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 res idues of glyphosate, dicamba, 2,4-D, bromoxynil or methylchlorophenoxy acetic acid (MCPA) in soil at two long-term tillage sites and one long -term manured site. The only detectable residues in soil were of diclo fop and triallate. Residues of bromoxynil, diclofop and MCPA but not d icamba, 2,4-D or triallate, were detected in the groundwater at the ma nured site. Diclofop was detected in 6% and bromoxynil and MCPA in 2% of 84 water samples collected at the manured site. Maximum concentrati ons of bromoxynil (6.5 mu g L(-1)) and diclofop (47 mu g L(-1)) in the groundwater at the manured site exceeded levels set by the Canadian d rinking 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 concentratio ns above the level set by the drinking water guidelines is cause for c oncern.