This study comprehensively evaluated the risk associations between cause-specific ambulance services, extreme temperatures, and mass concentrations of PM2.5 and its constituents. The significant cold effects on chest pain and headache/dizziness/vertigo/fainting/syncope and heat effects on coma and unconsciousness and lying at public were observed, while the risk of ambulance services of OHCA was elevated in both extreme heat and cold environments. Ambulance services of respiratory distress, lying at public, and OHCA increased as the PM2.5 concentration increased, and the risk was significant at the PM2.5 concentration of 20–60 60 μg/m3 for ambulance services of lying at public and higher than 60 μg/m3 for respiratory distress. After controlling for effects of daily average temperature and PM2.5 concentration, this study still identified the significant effects of sulfate and EC on ambulance services of lying at public and OC on headache/dizziness/vertigo/fainting/syncope as the concentrations of PM2.5 constituents were at 90th percentile.
Limited studies assessed associations between ambulance calls and ambient environment9,13,19,22,23,24,25,26,27. Studies in Emilia-Romagna in Italy23, Brisbane in Australia26, Taiwan19, and Huainan and Luoyang in China22,24, have indicated the numbers of ambulance calls associated with extreme heat; the risks generally increase as the daily temperature exceeds 27 °C19,23,26. However, no consistent finding for cold threshold was identified19,28. Kaohsiung City has a tropical climate (daily temperature ranging from 13.5 °C to 31.5 °C), but it is cooler than cities located near the equator, e.g., Singapore and Manila. Except for ambulance service of OHCA, we found that the significant risks associated with temperature were only identified in environments with extreme temperatures (< 5th and > 90th percentiles; Fig. 3).
Fine particulate matter (PM2.5) are characterized with a small diameter (< 2.5 µm) that can carry various toxic substances and reach the end of the respiratory tract with airflow, accumulate by diffusion, and damage other parts of the body through air exchange in the lungs29. A China review reported that organic aerosols account for 20%–45% of PM2.5 at sites across China with seasonal and spatial variation11. However, as the Taiwan Environmental Protection Administration has declared Kaohsiung City with the worst air quality in Taiwan, particulate sulfate was identified as a primary variable to explain the PM2.5 concentration for this metropolitan10. This study observed that the proportions of PM2.5 constituents were 12.1% for nitrate, 28.2% for sulfate, 25.5% for OC, and 7.56% for EC (Supplementary Fig. S3).
The European Study of Cohorts for Air Pollution Effects (ESCAPE) reported that the hazard ratio of PM2.5 should be 1.14 (95% CI: 1.04–1.26) per 10 μg/m3 for all-cause mortality2. A Korean study reported that the OHCA risk increased for 1.30% after 1 to 2 days exposure to PM2.5 by an elevation of 10 μg/m330. Our previous study19 identified that ambulance events are associated with high concentrations of PM2.5 (about 90 μg/m3) and significantly elevate the ambulance care for respiratory distress and OHCA. Previous research evaluated the health risks associated with components of PM2.5 in recent years3,5,7,8,14,31,32,33. Most studies identified significant short-term effects of PM2.5 and its constituents at lag0-28,14,33. Particulate matter significantly increased emergency ambulance dispatched at lag0-1 day in Japan34, at lag 0 in Chengdu, China35, and Sydney, Australia36.
A Beijing study reported combustion-related PM2.5 constituents, such as secondary nitrate and sulfate that accounted for 45.9% PM2.5 mass concentration, had significant impacts on supraventricular premature beats and atrial tachycardia31. Meanwhile, two Shanghai studies reported that the risk of ischemic stroke hospitalization is significantly associated with previous day EC and heavy metal (Cr, Fe, Cu, Zn, As, Se, and Pb) concentrations33; moreover, the mortality risks of cardiovascular diseases associated with previous 2-day exposure of OC, sulfate, ammonia, potassium, and heavy metals (Cu, As, and Pb) with RRs ranging from 1.02 to 1.03 per interquartile increase14. After adjusting the total PM concentration, hospital admissions of cardiovascular diseases were significantly associated with EC and sulfate of PM2.5 at lag 0, and those of respiratory diseases were associated with sulfate at lag 0 and OC and EC at lag 18. On the basis of the findings of the present study and previous reports, the risks of total PM2.5 and its constituents could be observed at lag0-2.
