Spray deposition of two insecticides into surface waters in a South African orchard area

Drift from pesticide spray application can result in contamination of nonta rget environments such as surface waters. Azinphos methyl (AZI) and endosul fan (END) deposition in containers of water was studied in fruit orchards i n the Western Cape, South Africa. Additionally, attention was given to the contamination in farm streams, as well as to the resulting contamination of the subsequent main channel (Lourens River) approx. 2.5 km downstream of t he tributary stream inlets. Spray deposit decreased with increasing distanc e downwind and ranged from 4.7 mg m(-2) within the target area to 0.2 mg m( -2) at 15 m downwind (AZI). Measured in stream concentrations of both pesti cides compared well with theoretical values calculated from deposition data for the respective distances. Furthermore, they were in the range of value s predicted by an exposure assessment based on 95th percentile values for b asic drift deposition (German Federal Biological Research Centre for Agricu lture and Forestry [BBA] and USEPA). Pesticide deposition in the tributarie s was followed by a measurable increase of contamination in the Lourens Riv er. Mortality of midges (Chironomus spp.) exposed for 24 h to samples obtai ned from the AZI trials decreased,vith decreasing concentrations (esti mate d LC50 from field samples = 10 mug L-1 AZI; lethal distance: LD50 = 13 m). Mortality in the tributary samples averaged 11% (0.5-1.7 mug L-1 AZI), whil e no mortality was discernible in the Lourens River samples (0.041 mug L-1) . The sublethal endpoint failure to form tubes from the glass beads provide d was significantly increased at all sites in comparison with the control ( analysis of variance [ANOVA], Fisher's protected least significant differen ce [PLSD], p < 0.01).