Reduction in polycyclic aromatic hydrocarbon exposure in Beijing following China's clean air actions
image:
Temporal trends of sources, ambient levels, and human exposure to PAHs following China’s clean air actions.
view moreCredit: ©Science China Press
PAHs are among the most important hazardous compounds present ubiquitously in the environment. As the largest emitter of PAHs, China accounted for over one fifth of the global PAHs emissions in 2007 – most of these emissions occurred in close proximity to general population (e.g., vehicular emissions). Substantial evidence has documented the presence of high levels of PAHs exposure in China, which was associated with a range of adverse health effects such as cancers, cardiovascular diseases and birth defects. While most of these studies were conducted before 2013, China has implemented the toughest-ever national clean air policies (i.e., APPCAP) in 2013-2017, followed by another national clean air plan of BSDW in 2018-2020. These efforts have unprecedentedly changed the anthropogenic emissions of combustion sources in China, but to what extent these actions have changed population exposure to PAHs is unknown.
In this study, a multidisciplinary team consisting of researchers from Peking University, University of California Los Angeles (UCLA), and Duke University has continuously monitored the ambient PAHs levels in Beijing from 2014 to 2021 and apportioned their major sources. The results indicated a remarkable decline of 96.6% in ambient PAH concentrations over 8 years. Greater reduction in PAHs concentrations was observed during the APPCAP phase owing to >80% emission reductions in traffic exhaust, coal combustion, and biomass burning. However, the decrease in ambient PAHs slowed down during the BSDW phase, because the reduction in coal and biomass emission were offset by flattened emissions from traffic sources. Furthermore, the results also supported the effectiveness of the clean heating renovation in 2017 in mitigating PAHs pollution, as evidenced by the drastic decrease in coal-originated PAHs during heating seasons from 2017 to 2018.
The team also bio-monitored PAHs exposure among five panels of UCLA students who traveled from Los Angeles to Beijing for 10 weeks in the summers of 2014-2018. The results indicated that the students’ exposure to PAHs were not changed in Los Angeles from 2014 to 2018, however, the PAHs exposure decreased by 52.3% in Beijing from 2014 to 2018, in associations with ambient concentrations of fine particles (PM2.5) or nitrogen dioxide (NO2). These results provide direct evidence demonstrating that air pollution control measures reduced human exposure to airborne toxins such as PAHs.
In this study, the team determines the effectiveness of air pollution control measures in reducing PAHs exposure using a natural experiment among international travelers, which allowed the use a country without such policies as control. Furthermore, the 8-year ambient monitoring also illustrated the changes of emission and ambient concentrations of PAHs, as two intermediate steps linking policy with human exposure. Taken together, this study provides compelling evidence to demonstrate the effectiveness of long-term air pollution control in reducing human exposure to PAHs. The unprecedented reduction in ambient PAH levels (by 97%) from 2014 to 2021 also highlights the need for future studies on the health effects of contemporary low-level PAH pollution in China.
Journal
Science Bulletin
Polycyclic Aromatic Hydrocarbon (PAH) concentration decreased by half after passing through the digestive tract of the marine worm
The purification ability of the marine worm in degrading PAHs in Tokyo Bay mud
Toho University
image:
Red circles in (A) and (B) show the location of the Yoro tidal flat. The dashed ellipse in (C) shows the sampling area, from where the fecal pellets of Marphysa sp. E were collected; reduced mud (RM) was collected from RM1, RM2, and RM3. (D) Image of the Yoro tidal flat (July 19, 2023).
view moreCredit: Dr. Atsuko Nishigaki
Dr. Atsuko Nishigaki and their research team from the Department of Environmental Science at the Faculty of Science, Toho University, discovered that the marine worm Marphysa sp. E (sensu Abe et al. 2019), an annelid living in the tidal flat sediments of Tokyo Bay, rapidly decreased the concentration of polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic environmental pollutants, by ingesting and excreting organic-rich reduced mud containing high concentrations of PAHs. The PAH concentration was halved within two hours.
