Arsenic　(As)　speciation　is　essential　in　assessing　health　risks　from　As-contaminated　soil.　Release　of　soil　bound　arsenic,　As　transformation　by　human　gut　microbiota,　and　the　subsequent　intestinal　absorption　of　soil　As　metabolites　were　evaluated.　A　colon　microbial　community　in　a　dynamic　human　gut　model　and　the　intestinal　epithelial　cell　line　Caco-2　were　cultured.　Arsenic　speciation　analysis　and　absorption　of　different　As　species　were　undertaken.　In　this　study,　soil　As　release　(3.7-581.2　mg　kg(-1))　was　observed　in　the　colon.　Arsenic　in　the　colon　digests　was　transformed　more　quickly　than　that　in　the　soil　solid　phase.　X-ray　absorption　near-edge　spectroscopy　(XANES)　analysis　showed　that　44.2-97.6%　of　arsenite　[As(III)]　generated　due　to　arsenate　[As(V)]　reduction　was　in　the　soil　solid　phase　after　the　colon　phase.　We　observed　a　high　degree　of　cellular　absorption　of　soil　As　metabolites,　exhibiting　that　the　intestinal　absorption　of　monomethylarsonic　acid　and　As(III)　(33.6%　and　30.2%　resp.)　was　slightly　higher　than　that　of　dimethylarsinic　acid　and　As(V)　(25.1%　and　21.7%　resp.).　Our　findings　demonstrate　that　human　gut　microbiota　can　directly　release　soil-bound　arsenic,　particularly　As-bearing　amorphous　Fe/Al-oxides.　Determining　As　transformation　and　intestinal　absorption　simultaneously　will　result　in　an　accurate　risk　assessment　of　human　health　with　soil　As　exposures.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.