Influence of Adjuvants on Pesticide Soil-Air Partition Coefficients: Laboratory Measurements and Predicted Effects on Volatilization

Authors

Supta Das, University of Otago
Kimberly J. Hageman, Utah State UniversityFollow

Document Type

Article

Journal/Book Title

Environmental Science & Technology

Publication Date

5-21-2020

Publisher

American Chemical Society

Volume

54

Issue

12

First Page

1

Last Page

22

Abstract

A solid-phase fugacity meter was used to measure the soil–air partition coefficients of three semivolatile pesticides (chlorpyrifos, pyrimethanil, and trifluralin) in the absence of additional adjuvants (K_{soil–air,AI}), as part of commercial formulations (K_{soil–air,formulation}), and as formulation mixtures with an additional spray adjuvant added (K_{soil–air,formulation+spray adjuvant}). Chlorpyrifos K_{soil–air,formulation} values were also measured over 15–30 °C, allowing for the change in internal energy of the phase transfer reaction (Δ_soil–airU) to be calculated and compared to the Δ_soil–airU for K_{soil–air,AI} from the literature. Measured K_soil–air values were then used as input parameters in a pesticide volatilization model to understand how their variability affects pesticide volatilization rates under different conditions. Initial experiments conducted at ∼24 °C indicated that all pesticides volatilized more readily in the presence of adjuvants than in their absence and that the additional spray adjuvant had minimal impact. The Δ_soil–airU values were 328 and 90 kJ/mol for chlorpyrifos in the absence and presence of formulation adjuvants, respectively, suggesting that adjuvants may weaken or disrupt intermolecular attractions between pesticide molecules and soil. At temperatures below 24.5 °C, modeled chlorpyrifos volatilization rates were higher in the presence of adjuvants than in their absence; however, the opposite occurred at temperatures above 24.5 °C.

Comments

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science & Technology, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.est.0c00964

Recommended Citation

Supta Das & Kimberly J. Hageman. Influence of Adjuvants on Pesticide Soil–Air Partition Coefficients: Laboratory Measurements and Predicted Effects on Volatilization. Environ. Sci. Technol. 2020, 54, 12, 7302–7308. https://doi.org/10.1021/acs.est.0c00964