Pesticide Sorption to Soilless Media Components Used for Ornamental Plant Production and Aluminum Water Treatment Residuals

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 differing affinities for the pesticides acephate, imidacloprid, metalaxyl, and plant growth regulator paclobutrazol. One-point 24 h equilibrium sorption assays were conducted to characterize sorption of the 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 sorptive 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% of the initial amounts for soilless media components and 63% in Al-WTRs. Al-WTRs were highly sorptive for imidacloprid as evidenced by a partition coefficient of KF = 3275.4 L kg–1. Pine bark was the most sorptive for metalaxyl-M with a measured KF = 195.0 L kg–1. Peat had the highest affinity for paclobutrazol (KF = 398.4 L kg–1). These results indicate that none of component of soilless media has a universally high attraction for all of the pesticides studied.

Assessment of Woodchip Bioreactor Characteristics and Their Influences on Joint Nitrate and Pesticide Removal

“…The nls­() function of base R was used to perform a nonlinear regression fitting the resulting data to a Freundlich isotherm model, yielding a Freundlich constant ( K F ) of 245 L/kg and exponent of nonlinearity (1/ n ) of 0.751 (Figure SI 9.2). Leiva et al observed K F values of 290.4 and 157.4 L/kg, and 1/ n values of 0.77 and 1 for imidacloprid on peat and pine bark, respectively. Mandal and Singh obtained a K F value of 85.71 L/kg, and a 1/ n value of 0.920 for imidacloprid sorption to eucalyptus bark.…”

Substrate Stratification: Layering Unique Substrates within a Container Increases Resource Efficiency without Impacting Growth of Shrub Rose

“…There is growing evidence that substrate engineering [9] can lead to more sustainable substrates by creating unique physiochemical characteristics [10] to address specific pitfalls in conventional substrates. Recent research has shown that designer or engineered substrates have the potential to reduce weed pressure [11], water use [12], nutrient leaching [13], pesticides leaching [14], and production times [15].…”

Losses of selected pesticides in drainage water from containerized ornamental plants

“…That study identified acephate, a highly water‐soluble pesticide, as having a low affinity (21–31% of pesticide applied) for sorption to most components. The intermediately soluble pesticide imidacloprid had a high affinity for coir, peat, and pine bark, sorbing 76.2–87.1% of the pesticide used in the incubations, whereas paclobutrazol (lowest water solubility of 26 μg L −1 ) showed the highest affinity for pine bark and peat (respectively), with sorption ranging from 88.9 to 92.9% of the total pesticide used in the incubations, and intermediate sorption to coir (70.4%) (Leiva, Wilson, Albano, Nkedi‐Kizza, & O'Conner, 2019). That study illustrates well the fact that media is heterogeneous and the interactions between different chemistries and media components can vary significantly.…”