Herbicide contamination of surface runoff waters /

Field and laboratory studies of the movement of herbicides were conducted to determine their potential as contaminants in irrigation return flow. Special emphasis was given to the use of herbicides for vegetation control along ditches, canals and watersheds where high dosages are required to control the excessive growth of grasses and broadleaved weeds. The following herbicides have been studies: substituted urea (diuron), triazines (summitol and atrazine), phenoxyacetic acid (2, 4-D and 2, 4, 5-T) and a substituted pyridine (picloram). The greatest tendency for transport of herbicides in water coming in contact with soils occurs during the initial storms following spray application. If the intensity of the initial precipitation is not sufficient to cause movement across the soil, the danger of herbicide movement is essentially eliminated. The highest concentratoins (ppm) of herbicide observed in surface waters were 1.8, 0.5, 4.2 and 2.7 for diuron, summitol, 2, 4-D, 2, 4, 5-T and picloram, respectively. These levels were observed immediately below treated areas receiving the higher recommended dosages of the herbicides. All herbicide concentrations dropped below the limit of detection within a few hundred meters below the sprayed areas. Presumably, soil filtration, adsorption and dilution are primarily responsible for the loss of herbicides from water."Project 13030 FDJ; Program Element 1B2039."Includes bibliographical references (pages 87-92).Conclusions -- Recommendations -- Introduction -- Literature review -- Materials and methods -- Results and discussion -- Summary -- Acknowledgments -- References -- Publications resulting from project -- Appendices.Field and laboratory studies of the movement of herbicides were conducted to determine their potential as contaminants in irrigation return flow. Special emphasis was given to the use of herbicides for vegetation control along ditches, canals and watersheds where high dosages are required to control the excessive growth of grasses and broadleaved weeds. The following herbicides have been studies: substituted urea (diuron), triazines (summitol and atrazine), phenoxyacetic acid (2, 4-D and 2, 4, 5-T) and a substituted pyridine (picloram). The greatest tendency for transport of herbicides in water coming in contact with soils occurs during the initial storms following spray application. If the intensity of the initial precipitation is not sufficient to cause movement across the soil, the danger of herbicide movement is essentially eliminated. The highest concentratoins (ppm) of herbicide observed in surface waters were 1.8, 0.5, 4.2 and 2.7 for diuron, summitol, 2, 4-D, 2, 4, 5-T and picloram, respectively. These levels were observed immediately below treated areas receiving the higher recommended dosages of the herbicides. All herbicide concentrations dropped below the limit of detection within a few hundred meters below the sprayed areas. Presumably, soil filtration, adsorption and dilution are primarily responsible for the loss of herbicides from water.Mode of access: Internet