2-Methly-4-chlorophenoxyacetic acid (MPCA) sorption and desorption as a function of biochar properties and pyrolysis temperature

Authors: NIAZ, ABDULLAH - Collaborator; Spokas, Kurt; GAMIZ, BEATRIZ - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC); MULLA, DAVID - University Of Minnesota; ARSHAD, KHALIQ - Collaborator; HUSSAIN, SARFRAZ - Collaborator

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2023
Publication Date: 9/8/2023
Citation: Niaz, A., Spokas, K.A., Gamiz, B., Mulla, D., Arshad, K.R., Hussain, S. 2023. 2-Methly-4-chlorophenoxyacetic acid (MPCA) sorption and desorption as a function of biochar properties and pyrolysis temperature. PLOS ONE. 18(9). Article e0291398. https://doi.org/10.1371/journal.pone.0291398.
DOI: https://doi.org/10.1371/journal.pone.0291398

Interpretive Summary: A complete understanding of the factors influencing the sorption capacity of biochar is still lacking. This study aimed to examine the influence of three different parent materials (wood pellet, poultry manure, and rice hulls) that were used to create biochars at 3 different pyrolysis temperatures (350, 500, and 800 °C) to examine the changes in sorption capacity for a common herbicide (2-methyl-4-chlorophenoxyacetic acid; MCPA). The results of this work showed that was a general relationship of higher pyrolysis temperatures increasing the observed sorption. However, the magnitudes of these increases were a function of the different feedstocks. Poultry manure and rice hulls when created at higher temperatures (500 and 800 °C) could be used for remediation efforts (such as spills or water filtration). On the other hand, wood pellets and rice hulls pyrolyzed at 350 °C could be used for direct field applications to limit losses (i.e., runoff and leaching), but still allowing some herbicidal action in the soil system with desorption. These results highlight the need to understand the mechanisms of chemical sorption as a function of feedstock and pyrolysis temperatures to properly assess both short- and longer-term impacts of biochar additions. These results are significant to farmers and policy makers and will assist scientists and engineers in understanding the potential pathways for improved mechanisms of biochar’s chemical sorption behavior.

Technical Abstract: 2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a highly mobile herbicide as is frequently detected in global potable water sources. One potential mitigation strategy is the sorption on biochar to limit harm to unidentified targets. However, irreversible sorption could restrict bioefficacy thereby compromising its usefulness as a vital crop herbicide. This research was planned to evaluate the effect of pyrolysis temperatures (350, 500 and 800 °C) on three feedstocks; poultry manure (PM), rice hulls (RH) and wood pellets (WP), particularly to examine the reversibility of MCPA sorption. Sorption increased with pyrolysis temperature from 350 to 800 °C. Sorption and desorption coefficients were strongly corelated with each other (R2 = 1.00; P < .05). Poultry manure and rice hulls pyrolyzed at 800 °C (PM800 and RH800) exhibited irreversible sorption while for wood pellets at 800 oC desorption was concentration dependent at higher concentrations some desorption was observed (36% at 50 ppm) but was reduced at lower concentrations (1-3% at < 5 ppm). Desorption decreased with increasing pyrolysis temperature. Sorption data was fit to Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models. Freundlich isotherms were better correlated with MCPA sorption (R2 ranging from 0.78 to 0.99). Poultry manure and rice hulls when pyrolyzed at higher temperatures (500 and 800 °C) could be used for remediation efforts (such as spills or water filtration), whereas wood pellets and rice hulls pyrolyzed at 350 °C could perform superior for field applications to limit indirect losses including runoff and leaching but possess the ability to release MCPA subsequently to potentially allow herbicidal action.