Pesticide sorption to soilless media components used for ornamental plant production and aluminum water treatment residuals

Authors: LEVIA, JORGE - Universidad De Costa Rica; WILSON, P CHRIS - University Of Florida; Albano, Joseph; NKEDI-KIZZA, PETER - University Of Florida; O'CONNOR, GEORGE - University Of Florida

Submitted to: ACS Omega
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2019
Publication Date: 1/15/2019
Citation: Levia, J.A., Wilson, P., Albano, J.P., Nkedi-Kizza, P., O'Connor, G.A. 2019. Pesticide sorption to soilless media components used for ornamental plant production and aluminum water treatment residuals. ACS Omega. 4:17782-17790.

Interpretive Summary: Commercial producers of containerized ornamental plants almost exclusively use soilless media as the substrate for growing the plants. Soilless media are composed primarily of organic materials as opposed to mineral soils. Significant amounts of pesticides can leach from pots containing soilless media to which pesticides have been added as drenches or top dressings. One of the goals of this project was to identify whether individual components comprising soilless media have different affinities for the pesticides acepahte, imidicloprid, metalaxy, and plant growth regulator paclobutrazol. One-point 24 hour equilibrium sorption assays were conducted to characterize sorption of pesticides to sand, perlite, vermiculite, coir, peat, pine bark, and aluminum-water treatment residuals (Al-WTRs). Results indicated significant differences in pesticide behavior with each substrate. Sorption of acephate to most of the substrate components was relatively low. Al-WTRs were highly sorptive for imidicloprid. Pine bark was the most sorptive for metalaxy-M. Peat had the highest affinity for paclobutrazol. These results indicate that none of the component of soilless media has a universally high attraction for all of the pesticides studied.

Technical Abstract: Commercial producers of containerized ornamental plants almost exclusively use soilless media as the substrate for growing the plants. Soilless media are composed primarily of organic materials as opposed to mineral soils. Significant amounts of pesticides can leach from pots containing soilless media to which pesticides have been added as drenches or top dressings. One of the goals of this project was to identify whether individual components comprising soilless media have different affinities for the pesticides acepahte, imidicloprid, metalaxy, and plant growth regulator paclobutrazol. One-point 24 hour equilibrium sorption assays were conducted to characterize sorption of pesticides to sand, perlite, vermiculite, coir, peat, pine bark, and aluminum-water treatment residuals (Al-WTRs). Five-point isotherms were then constructed for the more sportive peat and pine bark substrate components, and for the Al-WTRs. Results indicated significant differences in pesticide behavior with each substrate. Sorption of acephate to most of the substrate components was relatively low, comprising 21-31 percent of the initial amounts for soilless media components and 63 percent in Al-WTRs. Al-WTRs were highly sorptive for imidicloprid as evidenced by partition coefficient of Kf = 3275 L/kg. Pine bark was the most sorptive for metalaxy-M with a measured Kf = 195.0 L/kg. Peat had the highest affinity for paclobutrazol (Kf = 398.4 L/kg). These results indicate that none of the component of soilless media has a universally high attraction for all of the pesticides studied.