WASHINGTON (AP) — The U.S. Food and Drug Administration says consumers should not worry too much about levels of arsenic in rice — but should vary their diets just in case.

The agency is releasing a study of arsenic in 1,300 samples of rice and rice products that is the largest study to date looking at the carcinogen's presence in rice. It shows varying levels, with the most arsenic in brown rice and the least in instant rice.

The FDA says the amounts are so small that rice is safe to eat, but it is still studying long-term effects of consuming rice. The agency has long encouraged consumers to vary their diets to minimize risk.

Rice likely contains arsenic because it is grown in water on the ground, where the contaminant can be absorbed.