WASTES IN RELATION TO AGRICULTURE AND FORESTRY 



15 



sold in the United States and 97 million acres of 

 agricultural land were treated with these unique 

 chemicals. 



Although good progress has been made in the 

 technology of herbicide use, much research is 

 needed to refine this technology. Herbicides ap- 

 plied to control weeds in one crop may leave resi- 

 dues in the soil which prevent the growth of cer- 

 tain other crops planted immediately following 

 harvest of the treated crop. Diuron used for weed 

 control in irrigated cotton in the Southwest may 

 leave residues in the soil which could injure vege- 

 table crops such as lettuce, carrots, cabbage, and 

 cucumbers when planted in the winter following 

 cotton harvest. 



Spray drift of 2,4,5-T and 2,4-D from applica- 

 tions on nearby forests, cropland, roadsides, and 

 rights-of-way has damaged chemically sensitive 

 trees such as dogwood, paper birch, box elder, 

 chestnut, black locust, and other shade trees, 

 shrubs, and herbaceous ornamentals. In some situa- 

 tions injury has occurred as much as 10 miles 

 downwind from the target area. 



The aromatic solvents and other herbicides used 

 to control aquatic weeds in irrigation systems are 

 known to be toxic to fish at levels generally higher 

 than the amounts needed for weed control. How- 

 ever, judicious use of certain solvents or herbicides 

 will provide weed control with little or no fish 

 toxicity. 



Limited information is available on the behavior 

 of some herbicides in soils. It is a complex picture. 

 Adsorption of a herbicide by a soil is determined 

 by the specific surface of the soil, organic matter 

 content, nature of the clay mineral, moisture status, 

 temperature, nature and degree of base saturation, 

 and structure and polarity of the herbicide 

 molecule. 



Soil micro-organisms are important in detoxify- 

 ing herbicides in soils. It is largely because of these 

 soil micro-organisms and other dissipation mech- 

 anisms that most herbicide residues in soils do 

 not show progressive buildup. 



The fact still remains that the toxicology of 

 residual herbicides on succeeding crops is often 

 unpredictable. Consequently, there is a pressing 

 need for far better information on the fate of 

 herbicides in soils, including the cultural practices 

 and climatic conditions that incur a modifying 

 influence. 



There is a continuing urgency to develop su- 

 perior herbicides with greater specificity and fewer 

 adverse residual side effects. 



Concentrated research effort is needed on engi- 

 neering principles to develop better techniques to 

 reduce drift. 



There would appear to be tremendous economic 

 advantages in developing weed control chemicals 

 that are more specific; for example, a chemical 

 that would only inhibit pollen production on 

 ragweed. 



The extensive use of herbicides and the problems 

 arising from residues in soil and water or drifts in 

 the atmosphere focus on the need to emphasize in- 

 vestigative studies on the pertinent array of 

 problems. 



Fungicides 



Fungicides do not appear to be of major con- 

 cern in environmental contamination. The organic 

 mercury compounds are generally the most haz- 

 ardous to man, but these are used mostly for seed 

 treatment. Accidental feeding of such treated seeds 

 to livestock and poultry sometimes causes 

 poisoning. 



Apple orchards and vineyards that have had a 

 long record of spraying with copper fungicides 

 may have very high levels of copper in the sur- 

 face soils. Zinc and manganese can accumulate 

 to toxic level in soils, but evidence indicates thai- 

 application of fungicides is not at fault. 



In terms of residues contaminating the enciron- 

 ment, there are many other substances that cause 

 more concern than fungicides. 



Heat 



Heat acts as a water pollutant because the 

 amount of oxygen that water can hold in solution 

 diminishes with increasing temperature. The in- 

 troduction of heat in any substantial quantities 

 into surface water has the net effect of introducing 

 additional oxygen-demanding wastes. 



Heat also has a detrimental environmental effect 

 upon fish and other aquatic life. Some fish can 

 stand only a very few degrees of increase in tem- 

 perature, and a substantial increase in tem- 

 perature can result in the elimination of some 

 forms of aquatic life. 



There is little in agricultural and forestry en- 

 deavor that contributes heat to streams and lak 



