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McFadden M, Reber KP, Sivey JD, Cwiertny DM, LeFevre GH. Microbial Biotransformation Products and Pathways of Dichloroacetamide Herbicide Safeners. ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS 2023; 10:72-78. [PMID: 37091899 PMCID: PMC10111411 DOI: 10.1021/acs.estlett.2c00862] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Accepted: 11/29/2022] [Indexed: 05/03/2023]
Abstract
Dichloroacetamide safeners are common ingredients in commercial herbicide formulations. We previously investigated the environmental fate of dichloroacetamides via photolysis and hydrolysis, but other potentially important, environmentally relevant fate processes remain uncharacterized and may yield products of concern. Here, we examined microbial biotransformation of two dichloroacetamide safeners, benoxacor and dichlormid, to identify products and elucidate pathways. Using aerobic microcosms inoculated with river sediment, we demonstrated that microbial biotransformations of benoxacor and dichlormid proceed primarily, if not exclusively, via cometabolism. Benoxacor was transformed by both hydrolysis and microbial biotransformation processes; in most cases, biotransformation rates were faster than hydrolysis rates. We identified multiple novel products of benoxacor and dichlormid not previously observed for microbial processes, with several products similar to those reported for structurally related chloroacetamide herbicides, thus indicating potential for conserved biotransformation mechanisms across both chemical classes. Observed products include monochlorinated species such as the banned herbicide CDAA (from dichlormid), glutathione conjugates, and sulfur-containing species. We propose a transformation pathway wherein benoxacor and dichlormid are first dechlorinated, likely via microbial hydrolysis, and subsequently conjugated with glutathione. This is the first study reporting biological dechlorination of dichloroacetamides to yield monochlorinated products in aerobic environments.
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Affiliation(s)
- Monica
E. McFadden
- Department
of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242, United States
- IIHR-Hydroscience
and Engineering, University of Iowa, 100 C. Maxwell Stanley Hydraulics
Laboratory, Iowa City, Iowa 52242, United States
| | - Keith P. Reber
- Department
of Chemistry, Towson University, Towson, Maryland 21252, United States
| | - John D. Sivey
- Department
of Chemistry, Towson University, Towson, Maryland 21252, United States
| | - David M. Cwiertny
- Department
of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242, United States
- IIHR-Hydroscience
and Engineering, University of Iowa, 100 C. Maxwell Stanley Hydraulics
Laboratory, Iowa City, Iowa 52242, United States
- Center
for Health Effects of Environmental Contamination (CHEEC), University of Iowa, 251 North Capitol St., Chemistry Building, Room W195, Iowa City, Iowa 52242, United States
- Public
Policy Center, University of Iowa, 310 South Grand Ave., 209 South
Quadrangle, Iowa City, Iowa 52242, United States
| | - Gregory H. LeFevre
- Department
of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242, United States
- IIHR-Hydroscience
and Engineering, University of Iowa, 100 C. Maxwell Stanley Hydraulics
Laboratory, Iowa City, Iowa 52242, United States
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Luo T, Pokharel R, Chen T, Boily JF, Hanna K. Fate and Transport of Pharmaceuticals in Iron and Manganese Binary Oxide Coated Sand Columns. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:214-221. [PMID: 36469013 DOI: 10.1021/acs.est.2c05963] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Predicting the fate and transport of pharmaceuticals in terrestrial environments requires knowledge of their interactions with complex mineral assemblages. To advance knowledge along this front, we examined the reactivity of pipemidic acid (PIP), a typical quinolone antibiotic, with quartz particles coated with a mixture of manganese oxide (MnO2) and goethite (α-FeOOH) under static and dynamic flow conditions. Batch and dynamic column experiments showed that PIP binding to MnO2 proceeded through a heterogeneous redox reaction, while binding to goethite was not redox-reactive. Mixed columns of aggregated goethite-manganese particles however enhanced redox reactivity because (i) goethite facilitated the transport of dissolved Mn(II) ion and increased the retention of PIP oxidation products, and (ii) MnO2 was protected from passivation. This mobility behavior was predicted using transport models accounting for adsorption and transformation kinetics of PIP on both goethite and MnO2. This work sheds new light on reactivity changes of mixtures of Fe and Mn oxides under flow-through conditions and will have important implications in predicting the fate and transport of redox-active organic compounds as well as development of new geomedia filters for environmental remediation.
