California’s Fipronil Is 99.7 Percent Pest Control, and It Reaches Streams
Key result: Structural pest control accounted for 99.7 percent of the fipronil use reported in California in 2022 and 2023, and agriculture for almost none. Fipronil was detected in 16.9 percent of 2,489 California stream samples since 2015, and in more than half of samples in Alameda and Riverside counties.
Whose insecticide is it?
Water monitoring cannot say where a pesticide came from. Many insecticides found in streams are used both on farms and around buildings, so a detection could come from either. California’s pesticide use reports allow a partial answer, because they record use by sector: agricultural production, structural pest control, landscape maintenance, public health and other reported non-agricultural uses.
The department describes the reports as covering “nearly all types of agricultural pesticide uses and many non-agricultural pesticide uses”, including structural pest control, landscape maintenance and vector control. Products residents apply themselves and veterinary flea treatments are not in them. With that limit stated, we compared reported use by sector for five insecticides with their detection in California streams.
Reported use by sector
| Compound | Reported pounds a year, 2022-23 | Structural pest control | Agriculture | Landscape | Public health and other | Detected in California stream samples |
|---|---|---|---|---|---|---|
| Fipronil | 26,170 | 99.7% | 0.0% | 0.1% | 0.2% | 16.9% of 2,489 |
| Permethrin | 191,990 | 43.3% | 48.1% | 5.9% | 2.7% | 1.5% of 1,308 |
| Bifenthrin | 319,241 | 27.1% | 71.7% | 0.9% | 0.3% | 19.3% of 2,400 |
| Imidacloprid | 304,129 | 7.4% | 86.9% | 4.4% | 1.3% | 36.8% of 2,066 |
| Chlorpyrifos | 1,886 | 0.4% | 3.2% | 2.8% | 93.6% | 7.5% of 2,388 |
Sources: California Department of Pesticide Regulation, Pesticide Use Reports 2022 and 2023, pounds of active ingredient, average of the two years; Water Quality Portal, California stream sites, 2015 to 2025, hidden non-detects corrected. Author calculation.
What it means. Among reported uses, fipronil is a pest control chemical and almost nothing else: about 26,000 pounds a year, all but a fraction applied by structural pest control businesses. Its presence in California streams cannot be put down to farms on these data. The other compounds are mixed: imidacloprid and bifenthrin are mostly agricultural, permethrin split roughly evenly. Chlorpyrifos use has nearly disappeared, and what remains is mostly in categories other than these.
What limits it. Unreported uses matter most for fipronil. The National Pesticide Information Center lists “spot-on pet care products” among fipronil’s uses; those are not in the use reports and could reach water through washing. The 99.7 percent figure is a share of reported use, not of all fipronil in the environment.
Where fipronil is found in California streams
What it means. In the urban Bay Area and Inland Empire counties, fipronil is found in about half of stream samples: 58.7 percent in Alameda, 54.1 in Riverside and 46.9 in Contra Costa. In the Central Valley counties of San Joaquin, Sutter and Tulare it is found in about 6 percent of samples or fewer.
What limits it. Programmes sample different kinds of streams in different counties, and only 13 counties have at least 30 samples. The county pattern is a description, not a test.
Does more use mean more detection?
We tested whether counties with more structural fipronil use per square mile have higher detection rates, using a rank correlation across the 13 counties. The correlation was weak, at 0.20, and the same test for agricultural use of imidacloprid and bifenthrin gave 0.48 and 0.42. With so few counties, none of these is strong evidence either way. Alameda and Contra Costa, which have high fipronil use per square mile, also have high detection rates; Sacramento, which has the highest use per square mile of the 13, does not.
What it means. Use intensity alone does not predict detection county by county. Where and how often programmes sample, and unreported uses, are likely to matter as much.
Bifenthrin is found far more often in California than nationally
Bifenthrin was detected in 19.3 percent of California stream samples, against 2.6 percent nationally in our monitoring audit. Fipronil’s California rate, 16.9 percent, matches the national 17.0, and imidacloprid’s, 36.8 percent, is below the national 41.6. The bifenthrin difference may reflect California programmes’ sampling of urban runoff and their laboratories’ methods; these data do not distinguish.
