Phenoxyalkanoic acid herbicides in run-off

Between November 1991 and mid-September 1993, the surface run-off of the phenoxyalkanoic acid herbicides mecoprop (2-(4-chloro-2-methylphenoxy)propion acid) and dichlorprop (2-(2,4-dichlorophenoxy)propion acid) was monitored on a test field in Denmark with a mean slope of ∼ 12%. The test field was sprayed with mecoprop in November 1991 and 1992 and with dichlorprop in May 1992 and April 1993. The maximum concentrations, which have been detected in surface run-off, were 6.15 μg/l for mecoprop and 4.64 μg/l for dichlorprop. Totals of about 50 mg mecoprop and 5 mg dichlorprop have been transported via surface run-off to a stream over a period of nearly 2 years which correspond to 0.08‰ and 0.002‰ of the amount sprayed, respectively. More than one half of the total amount of phenoxyalkanoic acid herbicides was transferred to the stream with one surface run-off event immediately after one of the autumn applications.