Residue detections in soil and shallow groundwater after long-term herbicide applications in southern Alberta

After herbicide applications for 1–24 yr, there were no detectable residues of glyphosate, dicamba, 2,4-D, bromoxynil or methylchlorophenoxyacetic acid (MCPA) in soil at two long-term tillage sites and one long-term manured site. The only detectable residues in soil were of diclofop and triallate. Residues of bromoxynil, diclofop and MCPA but not dicamba, 2,4-D or triallate, were detected in the groundwater at the manured site. Diclofop was detected in 6% and bromoxynil and MCPA in 2% of 84 water samples collected at the manured site. Maximum concentrations of bromoxynil (6.5 μg L−1) and diclofop (47 μg L−1) in the groundwater at the manured site exceeded levels set by the Canadian drinking water guidelines. Long-term application of herbicides has not caused accumulation of harmful residues in southern Alberta soils, but the presence of certain herbicides in the groundwater at concentrations above the level set by the drinking water guidelines is cause for concern. Key words: Herbicide residues, tillage, ...