Tuesday, September 29, 2026

Largest-ever study of its kind shows California’s rodenticide restrictions are working, and flags new rodenticides rising in their place

A seven-year, 1,000-plus owl study gives some of the clearest evidence yet that science-based policy is reducing wildlife exposure to pesticides, even as researchers warn a second, less-regulated compound may be moving in.

Integral Ecology Research Center

Two Barred Owls — image:
An adult Barred Owl perches next to a juvenile.
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Credit: Daniel Hoftader

BLUE LAKE, Calif. September 25, 2026 - New research from the Integral Ecology Research Center (IERC) offers some of the clearest evidence yet that California’s efforts to restrict dangerous rodenticides are paying off in the wild, while also flagging a new contaminant that deserves close attention going forward.

The study, published in the journal Environmental Pollution, analyzed liver tissue from 1,003 Barred Owls collected across northwestern California between 2019 and 2025, the largest rodenticide biomonitoring dataset ever assembled for a single wildlife species in North America. Because the owls were removed as part of an ongoing regional conservation program rather than recovered as sick animals or dead carcasses, the sample is a far more representative picture of the population as a whole.

The findings are a mix of a genuine policy win and a new warning.

The policy win: Among young owls sampled in the study area, exposure to the most lethal class of rodenticides, known as second-generation anticoagulants, fell from about 50% of birds in 2019 to about 20% in 2024. That decline lines up closely with California’s phased statewide restrictions, most notably the California Ecosystems Protection Act (AB 1788), passed in 2020, along with a 2024 law extending restrictions to older-generation compounds (AB 2552). It also reflects a feedback loop central to IERC’s work: supplying the science that informs policy decisions, and then documenting the real-world benefit that policy delivers within just a few years.

The new concern: At the same time, the study screened for cholecalciferol (vitamin D3), a different type of rodenticide, for the first time in this species. It turned up in nearly one in five owls (18.5%), and detections rose over the same period that anticoagulant exposure was falling, a pattern suggesting product substitution as older compounds become harder to access. Overall, when all rodenticides were counted, as much as 46% of the owls sampled carried at least one rodenticide compound in their system.

The Spotted Owl connection: Female Barred Owls and older adults carried the highest exposure and the widest mix of compounds, consistent with pesticides accumulating over a lifetime. These are exactly the individuals, breeding-age females and established territory holders, that a population depends on most to sustain itself. Because Northern Spotted Owls are a closely related species with a higher proportion of rodents in their diets, this pattern may indicate added risk for Spotted Owl recovery.

“Nearly all rodenticide surveys rely on animals that turned up sick or dead, so they tend to capture the worst cases,” said Dr. Vitek Jirinec, lead author of the study and research scientist at IERC. “Our owls were apparently healthy birds going about their lives. That gives us a much truer picture of what’s circulating in the population, and more confidence that the trends we see are real.”

Dr. Greta M. Wengert, co-founder and co-director of IERC and principal investigator on the study, has tracked rodenticide contamination across the region for more than a decade. She said the results demonstrate something rare in conservation science, a policy translating directly into a measurable outcome for wildlife:

“We’ve watched illegal use and unregulated products drive rodenticide exposure in these forests for more than a decade,” said Wengert. “Seeing anticoagulant exposure actually decline within a few years of California’s regulations taking effect is proof that policy, when it’s grounded in good data from effective biomonitoring efforts, can improve outcomes for wildlife.”

The study also reinforces and extends findings from earlier IERC research. A 2012 IERC study first documented widespread anticoagulant exposure in Pacific fishers linked to trespass cannabis cultivation on public lands, and a 2018 IERC study found rodenticides in 70% of sampled Northern Spotted Owls in the same region. Barred Owls, Spotted Owls, fishers, and other sensitive wildlife all feed from the same contaminated food web, so this much larger dataset adds substantial weight to that earlier evidence. Across more than a decade of IERC research, the same underlying threat has persisted in multiple old-growth-dependent species, and it is now, for the first time, responding to policy.

The authors caution that the exact source of ongoing exposure is not fully resolved. State pesticide-use records only capture licensed commercial applicators, not household purchases or illegal use. Trespass cannabis cultivation, long documented by IERC as a major source of rodenticide contamination on public and tribal lands, remains untracked by any regulatory database, and legacy contamination from past illicit grow sites may also continue cycling through these forests well after active cultivation has stopped. Researchers say these hidden and historical sources likely explain at least part of the exposure that remains even as legal, regulated use declines.

About the Integral Ecology Research Center

Founded in Blue Lake, California, in 2004, IERC is a woman- and minority-founded nonprofit conservation science organization dedicated to conserving wildlife and the ecosystems they rely on across northwestern California and beyond. IERC partners with tribal, state, and federal agencies to conduct field research, from GPS telemetry and forensic wildlife science to toxicology and habitat monitoring, that translates directly into on-the-ground conservation action for species. Learn more at iercecology.org.