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Affiliation(s)
- Tao Luo
- Université de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226, F-35000Rennes, France
- Department of Chemistry, Umeå University, UmeåSE-901 87, Sweden
| | - Rasesh Pokharel
- Department of Earth Sciences, Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, 3584 CBUtrecht, Netherlands
| | - Tao Chen
- Université de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226, F-35000Rennes, France
| | | | - Khalil Hanna
- Université de Rennes, Ecole Nationale Supérieure de Chimie de Rennes, CNRS, ISCR-UMR 6226, F-35000Rennes, France
- Institut Universitaire de France (IUF), MESRI, 1 rue Descartes, 75231Paris, France
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Lanasa S, Niedzwiecki M, Reber KP, East A, Sivey JD, Salice CJ. Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2022; 41:1466-1476. [PMID: 35262227 DOI: 10.1002/etc.5327] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 12/08/2021] [Accepted: 03/07/2022] [Indexed: 06/14/2023]
Abstract
Chloroacetanilide herbicides are used worldwide to control weeds that affect crops such as corn, soybeans, and cotton. These herbicides are frequently paired with a "safener," which prevents herbicidal damage to the crop without diminishing weed control. Formulated herbicide products that include safeners and other ingredients are infrequently assessed for toxicity. Our goal was to understand the potential toxicity of safeners and herbicide + safener formulations relative to the toxicity of associated active ingredients. We quantified the concentration of safeners in commercially available formulations and tested effects on nontarget algae, Raphidocelis subcapitata, when exposed to individual herbicide active ingredients, safeners, and commercial formulations. The median effective concentrations (EC50s) causing 50% reduction in population growth for the herbicide active ingredients S-metolachlor and acetochlor were 0.046 and 0.003 ppm, respectively. The safeners benoxacor, AD-67, furilazole, and dichlormid were all substantially less toxic than the herbicides and were not toxic at environmentally relevant concentrations. The commercial formulations Dual II Magnum®, Me-Too-Lachlor II®, Harness®, and Surpass EC® all resulted in EC50 values that fell within the 95% confidence interval of the associated active ingredient herbicide. Interestingly, a significant increase in cell size was observed when algae were exposed to all the formulations, herbicides (acetochlor and S-metolachlor), and safener (dichlormid). The safener furilazole caused a significant decrease in cell size, whereas benoxacor and AD-67 had no observed effect on algae cell size. Significant algae cell size effects all occurred at or above the EC50 concentrations for each chemical, suggesting that other morphological effects may be occurring. Importantly, safeners in commercial formulations appeared not to impact toxicity to R. subcapitata compared with the active ingredient alone. Environ Toxicol Chem 2022;41:1466-1476. © 2022 SETAC.
