A new UCLA report is urging California leaders to overhaul the state’s pesticide regulatory system, warning that current oversight fails to account for the real-world dangers of exposure to multiple chemicals at once — a gap researchers say puts agricultural communities at heightened risk.
The report, Building Capacity for Robust Pesticide Regulation: Part I – Cumulative Impacts, calls for stronger state oversight, improved risk assessment tools, and legislative action to better protect public health.
Researchers found that although California law requires regulators to consider cumulative impacts when registering pesticides and issuing permits, agencies often evaluate chemicals individually rather than examining their combined effects.
That regulatory shortcoming comes as pesticide use remains widespread across the state. The agricultural industry relies heavily on chemical pesticides for high-value crops, many of which contain toxic ingredients that can evaporate into the air, seep into soil and groundwater, or linger as residue on food. Farmworkers, nearby residents, and consumers may all face exposure, and it’s often to more than one pesticide at a time.
According to the UCLA report, California currently has 12,793 registered pesticide products containing 1,047 active ingredients, making cumulative exposure a routine occurrence rather than a rare event.
The report frames cumulative pesticide exposure as an environmental justice concern, finding that disadvantaged communities often bear a greater burden due to their proximity to agricultural operations and higher exposure to other environmental stressors.
This dynamic is particularly relevant in heavily farmed regions such as the Central Valley, where residents frequently live near treated fields.
When pesticides mix, their effects may simply add together, but in some cases, the interaction can amplify toxicity beyond what scientists would predict when evaluating each chemical separately.
California maintains one of the nation’s most robust pesticide regulatory frameworks, featuring both state-level product registration and county-level permitting. The state also requires regulators to consider cumulative impacts in those decisions.
Yet prior UCLA research found county agricultural commissioners receive little guidance on how to conduct cumulative impact assessments and typically do not evaluate combined exposure during permitting.
According to this report, State officials have partly attributed the gap to a lack of practical methods for assessing cumulative risk. This is a challenge the report aims to address by identifying existing scientific tools and frameworks.
To close the oversight gap, the authors recommend adopting a formal cumulative risk assessment framework and making fuller use of existing resources, including California’s extensive pesticide use reporting system.
Among the proposed strategies are:
- Testing pesticide products as whole mixtures rather than focusing solely on individual active ingredients
- Using component-based analysis to understand how chemicals interact
- Developing predictive modeling tools to help regulators evaluate risks
- Aligning responsibilities across agencies and ensuring sustainable funding for expanded oversight
The report also suggests integrating CalEnviroScreen, a tool that measures environmental and socioeconomic burdens, to help regulators impose stricter protections in communities already facing elevated risks.
Researchers describe their recommendations as a conceptual roadmap, noting that scientific, technical, and funding challenges must still be addressed before the approach can be fully implemented.
Still, they argue the stakes are too high to maintain the status quo.
Cumulative exposures to pesticide mixtures “raise substantial concerns regarding human health and the environment,” the report concludes.
