title: Fate of the herbicides 2,4,5-T, atrazine, and DNOC in a shallow, anaerobic aquifer investigated by in situ passive diffusive emitters and laboratory batch experiments.
abstract: The fate of the three herbicides 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), atrazine (6-chloro-N-ethyl-N'-[1-methyl-ethyl]-1,3,5-triazine-2,4-diamine), and DNOC (4,6-dinitro-2-methylphenol) in an anaerobic sandy aquifer was investigated. In the field, each of the herbicides was released simultaneously with tritiated water (HTO) as tracer in the depth interval 3 to 4 mbs (meters below surface) by use of passive diffusive emitters. Atrazine and 2,4,5-T were persistent during the approximately 18 days residence time in the aquifer. In contrast, DNOC was rapidly removed from the water phase following first-order kinetics. The removal mechanism was likely an abiotic reduction. At day 25, the first-order rate constant was 1.47 d(-1), but it decreased with time and seemed to stabilize at 0.35 d(-1) after 150 to 200 days. In the laboratory, batch experiments were conducted with sediments from 3 to 4 mbs and from 8 to 9 mbs. In these incubations, formation of Fe2+ and depletion of sulfate showed iron and sulfate reduction in sediment from 3 to 3.5 mbs and sulfate reduction in 3.5 to 4 mbs sediment. In sediment from 8 to 9 mbs, the dominant redox process was methane formation. In sediment from 3 to 3.5 mbs, only 27% to 52% of the 2,4,5-T remained after 196 days. 2,4,5-trichlorophenol was identified as the major metabolite. A lag period of at least 50 days was observed, and no degradation occurred in HgCl2 amended controls, verifying that the process was microbially mediated. In the other 2,4,5-T incubations and all the atrazine incubations, concentrations decreased linearly, but less than 25% was removed within 200 to 250 days. No degradation products could be detected, and slow sorption was the likely explanation. In all the laboratory incubations DNOC was degraded, following first-order kinetics, and when normalized to the sediment/water-ratio, the field and laboratory derived rate constants compared well. The DNOC degradation in the methanogenic incubations (8 to 9 mbs) was up to 50 times faster than in the sediments from 3 to 4 mbs, likely due to the low redox potential.
authors.affiliation: Environment & Resources DTU and Groundwater Research Center, Technical University of Denmark, Lyngby.
authors.forename: N P
authors.initials: NP
authors.lastname: Arildskov
authors.forename: P G
authors.initials: PG
authors.lastname: Pedersen
authors.forename: H J
authors.initials: HJ
authors.lastname: Albrechtsen
mesh_terms: D015085:2,4,5-Trichlorophenoxyacetic Acid / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D001280:Atrazine / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D004138:Dinitrocresols / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D004784:Environmental Monitoring; D019605:Euryarchaeota / Q000502:physiology; D019015:Geologic Sediments / Q000737:chemistry; D006540:Herbicides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000032:analysis* / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000378:metabolism
chemical_list: D004138:Dinitrocresols; D006540:Herbicides; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; C024132:4,6-dinitro-o-cresol; D015085:2,4,5-Trichlorophenoxyacetic Acid; D001280:Atrazine