These are no more of a problem, or no safer, than new railroad ties. The creosote will not leach out of these ties into your soil very far so keeping plants roots 6 inches or more from the ties is all that is needed to prevent any uptake of that stuff plants might make.
Organic gardeners should be concerned about recycling and should practice that as often as possible, but there are some things that simply should not be recycled and RR ties are one.

loveapplefarm: Just as a point of fact, NO chemically treated wood is allowed in the production of organic or certified organic products. When your property/farm is inspected for certification, believe me, it's one of the FIRST things they look for. Thankfully, when we buy certified organic produce, we KNOW it was not grown in a bed surrounded by railroad ties or other chemically-treated wood. What is your motivation for wanting to use such material--because it's free, or cheap? If you think it through, even free material which has been injected with a known carcinogen, could be hazardhous to your (and your family's) health, and really not worth the risk. Organics is based on working with natural products. I, personally, wouldn't want that stuff anywhere on my property, whether it involved food production, or not. I have a friend who grows Kiwi Fruit in Southern California, and (because he works for the power company and gets them free) uses pieces of telephone poles for the poles in his trellis system. As much as I like Kiwi Fruit, I have to pass on the bushel of them he tries to give me each year.

How do you define safe? I have seen newish RR ties kill grass within 3 inches of itself, the ground was literally bare, not even weeds would grow.

I have seen older RR ties, I would guess around 20 years old, having grass grow right in the holes inside them.

There have been studies done on leeching from RR ties and kimmsr is correct that there shouldn't be any health concern with edible plants grown 6" away from them.

Marylandmojo is also correct that these wouldn't be allowed in any certified organic growing.

So, it really boils down to what you consider safe. My 2 cents is I wouldn't have any problem using the RR ties you describe, but I am not concerned about being certified organic.

Your call. I can tell you that if you have access to RR ties they work really well for raised beds as far as retaining soil and they are about the cheapest lumber you can buy assuming you are buying lumber.

The statement "organics is based on natural products" is not quite correct. May be it should be "non-toxic, non-carcinogenic natural products". Petroleum and tar ARE natural products, and so are a lot of poisons like strychnine...