I spent and "interesting" few months working for Coalite Chemicals near Bolsover in the late 80s. That place produced most of the creasote sold in the UK. I'm also a chemist with a specialist interest in envronmental pollution and the analysis of soil and water for environmental pollutants.
Creasote works because it contains a cocktail of phenolic and chlorinate phenolic molecules. They are mildly toxic, TCP antiseptic is a purified chlorinated phenolic.
BUT if burnt, especially at low temperature on an open fire the products of combustion are highly toxic and can contain dioxins. We can debate the real toxicity of dioxins for years, but the subject is so mired in mis-information that reasoned debate is almost impossible. Lets just agree they are "not a good thing"...
We live in a world where more and more chemicals are on the "hazardous" list because there is a view in Brussels that the Citizens must be protected from or made aware of every possible risk.
So, old, aged railway sleepers are essentially harmless, but:
1. If you cut or drill them wear gloves and a face mask, the dust isn't nice and you don't want it in your lungs.
2. Don't, ever, burn them or off-cuts.
3. Don't let water run off them directly into your fish pond, the fish won't like it and might die.
4. Don't eat the wood,
Oh, and finally,
5. Don't drop them on your foot, they are very heavy....