A plausible mechanism may explain the short-term association between risk of cardiorespiratory diseases and components of PM2.5. One researcher found that elevated blood pressure is associated with ambient increased concentrations of OC, EC, nitrate, and ammonium in patients comorbid with chronic obstructive pulmonary disease37. In addition, the linkages between elevations of airway (fractional exhaled nitric oxide)32 and circulating inflammatory biomarkers (interleukin-8, tumor necrosis factor-α, and monocyte chemoattractant protein-1)38 and increased ambient concentrations of sulfate and potassium at lag 0–2 were identified and reported.
No significant association was reported in a long-term exposure-risk assessment for PM2.5 constituents (Cu, Fe, K, Ni, S, Si, V, and Zn) and mortality from cardiovascular diseases in a study involving 19 European cohorts (ESCAPE and TRANSPHORM projects)2,7. However, increased risks of dementia, Alzheimer’s disease, autism spectrum disorder, and Parkinson’s disease were significantly associated with long-term PM2.5 exposure with RR ranging from 1.16 to 3.2639. Migraines are a significant risk factor for Alzheimer’s disease and all‐cause dementia40. After adjusting the effects of daily temperature and PM2.5, this study identified that increased ambulance service of headache/dizziness/vertigo/fainting/syncope was significantly associated with concentrations of OC and EC. Future studies may discuss detailed biological mechanisms between PM2.5 constituents and neurological disorders.
The present study holds several strengths. Confounders, such as the holiday effect, day of the week, long-term trend, and risk associated with infectious pneumonia and influenza, and effects of daily temperature and total PM2.5 level were considered in the data analysis models. Risk of cause-specific ambulance services associated with daily concentrations of PM2.5 components was evaluated using continuous hourly monitored data. To date, the risk of ambulance service associated with concentrations of PM2.5 components requires further study. The findings from this study can be the ground information to minimize the response time of allocation ambulance services, by knowing which variables should be observed and forecasted in the future41. In addition, the individuals can adapt their behavior to enhance health and resilience against the negative impacts from temperature and concentrations of mass and constituents of PM2.5.
This study also had several limitations. First, our work is an ecological study. Risk was not estimated with individual-based data. Given the lack of information on personal disease history, medicine usage, behaviors of drinking and exercise, and accessibility of medical services, we did not evaluate modifying effects (e.g., socio-economic status) on risk associated with the ambulance events. Cases’ diagnoses in the medical records of ambulance dispatches were based on observations made by medical personnel, and no ICD codes were provided. In addition, this study did not exclude the complicated conditions of ambulance services, including delayed arrival time, restricted service time, and a location hard to reach. Moreover, this study did not collect ions and heavy metal data of gases and aerosols during the study period, so these effects were not evaluated.
Understanding the short-term risk association between ambulance services and ambient environment is a critical concern for organizers of outdoor activities, especially in extreme temperatures and high air pollution events. The present study provides scientific evidence that, other than mortality from and morbidity of cardiorespiratory diseases3,5, cause-specific ambulance services, even for general health symptoms like headache/dizziness/vertigo/fainting/syncope, are associated with concentrations of PM2.5 constituents after adjusting the effects of daily temperature and total PM2.5 level. This study agreed with a review report3, who reported that EC has stronger association with health risks that means elevation of ambulance service in the present study. We also agree that constituents and its proportion of PM2.5 vary with the study area, thus, health risk assessment for various health outcomes and area are recommended1,2.
Source: Ecology - nature.com
