1. Institute of Ocean Sciences, Post Office Box 6000, Sidney, British Columbia V8L 4B2, Canada.
2. National Institute of Public Health and the Environment, 3720 BA Bilthoven, Netherlands
3. National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency (EPA), Research Triangle Park, NC 27711, USA
4. Institute of Virology, Erasmus University, 3015 GE Rotterdam, Netherlands