title: Combined isotope and enantiomer analysis to assess the fate of phenoxy acids in a heterogeneous geologic setting at an old landfill.
abstract: Phenoxy acid herbicides and their potential metabolites represent industrial or agricultural waste that impacts groundwater and surface waters through leaching from old landfills throughout the world. Fate assessment of dichlorprop and its putative metabolite 4-CPP (2-(4-chlorophenoxy)propionic acid) is frequently obstructed by inconclusive evidence from redox conditions, heterogeneous geologic settings (e.g. clay till) and ambiguous parent-daughter relationships (i.e. 4-CPP may be daughter product or impurity of dichlorprop). For the first time, a combination of four methods was tested to assess transformation of phenoxy acids at a contaminated landfill (Risby site): analysis of (i) parent and daughter compound concentrations, (ii) enantiomer ratios (iii) compound-specific isotope analysis and (iv) enantiomer-specific isotope analysis. Additionally, water isotopes and chloride were used as conservative tracers to delineate two distinct groundwater flow paths in the clay till. Metabolite concentrations and isotope ratios of chlorinated ethenes demonstrated dechlorination activity in the area with highest leachate concentrations (hotspot) indicating favorable conditions also for dechlorination of dichlorprop to 4-CPP and further to phenoxypropionic acid. Combined evidence from concentrations, enantiomer ratios and isotope ratios of dichlorprop and 4-CPP confirmed their dechlorination in the hotspot and gave evidence for further degradation of 4-CPP downgradient of the hotspot. A combination of 4-CPP enantiomer and isotope analysis indicated different enantioselectivity and isotope fractionation, i.e. different modes of 4-CPP degradation, at different locations. This combined information was beyond the reach of any of the methods applied alone demonstrating the power of the new combined approach.
authors.affiliation: Department of Environmental Engineering, Technical University of Denmark, Miljoevej, Building 113, DK-2800 Kgs. Lyngby, Denmark. nemm@env.dtu.dk
authors.forename: N
authors.initials: N
authors.lastname: Milosevic
authors.forename: S
authors.initials: S
authors.lastname: Qiu
authors.forename: M
authors.initials: M
authors.lastname: Elsner
authors.forename: F
authors.initials: F
authors.lastname: Einsiedl
authors.forename: M P
authors.initials: MP
authors.lastname: Maier
authors.forename: H K V
authors.initials: HK
authors.lastname: Bensch
authors.forename: H-J
authors.initials: HJ
authors.lastname: Albrechtsen
authors.forename: P L
authors.initials: PL
authors.lastname: Bjerg
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000031:analogs & derivatives / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D008456:2-Methyl-4-chlorophenoxyacetic Acid / Q000031:analogs & derivatives / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D000538:Aluminum Silicates / Q000737:chemistry; D002247:Carbon Isotopes; D000077215:Clay; D003718:Denmark; D003903:Deuterium; D004784:Environmental Monitoring / Q000379:methods; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D060587:Groundwater; D054879:Halogenation; D006540:Herbicides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D010103:Oxygen Isotopes; D010642:Phenoxyacetates / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D010647:Phenyl Ethers / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D011422:Propionates / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D045483:Rivers; D013237:Stereoisomerism; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D014877:Water Pollution, Chemical
chemical_list: C447201:2-phenoxypropionic acid; D000538:Aluminum Silicates; D002247:Carbon Isotopes; D006540:Herbicides; D010103:Oxygen Isotopes; D010642:Phenoxyacetates; D010647:Phenyl Ethers; D011422:Propionates; D014874:Water Pollutants, Chemical; D015084:2,4-Dichlorophenoxyacetic Acid; C048213:2-(4-chlorophenoxy)propionic acid; D003903:Deuterium; D008456:2-Methyl-4-chlorophenoxyacetic Acid; C010571:dichlorprop; D000077215:Clay