Colloidal phase transport of pesticides : a review with special reference to major UK aquifers

Several studies have highlighted the role of colloids in contaminant transport within the subsurface including notable reviews by McCarthy and Zachara (1989) and Ryan and Elimelech (1996). Colloid facilitated transport of contaminants in the environment has been the subject of intense investigation over the last twenty years. As a result much has been learnt about the formation, and transport of colloids as well as the mode of interaction between colloidal material and contaminants. A large amount of literature exists on colloid facilitated transport of pesticides, but the majority of the work described was laboratory-based study focussed on the soil zone and using isolated humic material. Some recent studies have investigated the transport of colloids in the unsaturated zone, however the issues of heterogeneity and complexities of recharge events are challenges that need further investigation. Few studies have addressed the issue of colloid-facilitated transport of pesticides in groundwater other than to suggest it as potentially significant transport mechanism. This report considers the likely aquifer systems in the UK which may lead to the formation and transport of colloidal material. This may increase the mobility of pesticides from the point of application to groundwater. Methods for sampling and extracting colloids and pesticides from groundwater are also discussed.