Submitted to: Acta Scientiae Circumstantiae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/1998
Publication Date: N/A
Citation: Interpretive Summary: The greatest potential for groundwater contamination is in areas that have sandy soils, which are used for agricultural crop production such as irrigated potato production. A two-year potato field study was conducted to determine the dissipation and movement of the herbicide metolachlor in a sandy loam soil in north central Minnesota. We found that metolachlor degraded rapidly (about 50 percent of applied chemical) in the surface soi during the first seven days after application, but then degrades much more slowly. By the end of the growing season about 50 percent of applied chemical still remained in the top 6 inches of soil. Although we could find no chemical in the soil between 6 and 24 inch depth during the growing season, we found very small amounts of metolachlor in water samples at a depth of 4 feet. These data indicate that very small amounts of applied metolachlor can move with water through this soil. However, these data also oshow that the threat of water contamination is not as great as the public believes. Further research is needed to develop crop production practices that will reduce the amount of residues in the surface 6 inches of soil to further reduce the potential risk of groundwater contamination by this chemical. Farmers can then use this information to show that responsible use of agricultural crop protection chemicals can have minimal impact on ground water quality.
Technical Abstract: Field and laboratory experiments were conducted to investigate the transport, degradation and persistence of metolachlor in a sandy loam soil. About 50 percent of applied metolachlor was found to dissipate during the first 7 days in the 0-15 cm layer soil. From 7 days after application (DAA) up to 107 days, the level of metolachlor in soil did not change significantly, and average residue level was 130 ug/kg. The half dissipation time of metolachlor was found 45 days in laboratory studies. Fifty percent of the field water samples at 135-cm depth contained detectable levels of metolachlor. The maximum and medial detectable concentration of metolachlor were 12.5 and 2.20 ug/kg in water samples, respectively. Metolachlor was detected in only 4 among 336 soil samples taken from 15 to 75 cm. The dissipation of metolachlor in 0 to 15 cm layer soil resulted from the combination of leaching and biological degradation processes.