The 1998 National Survey of Pesticides in Groundwater in New Zealand detected pesticides in 33 out of 95 wells (35%) that were sampled, generally at low concentrations (below 1 μg/L). About 75% of these pesticides were triazine herbicides. The 1998 survey analysed for two triazine metabolites, desethyl atrazine (DEA) and desisopropyl atrazine (DIA), for the first time. One or both of the metabolites were detected in 10% of wells sampled, with concentrations ranging between 0.01 – 0.26 μg/L. Both these metabolites have similar toxicological characteristics to atrazine, and tend to have greater mobility and similar persistence to atrazine.

The purpose of this study is to better understand pesticide degradation and sorption in a range of New Zealand soils and climatic conditions, which can be used to minimise pesticide contamination of groundwater in New Zealand.

The degradation of the triazine compounds atrazine and simazine, and their degradation products desethyl atrazine and desisopropyl atrazine were studied in two soils in a laboratory experiment under the controlled conditions of temperature and moisture. The sorption of the chemicals in the two soils was studied in a batch isotherm experiment. The soils used were a Horotui silt loam with significant levels (12%) of allophane and a Te Awa silt loam. Results from the laboratory experiments will be presented and the differences in results between the two soils will be discussed.