Simazine concentrations in soil, groundwater and stream water following application to Pinus plantations in the coastal lowlands of south-east Queensland

Abstract

A study was conducted to assess the fate of simazine applied to exotic Pinus plantations in the coastal lowlands of south-east Queensland. The study had two components, the first being a large-scale catchment study site (903 ha) which assessed the level of simazine residues being transported from the point of application to the shallow unconfmed aquifer and the major drainage stream over a 13-month period. The second component consisted of a separate study on a small-scale study site (0.1 ha) to assess simazine persistence and its potential to leach in the coarse textured and relatively infertile soils of the area.

An 80 ha clearfelled area within the large-scale study catchment was re-established with a second rotation plantation and routinely treated with simazine at 2.5 kg a.i. ha1 over an 11—month period. A stream monitoring station at the base of the catchment sampled streamwater, and two piezometers provided access for groundwater monitoring. At the small-scale study site, simazine was applied to small plots at the above rate and the soil profile and shallow groundwater were routinely sampled.

Simazine was regularly detected in streamwater after surface runoff events but was below the current Australian drinking water health value. The detection of simazine in the unconfined aquifers at both sites indicated that it has the potential to leach to groundwater. However, under routine applications it would seem that the groundwater concentrations were low and shortlived (persistence < 6 weeks). The results indicated that simazine has a relatively short half-life (mean 13 days) in the coarse textured soils of the coastal lowlands of south-east Queensland. Transport from point of application by runoff or leaching was thought to be a minor pathway for loss from these plantations. Recommendations for future monitoring and research directions are discussed.