Naohide Shinohara

The growing demand for plastic recycling has increased the use of mechanically recycled plastics as secondary feedstocks. However, systematic data on the elemental composition of recycled plastic pellets remain limited. This study investigated inorganic element concentrations in 38 recycled plastic pellet samples collected from nine recycling facilities in Japan. Elemental concentrations were measured using portable X-ray fluorescence, and statistical analyses evaluated variability and differences among feedstock origins and washing-process categories. Eight elements (Ca, Ti, Fe, Ni, Cu, Zn, Sr, and Pb) were detected in more than 50% of the samples and selected for further analyses. Several elements exhibited concentration ranges spanning multiple orders of magnitude. Significant differences in some elemental concentrations were observed among feedstock origins and washing-process categories. Spearman’s correlation analysis showed a strong positive correlation between Ti and Sr and strong negative correlations between Pb and both Ti and Sr. Factor analysis identified three factors accounting for 66.1% of the total variance, characterized primarily by Ti–Sr–Pb, Cu–Fe–Ni, and Ca–Fe–Zn associations. These results demonstrate substantial variability in the elemental composition of mechanically recycled plastic pellets and suggest that elemental profiles may provide useful supplementary information for chemical safety assessment, quality control, and material traceability.

Background: Reproduction numbers (R0 and Rt) are widely used to characterize transmissibility, but provide limited information regarding the transmission routes and environments underlying epidemic spread. Infection risks associated with respiratory infectious diseases vary substantially across transmission routes (droplets, fomites, and aerosols), and the effectiveness of preventive interventions depends on these differences. At the population level, transmission dynamics arise from the aggregation of infection risks across multiple transmission routes and microenvironments, yet no framework currently links these route-specific risks to population-level reproduction numbers in a mechanistic manner.Methods: We developed a mechanistic risk–reproduction framework (MRRF) linking route–specific infection risks across multiple respiratory transmission routes and microenvironments to population–level reproduction numbers. Individual infection risk was calculated considering groups, environments, distances, transmission routes, and exposure reduction interventions. The reproduction number was formulated mechanistically from individual infection risks. Parameters related to SARS-CoV-2 characteristics were used as inputs.Findings: The basic reproduction number increased with pathogen concentration, and presymptomatic transmission became dominant at higher viral concentrations. In addition, dominant transmission environments and routes shifted from home to workplace and community settings, from near-field to far-field transmission, and from droplet to aerosol transmission as viral concentration increased. The inferred transmission patterns were broadly consistent with epidemiological characteristics subsequently reported for SARS-CoV-2 and its variants. The framework also enabled quantitative estimation of intervention effectiveness and showed that single interventions were insufficient to reduce Rt below 1 at higher pathogen concentrations.Interpretation: These findings suggest that reproduction numbers may contain information regarding underlying transmission routes, environments, and intervention targets in respiratory infectious diseases, rather than serving solely as indicators of transmissibility. Mechanistic decomposition of reproduction numbers may support interpretation of epidemic dynamics and inform the selection of effective interventions during emerging respiratory infectious disease outbreaks.

Concerns regarding the health risks associated with employe exposure to volatile chemicals during gasoline refueling necessitates rigorous investigation and effective countermeasures. This study aims to evaluate the efficacy of vapor recovery systems in mitigating exposure risks during gasoline refueling. Employee exposure to volatile organic compounds, aldehydes, carbon monoxide, and fine particulate matter (PM_2.5) was assessed at gasoline stations with and without vapor recovery systems. Three stations each from the State of Mexico and Mexico City, equipped with gasoline vapor recovery systems, were compared with three stations in Guadalajara lacking such systems. The exposure concentrations (mean ± standard deviation) to benzene in Guadalajara, the State of Mexico, and Mexico City were 45 ± 29, 24 ± 20, and 18 ± 15 μg/m³, respectively, which were significantly higher than the background atmospheric concentrations at 1.6 ± 0.56, 0.72 ± 0.083, and 0.65 ± 0.14 μg/m³, respectively. Similarly, the exposure concentrations of toluene, ethylbenzene, and xylenes at gasoline stations were significantly higher than the background atmospheric concentrations. However, the exposure concentrations of formaldehyde and PM_2.5 were similar to the background atmospheric concentrations. The excess cancer risks due to benzene exposure were estimated at 1.2–4.2 × 10⁻⁵, 0.63–2.2 × 10⁻⁵, and 0.46–1.6 × 10⁻⁵ (mean) and 0.42–1.5 × 10⁻⁴, 0.29–1.0 × 10⁻⁴, and 2.4–8.6 × 10⁻⁵ (maximum) in Guadalajara, the State of Mexico, and Mexico City, respectively. The risk to employees in gasoline stations was reduced by 47–61% in service stations with gasoline vapor recovery systems.

To evaluate the COVID-19 infection risk and the effectiveness of countermeasures at mass-gathering events, we measured the dispersion and advective diffusion of artificial droplets and artificial droplet nuclei at the Tokyo Dome, Japan (capacity 55,000 people). We also measured and evaluated the effectiveness of wearing masks and increasing the space between seating areas. If people were seated facing forward, artificial droplets did not reach the mouths of surrounding people, suggesting low risk of droplet transmission. For an artificially generated cough or sneeze, the volume of droplets deposited on the hair, back of the neck, and back of the human in front, and the backs of the seats in front, decreased by two to three orders of magnitude when a mask was worn, regardless of the type of mask. However, when the mask was worn with the nose out, the amount deposited on the back of the seat in front was reduced by only 17%. Even in seats with the highest particle concentration in the vicinity of the source, only 0.097%–0.24% of the generated droplet nuclei (1.0–3.0 μm) from the source were inhaled. Our results suggest that the infection risk at the Tokyo Dome via droplet and airborne transmission was low.

Indoor dampness can promote the establishment of microbes in indoor environments, and as such, controlling dampness is important for maintaining a healthy indoor environment. Here, an index is proposed for evaluating indoor dampness based on checking for visible condensation, mold in living rooms and bedrooms, and moldy odors indoors. In this evaluation method, eight items related to visible condensation, presence of mold, and moldy odors are assigned a maximum score of 3 points; the total score (a maximum of 24 points) is then used as an index for the degree of dampness. We classified the total score into four rankings based on quartiles. Rank 4 represents the lowest rank and was assigned to houses that had the most severe levels of indoor dampness. We hypothesized that the lower the rank, the higher the incidence of sick housing syndrome (SHS) would be among young children. To clarify whether there was an association between child SHS and indoor dampness, we conducted an Internet-based cross-sectional survey on children aged 4–12 years. This study first identified potential confounding variables for exposure to indoor dampness using a directed acyclic graph. The results indicated that the higher the degree of dampness, the higher the health risk was for ocular, nasal, and throat symptoms. Dose-response relationships between indoor dampness and SHS were presented using the dampness index proposed in this study.