Abstract

Pesticides are indispensable in modern agricultural production; however, their off-site migration and detrimental effects on surface water and groundwater quality cause concern. Current pesticide usage and trend data show pesticide use is widespread in New Zealand. According to national surveys, concentrations of most pesticides in groundwater are usually low, and their occurrence has been attributed to non-point sources of contamination. Although it is well established that the environmental fate of pesticides is governed by complex interactions of many processes such as sorption, degradation, and transport, our understanding of these basic mechanisms in the vadoze zone is too far from complete to predict quantitatively the fate of trace residues of pesticides in various soil types within one geographical location. This is mainly due to the vexing issue of the complex nature of soil and its lateral heterogeneity, such as spatial and temporal variability in field-scale. The use of simulation models to predict the environmental fate of pesticides using laboratory- and field-derived parameters is discussed. The objective of this overview is to present past and recent environmental fate work on pesticides carried out under New Zealand conditions, to provide a wider perspective on the subject matter, and to give some recommendations for future research directions.