[1] USGS logo 
   
Pesticides found in major rivers and aquifers reflect contributions from
both agricultural and urban areas

   [2] U.S. Geological Circular 1225--The Quality of Our Nation's
   Waters--Nutrients and Pesticides
   


                       [3] Photo by Peter A. Steeves
                         [4] image size 39KB--jpeg
                                      
   Major rivers and streams draining areas of mixed land use contain
   pesticides from both agricultural and urban sources and from both past
   and present use. In water that comes mainly from agricultural areas,
   the most commonly found pesticides are the major herbicides atrazine
   (and DEA), metolachlor, cyanazine, and alachlor. In water that comes
   mainly from urban areas, the most common pesticides are the herbicides
   simazine and prometon and the insecticides diazinon and carbaryl.
   
   Like water, the fish and bed sediment of major rivers and streams with
   mixed land-use influences contain mixtures of organochlorine
   insecticides from agricultural and urban areas. Detection frequencies
   and concentrations of DDT, dieldrin, and chlordane were generally
   intermediate between those of agricultural and urban streams.
   
   Many large rivers with mixed land-use influences tend to have lower
   concentrations of pesticides compared with agricultural and urban
   streams because of a larger influence of undeveloped land. Some rivers
   in intensive agricultural regions, however, have concentrations that
   are similar to those in agricultural streams, although they are less
   variable over time. Rivers with mixed land uses almost always contain
   detectable pesticides that reflect the diversity of sources present.
   
   In contrast, ground water in major aquifers has a substantially lower
   frequency of pesticide occurrence than shallow ground water in
   agricultural and urban areas. This difference results from the
   generally deeper wells sampled in major aquifers and the greater
   influence of undeveloped areas. Additionally, owing to the slow rate
   of ground-water flow, much of the water sampled in the major aquifers
   may have infiltrated into the ground before pesticides were applied.
   The two most frequently detected compounds in major aquifers were
   atrazine and DEA, resulting from the high and extensive use of
   atrazine, the greater extent of agricultural land compared to urban
   land affecting most major aquifers sampled, and the high mobility and
   long-lived nature of atrazine and DEA.
   
   Because the pesticides found in major rivers and aquifers reflect
   contributions from both agricul-tural and urban land uses, efforts to
   improve the quality of these water resources will require management
   of nonpoint sources in both agricultural and urban areas.
     _________________________________________________________________
   
      [5] next arrow [6] Geographic distributions of pesticides follow
                   patterns in land use and pesticide use
   [7] back arrow [8] Different pesticides dominate in different land-use
                                   areas
     [9] up arrow [10] The Quality of Our Nation's Water--Nutrients and
                                 Pesticides

References

   0. http://water.usgs.gov/pubs/circ/circ1225/html/contributions.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/p63.html
   4. http://water.usgs.gov/pubs/circ/circ1225/images/p63.html
   5. http://water.usgs.gov/pubs/circ/circ1225/html/geographic.html
   6. http://water.usgs.gov/pubs/circ/circ1225/html/geographic.html
   7. http://water.usgs.gov/pubs/circ/circ1225/html/dominate.html
   8. http://water.usgs.gov/pubs/circ/circ1225/html/dominate.html
   9. http://water.usgs.gov/pubs/circ/circ1225/index.html
  10. http://water.usgs.gov/pubs/circ/circ1225/index.html