Assessment of the mutagenicity of two common indoor air pollutants, formaldehyde and toluene

Abstract

Traditionally, direct‐reading instruments have been used to directly determine the concentrations of indoor air pollutants that may exceed the regulation limits. However, these instruments cannot directly assess the potential health hazards of these pollutants to humans. In this study, we developed and improved a bacterial reverse mutation assay (Ames test) by using a direct gas exposure module to directly determine the mutagenicity of indoor air quality using five tester bacterial strains (TA98, TA100, TA102, TA1535, and TA1537). Thereafter, the module was used to evaluate the effects of exposure time, different concentrations of HCHO or toluene, and mutagenic activities. We found that TA100 was the most sensitive strain and was reverted by relatively lower concentrations of 0.035 ppm HCHO. Furthermore, 50 ppm of toluene exposures caused a significant increase in the number of revertant colonies of TA100 without S9 activation at the 1.5–8‐h exposure time intervals. Our findings provide new evidence that gaseous HCHO exposure could display weak but direct, time‐dependent, and dose‐dependent mutagenic activities. The weak, direct‐acting, indirect‐acting, and time‐dependent mutagen of 50 ppm toluene was also confirmed. Moreover, our improved Ames module and the exposure conditions provided in this study can be further applied to evaluate the mutagenicity of indoor air quality.

Development and application of the Ames test using a direct‐exposure module: The assessment of mutagenicity of incense and sidestream cigarette smoke

“…Toxic and mutagenic effects probably coexisted in the TA100 exposed to IS of 24–36 incense sticks, and the mutagenic effects may balance the toxicity. Our previous study also confirmed that long‐term HCHO or toluene exposure (14 h) could lead to toxic effects on tester TA100 26 . Early studies have reported that HCHO solution displayed toxic effects on specific tester strains, such as TM677 or Escherichia coli , 40,41 thereby partially supporting the above finding.…”

“…Thus, we speculate that the long-term exposure of this IS to TA100 may also contribute to toxic effects, as demonstrated from the toxic effect of HCHO exposure to TA00 in our previous report. 26 Furthermore, a dose-response effect was observed when the tester strain was exposed to IS of 6 and 12 incense sticks for 10 min in the presence of metabolic activation (Table 6), which was consistent with the IS of 3 and 6 incense sticks for 30 and 60 min, respectively. Additionally, a weak but significant time-response effect was observed when the tester strain was exposed to IS of 3 and 6 incense sticks at 10- relatively stronger mutagenic activities than that of brand A.…”

“…Our previous study showed that TA100 is the most sensitive strain and is reverted by relatively low concentrations of 0.035 ppm HCHO, which causes weak mutagenic activities when continued for 1.5 h. Furthermore, we demonstrated that 0.035, 0.175, 0.35, and 2.8 ppm HCHO caused significant increases in the number of revertant colonies of TA100 during the 0.5‐ to 8‐h exposure intervals, which could cause the highest ~(1.99‐fold) increase in revertant colonies relative to the control samples treated with 2.8 ppm HCHO, especially for 8 h exposure 26 . In comparison, HCHO levels in the IS of the present study were 0.4–1.96 ppm, and TA100 was exposed to IS for 10–60 min.…”

“…Our previous study also confirmed that long-term HCHO or toluene exposure (14 h) could lead to toxic effects on tester TA100. 26 Early studies have reported that HCHO solution displayed toxic effects on specific tester strains, such as TM677 or Escherichia coli, 40,41 thereby partially supporting the above finding. Furthermore, we recognized the highest numbers and SD of the revertant colonies, when TA100 was exposed to IS of the 36-incense stick group either with or without S9 enzyme activation.…”

“…Moreover, a fan was placed at the bottom of the desiccator to mix the gaseous sample well, which improved the consistency and reproducibility of revertant colonies from the repeated tests, as indicated in our previous work. 26 The prepared Petri dishes containing TA100 were then loosely stacked on the ceramic shelf, the desiccator was sealed, and air was evacuated using a pump. The gaseous samples of the negative control (filtered air) and the IS or SCS samples were placed in the desiccator until atmospheric pressure was reached.…”