LEACHING OF PICLORAM, ATRAZINE AND SIMAZINE THROUGH 2 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 monito red at approximately monthly intervals using suction cup lysimeters ov er the following 640 days. Leaching of all chemicals below 1.1 m was o bserved 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. A trazine 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 coeff icients (K-oc) for each pesticide were estimated by comparing the obse rved results with simulations using the GLEAMS model. Picloram was les s mobile but more persistent than available values quoted by Wauchope et al. [Wauchope, R.D., Buttler, T.M., Hornsby, A.G., Augustijn-Becker s, P.W.M., Burt, J.P., 1992. The SCS/ARS/CES Pesticide Database for En vironmental Decision Making. Reviews of Environmental Contamination an d Toxicology, Vol. 123, Springer-Verlag, 164 pp.] while atrazine and s imazine were more mobile and had about the same persistence as these v alues. The pesticides were more mobile (smaller K-oc) at the Te Awa si te 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.