2,4,5-T Residues in Stream Water after Aerial Spraying in the Narbethong Plantation, Victoria

SUMMARY In July 1977 a study was made of 2,4,5-T concentrations in Old Mill Stream, Narbethong, following aerial spraying to control woody weeds in a young pine plantation on the catchment. An area of 108 ha was sprayed at a rate of 1.12 kg 2,4,5-T/ha. The stream was sampled immediately below the sprayed area, twice daily for 5 days before spraying, and at 12 minute intervals for a period of 13 days during and following spraying. Six twelve minute samples were combined to give hourly samples before analysis. 2,4,5-T was detected in the samples only on the 7th and 8th day following spraying, during a period of heavy rain. On the 7th day the highest concentration recorded was 10 ug/1 over a one hour period with all other values 4.3 ug/i or less. On the 8th day the highest concentration was only 1.0 ug/1. According to National Health and Medical Research Council Standards the maximum safe level of 2,4,5-T in drinking water for human consumption is 20 ug/1. 2,4,5-T could not be detected (i.e. less than 0.3 ug/1) in samples collected 2.5 km downstream of the spray area at any time during the period of the study.