Pendimethalin is a dinitroaniline
herbicide used to control broadleaf weeds by inhibiting the formation of microtubules during cell division. Its use on a variety of crops leads to its potential entry into aquatic environments, but little is known about its sub-lethal toxicity to early developmental stages of aquatic vertebrates. To address this knowledge gap, we assessed the toxicity of
pendimethalin to zebrafish embryos and larvae by measuring mortality, developmental abnormalities, oxidative respiration,
reactive oxygen species, gene expression, and locomotor activity following exposure to the
herbicide throughout early development. Embryos at ~6 h post-fertilization (hpf) were exposed to either a
solvent control (0.1%
DMSO, v/v), embryo rearing medium (ERM), or one dose of either 1, 2.5, 5, or 25 μM
pendimethalin for up to 7-days post fertilization depending on the bioassay. Exposure to 25 μM
pendimethalin resulted in high prevalence of
spinal curvature, tail malformations, pericardial
edema, and yolk sac
edema at 4 dpf, while exposure to 5 μM
pendimethalin induced pericardial
edema and
lordosis in the fish exposed over 7 dpf. Exposure to
pendimethalin up to 5 μM did not negatively impact oxidative respiration (e.g., basal respiration,
oligomycin-induced
ATP production) in embryos following a 24-h exposure.
Pendimethalin did not induce
reactive oxygen species at concentrations of 1-5 μM. Levels of transcripts associated with oxidative respiration and damage response were altered in 7d-larvae; cox1
mRNA was increased in larvae fish exposed to 1 μM while cox5a1 and sod2
mRNA were decreased with 2.5 μM exposure. The Visual Motor Response (VMR) test for light-dark response revealed that larval activity in the dark period was reduced for zebrafish exposed to >1 μM
pendimethalin compared to ERM and
DMSO solvent control groups. These data inform on the sub-lethal toxicity of
pendimethalin to early stages of fish embryos and larvae.