A couple of weeks ago, prominent vegan physician Dr. Michael Greger did several videos on this topic.
I cross-checked this topic on the websites of the American Cancer Society, the U.S. Food & Drug Administration, and the United Nations (see links below), and they confirm that this is a real thing, though not as dangerous as certain websites may claim.
Arsenic is present in all foods, to some degree. Long-term exposure to higher levels of arsenic is associated with higher rates of skin, bladder and lung cancers, as well as heart disease.
Also, although rice is getting most of the publicity relative to this topic, elevated arsenic levels are also present in seafood, poultry, and mushrooms. The reason why so much attention is focused on rice is because it's a staple food for a huge percentage of the world's population, and because rice foods are fed to infants and young children.
The American Cancer Society and the U.S. Food & Drug Administration confirm that that (1) arsenic is a naturally-occurring element in the soil, (2) arsenic pollution also results from industrial activities, (3) rice tends to absorb higher levels of arsenic than do other crops, (4) arsenic levels are the same between organic and non-organic rice.
To reduce the arsenic in rice, the U.S. Food & Drug Adminstration recommends cooking rice with more water than is normally used, cooking the rice until it's ready, and then draining the excess water (the same way that pasta is cooked). See U.S. FDA's webpage below. Also, they advise that you can reduce your exposure by varying your grains more. This is especially important for infants being fed on rice foods and formula.
The American Cancer Society's webpage on arsenic in foods: https://www.cancer.org/cancer/cancer...s/arsenic.html
The U.S. Food & Drug Administration has published a webpage on this topic: https://www.fda.gov/food/foodborneil.../ucm319948.htm
The United Nations' webpage on arsenic in rice: http://www.un.org/apps/news/story.asp?NewsID=57193