Discovery of bromochloropyrene reveals unexpected biological properties

Environmental pollutants containing chlorine or bromine have been widely studied, but compounds containing both elements have remained largely unexplored. Researchers have now detected bromochloropyrene in industrial soils and harbor sediments, investigated its breakdown under simulated sunlight, and measured its activity through a biological receptor linked to toxic effects. The findings reveal distinct environmental and biological properties, highlighting the need to investigate other mixed-halogen pollutants and improve future environmental monitoring and risk assessment.

Halogenated polycyclic aromatic hydrocarbons (HPAHs) are pollutants produced by combustion and found in soil and sediment. Some contain halogen atoms, such as chlorine or bromine. These compounds can persist and affect biological systems. However, research has largely examined compounds containing either chlorine or bromine, leaving those with both elements poorly understood.

Addressing this challenge, a research team led by Professor Takeshi Ohura, along with graduate student Natsuki Nasuda from the Graduate School of Agriculture, Meijo University, Japan, and Dr. Keerthi S. Guruge, Senior Researcher from the Division of Hygiene Management Research, National Institute of Animal Health, National Agriculture and Food Research Organization, synthesized a reference standard of bromochloropyrene (BrClPy)—a representative halomix—and analyzed surface soils from 20 sites along Tokyo Bay and sediments from three sites in Nagoya Port, Japan. They tested its stability under simulated sunlight and ability to activate the aryl hydrocarbon receptor (AhR). Their findings were made available online on September 22, 2026 and will be published in Volume 12, Issue 4 of the journal Emerging Contaminants on December 01, 2026.

BrClPy was detected in 10 of the 20 soil samples, at a mean concentration of 0.13 nanograms per gram. It was also found in one of the three sediment samples, where the mean concentration was 0.42 nanograms per gram. In soil, BrClPy concentrations were strongly correlated with brominated pyrene compounds, suggesting that its formation may be more closely linked to bromination-related processes than to chlorinated pyrene. This hybrid behavior suggests that hetero-halogenation produces emergent properties not predictable from either chlorine- or bromine-substituted PAHs alone.

Laboratory tests showed that BrClPy was less stable under simulated sunlight than chlorinated pyrene, with photostability approximately twofold lower than that of 1-chloropyrene. As it broke down, it mainly lost bromine, producing 1-chloropyrene; the researchers did not observe the corresponding product formed by losing chlorine. In a yeast-based test, BrClPy activated AhR with an estimated potency of 0.18 relative to benzo[a]pyrene. This activity was similar to dichloropyrene and about four to five times higher than dibromopyrene. BrClPy therefore appears to combine brominated compounds’ environmental behavior with chlorinated compounds’ biological activity.

“Our study provides the first evidence that BrClPy categorized hetero-halogenated PAHs are contaminated in real surface soils and sediments in urban cities,” said Prof. Ohura. “The distinct photolytic pathways and receptor interactions observed underscore the need for mechanistic studies.”

Monitoring may overlook mixed-halogen pollutants, and many related compounds may remain unidentified with unclear toxicity. Further research should examine their formation, environmental fate, and effects on living organisms. Such knowledge could improve estimates of human exposure and inform future environmental regulation.

“We hope the findings of this research influence the regulation of environmental pollutants and allow for more accurate estimation of human exposure risks and their associated effects,” said Prof. Ohura.

Overall, the study establishes BrClPy as a new class of environmental contaminant detected in industrial-area soils and harbor sediments. It also shows that its environmental breakdown and AhR activity do not simply mirror those of either brominated or chlorinated pyrene. The researchers call for further research into related compounds, their transformation pathways, and their biological effects to support more informed monitoring and environmental protection.

About Meijo University

Meijo University traces its origin back to the establishment of the Nagoya Science and Technology Course in 1926, giving it a proud history of more than 100 years. As one of the largest universities in the Chubu region, Meijo University is a comprehensive learning institution that supports a wide range of academic fields from the humanities to physical sciences. With a network of more than 200,000 graduates and alumni, it strives to contribute not only to local industries but also to international communities in various fields. Meijo University is also known as the birthplace of the carbon nanotube. To foster the human resources of the next generation, the university continues to tackle ongoing challenges by further enhancing its campus and creating new faculties.

Website: https://www.meijo-u.ac.jp/english/

About Professor Takeshi Ohura from Meijo University

Prof. Takeshi Ohura is a Professor at the Graduate School of Agriculture, Meijo University, Japan. He specializes in environmental chemistry and pollution. His pioneering research focuses on monitoring and analyzing hazardous contaminants. Specifically, he investigates the distribution and biological effects of polycyclic aromatic hydrocarbons (PAHs) in indoor and outdoor environments. As a leader in his field, he specializes in halogenated PAHs, including chlorinated and brominated compounds in air, sediments, and agricultural products like animal feedstuffs. His work includes comparative air quality studies examining volatile organic compounds (VOCs) across urban spaces and residential exposures.

Funding information

Japan Society for the Promotion of Science KAKENHI grant no. 23K21754 and 25K15471.