Leaching of picloram, atrazine and simazine through two New Zealand soils

Picloram, atrazine, simazine, and bromide were applied to two sites, a Te Awa silt loam and a Twyford fine sandy loam, located in Hawkes Bay, New Zealand, in November 1993. Soil water concentrations were monitored at approximately monthly intervals using suction cup lysimeters over the following 640 days. Leaching of all chemicals below 1.1 m was observed at the Te Awa site but only bromide and picloram had reached 1.3 m depth at the Twyford site after 400 and 600 days, respectively. Atrazine and simazine were observed at 0.4 m depth but not at 0.8 or 1.3 m depth at the Twyford site. Soil half lives and soil sorption coefficients (K-oc) for each pesticide were estimated by comparing the observed results with simulations using the GLEAMS model. Picloram was less mobile but more persistent than available values quoted by Wauchope et al. [Wauchope, R.D., Buttler, T.M., Hornsby, A.G., Augustijn-Beckers, P.W.M., Burt, J.P., 1992. The SCS/ARS/CES Pesticide Database for Environmental Decision Making. Reviews of Environmental Contamination and Toxicology, Vol. 123, Springer-Verlag, 164 pp.] while atrazine and simazine were more mobile and had about the same persistence as these values. The pesticides were more mobile (smaller K-oc) at the Te Awa site than at the Twyford site, possibly because of preferential flow at the Te Awa (silt loam) site. (C) 1998 Elsevier Science B.V. All rights reserved.