Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/1999
Publication Date: N/A
Interpretive Summary: Contamination of surface water and ground water by pesticides has been a source of concern for the past several years. Mobility of many soil-applied pesticides is dependent on the mineralogical and organic components that make up soil. However, there is no data available on the relative behavior of pesticides in tropical soils, which are chemically and physically distinct from soils developed in non-tropical climates. These soils are subject to relatively high year round temperatures and occasional high rainfalls. The objective of the present study was to characterize the sorption of imidacloprid, a recently developed insecticide, and three of its breakdown products on typical tropical Brazilian soils. An understanding of the sorption phenomena would help in the safe and effective use of imidacloprid in tropicals soils such as in Brazil. It was found that the sorption of imidacloprid and its metabolites on the tropical lsoils was somewhat lower than in soils developed in non-tropical climates, presumably due to their lower soil organic carbon contents and their characteristic clay mineralogy. However, imidacloprid and its metabolites would still be considered to be slightly mobile to immobile in Brazilian soils. This research will inform users that proper use of the chemical appears to allow control of pests with a chemical that has minimal potential to adversely impact surface and ground waters.
Technical Abstract: The sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2- imidazolid-inimine) (IMI) and its metabolites imidacloprid-urea (1-[(6- chloro-3-pyridinyl)-methyl]-2-imidazol-idinone) (IU), imidacloprid- guanidine (1-[(6-chloro-3-pyridinyl)-methyl]-4,5-dihydro-1H-imidazol-2- amine) (IG), and imida-cloprid-guanidine-olefin (1-[(6-chloro-3- pyridinyl)methyl]-1H-imidazol-2-amine) (IGO) was determined on six typical Brazilian soils. Sorption of the chemicals on the soil was characterized using the batch equilibration method. The range and order of sorption (Kd) on the six soils was IG (4.75-13.4) IGO (2.87-72.3) > IMI (0.55 -16.9) > IU (0.31-9.50). For IMI and IU, Kd was correlated with soil organic carbon (OC) content and CEC, the latter due to the high correlation between OC and cation exchange capacity (CEC) (R2=0.98). For IG and IGO, there was no correlation of sorption to clay, pH, OC or CEC due to the high sorption on all soils. Average Koc values were IU = 170, IMI = 362, IGO = 2433, and IG = 3500. Although Kd and Koc values found were consistently lower than those found in soils developed in non-tropical climates, imidacloprid and its metabolites were still considered to be slightly mobile to immobile in Brazilian soils.