Co-Exposure to Noise, N,N-Dimethylformamide, and Toluene on 24-Hour Ambulatory Blood Pressure in Synthetic Leather Workers

Abstract

Independent exposure to noise, N,N-dimethylformamide (DMF), or toluene has been associated with cardiovascular effects, but the combined effects are not clear. This study investigated ambulatory systolic blood pressure (SBP) and diastolic blood pressure (DBP) in workers co-exposed to noise, DMF, and toluene. Twenty workers in a synthetic leather manufacturing company were recruited as study subjects. Personal noise exposure and ambulatory blood pressure were measured concomitantly for 24 hr; airborne co-exposure to DMF and toluene during the working period was also analyzed to identify solvents exposure. Linear mixed-effects regressions were used to estimate effects on ambulatory blood pressure by controlling potential confounders. Four high-combined-exposure workers (83 ± 8 dBA; DMF: 3.23 ± 2.15 ppm, toluene: 1.09 ± 1.13 ppm) had the higher means of 16 ± 7 mmHg in 24-hr DBP (p = 0.027) and 21 ± 8 mmHg in working-time DBP (p = 0.048) than seven low-combined-exposure workers (73 ± 12 dBA; DMF: 0.41 ± 0.02 ppm, toluene: 0.12 ± 0.01 ppm). Three high-noise-exposure workers (84 ± 7 dBA) also had a marginal increase of 13 ± 6 mmHg in DBP at work (p = 0.076) compared with the control group. No significant differences in SBP and DBP were found between six high-solvent-exposure workers (DMF: 1.24 ± 1.25 ppm, toluene: 2.63 ± 1.29 ppm) and office workers during any periods. After the Bonferroni correction, there were no significant differences in ambulatory blood pressure between three high-exposure groups and the low-exposure groups. Our findings suggest no interactive effects of co-exposure to noise, DMF, and toluene on workers' ambulatory blood pressure.

Keywords:

• ambulatory blood pressure
• co-exposure
• N,N-dimethylformamide
• occupational noise
• toluene

ACKNOWLEDGMENTS

We thank the National Science Council, Taiwan (NSC 94-2211-E-039-005 and NSC 94-2211-E-039-006) and China Medical University (CMU94-085) for the financial support. We also thank all individuals who participated in this study, and the graduate students who assisted with airborne sampling in the workplace. In addition, we would like to thank Dr. Yu-Fen Li who supports the statistical consultation with data analyses.

Notes

^A Kruskal-Wallis test of the difference among four groups.

^B Mann-Whitney test of the difference between exposure groups and the low-combined-exposure group.

^C Chi-square test of the difference among four groups.

^D Fisher's exact test of the difference between exposure groups and the low-combined-exposure group.

* p < 0.10

** p < 0.05.

^A Linear mixed-effects regression models were used to test the differences between exposure groups and the low-combined-exposure group (reference).

^B Statistical significance before the Bonferroni correction (p < 0.050).

^C Statistical significance after the Bonferroni correction (p < 0.017).

^A Mann-Whitney test of the difference between exposure groups and the low-combined-exposure group.

^B Kruskal-Wallis test of the difference among four groups.

^A Linear mixed-effect regression models adjusted for age, body mass index, regular exercise, working activity, smoking, coffee consumption, and family history of hypertension were used to test the differences between exposure groups and the low-combined-exposure group.

^B Statistical significance before the Bonferroni correction (p < 0.050).