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Tufts builds a better mousetrap; Research on poisons shapes EPA policy.

Byline: Susan Spencer

GRAFTON -- The most potent poisons used to control rats and mice don't just kill rodents. The products have also been linked to deaths in hawks, owls and other animals up the food chain. And federal officials say that more than 10,000 children a year were accidentally exposed to the toxic chemicals before tighter safety standards were initially introduced in 2008.

Thanks in part to research conducted by Dr. Maureen Murray, a veterinarian at Cummings School of Veterinary Medicine at Tufts University, the remaining mouse and rat poison products available with these chemicals will soon disappear from household use.

The U.S. Environmental Protection Agency announced in May that it had reached agreement with Reckitt Benckiser Inc. to cancel 12 d-CON mouse and rat poison products that do not comply with the agency's new safety standards for rodent killers.

Production of the products, which were the last to meet the standards, will stop by the end of the year and they will be off the shelf for household consumers by next April.

The particular type of rodent poisons will still be available through pest control companies and for agricultural use.

Dr. Murray served on the scientific panel convened after Reckitt Benckiser appealed the new safety standards in 2008.

The phase-out of poisons known as second-generation anticoagulant rodenticides, or SGARs, is based partly on research Dr. Murray published and continues to conduct at Tufts Wildlife Clinic.

"It was pretty cool to see the research directly applied to the policy decisions and to be involved with that,'' Dr. Murray said.

In 2011, Dr. Murray published a paper showing anticoagulant rodenticide residues in 86 percent of 161 birds of prey that were tested over five years at Tufts Wildlife Clinic.

Dr. Murray said that having data from before the time these rodenticides were removed from household use will allow researchers to measure whether any changes are found in exposure to the poisons after the rules go into effect.

While anticoagulant rodenticides have been used for decades, the more powerful second-generation anticoagulants were introduced in the late 1970s after there was concern about mice and rats becoming resistant to the first-generation products.

Anticoagulants work by causing the animal to bleed to death after ingesting the poison, a process that can take up to a week. First-generation anticoagulants, such as warfarin used in humans to prevent blood clots, usually require the animal to feed several times from the poison to get a deadly dose.

Second-generation products, including brodifacoum, bromadiolone, difenacoum and difethialone, are faster acting, typically causing death after a single feeding, Dr. Murray explained.

Also, SGARs accumulate and persist a lot longer in body tissue, stored in the liver.

"Birds of prey that hunt in the same territory might be continually feeding on something that has been contaminated,'' Dr. Murray said. "They can accumulate a toxic dose over time.''

The impact of SGARs on birds of prey was brought to the forefront in April when Ruby, a red-tailed hawk whose adventures with her mate, Buzz, were chronicled on a blog with many followers, was found dead on the ground beneath her perch by Fresh Pond in Cambridge.

Ruby was brought to Tufts and toxicology tests showed she had high concentrations of the SGAR brodifacoum, as well as other poisons, in her system.

Susan Moses, a Cambridge resident who had watched Ruby and Buzz since 2010 and found the lifeless bird, asked Tufts Wildlife Clinic to establish the Ruby Memorial Research Fund. The fund's initial goal is to raise $10,000 for research to monitor the health effects of rodenticides on birds of prey.

Dr. Murray said that $2,000 has already been raised. The money will pay for the expensive toxicology tests on the research animals.

But Dr. Murray doesn't just study the birds that show direct signs of exposure to rodenticides. Her research involves examining birds of prey, namely species of hawks and owls, that are brought into the clinic either after they have been found dead or that had to be humanely euthanized because they could not survive in the wild, due to illness or injury.

"The ones that are presented to the clinic (with suspected poisoning) are the tip of the iceberg,'' Dr. Murray said. "I'm sure there are others out there that aren't coming in here.''

Dr. Murray said she's seen exposure to rodenticides among pets brought into the small animal clinic, too, particularly in dogs that might eat a contaminated animal or even the poison pellets themselves.

Concern about exposing children to the poisons was a major factor in setting the new safety standards.

Besides eliminating the use of SGARs in consumer products, the EPA rules now require that bait stations securely contain the poison and offer tamper-resistant packaging. Loose bait forms are no longer permitted; instead the poison must be contained in a block or paste.

Manufacturers are replacing SGARs with some of the original first-generation anticoagulants and non-anticoagulants such as nerve toxins, massive doses of vitamin D3 (cholicalciferol) and zinc phosphide. These are not considered as dangerous to humans and other animals besides rodents, Dr. Murray said.

But she added, "There's no such thing as a safe poison.''

Dr. Murray offered the following tips on more safely controlling rodent infestations:

Explore other ways of managing the problem: Find out where the rodents are getting in and block access, where possible; remove food sources.

Use nonpoisonous lethal means, such as traps.

Read labels, if you're buying a rodenticide. Steer away from second-generation anticoagulants. A list of approved products is available on the EPA's website,

If using a pest control professional, look for integrated pest management and ask about safer alternatives to SGARs.

Contact Susan Spencer at Follow her on Twitter @SusanSpencerTG
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Title Annotation:Local
Author:Spencer, Susan
Publication:Telegram & Gazette (Worcester, MA)
Date:Jul 11, 2014
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