[1] USGS logo 
   
Insecticides in streams were highest in urban areas

   [2] U.S. Geological Circular 1225--The Quality of Our Nation's
   Waters--Nutrients and Pesticides
   
   Most urban streams sampled, plus two major rivers dominated by urban
   influences--the South Platte River downstream from Denver and the
   Trinity River downstream from Dallas-Fort Worth--had among the highest
   insecticide concentrations of all streams and rivers sampled. Nine of
   11 urban streams and both rivers had concentrations that exceeded
   aquatic-life guidelines, usually in more than 20 percent of the
   samples. The most common insecticides to exceed guidelines were
   diazinon, chlorpyrifos, and malathion. Chlorpyrifos and malathion have
   USEPA aquatic-life criteria of 0.041 µg/L and 0.100 µg/L,
   respectively, and diazinon has a guideline of 0.080 µg/L established
   by the International Joint Commission for the Great Lakes.
   
   Insecticides in urban streams, largely from use around homes and in
   gardens, parks, and commercial areas, frequently occur at levels of
   concern for aquatic life and may be a significant obstacle for
   restoring urban streams. 
   
   [3] Insecticides detected in water in Zollner Creek, Oregon, 1993 and
                                    94.
                                      
                         [4] image size 61KB--jpeg
                                      
   Most agricultural streams had moderate or low concentrations of
   insecticides but, as for herbicides, several streams that drain
   intensively farmed areas that are irrigated had among the highest
   insecticide levels. Although concentrations of insecticides in
   agricultural streams tended to be low compared to urban streams,
   concentrations above aquatic-life guidelines were common. For about
   one-half of the agricultural streams, samples exceeded a guideline for
   one or more insecticides. In addition to diazinon and chlorpyrifos, an
   insecticide that frequently exceeded its guideline in agricultural
   streams was methyl azinphos, which has a USEPA aquatic-life criterion
   of 0.010 µg/L.
   
   Insecticide concentrations in most major rivers usually were lower
   than those measured in urban streams and exceeded aquatic-life
   guidelines in relatively few samples. Exceptions are the San Joaquin
   River, which drains farmlands with some of the heaviest insecticide
   use in the Nation, and the South Platte and Trinity Rivers, which are
   affected by both point and nonpoint sources from urban areas.
   
   
    [5] A national ranking of insecticides in streams. [6] Urban streams
                 [7] Rivers and streams with mixed land use
                                      
                         [8] image size 51KB--jpeg
                                      
                         [9] image size 31KB--jpeg
                                      
                         [10] image size 39KB--jpeg
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   [11] next arrow [12] Organochlorine insecticides were highest in urban
   streams and where historical agricultural use was greatest
   [13] back arrow [14] Herbicides in streams and major rivers were
   highest in the most intensively farmed agricultural regions
   [15] up arrow [16] The Quality of Our Nation's Water--Nutrients and
   Pesticides

References

   0. http://water.usgs.gov/pubs/circ/circ1225/html/insecticides.html
   1. http://www.usgs.gov/
   2. http://water.usgs.gov/pubs/circ/circ1225/index.html
   3. http://water.usgs.gov/pubs/circ/circ1225/images/p68.html
   4. http://water.usgs.gov/pubs/circ/circ1225/images/p68.html
   5. http://water.usgs.gov/pubs/circ/circ1225/images/insecticideSW1.html
   6. http://water.usgs.gov/pubs/circ/circ1225/images/insecticideSW2.html
   7. http://water.usgs.gov/pubs/circ/circ1225/images/insecticideSW3.html
   8. http://water.usgs.gov/pubs/circ/circ1225/images/insecticideSW1.html
   9. http://water.usgs.gov/pubs/circ/circ1225/images/insecticideSW2.html
  10. http://water.usgs.gov/pubs/circ/circ1225/images/insecticideSW3.html
  11. http://water.usgs.gov/pubs/circ/circ1225/html/historical.html
  12. http://water.usgs.gov/pubs/circ/circ1225/html/historical.html
  13. http://water.usgs.gov/pubs/circ/circ1225/html/intensively.html
  14. http://water.usgs.gov/pubs/circ/circ1225/html/intensively.html
  15. http://water.usgs.gov/pubs/circ/circ1225/index.html
  16. http://water.usgs.gov/pubs/circ/circ1225/index.html