UNCORRECTED PROOFS PS1063.04/007 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Pest Management Science Pest Manag Sci 61:000–000 (2005) DOI: 10.1002/ps.1063 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 Rainfastness and adsorption of herbicides on hard surfaces Pieter Spanoghe, 1∗ Johan Claeys, 2 Luc Pinoy 2 and Walter Steurbaut 1 1 Ghent University, Faculty Agricultural and Applied Biological Sciences, Department of Crop Protection Chemistry, Coupure Links 653, B-9000 Ghent, Belgium 2 KaHo St-Lieven, Campus Rabot, Department of Chemical Engineering, Gebroeders Desmetstraat 1, B-9000 Ghent, Belgium Abstract: Herbicides are still used to control weeds on hard surfaces, including municipal, private and industrial sites. Used under unfavourable conditions, especially when rain occurs shortly after application, herbicides may run off to surface waters. Such losses of herbicides from hard surfaces are estimated to be much higher than for herbicides used in arable fields. In this study, three kinds of hard surface were evaluated: asphalt, concrete surface and gravel (fine and coarse). Three herbicides were applied: glyphosate, diuron and diflufenican. Adsorption isotherms of diuron and diflufenican to the three surfaces were determined. At different times after treatment with the herbicides, rainfall was simulated by use of a rain-droplet spray nozzle, and the run-off was collected for analysis. After this run-off event, the materials were immersed in water to measure desorption which, together with the compound in the run-off, gave a measure of the dislodgable residues. The apolar herbicides diuron and especially diflufenican adsorbed strongly to asphalt. The polar herbicide glyphosate lost 75% in run-off from asphalt but was adsorbed strongly to soil and concrete pavement.  2005 Society of Chemical Industry Keywords: rainfastness; hard surfaces; adsorption; run-off; herbicides; glyphosate; diuron; diflufenican 1 INTRODUCTION The use of herbicides in urban areas on hard surfaces such as footpaths, streets, pavements and other paved areas can be a major source of contamination of surface waters. Weeds deform surface structures and compromise both safety and aesthetics. In treating hard surfaces with herbicides, adsorption occurs, mainly as the result of physical and chemical sorption. When used under unfavourable conditions, especially when rain occurs shortly after application, herbicides can run off to surface waters. These herbicides may harm the aquatic ecosystem, or may cause problems for the use of drinking water. To assess the risks to surface waters, herbicide run-off needs to be incorporated into the development of environmental indicators for non-agricultural pesticide emissions. 1 Nevertheless scientific information about run-off of herbicides applied on hard surfaces is limited. Parker and Huntington 2 assess herbicides for the control of weeds on hard surfaces and present guidelines for their optimum use. The model SEPTWA estimates the general loss of pesticides from impermeable surfaces to be 2% of that applied. 3 Beltman et al 4 treated concrete bricks with herbicides, finding 18–44% of applied atrazine, 7–22% of amitrol and 11–23% of glyphosate in the run-off. Most herbicide (53–79% of the herbicide run-off) was found in the first 2 mm of rain wash-off. The behaviour of the different herbicides is explained by the difference in solubility of the compounds. Parsons et al 5 sprayed oxadiazon, isoproturon, diuron and atrazine onto surfaces of concrete paving slabs, asphalt and railway ballast. After, respectively, 20, 30 and 60 mm rainfall on each surface, maximum run-off of herbicides was obtained. The concrete surface showed most herbicide run-off, with diuron, isoproturon and atrazine being washed off to 80%. Oxadiazon was much less readily washed off (concrete 45%, asphalt 25% and ballast 5%) than other more water-soluble herbicides. The following ranking in increasing risk of run-off can be made for concrete and asphalt: oxadiazon < diuron < atrazine < isoproturon. Ramwell et al 6 investigated the behaviour of herbicides applied to 16 metres of asphalt road with a concrete kerb under actual weather conditions. The amounts lost in the run- off were: glyphosate 35%, atrazine 73%, diuron 66%, oxadiazon 6% and oryzalin 4%; isoxaben was not detected. The majority of herbicide removed was lost within the first 5 mm of rainfall following application, after which losses were very small. High-intensity rain was found to encourage run- off because of the removal of loosely bound and ∗ Correspondence to: Pieter Spanoghe, FLTBW, Department of Crop Protection Chemistry, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium E-mail: Pieter.Spanoghe@UGent.be (Received 13 January 2004; revised version received 4 February 2005; accepted 22 February 2005)  2005 Society of Chemical Industry. Pest Manag Sci 1526–498X/2005/$30.00 1