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Affiliation(s)
- Sarah Lanasa
- Environmental Science and Studies Program, Towson University, Towson, Maryland, USA
| | - Mark Niedzwiecki
- Department of Chemistry, Towson University, Towson, Maryland, USA
| | - Keith P Reber
- Department of Chemistry, Towson University, Towson, Maryland, USA
| | - Andrew East
- Environmental Science and Studies Program, Towson University, Towson, Maryland, USA
| | - John D Sivey
- Department of Chemistry, Towson University, Towson, Maryland, USA
| | - Christopher J Salice
- Environmental Science and Studies Program, Towson University, Towson, Maryland, USA
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Xu X, Gujarati PD, Okwor N, Sivey JD, Reber KP, Xu W. Reactivity of chloroacetamides toward sulfide + black carbon: Insights from structural analogues and dynamic NMR spectroscopy. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 803:150064. [PMID: 34525700 DOI: 10.1016/j.scitotenv.2021.150064] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 08/22/2021] [Accepted: 08/27/2021] [Indexed: 06/13/2023]
Abstract
Chloroacetamides are commonly used in herbicide formulations, and their occurrence has been reported in soils and groundwater. However, how their chemical structures affect transformation kinetics and pathways in the presence of environmental reagents such as hydrogen sulfide species and black carbon has not been investigated. In this work, we assessed the impact of increasing Cl substituents on reaction kinetics and pathways of six chloroacetamides. The contribution of individual pathways (reductive dechlorination vs. nucleophilic substitution) to the overall decay of selected chloroacetamides was differentiated using various experimental setups; both the transformation rates and product distributions were characterized. Our results suggest that the number of Cl substituents affected reaction pathways and kinetics: trichloroacetamides predominantly underwent reductive dechlorination whereas mono- and dichloroacetamides transformed via nucleophilic substitution. Furthermore, we synthesized eight dichloroacetamide analogs (Cl2CHC(=O)NRR') with differing R groups and characterized their transformation kinetics. Dynamic NMR spectroscopy was employed to quantify the rotational energy barriers of dichloroacetamides. Our results suggest that adsorption of dichloroacetamides on black carbon constrained R groups from approaching the dichloromethyl carbon and subsequently favored nucleophilic attack. This study provides new insights to better predict the fate of chloroacetamides in subsurface environments by linking their structural characteristics to transformation kinetics and pathways.
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Affiliation(s)
- Xiaolei Xu
- Department of Civil and Environmental Engineering, Villanova University, Villanova, PA 19085, USA
| | | | - Neechi Okwor
- Department of Chemistry, Towson University, Towson, MD 21252, USA
| | - John D Sivey
- Department of Chemistry, Towson University, Towson, MD 21252, USA
| | - Keith P Reber
- Department of Chemistry, Towson University, Towson, MD 21252, USA
| | - Wenqing Xu
- Department of Civil and Environmental Engineering, Villanova University, Villanova, PA 19085, USA.
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McFadden M, Patterson EV, Reber KP, Gilbert IW, Sivey JD, LeFevre GH, Cwiertny DM. Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:325-334. [PMID: 34920670 PMCID: PMC8733929 DOI: 10.1021/acs.est.1c05958] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Safeners are used extensively in commercial herbicide formulations. Although safeners are regulated as inert ingredients, some of their transformation products have enhanced biological activity. Here, to fill gaps in our understanding of safener environmental fate, we determined rate constants and transformation products associated with the acid- and base-mediated hydrolysis of dichloroacetamide safeners AD-67, benoxacor, dichlormid, and furilazole. Second-order rate constants for acid- (HCl) and base-mediated (NaOH) dichloroacetamide hydrolysis (2.8 × 10-3 to 0.46 and 0.3-500 M-1 h-1, respectively) were, in many cases (5 of 8), greater than those reported for their chloroacetamide herbicide co-formulants. In particular, the rate constant for base-mediated hydrolysis of benoxacor was 2 orders of magnitude greater than that of its active ingredient co-formulant, S-metolachlor. At circumneutral pH, only benoxacor underwent appreciable hydrolysis (5.3 × 10-4 h-1), and under high-pH conditions representative of lime-soda softening, benoxacor's half-life was 13 h─a timescale consistent with partial transformation during water treatment. Based on Orbitrap LC-MS/MS analysis of dichloroacetamide hydrolysis product mixtures, we propose structures for major products and three distinct mechanistic pathways that depend on the system pH and compound structure. These include base-mediated amide cleavage, acid-mediated amide cleavage, and acid-mediated oxazolidine ring opening. Collectively, this work will help to identify systems in which hydrolysis contributes to the transformation of dichloroacetamides, while also highlighting important differences in the reactivity of dichloroacetamides and their active chloroacetamide co-formulants.
