Methyl bromide remains in use in 36 of 58 California counties, and in both urban and rural areas

In a new study of the continuing use in California of the pesticide methyl bromide, a known developmental, neurologic, and respiratory toxin, researchers from UCLA and UC Irvine found the compound is still in widespread use across the state, from San Diego and Los Angeles counties north through the Central Valley.

In 2005, the U.S. government recommended the phaseout of methyl bromide (MeBr) because of known health and environmental impacts; these include cancer, respiratory issues, and damage to the kidneys, skin, and livers, with particular risk to both adults exposed in the workplace and children. Use of MeBr in farms in California largely ended in 2015, but exceptions have been allowed for the fumigation of freight containers and similar shipping needs; those uses continue to today, and are the focus of the study – “Exceptional use: examining methyl bromide applications in California 2016–2022” - published in the peer-reviewed journal Environmental Research Communications.

Because of the use of MeBr in shipping, the researchers found some of the most significant exposures are in port cities, including Long Beach and the Los Angeles neighborhoods of Wilmington and San Pedro. Between 2023-24, for example, air monitoring of the levels of MeBr found in western Long Beach were, on average, nearly double the state’s recommendation: 2.1 parts per billion (ppb), as opposed to 1.2 ppb, and the exposure levels were even higher on some days.

“These levels translate to a ‘hazard quotient’ of 1.6; values greater than 1.0 suggest an increased risk of negative health effects, and, in fact, we found exposures - on at least two occasions - reached hourly levels of more than 900 ppb,” said study co-author Dr. Yoshira Ornelas Van Horne, assistant professor in the UCLA Fielding School of Public Health’s Department of Environmental Health Sciences. “It is worth noting this same neighborhood is home to an elementary school, 600 homes, and parks, and is already ranked by the state as being in the top 25th percent of environmental hazards.”

The risks to children are uniformly higher than those of adults due to a greater inhalation rate-to-body weight ratio, but the inhalation of fumigation pesticides by children has been rarely investigated, the researchers said.

“Research in rural, agricultural communities have seen an association between proximity to agriculturally applied methyl bromide and restricted fetal growth,” said Dr. Jill Johnston, study co-author and associate professor of environmental and occupational health at the University of California, Irvine’s Joe C. Wen School of Population and Public Health. “Additionally, studies in California have found that an increase in the ambient air concentration of methyl bromide is associated with increased risk of emergency department visits for asthma among children.”

From 2016–2022, MeBr was used for in 36 out of 58 counties across California; these counties are home to more than 35 million people. The top counties reporting MeBr applications across all uses (i.e., fruits, vegetables, non-agricultural fumigation, soil fumigation, nursery/greenhouse, and other uses) are Siskiyou, Merced, Stanislaus, San Joaquin, and Los Angeles. Among the first four counties, all predominantly agricultural, top uses for MeBr were soil fumigation (Siskiyou and San Joaquin), and nursery/greenhouse uses (Merced, San Joaquin, and Stanislaus). In Los Angeles County, the primary use was non-agricultural fumigation, meaning commodity/shipping fumigation, the researchers said.

“Freight transported in containers is typically fumigated as a means to reduce potential infestations or inhibit the spread of pests,” Johnston said. “In the United States, foreign freight containers with certain produce, such as grapes, must be treated for pests, and in most cases, methyl bromide use is allowed at permitted facilities. These are important precautions, but the reality is there are potential alternatives to methyl bromide that pose lower health risks.”

The researchers caution the data that informed their analysis is limited; in the Long Beach area, for example, the California Air Resources Board monitoring systems that provided the regional data is only available from one monitor, and only since 2023.

Even with those limitations, however, the authors say the analysis that can be done on the available records makes clear the need for better coordination between federal, state, and local agencies; more monitoring and better warning systems for residents; and expediting the replacement of MeBr with less toxic materials for transportation-related fumigation purposes, as it has been largely replaced in the state’s fields and orchards.

“This work highlights the ongoing challenge of addressing community health concerns due to fumigation activities, and the lack of comprehensive health and safety assessments,” Ornelas Van Horne said. “It is clear the potential health burdens for continued MeBr use are concentrated in areas near fumigation activities, like Long Beach and the port areas, but it is equally clear there are gaps in information and oversight that need to be addressed; people’s health is at risk.”

Methods

The authors drew on records in multiple, separate databases maintained by the California Department of Pesticide Use Registry (CDPUR) and the California Air Resources Board (CARB), locally focused data for the ports of Los Angeles and Long Beach, as well as federal records from the United States Department of Agriculture (USDA). Standardized mapping and analysis followed, yielding findings for MeBr use across all 58 California counties, generally, and specifically in the Los Angeles-Long Beach region, which were peer-reviewed prior to publication.

Funding

The work was supported by faculty and staff with UCLA, and UCI, with funding, in part, from the U.S. National Institutes of Health through the Southern California Center for Children’s Environmental Health Research (NIH5P2CES033433) and the JPB Environmental Health Fellowship.