Some once-common insecticides linked to harmful human health impacts are disappearing from the air in the Great Lakes region, though others still persist, according to new research.
Some widely used insecticides are persistent in the environment, meaning they don’t break down quickly and can build up, causing problems for human and environmental health. Many insecticides used in agriculture or pest control in buildings are considered persistent and remain in the atmosphere, water and soil for years or even decades. But new research shows that in the Great Lakes region, at least three persistent insecticides are nearly eliminated, mostly as a result of regulatory action taken decades ago. Scientists say the results show the importance of swift action to ban the use of new persistent chemicals.
“For once we can report something positive,” Marta Venier, assistant professor of environmental chemistry at Indiana University's O'Neill School of Public and Environmental Affairs, told Environmental Health News (EHN). “A few of the chemicals we've been measuring for a long time are well underway to being eliminated from the atmosphere.”
Venier and her colleagues used atmospheric data from a binational monitoring program, run by American and Canadian researchers, which has tracked chemicals in the atmosphere since 1990. They found that the atmospheric concentrations of three persistent insecticides — lindane, ɑ-hexachlorocyclohexane (or ɑ-HCH) and endosulfan — had dropped close to the level of “virtual elimination,” a concentration at which scientists can no longer quantify how much of the chemical is present.
Airborne pesticides pose health risks to humans via inhalation, as the chemicals can irritate lungs and enter the bloodstream through the respiratory system. The health risks of airborne pesticides vary based on the concentration of the chemical in the air. Negative health outcomes have been associated with exposures in the range of the atmospheric levels observed in the paper, though many other factors play a part, Dana Barr, a professor of environmental health at Emory University who was not involved in the research, told EHN.
“Everyone doesn’t handle the exposures the same way,” she said. “Some may be more susceptible while others aren’t.”
Lindane and ɑ-HCH were used together as insecticide seed treatments. Manufacturers stopped using ɑ-HCH due to its lack of insecticidal properties by the mid 1980s, and the EPA banned agricultural uses of lindane in 2006. Global production and usage of both chemicals stopped in 2009 as a result of the Stockholm Convention, a global treaty meant to protect human health from the hazards posed by persistent chemicals. Lindane and ɑ-HCH have been linked to adverse health effects such as anemia, cardiac dysfunction and neurological problems. In 2010, the EPA announced a ban on endosulfan and all its uses were phased out by 2016. The chemical is an endocrine disruptor, which means it affects the human hormonal system.
In the new paper, researchers write that they expect lindane and ɑ-HCH to be virtually eliminated from the atmosphere near the Great Lakes in the next 5-10 years. They noted a similar trend for endosulfan, reporting that between 2000 and 2020, its concentration had dropped by nearly half.
Grasshopper effect
The results are interesting since persistent chemicals tend to evaporate from warmer regions and settle in colder climates, such as the Great Lakes, in a phenomenon known as the grasshopper effect, Barr said. The fact that some chemicals seem to be dissipating is “encouraging,” she said.
“Despite the fact that it took a very long time, all of the [regulatory] measures that have been enacted have worked,” Venier said. However, she added, monitoring needs to go on to see if the trend continues.
Some insecticides persist
Other persistent chemicals don’t seem to be disappearing, though. The researchers found that concentrations of toxic insecticides dichloro-diphenyl-trichloroethane (DDT), chlordane and hexachlorobenzene had not changed much, despite bans put in place decades ago. DDT, for example, has not been sold in the U.S. or Canada for more than 50 years due to its cancer-causing effects, but was still detected in all atmospheric samples in 2020.
The researchers suggest that the persistence of these insecticides in the atmosphere may be due to their accumulation in soil. Once persistent chemicals accumulate in the environment, soil acts as a reservoir from which the chemicals seep back into the atmosphere. That process is slow, and as a result, researchers expect the atmospheric levels of these chemicals to stay steady for a decade or more, Venier said.
“Until all reservoirs have been completely cleared, we will continue to see [these chemicals] in the environment,” she said. Remediation methods to clean soil, are usually limited to large accumulations of toxic chemicals like Superfund sites, and it would be much harder to enact to address the widespread contamination fueling the persistence of insecticides in the atmosphere.
Venier said she hopes regulators can learn from the research, especially regarding regulations of per- and poly-fluoroalkyl substances, or PFAS — persistent chemicals commonly used for their waterproofing and stain-resistant properties. Other chemicals in current use, like some flame retardants, phthalates (chemicals used to soften plastic) and UV light filters used in sunscreen also worry Venier.
“We should act in a different way with the new sets of chemicals,” she said. “We should prevent the release in the environment. Because once they are in the environment, it's really hard to eliminate them and it's going to take a long time for the environment to clear itself of these chemicals.”
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