In the early days of the COVID-19 pandemic, public health officials believed that one of the most effective ways to fight the spread of the virus was to disinfect highly touched surfaces.
That led China, South Korea, France, Spain, and several other countries to spray copious amounts of disinfectant throughout densely populated urban areas. Fleets of trucks, drones, and even robots doused streets, parks, playgrounds, and other outdoor public spaces with virus-killing chemicals.
In Indonesia, drones drenched homes in disinfectant from above. And in one village in Spain, tractors dumped hundreds of gallons of bleach onto a public beach.
Infectious-disease experts, including the World Health Organization, have since denounced the practice as both ineffective and a potential health hazard to people, in particular respiratory irritation from inhaling the chemicals. Combining disinfectants, such as bleach and ammonia, could also release potentially fatal gases, WHO warned.
And this month, biologists joined in, claiming in a new commentary in the journal Environmental Research that the indiscriminate use of such substances in urban settings poses a significant danger to wildlife. (Learn more about COVID-19’s impact on the environment.)
China was the first country, in January 2020, to start sanitizing its cities—and as soon as it did, reports of poisoned animals started coming in. In February, an investigation by the Chongqing Forestry Bureau in Chongqing, a huge city in southwestern China, found that at least 135 animals across 17 species—including wild boars, Siberian weasels, and blackbirds—had died after exposure to disinfectants, according to Chinese news agency Xinhua.
Disinfectant ingredients, mostly sodium hypochlorite, chlorine, and bleach, are “acutely toxic to both terrestrial and aquatic animals,” says Dongming Li, professor of ecology at Hebei Normal University and co-author of the Environmental Research analysis, which was based solely on the Chongqing Forestry Bureau’s investigation. Li and his colleagues did not personally examine the dead animals to confirm what had killed them.
Even so, the animals’ deaths are concerning evidence, Li believes, that “the overuse of disinfectants may contaminate the habitats of urban wildlife.” (Read more about how animals are moving into cities.)
Li’s team is now calling on world leaders to regulate the dispersal of disinfectants in urban areas, which they say is being done without input from the scientific community.
Chemical disinfectants kill viruses, bacteria, and other microorganisms by destroying their cell walls and damaging their proteins through oxidation. If inhaled or ingested by people or animals, these substances can irritate or corrode the mucous membranes of the respiratory and digestive tracts. In extreme cases, exposure can lead to death.
Investigations such as the one in Chongqing haven’t been conducted outside China, so it’s unclear how outdoor dispersal of disinfectants has harmed urban wildlife and ecosystems in other countries.
But it’s not hard to guess. “If you put toxicants into a system, they are going to travel through the food web,” says Christopher J. Schell, professor of urban ecology at the University of Washington, in Tacoma. “It’s ecology 101.”
Though the Chongqing deaths are the only widely known example of disinfectants harming wildlife, at least one other anecdotal observation of the phenomenon has been reported, Schell says. (Read “Wild Cities,” National Geographic’s ongoing series about urban wildlife.)
On Brickell Key, an artificial island off Miami, Florida, several local residents and their dogs fell ill after Brickell Key Master Association, which manages the island, implemented an outdoor sanitation program, with workers in hazmat suits spraying disinfectant daily on the island’s parks, walkways, and benches.
A week after the program began, several residents began experiencing painful headaches and at least two dogs came down with fits of vomiting, according to reporting by Local 10, a news outlet in Pembroke Park, Florida. A spokesperson with the Brickell Key Master Association told National Geographic in a written statement that residents were notified in advance about spraying, which was conduced at dawn to minimize contact with the public.
Following a complaint from an affected pet owner, a representative from the county's Department of Environmental Resources Management inspected the island on May 20. The inspector did not issue any violations, and "did not detect a chemical odor on the island," according to the spokesperson.
Save it, don’t spray it
While sanitizing frequently touched surfaces can help reduce the spread of the coronavirus, we now know that most people get the disease by breathing in droplets in the air from an infected person—not by coming into contact with a contaminated surface.
That’s why, in May, the World Health Organization advised against using disinfectants outdoors, both because streets and sidewalks are not “are not considered as routes of infection for COVID-19” and because spraying such chemicals “can be noxious for people’s health and cause eye, respiratory or skin irritation or damage.” The WHO didn’t mention the harm to wildlife as well.
“The ongoing COVID-19 pandemic has caused public fear in many countries. Many health agencies around the world may spray more disinfectants to ensure the virus is fully killed and to alleviate their worries of viral infection,” Li says. (See our coronavirus 101: What you need to know.)
But there’s a better approach, he says—encouraging people to stay home.
“Rather than indiscriminately spraying high volumes of disinfectants in biodiversity-rich areas such as urban parks, wetlands, and green spaces,” he writes, “it would be preferable to suspend human activities in such places.”
This story was updated with a comment from the Brickell Key Master Association on September 11, 2020.