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Affiliation(s)
- Monica
E. McFadden
- Department
of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242, United States
- IIHR-Hydroscience
and Engineering, University of Iowa, 100 C. Maxwell Stanley Hydraulics
Laboratory, Iowa City, Iowa 52242, United States
| | - Eric V. Patterson
- Department
of Chemistry, Stony Brook University, 100 Nicolls Road, 104 Chemistry, Stony Brook, New York 11790, United States
| | - Keith P. Reber
- Department
of Chemistry, Towson University, Towson, Maryland 21252, United States
| | - Ian W. Gilbert
- Department
of Chemistry, Towson University, Towson, Maryland 21252, United States
| | - John D. Sivey
- Department
of Chemistry, Towson University, Towson, Maryland 21252, United States
| | - Gregory H. LeFevre
- Department
of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242, United States
- IIHR-Hydroscience
and Engineering, University of Iowa, 100 C. Maxwell Stanley Hydraulics
Laboratory, Iowa City, Iowa 52242, United States
| | - David M. Cwiertny
- Department
of Civil and Environmental Engineering, University of Iowa, 4105 Seamans Center for the Engineering Arts and Sciences, Iowa City, Iowa 52242, United States
- IIHR-Hydroscience
and Engineering, University of Iowa, 100 C. Maxwell Stanley Hydraulics
Laboratory, Iowa City, Iowa 52242, United States
- Center
for Health Effects of Environmental Contamination (CHEEC), University of Iowa, 251 North Capitol Street, Chemistry Building—Room
W195, Iowa City, Iowa 52242, United States
- Department
of Chemistry, University of Iowa, E331 Chemistry Building, Iowa City, Iowa 52242, United States
- . Phone: (319) 335-1401
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Oloye FF, Femi-Oloye OP, Challis JK, Jones PD, Giesy JP. Dissipation, Fate, and Toxicity of Crop Protection Chemical Safeners in Aquatic Environments. REVIEWS OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2021; 258:27-53. [PMID: 34529146 DOI: 10.1007/398_2021_70] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Safeners are a group of chemicals applied with herbicides to protect crop plants from potential adverse effects of agricultural products used to kill weeds in monocotyledonous crops. Various routes of dissipation of safeners from their point of applications were evaluated. Despite the large numbers of safeners (over 18) commercially available and the relatively large quantities (~2 × 106 kg/year) used, there is little information on their mobility and fate in the environment and occurrence in various environmental matrices. The only class of safeners for which a significant amount of information is available is dichloroacetamide safeners, which have been observed in some rivers in the USA at concentrations ranging from 42 to 190 ng/L. Given this gap in the literature, there is a clear need to determine the occurrence, fate, and bioavailability of other classes of safeners. Furthermore, since safeners are typically used in commercial formulations, it is useful to study them in relation to their corresponding herbicides. Common routes of dissipation for herbicides and applied safeners are surface run off (erosion), hydrolysis, photolysis, sorption, leaching, volatilization, and microbial degradation. Toxic potencies of safeners vary among organisms and safener compounds, ranging from as low as the LC50 for fish (Oncorhynchus mykiss) for isoxadifen-ethyl, which was 0.34 mg/L, to as high as the LC50 for Daphnia magna from dichlormid, which was 161 mg/L. Solubilities and octanol-water partition coefficients seem to be the principal driving force in understanding safener mobilities. This paper provides an up-to-date literature review regarding the occurrence, behaviour, and toxic potency of herbicide safeners and identifies important knowledge gaps in our understanding of these compounds and the potential risks posed to potentially impacted ecosystems.
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Affiliation(s)
- Femi F Oloye
- Department of Chemical Sciences, Adekunle Ajasin University, Akungba-Akoko, Nigeria.
| | - Oluwabunmi P Femi-Oloye
- Toxicology Centre, University of Saskatchewan, Saskatoon, SK, Canada
- Department of Animal and Environmental Biology, Adekunle Ajasin University, Akungba-Akoko, Nigeria
| | | | - Paul D Jones
- Toxicology Centre, University of Saskatchewan, Saskatoon, SK, Canada
- School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, Canada
| | - John P Giesy
- Toxicology Centre, University of Saskatchewan, Saskatoon, SK, Canada
- Department of Biomedical Veterinary Sciences, University of Saskatchewan, Saskatoon, SK, Canada
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