After years of putting rat poison in storm drains to kill rodents, the city of Columbia has stopped the practice because of concerns about water pollution.
The city’s extensive network of drainage pipes discharges stormwater to creeks that flow into rivers such as the Congaree. But a small community outcry erupted recently, prompting the city to reassess the practice of baiting storm drains with blocks of rat poison.
“The city will work to identify other methods that should be considered to control the rat population,’’ according to a news release issued Wednesday.
City officials say they have no evidence the practice has violated environmental laws. They also said baiting drains with rat poison was done on a complaint basis and was not a routine practice.
But they conceded that using rat poison in drains was inconsistent with a campaign that discourages people from dumping anything in the stormwater drainage system to control water pollution.
Tracy Mitchell, the city’s stormwater manager, said she’d gotten a call from a resident asking why the city tells people not to dump leaves and pet waste into storm drains, but Columbia was putting poison in the drains.
Another city division charged with controlling rat populations was hanging blocks of the bait from storm drain grates, city officials said. The poison was not thrown directly into the drainage water, although runoff washes across the poison as it rushes into storm grates.
“I was really concerned when that came up, especially when I found it was another city department,’’ said Mitchell, who said she didn’t know about the rat baiting until recently. “That was not something we maybe communicated as effectively as we should have on.’’
It was unclear Wednesday how widespread the practice is in other cities, but Cayce city manager Rebecca Rhodes said her community does not use rat poison in storm drains or the sewer system. Columbia and Cayce have the largest sewer systems in the Midlands.
Columbia’s rivers are natural amenities that are increasingly attracting kayakers and anglers — and that interest has put an increased focus on keeping them clean.
Congaree Riverkeeper Bill Stangler said the threat of poison is a long-term concern, even though killing rats might reduce bacteria pollution from feces in stormwater. He said he’s glad the city is stopping the practice.
“Poisons have a potential to do more damage’’ than bacteria, he said, noting that toxins from rat bait could affect fish or other aquatic life. When “it goes up through food chain, I think it is a much greater (concern) than the potential to have higher bacteria levels because there might be larger rodent populations.’’
Rat poison often is made with an ingredient called Warfarin. The poison causes hemorrhaging in small animals. Larger animals and people might not be as greatly affected, depending on their weight, experts said.
The rat poison issue surfaced on social media sites earlier this month after Dave Bodiford stumbled across a block of the toxic material while walking his dogs in Heathwood. He then posted his experience on Facebook. One of his dogs, a 13-year-old Labrador retriever mix, ate some “crumbs’’ of rat poison one afternoon about two weeks ago, he said Wednesday. The dog spent the night at a veterinarian’s office, but is OK, Bodiford said.
“I guess my biggest surprise was the city was actually doing this,’’ he said.
Even so, city officials said they’re in a tough position because the public doesn’t want rats crawling out of storm drains.
“We would not be applying it if there weren’t a problem at all,’’ said Missy Gentry, an assistant Columbia city manager. “It’s not like there is an infestation that is out of control by any means. Myself, I see one mouse and there’s a problem to me. One constitutes a problem to many people.’’
For now, Columbia will continue to use rat poison in its sewer system to kill rodents, but officials say that won’t threaten the public or water quality because wastewater does not flow directly into rivers. Everything goes through the city sewage treatment plant before being released to the Congaree.
It was not immediately known if the city’s treatment plant is set up to filter out rat poison. The city will also monitor the rat population in the storm drain system to determine its next step. The application of pesticides in South Carolina is overseen by Clemson University, although there was no indication the city had misapplied rat poison.