This website was created for Biology 361: Genetically Modified Organisms at Davidson College.by Mike Chase and Monica Siegenthaler

 

Environmental Effects

Permission pending from http://www.redsidedace.com/ agrithreat.html

Herbicide runoff from farms and industries polute rivers and streams.

 

Permission pending from
http://www.lakedoctoroftexas.com/

 

Types of Herbicide Transport (Fate 2002):

  1. leaching- down into the soil
  2. run-off- across the soil surface
  3. volatilization- into the air

Degradation (Fate 2002):

Degradation is the process of chemical modification of pesticides by biotic and abiotic processes.  The first steps in degradation are:

  1. detoxification:  loss of ecological toxicity as a result of an abiotic reaction (sunlight, catalytic surfaces)
  2. inactivation: loss of pesticidal activity as a result of an abiotic reaction

Abiotic reaction result in partial modification.  Biotic processes  (bacteria, fungi) are almost always required for complete degradation.

Herbicides and Water Quality:

Residues of some herbicides (atrazine, metolachlor, alachlor, cyanazine, and metribuzin) have been found in surface and ground water.  For example, the US Geological Survey detected the herbicide atrazine in each of 146 water samples collected at 8 locations throughout the Mississippi drainage basin.  Over 74% of the samples also contained alachlor, metachlor, or cyanazine.  Atrazine concentration exceeded the EPA maximum contaminant level for several weeks in rivers as large as the Missouri and Mississippi.  The central US rivers supply drinking water to 18 million people and many herbicides are not removed from drinking water by conventional filtration and treatment  (Liebman et al 1993). 

The Acetanilides (alachlor, metolachlor, and acetochlor) and the Triazins (atrazine, cyanazine, and simazine) are most commonly found in water supplies.  Both types of herbicides are persistent as well as mobile to highly mobile in soil.  This explains why they normally leach into the water.  As a result, the EPA has taken regulatory measures in attempts to minimize the amount of run-off and leaching.  For example, the EPA conditionally registered acetochlor in 1994.  This limited the use of metolachlor to certified applicants, prevented aerial application, restricted the types of soil on which it can be used, and prohibited application to water.  When water samples exceed 2.0 parts per billion, further restrictions are placed on the use of acetochlor (“Herbicides” 1997).

Herbicide-contaminated waters pose health risks to humans and affect the biodiversity of the ecosystem.  Mayflies, for instance, are in danger of extinction as their aquatic habits are increasingly polluted with herbicides and other xenobiotic chemical substances (Mitchell 1998).  Polluted waters are also affecting fish populations in streams, rivers, and oceans (Tilman et al 2002).  Sewalk et al studied the effects of diquat on the development of mallard embryos.  Defects associated with diquat included defects of the brain, eye, bill, limb, and pelvis; skeletal scoliosis; and incomplete ossification (Sewalk et al 2001).  Such defects affect the fitness of mallards, and are factors that could lead to endangerment.

 

 

 

© Copyright 2002 Department of Biology, Davidson College, Davidson, NC 28035
Send comments, questions, and suggestions to: michase@davidson.edu or mosiegenthaler@davidson.edu