Influence of organic matter, nutrients, and cyclodextrin on microbial and chemical herbicide and degradate dissipation in subsurface sediment slurries

Highlights: • Herbicides and degradation products are found in groundwater, treatment required. • Microbial and chemical dissipation was studied in subsurface sediment slurries. • Peat and/or compost-peat-sand mixture enhanced chemical dissipation of triazines. • Dichlobenil dissipated under aerobic and anaerobic conditions, BAM did not. • Pseudomonas ADP degraded atrazine, but indigenous sediment microbes did not. Pesticides leaching from soil to surface and groundwater are a global threat for drinking water safety, as no cleaning methods occur for groundwater environment. We examined whether peat, compost-peat-sand (CPS) mixture, NH₄NO₃, NH₄NO₃ with sodium citrate (Na-citrate), and the surfactant methyl-β-cyclodextrin additions enhance atrazine, simazine, hexazinone, dichlobenil, and the degradate 2,6-dichlorobenzamide (BAM) dissipations in sediment slurries under aerobic and anaerobic conditions, with sterilized controls. The vadose zone sediment cores were drilled from a depth of 11.3–14.6 m in an herbicide-contaminated groundwater area. The peat and CPS enhanced chemical atrazine and simazine dissipation, and the peat enhanced chemical hexazinone dissipation, all oxygen-independently. Dichlobenil dissipated under all conditions, while BAM dissipation was fairly slow and half-lives could not be calculated. The chemical dissipation rates could be associated with the chemical structures and properties of the herbicides, and additive compositions, not with pH. Microbial atrazine degradation was only observed in the Pseudomonas sp. ADP amended slurries, although the sediment slurries were known to contain atrazine-degrading microorganisms. The bioavailability of atrazine in the water phase seemed to be limited, which could be due to complex formation with organic and inorganic colloids. Atrazine degradation by indigenous microbes could not be stimulated by the surfactant methyl-β-cyclodextrin, or by the additives NH₄NO₃ and NH₄NO₃ with Na-citrate, although the nitrogen additives increased microbial growth.