Urinary mutagenicity and other biomarkers of occupational smoke exposure of wildland firefighters and oxidative stress

Abstract

Background: Wildland firefighters conducting prescribed burns are exposed to a complex mixture of pollutants, requiring an integrated measure of exposure. Objective: We used urinary mutagenicity to assess if systemic exposure to mutagens is higher in firefighters after working at prescribed burns versus after non-burn work days. Other biomarkers of exposure and oxidative stress markers were also measured. Methods: Using a repeated measures study design, we collected urine before, immediately after, and the morning after a work shift on prescribed burn and non-burn work days from 12 healthy subjects, and analyzed for malondialdehyde (MDA), 8-isoprostane, 1-hydroxypyrene (OH-pyrene), and mutagenicity in Salmonella YG1041 +S9. Particulate matter (PM_2.5) and carbon monoxide (CO) were measured by personal monitoring. Light-absorbing carbon (LAC) of PM_2.5 was measured as a surrogate for black carbon exposure. Linear mixed-effect models were used to assess cross-work shift changes in urinary biomarkers. Results: No significant differences occurred in creatinine-adjusted urinary mutagenicity across the work shift between burn days and non-burn days. Firefighters lighting fires had a non-significant, 1.6-fold increase in urinary mutagenicity for burn versus non-burn day exposures. Positive associations were found between cross-work shift changes in creatinine-adjusted urinary mutagenicity and MDA (p = 0.0010), OH-pyrene (p = 0.0001), and mass absorption efficiency which is the LAC/PM_2.5 ratio (p = 0.2245), respectively. No significant effect of day type or work task on cross-work shift changes in MDA or 8-isoprostane was observed. Conclusion: Urinary mutagenicity may serve as a suitable measure of occupational smoke exposures among wildland firefighters, especially among those lighting fires for prescribed burns.

Keywords: Mutagenicity; particulate matter; prescribed burns; wildland fire smoke; wildland firefighters; wood smoke; work task.

Figures 1(a-d).. Adjusted Cross-Work Shift Changes in Crude and Creatinine-adjusted Urinary Mutagenicity Concentrations according to Day Type.

Pre- to post-work shift changes are depicted in Figs. 1a and 1b. Pre to morning-after (MA) work shift changes are depicted in Figs. 1c and 2d. No significant difference was observed between burn day and non-burn day samples for all figures. Note: n= person-day pre-post paired or pre-MA paired samples, respectively; Cross-work-shift changes are reported as post-work-shift/pre-work-shift ratios or morning-after-work-shift/pre-work-shift ratios, respectively. Where 95% confidence limits do not cross the x-axis, cross-work-shift changes are statistically different from 1 (p-values < 0.05).

Figures 2(a-d).. Adjusted Cross-Work Shift Changes in Crude and Creatinine-adjusted Urinary Mutagenicity Concentrations according to Work Tasks.

Pre-to post-work shift changes are depicted in Figs. 2a and 2b. Pre to morning-after (MA) work shift changes are depicted in Figs. 2c and 2d. No significant difference was observed across work tasks for all figures. Note: n= person-day pre-post paired or pre-MA paired samples, respectively; Cross-work-shift changes are reported as post-work-shift/pre-work-shift ratios or morning-after-work-shift/pre-work-shift ratios, respectively. Where 95% confidence limits do not cross the x-axis, cross-work-shift changes are statistically different from 1 (p-values < 0.05).

Figures 3(a-d).. Adjusted Cross-Work Shift Changes in Crude and Creatinine-adjusted Urinary Malondialdehyde Concentrations according to Day Type.

Pre- to post-work shift changes are depicted in Figs. 3a and 3b. Pre to morning-after (MA) work shift changes are depicted in Figs. 3c and 3d. No significant difference was observed between burn day and non-burn day samples for Figs. 3a, 3b, or 3d, however marginal significant differences were observed in Fig. 3c (p-value <0.05 was considered significant). Note: n= person-day pre-post paired or pre-MA paired samples, respectively; Cross-work-shift changes are reported as post-work-shift/pre-work-shift ratios or morning-after-work-shift/pre-work-shift ratios, respectively. Where 95% confidence limits do not cross the x-axis, cross-work-shift changes are statistically different from 1 (p-values < 0.05).

Figures 4(a-d).. Adjusted Cross-Work Shift Changes in Crude and Creatinine-adjusted Urinary Malondialdehyde Concentrations according to Work Tasks.

Pre-to post-work shift changes are depicted in Figs. 4a and 4b. Pre to morning-after (MA) work shift changes are depicted in Figs. 4c and 4d. No significant difference was observed across work tasks for all figures. Note: n= person-day pre-post paired or pre-MA paired samples, respectively; Cross-work-shift changes are reported as post-work-shift/pre-work-shift ratios or morning-after-work-shift/pre-work-shift ratios, respectively. Where 95% confidence limits do not cross the x-axis, cross-work-shift changes are statistically different from 1 (p-values < 0.05).

Figure 5.. Correlation between Log-transformed Cross-Work Shift (Pre- to Post-) Changes in Creatinine-adjusted Urinary Mutagenicity and Log-transformed Creatinine-adjusted MDA.

Person days are indicated as n. Linear mixed effect model results showed a positive significant correlation (p = 0.0010).

Figure 6.. Correlation between Log-transformed Cross-Work Shift (Pre- to Post-) Changes in Creatinine-adjusted Urinary Mutagenicity and Log-transformed Creatinine-adjusted OH-Pyrene.

Person days are indicated as n. Linear mixed effect model results showed a positive significant correlation (p = 0.0001).

Figure 7.. Correlation between Arcsine-square root Transformed Mass Absorption Efficiency (Surrogate for Black Carbon/PM_2.5 Ratio) and Log-transformed Cross-Work Shift (Pre- to Post-) Changes in Creatinine-adjusted Urinary Mutagenicity.

Person days are indicated as n. Linear mixed effect model results showed a cluster of data by work task and a positive (though not significant) correlation (p=0.2245).