Abstract
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.
Highlights
The herbicide atrazine (6-chloro-N-ethyl-N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine) is used to control the growth of broad-leaved and grassy weeds
Sonication effects on atrazine dissipation were studied in the slurries and sterilized slurries, to separate microbial and chemical dissipation
The results of this study showed that microbes able to degrade atrazine occur in the drilling site sediments collected from the groundwater recharge area, but the microbial atrazine degradation ceased at high concentrations
Summary
The herbicide atrazine (6-chloro-N-ethyl-N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine) is used to control the growth of broad-leaved and grassy weeds. It and its degradation products are commonly found in the soil and surface water, and they can elute through the subsurface sediments to groundwater [1,2]. To protect the drinking water quality, the European Commission prohibited the sale of atrazine in 1992 [8]. Methods for the removal of atrazine from soil, subsurface sediments, and groundwater are needed. Microbes and microbial consortia can degrade and even mineralize atrazine [3,9], though the degradation rate is slow in subsurface sediments [5,10,11]
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