Widespread occurrence of dimethylmonothioarsenate (DMMTA) in rice cakes: Effects of puffing and storage

Thioarsenates have recently been detected in rice and rice-based products, with particularly high contents in puffed rice cakes. Here, we show that puffing rice can cause almost complete transformation of dimethylarsenate (DMA) to dimethyldithioarsenate (DMDTA) and dimethylmonothioarsenate (DMMTA). Analysis of puffed rice cakes after 3 months of non-sealed storage at room temperature showed transformation of DMDTA mainly into DMMTA. From a food safety perspective, this likely represents an increased risk because DMMTA is highly cytotoxic and misidentified as non-regulated DMA by routine acid extractions. Analysis of 80 commercial puffed rice cakes confirmed widespread occurrence of thioarsenates. The sum of non-regulated, but potentially toxic DMMTA and DMDTA reached values up to 537 µg·kg^-1 and 241 µg·kg^-1 for generic and infant-labeled rice cakes, respectively. Our results highlight the importance of better understanding (de)thiolation processes along the rice cake-production chain and potentially revising current thresholds set for iAs to include DMMTA and DMDTA.