2-Methyl-4-chlorophenoxyacetic acid (MCPA) sorption and desorption as a function of biochar properties and pyrolysis temperature.

2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a highly mobile herbicide that 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 evaluated the effect of pyrolysis temperatures (350, 500 and 800°C) on three feedstocks; poultry manure, rice hulls and wood pellets, particularly to examine effects on the magnitude and 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 = 0.99; P < .05). Poultry manure and rice hulls pyrolyzed at 800°C exhibited irreversible sorption while for wood pellets at 800°C 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 were analyzed with Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. Freundlich isotherms were better predictors of 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), due to the lack of desorption observed. On the other hand, un-pyrolyzed feedstocks or biochars created at 350°C could perform superior for direct field applications to limit indirect losses including runoff and leaching, since these materials also possess the ability to release MCPA subsequently to potentially allow herbicidal action.

Microbial degradation of chlorpyrifos in liquid media and soil.

Chlorpyrifos is a broad-spectrum insecticide which is used extensively in agriculture worldwide. Its massive application has led to the contamination of water and soil, and disruption of biogeochemical cycles. In addition, its residues have been detected in various ecological systems. A number of methods are currently available that can be used for the detoxification of such pesticides, however, this review focuses on microbial biodegradation which is considered to be one of the most viable options for the removal of organophosphate pesticides from the environment. Identification of genes and enzymes responsible for the cleavage of specific functional groups of the pesticide and understanding the kinetics of biodegradation are critical to accomplish successful bioremediation. Recently, the use of indigenous or genetically modified microorganisms and/or plants has increased the chances for in-situ bioremediation of contaminated sites. The literature provides evidence that the bioremediation process can be enhanced by maintaining an effective chlorpyrifos-degrading microbial community in the contaminated site and optimizing environmental conditions.