By Zingari
United Kingdom 
Used railway sleepers have often been treated with creosote. If used to contain a raised bed of say 2 metres by 1 metre, is the creosote unlikely to contaminate significantly the bed.
15 Jun, 2015
It's likely that it will be a long time since they were treated with creosote but if you're concerned then line the inside of the walls with a membrane (such as pond liner)
15 Jun, 2015