Open Access. The published version of this work has been reproduced here with permission. This work may be downloaded for personal use only. Permission to reproduce this work must be sought from Environmental Health Australia. This article was first published in Environmental Health, 1(2): p. 18-26, 2001 by Environmental Health Australia. More information about this publication may be found at http://journal.eh.org.au/. Copyright (2001) Environmental Health Australia.