Arsenic bioavailability and transformation from As(V)-sorbed aluminum oxides: The influence of Fe(III) and human gut microbiota

Minerals control on the oral bioavailability of arsenic (As) in soil has been evidenced in human health risk assessments. However, little is known about the metabolism of soil mineral-associated As by human gut microbiota. This study evaluated the relative bioavailability (RBA) and bioaccessibility of As in As(V)-sorbed Aluminum (Al) oxides (α-Al₂O₃ and γ-Al₂O₃), affected by gut microbiota and Fe(III). The in vitro method yielded higher As bioaccessibility in the small intestinal phase of α-Al₂O₃ (30.3 %–54.8 %) and in the colon phase of γ-Al₂O₃ (29.7 %–45.6 %), respectively. In the presence of Fe, As release was decreased by14.5 %–48.1 % in the small intestine but increased by 37.5 %–86.3 % in the colon (p < 0.05). Speciation analysis revealed that gut microbiota reduced nearly half of the As(V) to As(III) in the colon digests, with up to 21.0 % of As(III) remaining in the solid phase. More than 92.0 % of Fe(III) in the colon digests was reduced to Fe(II), which would facilitate As reduction but inhibit methylation. A mouse bioassay was conducted to estimate As-RBA (21.3 %–58.8 %) in Al oxides, decreased by Fe(III) addition under high As exposure. Our findings provide new insights into the role of Al oxides in the risk assessment from inadvertent oral ingestion of As-contaminated soils.