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Organoarsenics are widely used as excellent feed additives in animal production in the world. Roxarsone (ROX) and arsanilic acid (ASA) are two organoarsenics permitted to be used in China. We collected 146 animal feed samples to investigate the appearance of ROX, ASA, and potential metabolites, including 3-amino-4-hydroxyphenylarsonic acid (3-A-HPA), 4-hydroxyphenylarsonic acid (4-HPA), As(V), As(III), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) in feeds. The stability of ROX in both ROX additives and animal feeds was also examined. The results show that 25.4% of the 146 animal feeds contained organoarsenics, with average contents of ROX and ASA as 7.0 and 21.2 mg of As/kg, respectively. Unexpectedly, As(III) and MMA frequently occurred as As impurities in feeds bearing organoarsenics, with higher contents than organoarsenics in some samples. 3-A-HPA, 4-HPA, and DMA were not detected in all samples. ROX and As impurities in both ROX additives and feeds stayed unchanged in the shelf life. It suggests that As impurities in animal feeds bearing organoarsenics should generate from the use of organoarsenics containing As impurities. This constitutes the first report of As impurities in organoarsenics.

Roxarsone (ROX) is widely used as a feed additive in intensive animal production. While animals are fed with ROX, the most commonly detectable As forms in fresh manures include ROX and small quantities of its metabolites such as arsenate (As(V)), arsenite (As(III)), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). A pot experiment was conducted to investigate the uptake, translocation and distribution of ROX, As(V), As(III), MMA and DMA in turnips, with the soil amended with 2% and 3% (w/w) chicken manure (CM) bearing ROX and its metabolites. Soil without any fertilizer was the control. The results show that only As(V) and As(III) were detected in turnip control samples. As(V), As(III) and DMA were found in all CM applied samples, but not ROX or MMA. This implies that turnip cannot take up ROX directly and accumulate MMA at detectable levels. The contents of DMA in tubers and the three As species in shoots increased with the CM rate in contrast to reduced levels of As(V) and As(III) in tubers. Increased CM rate enhanced the translocation of the three As species, especially for DMA, from tubers to shoots. DMA was the major form (42.9-61.4% in tubers and 38.1-76.3% in shoots), followed by As(III), in turnip plants fertilized with CM. The results indicate that ROX and its metabolites in animal manures can be introduced into human food chain by the way ROX → animal → manure → soil → crop.

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