Accountants talk about laundering money in a different sense than actually making the money cleaner.
Health professionals talk about the germs that money carries. Canadian currency is no longer made of paper so it harbours fewer germs, genetic material and cocaine on its surface than US money. This is yet another way that Canada is a more advanced country than the USA we also have the metric system and chip and pin technology on our credit cards. Modern advances that have yet to be adopted by our neighbours to the south.
Even coins have material attached. Hygiene is yet another reason why we should move towards digital transactions rather than exchanging paper and coins.