm volcanic particles, respectively.…”

“…Damby et al, 2013;Hincks et al, 2006;Horwell et al, 2003Horwell et al, , 2007Le Blond et al, 2010;Searl et al, 2002;Wilson et al, 2011). The finer particles, especially particulate matter with dimensions ≤10 µm or PM 10 in aerodynamic equivalent diameter (i.e.…”

A fast GIS-based risk assessment for tephra fallout: the example of Cotopaxi volcano, Ecuador-Part II: vulnerability and risk assessment

“…Impacts of tephra fallout on human populations range from acute and chronic health effects (Blong 1984;Sigurdsson et al 2000;Horwell and Baxter 2006;Hincks et al 2006) to pollution of water supply (Blong 1984;Stewart et al 2006) and disruption of the economy (Blong 1984). Precise studies after major eruptions have shown the complex and nonlinear response of these aspects to tephra fallout (Johnston et al 2000).…”

“…Precise studies after major eruptions have shown the complex and nonlinear response of these aspects to tephra fallout (Johnston et al 2000). Therefore, uncertain and wide ranges of individual exposures, natural variation in individual response, change in eruptive behaviour with time and meteorological conditions at the time of the eruption increase the difficulty of producing risk assessment for social aspects (Hincks et al 2006). As an example, our social vulnerability maps are very simplified and only consider the aspects of (1) total population, (2) education level and (3) age classes, on which the effects of tephra fallout are mainly unclear and indirect.…”