Subchronic Toxicity of 2,4‐Dichlorophenoxyacetic Acid (2,4‐D) to Early Life Stages of Fish

Effects of Low, Subchronic Exposure of 2,4‐Dichlorophenoxyacetic Acid (2,4‐d) and Commercial 2,4‐d Formulations on Early Life Stages of Fathead Minnows (Pimephales promelas)

“…Based on our replicated findings, we made the cautious suggestion that permitting these herbicide formulations should be re-evaluated. In fact, we suggest that the present range of interest for new studies should be between 0 and 2.00 ppm 2,4-D. Giddings and Habig (2019) took issue with several features of water chemistry and modifications to the early life stage exposure assay in our experiments. In fact, total hardness, measured using a titration method of 20 water samples randomly chosen from all experiments, averaged 238 ± 8 mg CaCO 3 /L (n = 10, 0.00 ppm 2,4-D; n = 10, 2.00 ppm 2,4-D; US Environmental Protection Agency 1982), which is within range of concentrations found in Wisconsin lakes (0-370 ppm; National Water Quality Monitoring Council 2016) and within range of USEPA guidelines (0-250 ppm; US Environmental Protection Agency 2016a, 2016b).…”

“…These were the goals of Dehnert et al (2018), which became the subject of a recent letter to the editor of this journal by Giddings and Habig (2019). Giddings and Habig (2019) stated, "Dehnert et al suggest that their study was the first study of this type (exposure of eggs, hatchlings, and juvenile fish) using 2,4-D," which was not what was written in our peer-reviewed publication. We were aware of an earlier industry-sourced report referenced by Giddings and Habig (Mayes et al 1990) that was not published in peer-reviewed literature nor available to the public, and we specifically wrote "To our knowledge, no published studies have tested the impacts of environmentally relevant doses (0.00-2.00 ppm) of pure 2,4-D exposure on survival from fertilization to 14 d post hatch (dph) in any fish species."…”

“…In each of the experiments, we observed >95% survival for control larvae, which exceeded the USEPA's minimum of 70% survival for posthatch fathead minnows (US Environmental Protection Agency 2016b). Contrary to the assertions of Giddings and Habig (2019), all water parameters in Dehnert et al (2018) are highly appropriate and all modifications made (i.e., aeration, flow rate, concentration groups) to the early life stage exposure assay are scientifically sound and reasonable in allowing us to assess the impacts of ecologically relevant concentrations of 2,4-D and 2,4-D commercial herbicide formulations on fathead minnows. Giddings and Habig (2019) took issue with Dehnert et al's (2018) measurement of 2,4-D concentrations in exposure tanks.…”

“…Contrary to the assertions of Giddings and Habig (2019), all water parameters in Dehnert et al (2018) are highly appropriate and all modifications made (i.e., aeration, flow rate, concentration groups) to the early life stage exposure assay are scientifically sound and reasonable in allowing us to assess the impacts of ecologically relevant concentrations of 2,4-D and 2,4-D commercial herbicide formulations on fathead minnows. Giddings and Habig (2019) took issue with Dehnert et al's (2018) measurement of 2,4-D concentrations in exposure tanks. All 2,4-D concentrations were measured using an enzyme-linked immunosorbent assay (ELISA) and were reported as 2,4-D ppm in Dehnert et al (2018), which referred to 2,4-D ppm acid equivalence (a.e.…”

“…Over all 30-d exposure experiments, Dehnert et al (2018) reported 3 significantly distinct concentration groups that never overlapped and contained appropriate control groups that remained free of 2,4-D (below the detection level of ≤1 ppb 2,4-D; Figure 1). Giddings and Habig (2019) suggest that "2,4-D degrades rapidly in aquatic systems and is not persistent" and therefore could not have putative impacts in ecological situations. Granted, in a laboratory setting and under highly aerobic conditions, 2,4-D undergoes rapid degradation (half-life of 15 d) and is also susceptible to aqueous photolysis (half-life of 12.9 d; US Environmental Protection Agency 2005); however, this is not representative of ecological scenarios in which 2,4-D is used.…”