The preparation of this review, and the final writing up, was only made possible by generous support from two organisations, namely the Water Research Centre, Medmenham, Marlow, Buckinghamshire, UK, and Jealotts Hill Research Station (ICI Plant Protection), Bracknell, Berkshire. I am greatly indebted to the sponsors concerned, Mr J. F. Solbe of the WRC and Dr B. G. Johnen of ICI for authorising donations without which this project would not have seen the light of day. Their assistance was particularly vital, coming as it did at a period when research funding in general, and in this field in particular, was being severely restricted in this country.

I am also grateful for the cooperation of many colleagues through correspondence from overseas, who have not only been kind enough to send reports and material not easily available here, but who have also – by correspondence – provided up-to-date progress information and comments. I am particularly indebted to the following: Dr Peter Kingsbury of the Canadian Forest Service; Dr D. C. Eidt of the Maritime Forest Research Centre, New Brunswick; Dr P. E. K. Symons of the Fisheries Research Board, Canada; Dr W. 0. Haufe of the Animal Parasitology Research Station, Lethbridge, Alberta; Dr Joan Trial of the Department of Zoology, University of Maine, US; Prof. John Giesy of the Pesticide Research Centre, Michigan State University, US; Dr. Aarne Lamsa, of the Great Lakes Fishery Commission, Ann Arbor, Michigan; Dr L. A. Norris of the USDA Forest Service, Oregon State University, US;