The epidemiological evidence on the interaction between heat and ambient air pollution on mortality is still inconsistent. To investigate the interaction between heat and ambient air pollution on daily mortality in a large dataset of 620 cities from 36 countries. We used daily data on all-cause mortality, air temperature, particulate matter ≤ 10 μm (PM₁₀), PM ≤ 2.5 μm (PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃) from 620 cities in 36 countries in the period 1995-2020. We restricted the analysis to the six consecutive warmest months in each city. City-specific data were analysed with over-dispersed Poisson regression models, followed by a multilevel random-effects meta-analysis. The joint association between air temperature and air pollutants was modelled with product terms between non-linear functions for air temperature and linear functions for air pollutants. We analyzed 22,630,598 deaths. An increase in mean temperature from the 75^th to the 99^th percentile of city-specific distributions was associated with an average 8.9 % (95 % confidence interval: 7.1 %, 10.7 %) mortality increment, ranging between 5.3 % (3.8 %, 6.9 %) and 12.8 % (8.7 %, 17.0 %), when daily PM₁₀ was equal to 10 or 90 μg/m³, respectively. Corresponding estimates when daily O₃ concentrations were 40 or 160 μg/m³ were 2.9 % (1.1 %, 4.7 %) and 12.5 % (6.9 %, 18.5 %), respectively. Similarly, a 10 μg/m³ increment in PM₁₀ was associated with a 0.54 % (0.10 %, 0.98 %) and 1.21 % (0.69 %, 1.72 %) increase in mortality when daily air temperature was set to the 1^st and 99^th city-specific percentiles, respectively. Corresponding mortality estimate for O₃ across these temperature percentiles were 0.00 % (-0.44 %, 0.44 %) and 0.53 % (0.38 %, 0.68 %). Similar effect modification results, although slightly weaker, were found for PM_2.5 and NO₂. Suggestive evidence of effect modification between air temperature and air pollutants on mortality during the warm period was found in a global dataset of 620 cities.

Introduction: Air pollutants are classified as carcinogens by the International Agency for Research on Cancer. Long-term exposure to ambient particulate matter with an aerodiameter of 2.5 μm or lower (PM2.5) has been reported to be linked with increased mortality due to hepatocellular carcinoma (HCC). However, the effects of air pollutants other than PM2.5 on HCC-related mortality have not been fully investigated. Accordingly, we conducted this study to assess the effect of long-term exposure to air pollutants (PM2.5 and nitrogen dioxide [NO2]) on HCC-related mortality. Method: In 2005, the Taiwan Liver Cancer Network (TLCN) was established by the National Research Program for Genomic Medicine to recruit liver cancer patients from 5 major medical centers in northern, central, and southern Taiwan. The TLCN had successfully recruited 9,344 patients by the end of 2018. In this study, we included 1,000 patients randomly sampled from the TLCN to assess the effect of exposure to air pollutants on HCC mortality after HCC diagnosis. Daily averages of PM2.5 and NO2 concentrations were retrieved from 77 air quality-monitoring stations and interpolated to the townships of patients’ residences by using the Kriging method. The effect of air pollutants on HCC survival was assessed using a Cox proportional hazards model. Results: A total of 940 patients were included in the analysis. After adjusting for potential confounders and mutually adjusting for co-pollutants, we observed that the hazards ratio (95% confidence interval) for HCC-related mortality for every 1-μg/m3 increase in PM2.5 concentration was 1.11 (1.08–1.14) and that for every 1-ppb increase in NO2 concentration was 1.08 (1.03–1.13). Conclusion: Our study suggests that long-term exposure to PM2.5 and NO2 was associated with decreased survival time in patients with HCC in Taiwan.

Temperature variability (TV) is associated with increased mortality risk. However, it is still unknown whether intra-day or inter-day TV has different effects. We aimed to assess the association of intra-day TV and inter-day TV with all-cause, cardiovascular, and respiratory mortality. We collected data on total, cardiovascular, and respiratory mortality and meteorology from 758 locations in 47 countries or regions from 1972 to 2020. We defined inter-day TV as the standard deviation (SD) of daily mean temperatures across the lag interval, and intra-day TV as the average SD of minimum and maximum temperatures on each day. In the first stage, inter-day and intra-day TVs were modelled simultaneously in the quasi-Poisson time-series model for each location. In the second stage, a multi-level analysis was used to pool the location-specific estimates. Overall, the mortality risk due to each interquartile range [IQR] increase was higher for intra-day TV than for inter-day TV. The risk increased by 0.59% (95% confidence interval [CI]: 0.53, 0.65) for all-cause mortality, 0.64% (95% CI: 0.56, 0.73) for cardiovascular mortality, and 0.65% (95% CI: 0.49, 0.80) for respiratory mortality per IQR increase in intra-day TV_0-7 (0.9 °C). An IQR increase in inter-day TV_0-7 (1.6 °C) was associated with 0.22% (95% CI: 0.18, 0.26) increase in all-cause mortality, 0.44% (95% CI: 0.37, 0.50) increase in cardiovascular mortality, and 0.31% (95% CI: 0.21, 0.41) increase in respiratory mortality. The proportion of all-cause deaths attributable to intra-day TV_0-7 and inter-day TV_0-7 was 1.45% and 0.35%, respectively. The mortality risks varied by lag interval, climate area, season, and climate type. Our results indicated that intra-day TV may explain the main part of the mortality risk related to TV and suggested that comprehensive evaluations should be proposed in more countries to help protect human health.

The neurotoxic effects of certain heavy metals are well established, but only a few studies have investigated the joint effect of concurrent exposure to multiple ones. The study aims to evaluate the association between mixed exposure to neurotoxic metals and the psychosocial behavior of preschool children. Using a stratified sampling strategy, we recruited participants from 105 kindergartens in 41 townships of Taiwan and excluded those with blood lead levels ≥ 3.5 µg/L. The first-morning void urines were collected and analyzed for cadmium, manganese, arsenic, chromium, lead, and nickel concentrations using inductively coupled plasma mass spectrometry. We applied the parentally reported Strengths and Difficulties Questionnaire (SDQ) and Swanson, Nolan, and Pelham IV (SNAP-IV) scales to evaluate the psychosocial behaviors. Multiple linear regressions were utilized to evaluate the associations between each heavy metal and the outcomes, while the mixed effect of concurrent exposure was estimated by using a Quantile g-computation approach. A total of 977 preschool children were included in the study, and the mean (SD) age was 5.7 (0.7) years old. In single pollutant models, we observed adverse effects of urinary manganese, nickel, arsenic, and lead on the specific subsets of SDQ. Furthermore, the combined effect of six heavy metals significantly affected the hyperactivity/inattention symptoms (beta = 0.46, 95% CI: 0.13-0.78, with all metals increased by one quartile), and chromium and lead were the two major contributors. Similar detrimental effects of urinary cadmium and lead were also observed in the SNAP-IV subsets, although the joint effect analysis was not significant. The study provided evidence that concurrent exposure to multiple heavy metals may exert increased risks of hyperactivity/inattention in children compared to single pollutant exposure. Further studies are needed to verify our findings regarding mixed exposure to multiple neurotoxic metals.