Well understood and respected as one's health is clearly a matter for a personal risk assessment. All the exposure to which I referred above would have to be subject to a COSHH assessment and appropriate PPE and other measures. Clearly, using no preservatives is safest for you and quite within your perogative but not using them will without question produce a less durable end product for the client. I do feel that you may have been influenced by what was bad practice 20 years ago in terms of active ingredients in wood preservative and that, if you are as concerned as you are about wood-preserving chemicals as they are allowed today, you should also to look equally at other activities.... bleach under the kitchen sink, most organic solvent paints, every time you fill up a car with petrol, not to mention lots of the food we gaily buy from the supermarkets!
I would also like to add that my advice is not just from behind a desk and that (if it was not clear from the tenor of my advice - I apologise) I am also a "practitioner" that my advice is based on working on site (on and off) since 1975. chris