A probabilistic model for acute bystander exposure and risk assessment for soil fumigants

There is currently significant regulatory interest in estimating exposures and risks to bystanders following applications of soil fumigants. Soil fumigants are generally volatile and some of the fumigant mass will escape the field causing downwind exposures to resident populations. Regulatory agencies in the US are currently considering implementing buffer zones for many of the fumigants. These buffer zones would provide a restricted-entry zone around fumigant applications to mitigate potential exposures. This paper describes a probabilistic dispersion modeling application that has been developed to address this issue. The Probabilistic Exposure and Risk Model for FUMigants (PERFUM) employs the Gaussian dispersion algorithms developed by the US Environmental Protection Agency (US EPA). The model adapts EPA air dispersion algorithms to develop probabilistic estimates of acute exposures to bystanders following fumigant applications. The model considers the potential variability in exposures caused by differences in mass emission rates of the fumigants and the meteorological conditions following the application. The model is generalized to model exposures for fumigants with different exposure averaging times of concern to regulators (1–24h), varying field sizes (up to 40acres), and field dimensions. PERFUM also outputs the probabilistic exposures both based on the whole population surrounding the field and for the maximally exposed location only. The model is non-proprietary and publicly available.

目前，监管机构对估算土壤熏蒸剂使用后对旁观者的暴露量和风险非常感兴趣。土壤熏蒸剂通常具有挥发性，部分熏蒸剂会逸出田地，导致下风向的居民暴露其中。美国的监管机构目前正在考虑对许多熏蒸剂设置缓冲区。这些缓冲区将在熏蒸剂使用区域周围设置限制进入区，以减少潜在的暴露。本文介绍了一种为解决这一问题而开发的概率扩散模型应用。熏蒸剂概率暴露与风险模型（PERFUM）采用了美国环境保护署（US EPA）开发的高斯扩散算法。该模型改编了美国环保署的空气扩散算法，以对熏蒸剂使用后旁观者的急性暴露进行概率估计。该模型考虑了熏蒸剂质量排放率差异以及使用后的气象条件所导致的暴露潜在变异性。该模型具有通用性，可对监管机构关注的不同暴露平均时间（1 - 24小时）、不同田地面积（最大40英亩）和田地尺寸的熏蒸剂暴露情况进行建模。PERFUM还输出基于田地周围整个人群以及仅基于暴露量最大位置的概率暴露情况。该模型是非专利的，可公开获取。