Abstract
Views on the entry of organic pollutants into the organic matter (OM) decaying process are divergent, and in part poorly understood. To clarify these interactions, pesticide dissipation was monitored in organic and mineral soils not adapted to contaminants for 241 days; in groundwater sediment slurries adapted to pesticides for 399 days; and in their sterilized counterparts with and without peat (5%) or compost-peat-sand (CPS, 15%) mixture addition. The results showed that simazine, atrazine and terbuthylazine (not sediment slurries) were chemically dissipated in the organic soil, and peat or CPS-amended soils and sediment slurries, but not in the mineral soil or sediment slurries. Hexazinone was chemically dissipated best in the peat amended mineral soil and sediment slurries. In contrast, dichlobenil chemically dissipated in the mineral soil and sediment slurries. The dissipation product 2,6-dichlorobenzamide (BAM) concentrations were lowest in the mineral soil, while dissipation was generally poor regardless of plant-derived OM, only algal agar enhanced its chemical dissipation. Based on sterilized counterparts, only terbutryn appeared to be microbially degraded in the organic soil, i.e., chemical dissipation of pesticides would appear to be utmost important, and could be the first response in the natural cleansing capacity of the environment, during which microbial degradation evolves. Consistent with compound-specific dissipation in the mineral or organic environments, long-term concentrations of pentachloroaniline and hexachlorobenzene were lowest in the mineral-rich soils, while concentrations of dichlorodiphenyltrichloroethane (DTT) and metabolites were lowest in the organic soils of old market gardens. OM amendments changed pesticide dissipation in the mineral soil towards that observed in the organic soil; that is OM accelerated, slowed down or stopped dissipation.
Highlights
Soil organic matter (OM) formation and litter decomposition have initially been thought to be separate processes in so called “humification”
To investigate the relationship between OM and organic pollutant dissipation, pesticides were used as model compounds in a three-factor experiment in low OM mineral soil (OM, 29 ± 4 mg g−1), rich OM organic soil (OM, 123 ± 3 mg g−1), and in similar autoclave-sterilized counterparts in the dark (Table 1)
The long-term relationship between OM and pesticide dissipation was further investigated in a three-factor experiment in low OM (4.3 ± 0.2 mg g−1) groundwater sediment slurries and their sterilized counterparts in aerobic and anaerobic conditions (Table 1; Kerminen et al, 2018)
Summary
Soil organic matter (OM) formation and litter decomposition have initially been thought to be separate processes in so called “humification”. After the discovery that soil OM consists of mixtures of microbial and, to lesser extent, plant constituents and their derivatives at different stages of degradation, the Organic Matter Enhancing Pollutant Dissipation super constructions they form were thought to be stabilized by e.g., hydrogen and hydrophobic bonds, occlusion, intercalation, and encapsulation (Sollins et al, 1996; Burdon, 2001; Lützow et al, 2006; Cotrufo et al, 2013). Abiotic dissipation pathways have been regarded as minor in selective preservation and progressive decomposition models (Burdon, 2001; Lützow et al, 2006), while OM as a nutrient in soil has been thought to increase microbial activity and thereby the microbial degradation of harmful persistent compounds (Burauel and Baßmann, 2005; Krutz et al, 2010; Fenner et al, 2013). Chemical and physical mechanisms are regarded to stabilize soil OM e.g., via organo-mineral bonds (Lehmann and Kleber, 2015; Totsche et al, 2018; Baveye and Wander, 2019; Lavallee et al, 2020)
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