Dust and endosulfan deposition in a cotton-growing area of northern New South Wales, Australia

Abstract

The pesticide endosulfan (6,7,8,9,10,10‐hexachloro‐1,5,5a,6,9,9a‐hexahydro‐6,9‐methano‐2,4,3‐benzodioxathiepin‐3‐oxide) has been detected in rivers in the cotton (Gossypium hirsutum L.)‐growing area of northern New South Wales at a 5 yr mean (1991–1995) concentration of 0.06 µg L−1. One pathway by which endosulfan reaches the riverine environment is transport on contaminated dust. Our objectives were to examine: (i) dust deposition from vehicular traffic on an unsealed road on a cotton farm, and around a cotton field in the 11 to 65 h period after endosulfan application; (ii) endosulfan deposition in the 11 to 65 h period after endosulfan application, and over a 3‐mo period at on‐farm and off‐farm (nontarget) locations. Dust deposition rates from vehicular traffic varied from 0.013 g m−2 vehicle−1 at 1 m distance, to 0.002 g m−2 vehicle−1 at 100 m distance from an unsealed road (soil surface, no gravel added). The maximum endosulfan deposition in the 11 to 65 h post‐spraying period was 95 µg m−2 at 5 m from the field. Over a 3‐mo monitoring period (December 1996–March 1997), the average daily deposition rate of endosulfan was 0.16 µg m−2 d−1 for the off‐farm sites compared with 0.35 µg m−2 d−1 for the on‐farm site. As the measurement period was one of the wettest on record and the number of endosulfan applications was less‐than‐normal, the dust and endosulfan deposition results may be interpreted as minima.