DPR Statement on CDFA Recalling and Voiding of 1,3‑D and Methyl Bromide Air Monitoring Data

The California Department of Food and Agriculture (CDFA) has notified the California Department of Pesticide Regulation (DPR) that it is recalling and voiding all 1,3-dichloropropene (1,3-D) and methyl bromide (MeBr) monitoring results from Oct. 24, 2025, through June 30, 2026, impacting samples collected by DPR beginning in early October. CDFA determined the laboratory reference standard used to analyze 1,3-D (cis and trans isomers) and methyl bromide samples significantly degraded over 9 months, resulting in unusable and inaccurate analysis during this time. DPR is actively working to identify modeling approaches to respond to the voided data. 

DPR contracts with CDFA to provide laboratory-validated air monitoring data. The department relies on this data to inform its continuous evaluation of pesticides and potential impacts to human health and the environment, including assessing whether its regulatory programs are working as expected. DPR’s continuous evaluation process includes regular review of the monitoring results, which includes identifying any abnormal trends and conducting closer reviews, as needed. 

In mid-July 2026, CDFA and DPR identified abnormal patterns in the 1,3-D air monitoring results for 2026. These results were assessed and compared with previous monitoring results, which validated longer-term abnormalities and prompted an in-depth review and assessment.  Upon further review, CDFA identified and verified that the laboratory reference standard used to analyze 1,3‑D in air samples collected beginning in early October 2025 through June 30, 2026, had significantly degraded. A laboratory standard is a sample with a precisely measured concentration, certified by a manufacturer, that ensures lab equipment is measuring chemicals correctly. When a standard degrades, labs can no longer measure chemical amounts correctly. If a sample is compared against a degraded standard that reads lower than it should, test results will appear artificially higher. CDFA found the standard had degraded significantly, between 18-96 percent, which caused the reported methyl bromide and 1,3‑D air concentrations to be inaccurately elevated compared to their actual value.

CDFA attempted to develop methods to correct the impacted monitoring data but determined that any adjusted numbers would fall short of the data quality and the confidence required to be used for regulatory or legal purposes.  As a result, CDFA notified DPR on Sept. 18 of its decision to recall and void all 1,3‑D and MeBr results for most of Q4 2025 through Q2 2026 and provided a memo to DPR on Sept. 30.

CDFA’s voided data is concerning for the department as well as communities and others who closely follow air monitoring.

Given recent regulatory action on 1,3-D, DPR will model estimated air concentrations for Q4 of 2025, and Q1 and Q2 of 2026 using pesticide use information and weather data. While modeled data cannot replace laboratory-measured monitoring results, it will give DPR and the public a better understanding of expected air concentrations during the period when monitoring data is unavailable.

The voided data impacts DPR’s 2025 Air Monitoring Network Results, Study 309 Report, and 2025 1,3-D Draft Annual Report. DPR plans to address these impacts as follows:

• By October 16, 2026, DPR will release the 2025 Air Monitoring Network Results report without 1,3‑D or MeBr results.  Reporting data we know is inaccurate is misleading and can create confusion about potential health risks or the effectiveness of regulatory requirements.
• DPR expects to release revised versions of the 2025 Air Monitoring Network Results, Study 309 Report, and 2025 1,3-D Draft Annual Report following the completion of modeling to fill in where CDFA voided data has left gaps. DPR will provide these updated reports as soon as feasible.
• DPR has updated Q4 2025 air monitoring data to reflect CDFA’s decision to recall and void the impacted data.
• DPR released Q1 2026 air monitoring data for the 38 pesticides not affected by the degraded standard on its website.

Moving forward, DPR and CDFA have agreed on additional quality-control measures to make sure future air monitoring data is not compromised by similar problems, including:

• The use of blind spikes during CDFA lab testing of air samples. These are test samples that contain a known amount of the chemical being measured that DPR will provide alongside its regular monitoring samples. The lab will not know which samples are blind spikes when it analyzes them. By comparing the lab’s reported results to the known values, DPR and CDFA can verify that instruments are properly calibrated and producing dependable measurements.
• The use of two separately-sourced standards. CDFA will analyze routine batches of monitoring samples using two independent separately-sourced laboratory standards – a primary standard and a secondary standard from a different source. If both standards produce consistent results, it provides an additional check on accuracy and precision. This helps make sure the lab identifies any problems with a single standard early and prevents future discrepancies in reported concentrations.

DPR will provide updates to the public as reports and analyses become available as part of the department’s work to protect people and the environment.