Pesticides in selected aquatic ecosystems 2003 to 2005

In Canada, more than 500 pesticides have been officially approved to date. They are generally classified as herbicides, insecticides or fungicides and are used to control targeted species of plants, insects and molds. However, applying these pesticides can cause environmental problems. Pesticides may be transported to non-targeted areas such as aquatic ecosystems by surface runoff, erosion and wind, which all contribute to agricultural contamination.

The largest area of agricultural production in Canada is the Prairies region of western Canada that includes Alberta, Saskatchewan and Manitoba. Because of the large land areas producing grains and oilseeds, more pesticides are applied in the Prairies than in any other region of Canada.

As part of the National Water Quality Surveillance Program launched in 2003, Environment Canada scientists monitor the presence and levels of pesticides in selected aquatic ecosystems and sensitive surface waters. A nation-wide study was conducted from 2003 to 2005 based on the findings of an analysis of 141 current-use pesticides, including their transformation products. In total, samples were taken from approximately 140 sites in about 15 watersheds of various sizes during this period. Below are a few highlights of the program's findings.

Key Facts on the Presence and Levels of Pesticides

Throughout Canada, 102 of the 141 pesticides analyzed were detected in precipitation, surface water, groundwater or runoff between 2003 and 2005. The most frequently detected pesticides (found in at least four regions) include the following:

  • atrazine
  • bromoxynil
  • chlorpyrifos
  • deethylatrazine
  • dicamba
  • dimethoate
  • linuron
  • mecoprop (MCPP)
  • metolachlor
  • metribuzin
  • simazine
  • 2,4-D

Number of Pesticides Detected/Number of Pesticides Analyzed (2003-2005)

  • British Columbia: 63/85 = 74%
  • Prairies: 34/47 = 72%
  • Ontario: 61/77 = 79%
  • Quebec: 28/58 = 48%
  • Atlantic: 15/25 = 60%

The largest number of pesticides was detected in British Columbia and Ontario.

Pesticides Most Frequently Detected in Surface Waters (2003-2005)
(Detection % = Number of Detections/Number of Samples Analyzed)

British Columbia

  • Endosulfan (98%)
  • MCPA (90%)
  • Dacthal (90%)
  • alpha-HCH (87%)
  • Diazinon (81%)

Prairies

  • 2,4-D (92%)
  • MCPA (92%)
  • Clopyralid (84%)
  • Dicamba (83%)
  • 2,4-DP (dichlorprop) (50%)

Ontario (2005 data only)

  • Atrazine (91%)
  • 2,4-D (79%)
  • Dicamba (74%)
  • Deethylatrazine (61%)
  • Mecoprop (58%)

Quebec (2005 data only)

  • Atrazine (95%)
  • Metolachlor (58%)
  • Dicamba (46%)
  • Deethylatrazine (45%)
  • Bentazon (31%)

Atlantic

  • Metalaxyl (8%)
  • Metribuzin (6%)
  • Chlorothalonil (6%)
  • Linuron (5%)
  • Azinphos-methyl (2%)

In surface waters, atrazine was frequently detected in Quebec and Ontario, while MCPA was the chemical found most often in the Prairies and British Columbia. In the Atlantic Region, pesticides were detected in up to 8% of the samples analyzed.

Percentage of Samples (1% of Samples or More)
that Exceeded Reference Values in Surface Waters, 2003-2005
Pesticide British Columbia Prairies Ontario Quebec
Chlorpyrifos 6% 17% (*) 4% 15%
Diazinon (diazinon-oxon) 4%   10%  
Dichlorvos 6%      
Atrazine     6%  
Endosulfan     4%  
2,4-D   2% (**) 2%  
MCPA   3% (**)    
Azinphos-methyl 1%   2%  
Cypermethrin 2%      
Clopyralid     2%  
Atrazine       2%
Malathion     2%  
Metribuzin     2%  
Dicamba     1%  

(*) Measured in reservoir water. (**) Measured in wetlands.

A total of 14 pesticides exceeded reference values. The most exceedances were observed for chlorpyrifos, particularly in the Prairies and Quebec, followed by diazinon, for which reference values were exceeded by 10% in Ontario. Ontario also had the greatest number of exceedances.

Environment Canada. 2011. Accessible PDF (2500 KB). Water Science & Technology Directorate

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