Residues of hexazinone in streamwater after aerial application to an experimental catchment planted with radiata pine

Abstract

Residues of hexazinone in stream water were monitored over a nine-week period after helicopter application of the herbicide at a rate of 2 kg ha-1 to a 46.4 ha experimental catchment. The aerial application was made in December 1981 following conversion of a steeply sloping catchment from native forest to Pinus radiata two years previously. Automatic samplers were used to sample stream water at intervals of 0.25-2.0 h throughout the nine weeks, with the more intensive sampling occurring during and immediately following spraying and during the only substantial storm event. A total of 69 representative samples were analysed, and 4 p.g L-1 hexazinone only was detected in six of these samples, which was well below the maximum recommended concentration for potable water of 600 p.g L-1 • Such low residues were attributed to several factors including the way the spraying operation was conducted (with respect to soil moisture, meteorological conditions and droplet size) and the presence of a 30 m wide vegetation reserve on each side of the stream.

Aquatic Fate of Aerially Applied Hexazinone and Terbuthylazine in a New Zealand Planted Forest

“…This finding was most likely a combined effect of the timing (DAT) and the quantity and duration of rainfall along with other factors such as the presence of SMZ's, preceding catchment saturation, geology and soils, hydrology and flow pathways DeGraff et al, 2007). In other studies, greater quantities of hexazinone tended to reach streams in wet conditions or where the first storm event occurred shortly after herbicide applications Michael et al, 1999;McBroom et al, 2013) with lower concentrations associated with drier climatic conditions (Leitch and Flinn, 1983; this study). The persistence of hexazinone in the aquatic environment (as indicated by the DAT until concentrations fell below detection limits in Table 3) varied between studies, with trace concentrations persisting for several years after application in some instances (Table 3).…”

“…During Year 1, terbuthylazine, terbuthylazine-desethyl and hexazinone concentrations in algae were 8100, 33 and 600 µg kg -1 respectively, on the spray day but remained below detection limits up until the end of the trial (182 DAT). During Year 2, only terbuthylazine was detected in algal samples on the spray day (110 µg kg Miller and Bace, 1980; 2 Fagg et al, 1982;3 Neary et al, 1983;4 Neary, 1983; 5 Leitch and Flinn, 1983;6 Lavy et al, 1989;7 Neary et al, 1985;8 Bouchard et al, 1985;9 McBroom et al, 2013;10 this study. † SMZ (streamside management zone); DL (detection limit); DAT (days after treatment).…”

“…The highest risks of herbicide contamination of water bodies were associated with herbicide application directly over perennial and ephemeral stream channels and in the first high flow event after spraying. Thereafter, concentrations in receiving freshwater environments usually declined within days or several months of application to concentrations <10 µg L -1 , or below detection limits (Fagg et al, 1982;Leitch and Flinn, 1983). Field studies on the aquatic fate of hexazinone in forests found that when used according to manufacturer's instructions and applied using the Best ManageJournal of Sustainable Watershed Science & Management -ISSN 1949-1425.…”

Cumulative Effects Analysis of the Water Quality Risk of Herbicides Used for Site Preparation in the Central North Island, New Zealand

“…The fate and movement of herbicides in forested catchments has been fairly well documented, particularly by research in the USA and Australia [17][18][19][20]. Some contradictory results have been produced due to differences in application rates, distribution equipment, and levels of Best Management Practices.…”

“…Whether applied aerially or through ground application, peaked herbicide concentrations were usually detected on the day of application or in storm run-off, particularly in the first few weeks following herbicide application (i.e., [23][24][25][26][27][28][29][30]). Otherwise, herbicide use in forests has generally resulted in low concentrations in streamflow (0 to 4 µg·L −1 ) for short durations, often below detection limits [18,19,22,23]. All of these studies have been conducted at the level of small stands or catchments.…”