Exceptional use: examining methyl bromide applications in California 2016–2022

Abstract Methyl bromide (MeBr) has been widely used as a fumigant to control for pests, fungi and weeds as well as for disinfection of warehouses, shipping containers, and other commodities. MeBr is a known developmental, neurologic and respiratory toxin. Due to its ozone-depleting properties, MeBr was listed under the Montreal Protocol in 1992. While MeBr use was set to phase out by 2005, the Montreal Protocol and the US Clean Air Act allows critical use exemptions, such as fumigation of freight containers for quarantine and preshipment purposes. To evaluate state-wide spatial and temporal patterns, we examine publicly available pesticide data on the use of MeBr in California from 2016–2022. We found that MeBr applications continue in 36 out of 58 CA counties. For non-agricultural fumigation applications (e.g., commodity fumigation) of MeBr from 2016–2022, a total of 582,050 kilograms (1,283,201 pounds) were applied across 25 counties in CA, home to 24 million people. Los Angeles ranks as the highest use county, with a total of 269,571 or 46% of the total kilograms (594,302 pounds) applied from 2016–2022 for non-agricultural fumigation applications. Additionally, we characterized ambient MeBr concentrations in the West Long Beach community of LA County, based on a state monitor active since 2023, observing concentrations exceeding CA standards. This study underscores the importance of evaluating chemical phaseouts and improving enforcement and monitoring to ensure public health protections.