The association between long-term exposure to low-level PM2.5 and mortality in the state of Queensland, Australia: A modelling study with the difference-in-differences approach.

Wenhua Yu,Shanshan Li,Yuming Guo,Liuhua Shi,Ellen Kirrane

doi:10.1371/journal.pmed.1003141

Wenhua Yu, Shanshan Li + Show 3 more

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https://doi.org/10.1371/journal.pmed.1003141

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Abstract

BackgroundTo date, few studies have investigated the causal relationship between mortality and long-term exposure to a low level of fine particulate matter (PM2.5) concentrations.Methods and findingsWe studied 242,320 registered deaths in Queensland between January 1, 1998, and December 31, 2013, with satellite-retrieved annual average PM2.5 concentrations to each postcode. A variant of difference-in-differences (DID) approach was used to investigate the association of long-term PM2.5 exposure with total mortality and cause-specific (cardiovascular, respiratory, and non-accidental) mortality. We observed 217,510 non-accidental deaths, 133,661 cardiovascular deaths, and 30,748 respiratory deaths in Queensland during the study period. The annual average PM2.5 concentrations ranged from 1.6 to 9.0 μg/m3, which were well below the current World Health Organization (WHO) annual standard (10 μg/m3). Long-term exposure to PM2.5 was associated with increased total mortality and cause-specific mortality. For each 1 μg/m3 increase in annual PM2.5, we found a 2.02% (95% CI 1.41%–2.63%; p < 0.01) increase in total mortality. Higher effect estimates were observed in Brisbane than those in Queensland for all types of mortality. A major limitation of our study is that the DID design is under the assumption that no predictors other than seasonal temperature exhibit different spatial-temporal variations in relation to PM2.5 exposure. However, if this assumption is violated (e.g., socioeconomic status [SES] and outdoor physical activities), the DID design is still subject to confounding.ConclusionsLong-term exposure to PM2.5 was associated with total, non-accidental, cardiovascular, and respiratory mortality in Queensland, Australia, where PM2.5 levels were measured well below the WHO air quality standard.

Highlights

Ambient particulate matter with diameters less than 2.5 micrometers has been identified as the fifth leading mortality risk factor in 2015, contributing to 4.2 million deaths [1]
We studied 242,320 deaths in 7 categories of diseases (ICD10: F00–F99, G00–G99, I00–I99, J00–J99, K00–K93, N00–N99, V01–Y98) from 1998 to 2013, which accounted for 60.5% of registered deaths during the study period
81.9% of deaths were over 65 years old and 50.8% were male

Summary

Introduction

Ambient particulate matter with diameters less than 2.5 micrometers (fine particulate matter; PM2.5) has been identified as the fifth leading mortality risk factor in 2015, contributing to 4.2 million deaths [1]. Causal model approaches seek to mimic randomized controlled trials, whereby exposure is measured independent of the other predictors of the health outcome. This effectively eliminates the possibility of confounding. Wang and colleagues employed a doubly robust causal modelling approach with inverse probability weights to estimate the hazards of long-term exposure to PM2.5 on survival in the southeast United States [9]. This method only accounts for measured confounders and unmeasured biases that are highly correlated with the measured confounders [10]. Few studies have investigated the causal relationship between mortality and longterm exposure to a low level of fine particulate matter (PM2.5) concentrations

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