To assess the exposure to polycyclic aromatic hydrocarbons (PAHs) it is important to understand the binding mechanisms between specific soil constituents and the organic pollutant. In this study, sorptive bioaccessibility extraction (SBE) was applied to quantify the accessible PAH fraction in industrially contaminated soil with and without passive dosing of a competitive sorbate. SBE experiments revealed an accessible PAH fraction of 41 ± 1% (∑16 US EPA PAHs + 5 further PAHs). The passive dosing of toluene below its saturation level revealed competitive binding and resulted in an average increase of the accessible fraction to 49 ± 2%, whereby primarily the accessibility of higher molecular weight PAHs (log K > 6) was affected. Competitive binding was verified using the same soil with only desorption-resistant PAHs present. In this experiment, passive dosing of toluene resulted in desorption of 13 ± 0.4% PAH. We explain increased PAH desorption after addition of toluene by competitive adsorption to high-affinity sorption sites while acknowledging that toluene could additionally have increased PAH mobility within the soil matrix. Findings suggest that the presence of copollutants at contaminated sites deserves specific considerations as these may increase accessibility and thereby exposure and mobility of PAHs.

The potential of lignosulfonates as widely underutilized byproducts of the pulp and paper industry for the synthesis of a biodegradable pesticide carrier system was assessed in this study. Design of experiment software MODDE Pro was for the first time applied to optimize lignosulfonate granule production using Myceliophthora thermophila laccase as a biocatalyst. Enzymatic cross-linking was monitored using size exclusion chromatography coupled online to multiangle laser light scattering, viscosity measurement, and enzyme activity. The determined optimal and experimentally confirmed incubation conditions were: 33 °C, 30 cm3/min O2 supply, and 190 min reaction time. The granules were thereafter loaded with 2 g/kg 3,6-dichloro-2-methoxybenzoic acid (Dicamba), a broad-spectrum herbicide. According to the HPLC analysis, complete release of Dicamba was achieved after 48 h of release. This study showed the green production of a 100% lignosulfonate-based biodegradable solid carrier with potential application in agriculture.

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