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The Dirt on Flea Control

By Ariel Rubissow Okamoto

It’s hard to go to the big box pet store and not stumble over the flea control displays. Most pet owners have dabbed or squirted Frontline or Advantage between their cat’s shoulder bones or onto the back of their dog’s neck, but who would guess this same chemical would make its way off our pet’s fur, down the drain, through wastewater treatment, and into the Bay? Apparently all the petting and shedding and subsequent washing of hands, doggies, and floors is moving flea-killing chemicals into our household wastewater, and the treatment plants aren’t getting it out again.

“Sewage treatment plants were not designed to treat and remove all the industrial chemicals we are now using in our homes,” says Kelly Moran of TDC Environmental, one of a group of scientists, regulators, and dischargers collaborating on a new study conducted under the Regional Monitoring Program (RMP).

DPR captures and tests doggie wash water post flea treatment.

The study monitored two ingredients in common “spot-on” flea killers – fipronil and imidacloprid – during drought conditions at eight wastewater treatment plants around San Francisco Bay. Scientists tested both the “influent” and “effluent” of the eight plants, which ranged in size, location and treatment technology. Regardless of how advanced the treatment, very little, if any, of these pesticides were removed.

“Many of us had thought spot-on treatments were relatively benign,” says the San Francisco Estuary Institute’s Rebecca Sutton, the lead scientist for the project. “These results opened all our eyes to something that might need control at the source.”

A few years ago, the RMP had flagged fipronil as a moderate concern for San Francisco Bay because it had been found in Bay sediment at levels that would kill freshwater invertebrates (toxicity tests in the saltwater environment are still in the works). In terms of overall levels found in untreated wastewater as part of this study, results varied, with total fipronil and breakdown products ranging from 20-120 parts per trillion (ppt), and imidacloprid from 58-310 ppt.

To help pinpoint the source, researchers divided results per plant by population served. “Results were so ubiquitous, and of such magnitude, it helped us eliminate sources like occasional improper disposal or material tracked in from outdoor ant sprays,” says Moran. Low daily variability in per capita contamination suggests widespread use.

fleas3Researchers and regulators are now scrutinizing other portions of this pollution pathway for more clues. The California Department of Pesticide Regulation (DPR)’s Jennifer Teerlink just completed a study in which they washed dogs 2, 7, and 28 days after spot-on treatments and captured and tested the wash water for fipronil and breakdown products. Results are still forthcoming. DPR is also conducting sampling throughout a municipal “sewershed” to see if homes, businesses, schools, or other facilities may be more or less important sources.

One interesting finding of the RMP study is that the San Francisco Airport treatment plant, a place where no one does much in the way of flea care for pets, had lower but still significant levels. “We checked pretty thoroughly that these particular chemicals weren’t being used to spray for ants, or as pest control for shopkeepers,” says Sutton. Since that was not the case, people must be bringing it to the airport on them, with them, or in them.

“People think that putting flea control on the outside of their pet is better for their pet because it’s not inside the pet,” adds Moran. Results suggest, however, that it may be getting inside of all kinds of things, perhaps even our own bodies.

While DPR is exploring the human health effects of topical products containing fipronil, pet pills appear to be a reasonable alternative. “It’s amazingly timely that there are new oral meds on the market,’ says Stephanie Hughes, a pollution prevention consultant for a Bay Area wastewater agencies.

The switch could be tricky, however. Getting these pills will require a trip to the vet, and a prescription, not just tripping over the display at your local superstore. Big pharma is sure to have something to say about potential losses of such large outlets to smaller veterinary businesses.

DPR won’t have any say over pet pills; that’s a veterinary matter. They do have a lot of say, however, about pesticide pathways from more conventional sources. “If someone applies a pesticide to a field, we have a record, if someone applies it to a dog, we don’t,” says Teerlink.

fleas1While no one is suggesting home recordkeeping, more information about effective flea control could help, says Hughes. The scientific literature suggests that only five percent of the flea’s life cycle is on your pet at any given time, she says. The other 95 percent mix of eggs, larvae, and pupa (which have a hard shell no flea bomb can penetrate) exists in a reservoir in your home. “Thoroughly and frequently vacuuming carpets, floors under furniture, cracks, crevices, the guest bedroom you never use, that’s what’s necessary,” says Hughes. “You might not catch the fleas in the carpet fibers the first time, but with frequency, the vibrations will encourage the pupae out of their shells, and you’ll get them the next time.”

For now, Bay Area wastewater treatment plants have done their bit to unearth pathways to the Bay, and scientists, regulators, and pollution prevention experts have helped narrow the search. “From a science policy perspective, these types of collaborative studies with the wastewater community are really important,” says Teerlink. “We’re looking at data driven solutions, and having a large real world study is crucial.”


2016 Article in Environmental Toxicology & Chemistry

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About the author

Ariel Rubissow Okamoto is both today’s editor-in-chief and the founding editor of ESTUARY magazine (1992-2001). She enjoys writing in-depth, silo-crossing stories about water, restoration, and science. She’s a co-author of a Natural History of San Francisco Bay (UC Press 2011), frequent contributor of climate change stories to Bay Nature magazine, and occasional essayist for publications like the San Francisco Chronicle (see her Portfolio here). In other lives, she has been a vintner, soccer mom, and waitress. She lives in San Francisco close to the Bay with her architect husband Paul Okamoto.

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