Publication: Jirinec, V., Gabriel, M.W., Peery, M.Z., Higley, J.M., Hofstadter, D.F., Varian, C.P., Rex, A., Franklin, A.B., Poppenga, R.H., Woods, L.W., Volker, S.F., Wengert, G.M. 2026. Forest food web contamination by rodenticides is pervasive but responsive to regulation: Insights from Barred Owl biomonitoring. Environmental Pollution, https://doi.org/10.1016/j.envpol.2026.129205

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Journal

Environmental Pollution

DOI

10.1016/j.envpol.2026.129205

Method of Research

Observational study

Subject of Research

Animals

Article Title

Forest food web contamination by rodenticides is pervasive but responsive to regulation: Insights from Barred Owl biomonitoring

Article Publication Date

26-Sep-2026

Sunset over Northern California forest

Credit

Morgan Heim

A young Barred Owl with a squirrel

Credit

Daniel Hofstader

Northern California forest and mountains

Credit

Vitek Jirinec

Wearable nanotech could combat nerve agents

Water-activated nanoparticles absorb deadly toxins faced by soldiers and farmers

Northwestern University

EVANSTON, Ill. — Nanoparticles could someday provide a new way to help soldiers fight back against deadly nerve agents on the frontline.

In a new study, Northwestern University scientists developed a nanoparticle-based compound that, when mixed into clothing dyes, could limit the impact of chemicals commonly found in pesticides, insecticides and nerve agents.

Manufacturers potentially could add the nanoparticles to clothing used by those most at risk, such as farmers’ masks and gloves or soldiers’ uniforms and tactical gear. Or, if someone is exposed to a potentially deadly chemical, they could spray their clothing with water mixed with the compound to deactivate the chemical before its damaging effects take hold.

The study was published recently (Aug. 25) in the journal ACS Nano.

“Our bioinspired melanins are non-toxic and can be used as an additive in clothing or facemasks and beyond. We previously have shown the ability to use them in dyeing synthetic fabrics,” said Northwestern’s Nathan Gianneschi, a corresponding author on the study. “You could imagine using this approach to make protective clothing, or breathing equipment for workers who make or use these materials to provide everyday protection.”

Gianneschi is a co-corresponding author with Omar Farha. Farha is the Charles E. and Emma H. Morrison Professor of Chemistry in Weinberg College of Arts and Sciences and chair of the Department of Chemistry. Gianneschi is the Jacob & Rosaline Cohn Professor of Chemistry at Weinberg and a professor of materials science and engineering and biomedical engineering at the McCormick School of Engineering.

In the new study, Gianneschi, Farha and their teams sought to mimic how nature can counteract substances like organophosphorus compounds, the toxic chemicals found in nerve agents and pesticides. Specifically, they explored allomelanin, a renewable, biodegradable pigment that deepens the color of plants and fungi.

To develop the new nanoparticles, the researchers started with synthetic allomelanin. Naturally porous, allomelanin contains a network of tiny pores that can grab and capture harmful chemicals. Then, they added a zirconium cluster, a metal cluster with an ability to catalyze chemical reactions. Working together, the allomelanin absorbed the toxic chemicals and the zirconium destroyed them.

“This intrinsic microporosity is required,” said Sofia Aman, a graduate student in Gianneschi’s lab and the study’s co-first author. “When we tested other melanin-like materials, they didn’t work as well. So, we do need this porosity, and that just makes this allomelanin much more unique and a better substrate.”

For the chemical reaction to work, the environment needs to be entirely basic — reaching a pH of 10 or higher. Instead of adding an external basic compound, the researchers incorporated basic chemical groups onto the nanoparticles’ surface. Then, water activates the particles, enabling them to break down the harmful chemicals. When the organophosphorus compound breaks down, it releases two chemicals — and this is where the danger lies.

While one of the chemicals (dimethyl phosphate) is nontoxic, the second chemical (methyl nitrophenyl) stops enzymes in the blood from breaking down a critical neurotransmitter, acetylcholine. If the enzymes cannot break down acetylcholine, it builds up in the nervous system and prevents the brain from communicating with the rest of the body.

But the new study found researchers can limit exposure, both by decreasing the amount of toxic chemicals and their potency. The allomelanin grabbed hold of the toxic chemical and broke it down and left the nontoxic chemical alone. Within 10 minutes, the toxic byproduct decreased by 50% and continued to decrease with more melanin and with sunlight exposure.

“Previously, our group developed catalytic metal-organic frameworks (MOFs), which are exceptionally powerful materials in the absorption and processing of chemical warfare agents,” Farha said. “This work takes those learnings and advances them towards melanin-inspired materials which are inherently adhesive, acting as dyes for various fibers and fabrics. In fact, melanin is nature’s pigment, as well as being an efficient absorbent of small molecules and heavy metal ions in biological organisms. We couple those natural functions with catalysis using a combination of synthetic inorganic chemistry, from my group and biomimetic polymer science from Gianneschi’s team.”

Researchers also found that melanin had additional natural benefits. Melanin reacts with sunlight and absorbs heat. So, when allomelanin is exposed to sunlight, the detoxification process accelerates.

“We have worked on melanin for over 12 years, trying to learn about its myriad functions in nature and learning how to optimize, develop and engineer mimetic materials for scalable, translational applications,” Gianneschi said. “This provides us with a treasure trove of approaches and materials to optimize and develop for applications like this. In many ways, it’s a proof of concept for a new direction in how we think about protective materials and coatings design."

The study is title, “Catalytic Porous Metallized Melanin for the Remediation of Organophosphorus Agents.” It was supported by the Air Force Office of Scientific Research (FA 9550-18-1-0142 and FA 9550-18-1-0477), the Army Synthetic Biology Centre for Predictive Materials Design (W911NF2220246 P00002) and the Catalyst Design for Decarbonization Center (DE-SC0023383).