Dr. Macdonald directs interdisciplinary programs to study the environmental pathways of contaminants including their delivery, transport, and elimination from aquatic systems. A variety of settings are studied including Arctic shelves and basins, British Columbia fjords, the Strait of Georgia, and lakes in the Fraser River basin. He determines the behaviour of contaminants in the context of natural systems bringing to bear such tools as water-mass analysis, transient and steady state tracers, stable isotope analyses (oxygen, carbon and lead), the determination of particle fluxes and sedimentation rates, multivariate statistics and modeling. Most of the major contaminant groups have been studied including PAH, metals, radionuclides, organochlorines, and other synthetic organic compounds like the nonylphenol ethoxylates. Dr. Macdonald focuses on site-specific contaminant sources including chlor-alkali plants, pulp mills, mine-tailing disposal and municipal outfalls, as well as broader contaminant issues such as long-range atmospheric transport of semi-volatile contaminants to the Arctic Ocean and Georgia Basin, and the potential impacts of oil exploration on Canada's western Arctic shelves. Contaminants are studied according to how they enter and leave natural water bodies and how they impinge on natural biogeochemical cycles. Multivariate statistical techniques as well as dated sediment cores are used to distinguish between anthropogenic contaminants and their natural counterparts. Often, more than one anthropogenic source contributes to contaminant loadings, in which case the same techniques are used to work out the relative strength of each source. Insight and data developed through these studies is incorporated into national and international environmental assessments.