2011-present: Professor at Geochemistry - Faculty of Geosciences, UtrechtUniversity in the field of nutrient transport from land to sea.

1996-present: Soil and Ground Water Laboratory (1996 up till 2003), team Climate Change and Global Sustainability (from 2003) and team Water, Agriculture and Food (from 2010) of the Netherlands Environmental Assessment Agency (PBL), formerly National Institute for Public Health and the Environment (RIVM) , Netherlands.

1990-1996: Laboratory for Waste Materials and Emissions at Laboratory of the National Institute for Public Health and the Environment (RIVM), Bilthoven, Netherlands.

1986-1990: International Soil Reference and Information Centre (ISRIC), Wageningen, Netherlands.

1984-1986: Dutch Directorate General for International Development Cooperation, Jamaica

1982-1984: Food and Agriculture Organization of the United Nations, Ecuador.