........... Background on Pesticide Research: 
 The Realities and Challenges of Crop Protection 

Guidelines for Water Quality in Canada  

     Whether from point or non-point sources, the use of pesticides may result in their movement to non-target areas such as water systems.  As noted by Currie and Williamson1, "movement of agricultural pesticides from the application site to the ecosystem may occur by both direct and in-direct mechanisms." 
  
     Direct Mechanisms: can occur during the preparation of pesticide solutions, through spray drift during application, and by volatilization of pesticide residues (vapours entering the air) following application2.  

     Indirect Mechanisms: include pesticide losses from the soil during rainstorm or snowmelt surface runoff, and through internal, subsurface soil drainage.  Airborne (volatilized) pesticide elements may also be carried long distances within the atmosphere.  
  
     The amount of loss, rate of transfer, and environmental fate of lost pesticide is dependent on numerous factors including: formulation, mode and rate of application, and physical-chemical characteristics of individual pesticides.  Pesticide fate can also be affected by the micro-climatic conditions at the application site, such as rain fall and wind that happens during or after application, soil type, moisture content, and pH and tillage practices3.  
  

Atmospheric transport is one indirect mechanism by which pesticides may be transferred from one source/location to local water systems.
Atmospheric transport is a mechanism that may transport pesticides in the ecosystem.   
 
     Before any pesticide is licensed for use in Canada, it is subject to rigorous testing and review procedures to examine potential impacts on drinking water, freshwater aquatic life, irrigation, and livestock water uses.  Water quality guidelines exist for most pesticides, and these are routinely being reviewed and updated as new products are developed4.  
  
     Water quality guidelines for specific pesticides, are typically expressed using the term "parts per million" (ppm) which is derived from a pesticide concentration in milligrams per litre (mg/L).  For example, the Canadian Water Quality Guidelines for Atrazine (discussed above) are currently as follows.  
  
Canadian Water Quality Guidelines for Atrazine (CWQG, 1995) 
Drinking 
Aquatic Life 
Irrigation 
Livestock 
Level (mg/L) 0.005
0.002 
0.010 
0.060 
     Occasionally, other measures are used to simplify monitoring or provide increased detail for chemical analysis.  Micrograms per litre (ug/L = parts per billion) and nanograms per litre (ng/L = parts per trillion) are also commonly used.  A microgram (ug) is one thousand times smaller than a milligram, and a nanogram (ng) is one thousand times smaller than a microgram.  
  
 The atrazine guideline to ensure safe drinking water quality is .005 milligrams per litre (.005 mg/L or .005 ppm = 5 ug/L = 5000 ng/L).  

     1Currie, R.S. and D.A. Williamson, 1995.  An Assessment of Pesticide Residues in Surface Waters of Manitoba, Canada: Manitoba Environmental Report #95-08, 1995. back 
     2Muir, D.C.G., 1991.  Dissipation and Transformations in Water and Sediment, p.1-87.  In: R. Grover and A.J. Cessna (eds.) Envirnomental Chemistry of Herbicides, vol.II CRC Press, Boca Rocan.back to text 
     3Willis, G.H. and L.L. McDowell, 1982.  Review: Pesticides in Agriculturall Runoff and their Effects on downstream Water Quality. Eenviro. Toxicol. Chem. 1:267-279.  In Currie and Williamson, 1995.back to text 
    4Health Canada /  Environment Canada, 1995.  Canadian Water Quality Guidelines: Summary Brochure, Supply and Services Canada, 4pp.back to text 
  
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Last Updated January 1998.