In vitro assessment oral and respiratory bioaccessibility of Mn in school dust: Insight of seasonality in a semiarid environment

In school environments in the Sonoran Desert, dust contains anomalously high manganese (Mn) of geogenic origin, similar to those reported at industrial sites. Non-carcinogenic risk assessment for children exposed to Mn was estimated for two sampling seasons (pre-monsoon, post-monsoon). We determined the total Mn content in school dust samples by portable X-ray fluorescence (PXRF), and we used geochemical indices for Mn-source apportionment. We identified dust mineralogy by X-ray diffraction (XRD). We obtained the oral and lung bioaccessibility by in vitro tests. The results showed a much higher total Mn content (1725.7 mg.kg(-1)) in the <20 mu m school dust size fraction in the pre-monsoon season compared to the average value post-monsoon (582.9 mg.kg(-1)). Moreover, in pre-monsoon season, the estimated hazard quotient (HQ) and hazard index (HI) for Mn were higher than 1, representing a potential health risk. Mn's oral and lung bioaccessibility also differed significantly between the sampling seasons, but the behavior was opposite to total Mn-content. The maximum gastric/intestinal bioaccessibility for Mn ranged from 10.6/1.7 pre-monsoon to 28.5/9.0% post-monsoon. In the simulated lung fluid, the maximum bioaccessibility of Mn ranged from 15.6% pre-monsoon to 64.1% postmonsoon. This variability was probably due to differences in Mn mineralogy (todorokite in pre-monsoon dust; an unknown phase in post-monsoon dust). Our results show that it is necessary to integrate seasonal sampling into risk assessment in arid zones worldwide, where dust resuspension processes commonly occur.

Automated summary

In school environments in the Sonoran Desert, dust contains anomalously high manganese (Mn) of geogenic origin, and non-carcinogenic risk assessment for children exposed to Mn showed potential health risks. Seasonal sampling revealed differences in manganese bioaccessibility and health hazards, highlighting the importance of considering seasonal factors in risk assessment in arid zones.