Degradation of Roxarsone in Poultry Litter

Roxarsone (fig. 1), 3-nitro-4-hydroxyphenylarsonic acid, is an arsenic-containing feed additive that is used extensively in the broiler poultry industry to promote growth by controlling coccidial intestinal parasites. Most of the roxarsone is excreted unchanged (Morrison, 1969; Gregory, 1993) in the manure to accumulate in the poultry bedding. Each broiler excretes about 150 milligrams (mg) of roxarsone in the 42-day growth period for administering roxarsone. Litter collected following this period contains from 30 to 50 milligrams per kilogram (mg/kg) of total arsenic. In poultry houses where more than 200 million broilers per year are raised, a volume not uncommon for major poultry-producing areas, litter that contains more than 8 x 10 kg of arsenic would be produced. Generally, all the litter is used as nitrogen-containing fertilizer in nearby fields. Litter is routinely tilled into cornfields or applied to pastureland at a rate of between 1 and 2 metric tons per hectare. If a 100-hectare field was fertilized at 2 metric tons per hectare, about 10 kg of arsenic would be introduced to the environment. During crop rotation, the litter is stored in covered or uncovered windrows for up to 1 year. Soils amended with arsenic-containing poultry litter and the practice of using uncovered windrows for litter storage could be providing sources for arsenic contamination of surface and ground water. However, the extractability of roxarsone from the poultry litter and the stability of the mobilized roxarsone in the environment are unknown.