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, NHNO, NHNO 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 11.3-14.6m 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 NHNO and NHNO with Na-citrate, although the nitrogen additives increased microbial growth.

The pesticide atrazine, its degradation products, and 2,6-dichlorobenzamide (BAM) are persistent in groundwater environment. We studied whether their dissipation can be enhanced with a mixture of a complex carbon source and zero-valent iron (ZVI) called EHC®. The application rates were 1.0% and 2.0% (by weight) in subsurface sediments slurries (atrazine 30mg/L), and 2.0% in 1.5m pilot-scale sediment columns with groundwater flowing through (atrazine 0.08, desethylatrazine DEA 0.03, BAM 0.02μg/L). In the slurries under aerobic conditions, atrazine of 0.88±0.14mg/g of EHC® was dissipated chemically, as concentrations did not differ significantly between the slurries and their sterilized controls. No degradation occurred in the slurries under anaerobic conditions. In the pilot-scale columns under water-saturated conditions, atrazine, DEA and BAM were not detected in effluents during 33, 64 and 64days from the beginning of the water flow through EHC® columns, respectively, but thereafter traces of compounds could be detected. No atrazine or degradation products (BAM, DEA, deisopropylatrazine, desethyldeisopropylatrazine) could be extracted from the column sediments at the end of the experiment. As a result, the sum of dissipated pesticides was about 7.6μg/g of EHC® in columns under water-saturated conditions, and 0.88mg/g of EHC® in slurries under aerobic conditions. EHC® can be used to enhance the dissipation of studied pesticides in small quantities, preferentially under aerobic conditions.

Herbicide atrazine easily leaches to groundwater, where it is persistent. We studied whether sonication accelerates atrazine dissipation (100 mg·L −1 ) in vadose zone sediment slurries. Sediments were from 11.3 to 14.6 m depths in an atrazine-contaminated groundwater area. The slurries and autoclave-sterilized slurries were sonicated (bath, 43 kHz, 320 W) for 0, 5, 10, 20, or 30 min once/twice a day, and atrazine concentrations were followed. Atrazine concentrations raised in the sterilized slurries sonicated twice a day for 10 min (86.0 ± 7.7 mg·L −1 ), while they remained low in the slurries (56.6 ± 10.9 mg·L −1 ) due to microbial degradation. Twice a day sonications for 20-30 min did not enhance microbial atrazine degradation. Chemical dissipation may have occurred in the sterilized slurries sonicated twice a day for 30 min. However, sonication did not decrease atrazine concentrations below those in the non-sonicated slurries (55.1 ± 7.8 mg·L −1 ) and sterilized slurries (67.1 ± 7.9 mg·L −1 ). Atrazine concentrations in the sterilized slurries were higher than in the slurries, indicating changes in sediment structure and adsorption due to autoclaving. Sonication parameters needed for releasing atrazine from interactions with particles may be close to those damaging microbial cells. This suggests difficulties in enhancing microbial atrazine degradation by sonication, though chemical degradation can be enhanced.

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.