Levels of 2,4-D — Mecoprop — Dicamba (Pesticide) in Quebec Water Systems (2001-2002) of little concern. [ONTARIO] MOE justifies Pesticide Ban with Stream Water Evaluation 2009-2010


Re-evaluation Decision Document: Dicamba
5 August 2008

4.7 Comment

2,4-D, mecoprop and dicamba were found in seven water treatment plants sampled in Quebec City at maximum concentrations of 5.7, 6.3 and 0.68 μg/L, respectively, because the application of these herbicides is often just before heavy rains or thunderstorms. These herbicides were detected at the six sampled storm drains (stream outlets) in Quebec City. They were also found in measurable concentrations These herbicides were detected at the six sampled storm drains (stream outlets) in Quebec City. They were also found in measurable concentrations in water source samples taken downstream from rainwater outlets (storm drains). All samples were taken during the summers of 2001-2002. The mentioned report confirmed the presence of urban pesticides in water treatment plant effluents in Montreal and Longueuil. These results should be considered when re-evaluating the risk of dicamba to aquatic organisms. No data regarding the assessment of these environments (effluents) were found in PACR2007-02.


The assessment for lawn and turf uses was completed prior to the assessment for agricultural uses (PRVD2007-05) but they were released at the same time. The assessment described in PRVD2007-05 included a large amount of known dicamba detections for ambient surface water, which was taken into consideration in the environmental risk assessment. The levels of dicamba in ambient surface water assessed for agricultural uses (PRVD2007-05) were higher than those reported above. The drinking water assessment for all uses was conducted when the lawn and turf assessment was completed. Therefore, it was not amended when the agricultural assessment was completed. As a result, the new information regarding water monitoring in water treatment plants was not taken into consideration for the drinking water assessment. Upon review of the new monitoring data, it was determined that inclusion of these data will not result in increased drinking water estimates nor increased risk to the environment.