Are cement blocks safe for raised garden beds?

This home talker did it. www.hometalk.com/diy/grow/square-footing-it-with-concrete-blocks-1726197

I see many people write about using these CMUs or cinder, cement, concrete blocks to build raised beds and also to plant directly inside the cells of this block. I am offering a warning of the possibility of poisons in this product and stressing that I would never grow my food in it. The product Fly Ash is used as a Portland Cement replacement for up to 30% of the cement used to manufacture these products. For those of you unaware, Fly Ash is a by product of burning coal. The EPA is and has for the last year been doing a study to decide whether or not to label Fly Ash as a Hazardous Waste due to the high levels of mercury, arsenic, and lead; leaving some "Industry Folk" to refer to concrete as the "New Asbestos" or the "New Lead Paint". Though there is no definite date set for a decision the ball has started rolling. The EPA knows this product is unhealthy, I know this product is unhealthy (and wouldn't dare chance putting it into my children's mouth), and now you can make an informed decision on how you feel about it. Just google "Is Fly Ash Toxic" and you will see all the information available on this material allowing you to make an informed decision of your own. With all the trials and tribulations we face I would hate to know that I was poisoning myself with the very food I prepped to save me.