Reductive transformations of dichloroacetamide safeners: effects of agrochemical co-formulants and iron oxide + manganese oxide binary-mineral systems

Ricko, Allison N.; Psoras, Andrew W.; Sivey, John D.

doi:10.1039/d0em00331j

Cited by 8 publications

(10 citation statements)

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“…Importantly, dichloroacetamide safeners can undergo photolysis (Kral et al, 2019;Su et al, 2019), hydrolysis (McFadden et al, 2022), abiotic reductive dechlorination (Ricko et al, 2020;Sivey & Roberts, 2012;Xu et al, 2020Xu et al, , 2022, and *Indicates significant difference compared with controls (shown as 0 for each figure). AD, AD-67.…”

Section: Discussionmentioning

confidence: 99%

“…Importantly, dichloroacetamide safeners can undergo photolysis (Kral et al, 2019; Su et al, 2019), hydrolysis (McFadden et al, 2022), abiotic reductive dechlorination (Ricko et al, 2020; Sivey & Roberts, 2012; Xu et al, 2020, 2022), and biotransformation (Abu‐Qare & Duncan, 2002) in the environment. These processes can result in the safener changing into structures like those of herbicides, which could be more toxic than the parent (Abu‐Qare & Duncan, 2002; Sivey & Roberts, 2012).…”

Section: Discussionmentioning

confidence: 99%

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Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

Lanasa

Niedzwiecki

Reber

et al. 2022

Enviro Toxic and Chemistry

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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.

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Section: Discussionmentioning

confidence: 99%

“…Importantly, dichloroacetamide safeners can undergo photolysis (Kral et al, 2019; Su et al, 2019), hydrolysis (McFadden et al, 2022), abiotic reductive dechlorination (Ricko et al, 2020; Sivey & Roberts, 2012; Xu et al, 2020, 2022), and biotransformation (Abu‐Qare & Duncan, 2002) in the environment. These processes can result in the safener changing into structures like those of herbicides, which could be more toxic than the parent (Abu‐Qare & Duncan, 2002; Sivey & Roberts, 2012).…”

Section: Discussionmentioning

confidence: 99%

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

Lanasa

Niedzwiecki

Reber

et al. 2022

Enviro Toxic and Chemistry

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“…For example, abiotic reductive dechlorination of dichlormid and benoxacor can, respectively, yield the regulated herbicide allidochlor ( N , N -diallyl-2-chloroacetamide, commonly known as CDAA) and a known degradate, monochloro-benoxacor, which is toxic toward insect larvae. 7 , 8 , 15 , 16 …”

Section: Introductionmentioning

confidence: 99%

“…The EPA has also identified AD-67 and furilazole as “likely to be carcinogenic to humans”. , Furthermore, some dichloroacetamide safeners, including dichlormid and benoxacor, can transform under environmentally relevant conditions to yield products with increased biological activity that may pose even greater risks to the environment and human health. For example, abiotic reductive dechlorination of dichlormid and benoxacor can, respectively, yield the regulated herbicide allidochlor ( N , N -diallyl-2-chloroacetamide, commonly known as CDAA) and a known degradate, monochloro-benoxacor, which is toxic toward insect larvae. ,,, …”

Section: Introductionmentioning

confidence: 99%

Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners

McFadden

Patterson

Reber

et al. 2021

Environ. Sci. Technol.

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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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“…2,3 As a result, birnessite-type manganese oxides play a significant role in controlling the cycles of several key nutrients as well as the fate and mobility of inorganic and organic contaminants. [4][5][6][7][8][9] Acid birnessite has been widely investigated because it is structurally similar to biogenic "natural" manganese oxides. [10][11][12][13] The birnessite reactivity is mainly affected by solution pH, surface properties and composition of MnO2 and structural characteristics of redox-active contaminants.…”

Section: Introductionmentioning

confidence: 99%

Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO₂ particles

Jia

Luo

et al. 2021

Environ. Sci.: Processes Impacts

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Reductive transformations of dichloroacetamide safeners: effects of agrochemical co-formulants and iron oxide + manganese oxide binary-mineral systems

Abstract: Abiotic redox transformation rates of dichloroacetamide safeners slow when birnessite is added to slurries of Fe(ii)-amended hematite.

Cited by 8 publications

References 54 publications

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners

Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO₂ particles

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Reductive transformations of dichloroacetamide safeners: effects of agrochemical co-formulants and iron oxide + manganese oxide binary-mineral systems

Abstract: Abiotic redox transformation rates of dichloroacetamide safeners slow when birnessite is added to slurries of Fe(ii)-amended hematite.

Cited by 8 publications

References 54 publications

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners

Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO2 particles

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Product

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Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO₂ particles