Key Points:
- The annelid Marphysa sp. E selectively ingests and excretes reduced organic mud, which contains high concentrations of PAHs, persistent organic environmental pollutants.
- While the PAH concentration in the feces of the worms decreases by 46% within two hours, the concentration in the reduced mud decreases by only 8% during the same period.
- For the rapid degradation of PAHs, the reduced organic mud must pass through the digestive tract of the marine worm .
- The significant degradation of PAHs in worms’ feces appears to be linked to the microorganisms or enzymes present in the digestive tract of the marine worm . Marphysa sp. E is thought to play a significant role in the purification of tidal flat environments through its feeding and excretion behaviors.
Research Overview:
Benthic organisms living in tidal flat sediments are believed to contribute to material circulation in sediment environments by burrowing and feeding. A previous study reported that the feces of the annelid Marphysa sp. E , which resides in the tidal flat sediments of Tokyo Bay, contained high concentrations of PAHs that were halved within two hours of excretion. The study findings also revealed that the PAHs in the worms’ feces originated from reduced organic mud scattered in tidal flat sediments. Marphysa sp. E selectively ingested and excreted this reduced organic mud, which contained high concentrations of PAHs. The halving of the PAH concentration observed in worm feces within two hours was extremely rapid compared to the general half-life of PAHs in sediments, which ranges from several weeks to several months. However, whether this degradation activity could be attributed to the passage of the reduced organic mud through the digestive tract of Marphysa sp. E or if the reduced mud itself had degradation activity remained unclear. In this study, we examined the time-course changes in PAH concentrations in feces and reduced organic mud using gas chromatography-mass spectrometry (GC-MS), followed by a statistical analysis. The results showed that such a rapid decrease in the PAH concentration did not occur in the reduced mud itself; rather, it occurred when the mud passed through the digestive tract of Marphysa sp. E . Based on these findings, we concluded that Marphysa sp. E contributes to the environmental purification of Tokyo Bay by ingesting and excreting reduced organic mud containing high concentrations of PAHs.
Title:
Changes in the concentration of polycyclic aromatic hydrocarbons in fecal pellets of Marphysa sp. E and reduced mud in the Yoro tidal flat, Japan
(A) Reduced mud (marked by red dashed lines) is a black sediment with high viscosity scattered over a large area of the tidal flat. (B) A mound of fecal pellets of Marphysa sp. E excreted on the surface of the tidal flat.
Credit
Dr. Atsuko Nishigaki
Live coloration of Marphysa sp. E sensu Abe et al. (2019). (A) entire body, with its head towards right, (B) magnification of anterior end.
Source: Yuichiro Osaka, Satoshi Abe, Hirokazu Abe, Masaatsu Tanaka, Mayu Onozato, Kenji Okoshi, Atsuko Nishigaki, “Sources of Polycyclic Aromatic Hydrocarbons in Fecal Pellets of a Marphysa Species (Annelida: Eunicidae) in the Yoro Tidal Flat, Japan,” Zoological Science, 40(4), 292-299 (2023).
Changes in the concentration of polycyclic aromatic hydrocarbons in fecal pellets of Marphysa sp. E and reduced mud.
Credit
Atsuko Nishigaki
From left: Dr. Kenji Okoshi, Mr. Yuichiro Osaka, Dr. Mayu Onozato, Dr. Atsuko Nishigaki
Credit
Dr. Kenji Okoshi, Mr. Yuichiro Osaka, Dr. Mayu Onozato, Dr. Atsuko Nishigaki
DOI:
10.1016/j.marpolbul.2024.116977
Journal
Marine Pollution Bulletin
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Changes in the concentration of polycyclic aromatic hydrocarbons in fecal pellets of Marphysa sp. E and reduced mud in the Yoro tidal flat, Japan
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