You may want to stay away from conventionally raised chicken altogether after learning more about Roxarsone, a common arsenic-based additive in chicken feed used to spur growth, kill parasites and improve the color of chicken meat.

The problem stems from Roxarsone changing over from its original benign composition -- on farm land (in chicken litter or fertilizer) and in chickens -- to more toxic kinds of inorganic arsenic.

Even though America's largest poultry producer, Tyson Foods, along with Foster Farms has banned Roxarsone, 70 percent of an estimated 9 BILLION broiler chickens produced in this country are still tainted with this arsenic-laced chemical. And, neither the USDA or FDA have a clue as to how much arsenic you may be consuming in chicken either.

In the only testing that has measured arsenic in chicken so far, nearly 75 percent of the raw meat sampled from conventional sources in Minnesota and California contain detectable levels of arsenic along with a third of the samples taken from organic and "premium" sources.

Still, organic chicken -- preferably those raised on farms near you -- is the best choice for your health.
http://pubs.acs.org/cen/government/85/8515gov2.html