Checks
1. County matching
Method. Stream sites assigned to counties from the portal’s station records; use assigned by the county of use in the pesticide use reports, matched by county code.
2. Corrected detections
Method. The hidden non-detect corrections from our monitoring audit were applied before any rate was computed.
Download the data
The tables in this report are published as CSV files under a Creative Commons Attribution 4.0 licence. You may republish, remix and build on them, including commercially, with attribution to The Pest Control Brief and a link to this page.
- Reported use of five insecticides by sector, California, 2022-23 (CSV, 25 rows)
- Stream detection rates and use per square mile by county for five insecticides (CSV, 70 rows)
How to cite this report
The Pest Control Brief, “In California, Reported Fipronil Use Is 99.7 Percent Pest Control. It Turns Up in One Stream Sample in Six”, 2 October 2026. https://thepestcontrolbrief.com/california-fipronil-use-and-streams/
References
- California Department of Pesticide Regulation. Pesticide Use Reporting. cdpr.ca.gov pesticide use reporting. Accessed 4 October 2026. Source of the description of reporting scope.
- California Department of Pesticide Regulation. Pesticide Use Report annual archives for 2022 and 2023. files.cdpr.ca.gov/pub/outgoing/pur_archives/. Accessed 2 October 2026.
- Water Quality Portal. Result and Station searches, siteType=Stream, from 1 January 2015. waterqualitydata.us. Retrieved 25 September to 3 October 2026.
- National Pesticide Information Center, Oregon State University. Fipronil general fact sheet. npic.orst.edu fipronil. Accessed 4 October 2026. Source of the list of fipronil product types.
- US Census Bureau. 2023 Gazetteer Files, counties. www2.census.gov gazetteer. Accessed 4 October 2026. Source of county land areas.
How the comparison was built
Sectors. Structural pest control is site code 10; landscape maintenance site code 30; public health site code 50; agriculture is records the department codes as production agriculture; the remainder is other reported non-agricultural use.
Use. Pounds of active ingredient, averaged over 2022 and 2023.
Water. California stream-site water results since 2015, corrected for hidden non-detects.
Limitations. Unreported uses, including consumer and veterinary products, are missing. Monitoring years and use years differ. Few counties have enough samples.
Last reviewed: 4 October 2026.
For reporters
Most quotable statistics
- Structural pest control accounted for 99.7 percent of reported fipronil use in California in 2022 and 2023.
- Fipronil was detected in 16.9 percent of 2,489 California stream samples since 2015.
- In Alameda and Riverside counties, fipronil was found in more than half of stream samples.
- Imidacloprid’s reported California use is 86.9 percent agricultural; bifenthrin’s 71.7 percent.
Caveats that travel with them
Pet flea treatments and products residents apply themselves are not in the use reports. Detection cannot be attributed to a source.
Press summary
Almost all of the fipronil reported used in California is applied by structural pest control businesses, according to an analysis of state pesticide use reports and stream monitoring by The Pest Control Brief. Pest control accounted for 99.7 percent of reported fipronil use in 2022 and 2023, and agriculture for almost none. Fipronil was detected in 16.9 percent of California stream samples since 2015 and in more than half of samples in Alameda and Riverside counties. Pet flea treatments, which also contain fipronil, are not in the reports.
Headlines editors could use
- In California, fipronil is a pest control chemical, and it is in the streams
- Half of stream samples in Alameda County contain fipronil
- Farm or exterminator? Who uses the insecticides found in California streams
Questions
Where does fipronil in California streams come from?
The data cannot say for certain. Among reported uses, 99.7 percent is structural pest control, but pet flea and tick products, which are not reported, also contain fipronil.
Is fipronil used in agriculture in California?
Almost not at all on reported use: agriculture accounted for under 0.1 percent of reported fipronil pounds in 2022 and 2023.
How often is fipronil found in California streams?
In 16.9 percent of 2,489 stream samples since 2015, and in about half of samples in Alameda, Riverside and Contra Costa counties.
Which sector uses most imidacloprid and bifenthrin in California?
Agriculture: 86.9 percent of reported imidacloprid and 71.7 percent of reported bifenthrin use.
Where can I get the data?
Both tables are in the CSV files above.
