California Air Resources Board

In 2023 and 2024, the California Air Resources Board (CARB) monitored outside air for concentrations of methyl bromide (MeBr) near Hudson Elementary School in West Long Beach. South Coast Air Quality Management District (South Coast AQMD) confirmed CARB's findings through eleven days’ worth of measurements in 2024. CARB is coordinating with South Coast AQMD, the Department of Pesticide Regulation (DPR), the Office of Environmental Health Hazard Assessment (OEHHA), and the Los Angeles County Agricultural Commissioner’s (LA CAC) Office to assess potential community exposure and determine potential impact on people’s health.

What is MeBr and why is it used in the United States?

MeBr is a colorless, odorless pesticide used to fumigate agricultural products for insect pests to protect public health and to meet international import and export standards. MeBr is highly regulated as a pesticide by the U.S. Environmental Protection Agency (EPA), DPR, and LA CAC. It is classified by EPA as a hazardous air pollutant (HAP) and by CARB and DPR as a toxic air contaminant (TAC). MeBr is also a volatile organic compound (VOC); VOCs are regulated federally and in California mainly because of their ability to contribute to photochemical smog.

What agencies are responsible for regulating MeBr use and emissions in Los Angeles County?

Five agencies are responsible for regulating the use and emissions of MeBr at fumigation facilities: CARB, DPR, LA CAC, the South Coast AQMD, and U.S. EPA:

• CARB: State agency responsible for identifying and regulating emissions of TACs. Monitors air quality and sets reporting requirements for air pollutants.
• DPR: State agency responsible for regulating pesticide use to protect human health and the environment and fostering sustainable pest management. Pesticides must be evaluated prior to registration for use in California. DPR continues to evaluate potential risks from registered pesticide by monitoring for potential exposures and illness cases.
• Los Angeles CAC: County agency responsible for issuing and enforcing permits for pesticidal use of MeBr in commodity fumigation and conducting site inspections. LA CAC permits can be conditioned by the CAC to account for local conditions and/or incorporate DPR recommended permit conditions for MeBr.
• South Coast AQMD: Local air agency responsible for implementing the Air Toxics “Hot Spots” Program and regulating sources of air contaminants and monitoring air quality.
• U.S. EPA: Federal agency that approves and registers pesticide products for sale and specifies restrictions and requirements for use on product labels.  U.S. EPA sets regulatory requirements for MeBr as an air pollutant that is a VOC and a HAP.

Why did CARB decide to monitor for MeBr?

During a community tour of the Long Beach area, CARB heard concerns expressed about MeBr fumigation near residential neighborhoods. In response, CARB reviewed available background information, including data from South Coast AQMD’s Multiple Air Toxics Exposure Study, to identify potential locations for air monitoring. CARB established a temporary air monitoring site (identified on the map) to measure MeBr concentrations in the AB 617 community of Wilmington, Carson and West Long Beach. The monitoring site is located just north of Hudson Elementary School in Long Beach and was chosen because it is downwind of two fumigation facilities.

What were the findings from CARB’s MeBr monitoring?

Hourly MeBr monitoring began at CARB’s air monitoring site on January 12, 2023. Monitoring is ongoing, but the results addressed in this website reflect data gathered from January 12, 2023, to April 30, 2024. The monitoring measured MeBr concentrations which were compared to health-based Reference Exposure Levels (REL) set by OEHHA and screening levels set by DPR. A REL is the airborne level of a chemical that is not expected to cause adverse non-cancer health effects for specified exposure durations. DPR’s screening levels established a threshold for evaluating potential risks from pesticide exposures and are set based on human health risk assessments conducted to evaluate the risk associated with pesticide use.

The average concentration of MeBr between January 12, 2023, and April 30, 2024, was 2.1 parts per billion or “ppb.” This value exceeds OEHHA’s chronic (annual average) REL of 1 ppb, which is also the screening value that DPR uses for a one-year time period. This has prompted CARB to continue monitoring MeBr in the community.

Two measurements were close to the OEHHA acute REL of 1,000 ppb. The greatest measured hourly concentrations were 983 ppb on February 29, 2024, and 966 ppb on March 5, 2024, between 9 p.m. and 10 p.m. In both instances, these concentrations decreased significantly over the subsequent hours, returning close to the ambient background concentrations. Elevated concentrations were usually observed between 6 p.m. and 11 p.m. and higher-concentration events were most common between early February and late April. All other measured concentrations were well below the acute REL.

The results are summarized in the following table, which shows the monitored results relative to the OEHHA RELs and DPR screening levels, and can also be accessed via CARB’s AQview website. Agencies are continuing to assess these concentrations.

1. Listed data points are the two maximum readings from January 12, 2023, to April 30, 2024.

What are the potential health effects of MeBr exposure?

MeBr is a TAC that can affect the respiratory and nervous systems. Short-term exposure above acute RELs can cause headaches, dizziness, nausea, and difficulty breathing. Long-term exposure above chronic RELs may lead to more serious health problems, such as nervous system or developmental issues. There isn’t enough information to determine whether or not MeBr causes cancer.