Editorial: Rat poison almost killed P-22. We can save more lions and other wildlife if we ban rodenticides

Los Angeles Times Editorial Board, Los Angeles Times on

Published in Op Eds

When research scientists tracking P-22, the late beloved lion of Griffith Park, went to change the batteries in his GPS collar in 2014, they found him suffering from mange, a parasitic disease of the skin and hair that is connected to rodenticide poisoning.

Blood tests would later show that P-22 had two rodenticides in his system, one of which was diphacinone, a first-generation anticoagulant intended to kill rats. P-22 was lucky — the scientists treated him in the field with a topical medicine. He went on to live another eight years.

But other animals are not so lucky. Diphacinone has cropped up widely in the bloodstreams and livers of living and dead wildlife that it was not meant to kill. After P-22 was euthanized last year, a necropsy revealed that while his death was the direct result of injuries and disease, he again had diphacinone in his system — along with four other anticoagulant pesticides.

The powerful anticoagulant thins the blood and leaves rodents dead from internal bleeding. Perversely, diphacinone often ends up killing the natural predators of rodents, such as hawks and pumas, who are exposed when feeding on a rat that ingested poison.

Second-generation anticoagulant rodenticides, which are particularly lethal and fast-acting, were banned in 2014 for use by consumers. A law passed in 2020 put a moratorium on their use by professional exterminators, except in some agricultural settings and in public health emergencies.

However, first-generation anticoagulants have remained available because they are less toxic. Second-generation anticoagulants that can kill a rat after a single feeding are then very toxic to wildlife who prey on the rat, or on the animals who preyed on the rat, and stay in their systems a long time. First-generation anticoagulants tend to kill rodents after several successive feedings. For the predators, the first-generation rodenticides may not stay in their systems long but they can do severe damage nonetheless. Being less toxic is still unacceptably dangerous to the wildlife we want to protect from the many perils of life in California.

Legislation on Gov. Gavin Newson’s desk, Assembly Bill 1322, bans the use of diphacinone, the first-generation anticoagulant most widely found in poisoned wild animals. (Anticoagulant rodenticides kill pets as well.) Although diphacinone isn’t as toxic to wildlife as a second-generation pesticide, it is still debilitating, capable of causing internal hemorrhaging and making it difficult for animals to hunt, avoid predators or survive an injury. It can weaken an animal’s immune system. And if a wild animal feasts on one poisoned creature after another, the build-up of diphacinone in the system can kill.


Diphacinone has been found in the bodies of dead raptors, mountain lions, bobcats and other mammals. In its 2018 investigation of anticoagulant rodenticides, the California Department of Pesticide Regulation cited state data that indicate 59% of 64 dead mountain lions tested between 2015 and 2016 were exposed to diphacinone. Another 2015 study cited found that diphacinone was detected in 40% of liver samples from dead bobcats near Los Angeles between 1997 and 2012. The department announced that since 2018 there had been “a substantial increase” in exposure of wildlife to diphacinone and that sales and use of the rodenticide had increased. Clearly, diphacinone has become the pest killer of choice.

An appellate court decision in September 2022 in a case brought by a group called Raptors Are the Solution ordered the agency to analyze and assess the impact of diphacinone on the environment, including its prevalence and effect on non-target wildlife. In May the department officially proposed a reevaluation of diphacinone and solicited public comments. But it can take years to formally launch a reevaluation and get regulations in place.

Wildlife don’t have that long to wait. And they shouldn’t have to. The bill puts an immediate moratorium on the use of diphacinone — and requires the Department of Pesticide Regulation to develop and adopt necessary restrictions to protect wildlife. Without the bill, there would be no moratorium on diphacinone regardless of whether the agency decides to go through formal reevaluation.

The legislation also allows for the pesticide to be used in certain agricultural settings and in public health emergencies. As for battling rats, there are other pesticides available, but more importantly there are nonlethal ways to keep rats at bay, including increasing sanitation efforts.

Newsom should sign this bill into law to protect California’s precious wildlife from a hazard they should not have to encounter.

©2023 Los Angeles Times. Visit at latimes.com. Distributed by Tribune Content Agency, LLC.


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