Roxarsone and it metabolites in organic fertilizer lead to human exposure to arsenic

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) is an organoarsenic feed additive to promote growth, control intestinal parasites and improve feed efficiency in animal production. First approved as animal feed additives in the 1940s, roxarsone and three other very similar arsenic-containing compounds remain legal for use in U.S. chicken, turkey, and swine production. They were never approved as safe for animal feed in the European Union, Japan, and many other countries. In 2006, approximately one million kilograms of roxarsone were produced in the U.S. The toxicity of roxarsone is low but it can be degraded into higher toxic metabolites soon after being excreted by the fed animals or after the animal manure enters environment or when the animal manure is composted. The use of roxarsone as a feed additive had been banned by the European Union in 1999 and the sales of roxarsone also had been suspended by the United States in 2011. However, the voluntary suspension does not preempt Pfizer from selling roxarsone in the future, as FDA has not withdrawn its approval to market the drug in the U.S, and also roxarsone was approved for use in 14 other countries including China.

The new study:
A new study from chinese researchers now shows that more than 96% of roxarsone added in chicken feed was degraded and converted to higher toxic As forms such as arsenite, mono- methylarsonic acid, dimethylarsinic acid, arsenate, 4-hydroxyphenylarsonic acid and other unknown As species. Arsenite and arsenate could be found in roots of vegetables grown in  soil amended with chicken manure,  but only arsenite transported up to shoots. Chicken manure bearing roxarsone and its metabolites increased the arsenic plant uptake by 33–175% for  arsenite, by 28%∼seven times of arsenate in vegetable roots and by 68–175% of arsenite in edible vegetable shoots. Arsenite, the most toxic As form, was the major extractable As species in vegetables accounted for 79–98%. The results reflected that the toxic element As could come into human body via the way: roxarsone in feed → animal → animal manure → soil → crop. It follows, that regarding food security not only chicken meat should be watched carefully but also vegetables applied with animal manure containing roxarsone and its metabolites need to be investigated with great attention.

In 2005 (see the EVISA's News below) we commented that the discussion about the human exposure resulting from the use of Roxarsone should motivate analytical scientists to study exposure routes in more detail. 9 years later, this study shows that the use of roxarsone indeed is responsible for human exposure to arsenic. Also a study published 2013 by Nachman et al. (see below) reveals that, despite the voluntarily withdrawal by Pfizer of its arsenical drug roxarsone back in 2011, similar drugs continue to quietly be used in both factory chicken and turkey meat, which may be exposing the public to elevated levels of inorganic arsenic (iAs).