Just because something grows on trees doesn't make it inexhaustible. Take wood. It doesn't just grow on trees, it is the tree. But people still want to use less of it if possible. A prime example is wooden railroad ties. The material of choice for the railway industry since it first began way back when, timber ties are increasingly being replaced by alternatives, not only due to concerns about deforestation — millions of hardwood trees are consumed to make railway ties in North America every year — but also because of creosote, which has long been used to prevent the wood ties from rotting. Creosote has recently been classified as a probable carcinogen, and creosote-treated railway ties also have the nasty side effect of creating toxic run-off water that in turn contaminates the surrounding surface soil and river ways. How bad a problem is it? Each wooden tie can leach up to 15 kg of creosote over its lifetime. For this reason, Europe will ban the use of creosote-treated wood rail ties by 2018, and similar legislation in Canada might not be that far off.
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