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)

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

“…However, fish early life stage testing following USEPA guidelines (US Environmental Protection Agency, 2016b) was conducted more than 25 yr ago using technical 2,4-D acid, 2, 4-D amines, and 2,4-D esters. The NOECs for fish early life stage testing with 2,4-D acid and 2,4-D amines range from 14.2 to 63.4 mg a.e./L (Mayes et al, 1990; US Environmental Protection Agency, 2005); the Dehnert et al (2018) results, with a NOEC of less than 0.05 mg/L for WAM40 based on larval survival, are inconsistent with these guideline-compliant studies.Finally, Dehnert et al (2018) speculate that fish could be exposed to toxicologically significant 2,4-D concentrations in the water column for an extended period of time following application. However, 2,4-D undergoes rapid degradation under aerobic aquatic testing (half-life of 15 d) and is also susceptible to aqueous photolysis (half-life of 12.9 d; US Environmental Protection Agency, 2005).…”

“…The US Army Corps of Engineers (2012) has identified 2,4-D as an efficient, cost-effective, and selective tool for control of invasive weeds and improvement of natural habitat for fish and other aquatic organisms. However, a recent publication in this journal (Dehnert et al, 2018) suggests that current permitting regulations, which are based on testing following standard guidelines and conducted under good laboratory practice, should be re-evaluated based on new, conflicting data obtained using nonstandard (and non-good laboratory practice-compliant) testing. These authors present the results of fish early life stage testing on fathead minnow (Pimephales promelas) with two 2,4-D amine formulations and technical grade 2,4-D acid, which they interpret as indicating possible impacts on recently hatched fish.…”

“…Some of the observed results indicated no difference from the controls at the lower 2 concentrations, but significantly higher growth at the highest concentration (2.0 mg/L). As an attempt to explain the study results, Dehnert et al (2018) included a discussion on possible endocrine disruption effects. This discussion is purely speculative, because the study did not evaluate any endocrinespecific endpoints.…”

“…However, 2,4-D has undergone the USEPA's standard fish short-term endocrine disruption testing with fathead minnows, with the only significant effect being a reduction in adult female fecundity at the highest test concentration (96.5 mg a.e./L); there were no effects on the multiple endocrine-specific endpoints evaluated in that study (Marino et al, 2010). Until an adequate explanation can be provided for the Dehnert et al (2018) results, it would be irresponsible to use them as the basis for regulatory decisions concerning the use of 2,4-D for aquatic weed control. Dehnert et al (2018) suggest that their study was the first of its type (exposure of eggs, hatchlings, and juvenile fish) using 2,4-D.…”

“…Until an adequate explanation can be provided for the Dehnert et al (2018) results, it would be irresponsible to use them as the basis for regulatory decisions concerning the use of 2,4-D for aquatic weed control. Dehnert et al (2018) suggest that their study was the first of its type (exposure of eggs, hatchlings, and juvenile fish) using 2,4-D. However, fish early life stage testing following USEPA guidelines (US Environmental Protection Agency, 2016b) was conducted more than 25 yr ago using technical 2,4-D acid, 2, 4-D amines, and 2,4-D esters.…”