Associations between long-term exposure to wildfire-related particulate matter and site-specific cancer mortality: a national study in Brazil, 2010–16

Abstract

With the increasing frequency and duration of wildfires over the past 10 years, the effects of wildfire on health need to be better understood. Long-term exposure to particulate matter less than 2·5 μm in diameter (PM2·5) has been linked to cancer mortality. However, the long-term effects of wildfire-related PM2·5 exposure on cancer mortality risk were unknown. The aim of this study was to assess the association between wildfire-related PM2·5 and cancer mortality in Brazil on the basis of nationwide death records for the period of 2010-16. Nationwide cancer death records for the period of January 1 to December 31, 2010-16 were collected and linked with municipal-level, wildfire-related and non-wildfire-related PM2·5 concentrations at a 2·0° latitude by 2·5° longitude resolution. We applied a difference-in-difference approach with quasi-Poisson regression for data analysis. Relative risks (RRs) and 95% CIs for the exposure on specific cancer sites were estimated, and attributable fractions and cancer deaths were also calculated. 1 332 526 cancer deaths in adults (ie, individuals aged 20 years or older) from 5565 Brazilian municipalities covering a population of 136 million adults were included. The annual wildfire-related PM2·5 concentration was 2·38 μg/m3 and the non-wildfire-related PM2·5 was 8·20 μg/m3. The RR for mortality from all cancers was 1·02 (95% CI 1·01-1·03) per μg/m3 increase of wildfire-related PM2·5 concentration, which was higher than other sources of PM2·5 (1·01 [1·00-1·01]; p=0·0029). Wildfire-related PM2·5 was associated with higher mortality from cancers of the nasopharynx (RR 1·10 [95% CI 1·04-1·16]; p=0·0015), oesophagus (1·05 [1·01-1·08]; p=0·012), stomach (1·03 [1·01-1·06]; p=0·017), colon and rectum (1·08 [1·05-1·11]; p<0·0001), larynx (1·06 [1·02-1·11]; p=0·0031), skin (1·06 [1·00-1·12]; p=0·033), breast (1·04 [1·01-1·06]; p=0·0074), prostate (1·03 [1·01-1·06]; p=0·019), and testis (1·10 [1·03-1·17]; p=0·0022). For all-cancers combined, the attributable deaths were 37 per 100 000 people during the study period. Long-term exposure to wildfire-related PM2·5 can increase the risk of cancer mortality at various sites. The effect was greater for wildfire-related PM2·5 than for PM2·5 from other sources. Australian Research Council and National Health & Medical Research Council; China Scholarship Council.