Factors affecting the loss of six herbicides from hard surfaces

Studies of the environmental fate of herbicides have focused almost exclusi vely on the agricultural environment. Here we report initial results from a series of studies investigating the fate of six; herbicides (glyphosate, i soxaben, oryzalin, oxadiazon, diuron and atrazine) with varying physico-che mical properties, applied to different types of man-made surfaces, asphalt, concrete and ballast. Losses of each herbicide were studied under replicat ed, semi-controlled environmental conditions. Following herbicide applicati on, simulated rainfall was applied at varying rates and different time lag intervals. All surfaces were new and free from weed infestations. Results indicated that, for all but one compound, accumulated wash-off (% A S) was significantly different for all three surfaces, concrete being the w orst. In general, a 5mm rainfall event produced significantly less accumula ted losses than events of 10 and 15mm. With the exception of one compound ( glyphosate), time lag events had no significant effect on losses from aspha lt. In contrast, significant differences were recorded between time lag eve nts for five of the compounds, on ballast. On concrete, three of the six co mpounds showed significantly smaller accumulated losses after a 6 hour time lag compared to those of 12, 24 and 168 hours, and two showed significantl y greater losses after the 168 hour interval.