A recent study found that Detroit soil and street dust contain high levels of two toxic and persistent contaminants that could pose a threat to human health.
Polychlorinated naphthalenes (PCNs) and polychlorinated biphenyls (PCBs) were present in most sites tested at levels above health-based guidelines. The researchers behind the study, published in January, say it was the first to investigate PCNs in soils and street dust in Detroit.
PCNs have been historically found in wood preservatives, additives in paints and engine oils, insulators in wire and electrical capacitors, and insect repellents for farming. PCBs were historically used in electrical and hydraulic equipment, copy paper, and elastomers, a polymer similar to rubber. Both contaminants cannot be used in industrial production today.
The chemicals have been phased out since their inceptions in the 1910s and 1920s. PCNs were voluntarily removed from industrial uses in the 1970s and 1980s. PCBs were banned in 1979. While intentional industrial production of both contaminants has stopped, unintentional releases continue today.
PCNs and PCBs can be accidentally generated in modern industrial processes. PCNs are accidentally produced when chlorine is present at sources like waste incinerators, cement and magnesia production facilities, and refineries. PCBs are released during the disposal of e-waste.
PCNs and PCBs that were produced decades ago are called legacy compounds. Stuart Batterman, an author of the study and a professor of environmental health sciences at the University of Michigan, said these legacy compounds and new, accidentally created PCNs and PCBs make up the contamination found in Detroit today.
“Some of these [compounds] are produced inadvertently when we incinerate or burn waste and produce coke and steel and things like this,” Batterman told Michigan Public. “So there's both the combination of these old legacy sources, plus the newly deposited material just that are incidentally produced.”
These contaminants have negative health effects for people exposed. Health effects vary depending on factors like exposure amount, the timing of the exposure, and the frequency of the exposure.
Exposure to PCNs can cause severe skin rashes and an increased risk of liver disease and risk of cancer. PCB exposure can lead to endocrine disruption, immune system problems, an increased risk of cancer, and reproductive and development problems.
PCNs and PCBs have bioaccumulation properties, which means they build up in living organisms. In previous studies, they have been detected in air, soil, sediment, dust, and humans. Both contaminants are found in higher concentrations in urban and industrial areas.
Humans are primarily exposed to PCBs and PCNs through ingestion of contaminated foods like fish or inhalation.
In the University of Michigan study, researchers tested 19 residential, commercial, and industrial areas in Detroit for 32 types of PCNs and 37 types of PCBs in October and November of 2022.
The findings suggest that road dust near a scrap metal facility and residential soils in Detroit have higher concentrations of PCNs and PCBs when compared to similar tested areas in many other countries, such as China and Germany.
Batterman told Michigan Public that contamination levels are dependent on location.
“The study showed that in areas where soil had been replaced — for example, a baseball field — levels were really low,” Batterman said. “The problem happens to be near waste sites or waste piles that aren't really controlled, and those contaminants spread around and pose the risk of exposure. So removing these waste piles, characterizing the soils, covering them with clean fill, this is a way to control the problem.”
The study also suggests that the relatively high concentration of PCNs and PCBs in Detroit might be due to factors like the city's historical industrial activities, such as metal production and processing, manufacturing, and waste treatment and incineration.
The high concentrations can also result from emissions byproducts, waste management, landfilling, and improper disposal practices, according to the study. Lower concentrations of PCNs and PCBs seen in other countries tested may also be due to more effective pollution management strategies.
The study found that all the sites tested in Detroit exceeded Canada’s health-based toxic equivalency concentration for dioxins in agricultural soils. The sum of PCBs at every site also exceeded the World Health Organization’s guidelines for residential areas, while three sites near a Detroit metal scrap processor exceeded its guidelines for industrial areas.
The U.S. Environmental Protection Agency does not require action for PCB contamination unless more than one milligram of PCBs is present per kilogram of soil. Three Detroit sites’ levels exceeded this limit.
The EPA also requires removal and off-site disposal of PCB contamination that contains more than 10 milligrams of PCBs per kilogram of soil. In Detroit, two sites exceeded this limit, suggesting further investigation and remediation might be necessary, the researchers said.
Batterman said he hopes the study brings attention to PCN and PCB contamination in Detroit and motivates government officials to take action.
“I'd like to see some of the city and state offices pay more attention to contaminants in soil,” Batterman said. “We know the soil is the resting place for many of these contaminants. They just don't go away. They just stay in the soil. And so it's a long-term problem that we need to be aware of and, ultimately, to address so that we don't have exposure.”
