Characterizing the effect of Poast on Chlorella vulgaris, a non-target organism

• Published in: Chemosphere (Oxford) Vol. 219; pp. 704 - 712
• Main Authors: Smythers, Amanda L., Garmany, Armin, Perry, Nicole L., Higginbotham, Ethan L., Adkins, P. Ethan, Kolling, Derrick R.J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.03.2019
• Subjects: Chlorella; Chlorophyll a fluorescence transient; Herbicide; Photosynthesis; Chlorella; PSII; Chl a; Photosynthesis; OEC; acetyl-CoA carboxylase; Herbicide; Chlorophyll a fluorescence transient
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2018.12.050

Herbicides may cause unexpected damage to non-target organisms as it is challenging to predict undesirable biotic interactions. Poast is a widely used herbicide formulation that contains sethoxydim and targets the acetyl-CoA carboxylase of perennial grasses. In this study, Chlorella vulgaris, a unicellular green microalga, was exposed to a 0.08% working concentration of Poast and the physiological and biochemical changes that took place were monitored using biochemical assays, fluorometry, oximetry, and immunoblotting. Within 15 min, severe photosynthetic damage was observed through a reduction in oxygen production and a reduced rate of electron transfer beyond photosystem II. In addition to direct damage to the photosynthetic machinery, it was shown that cells experienced membrane fragmentation. Within 30 min, over 90% of the exposed cells were nonviable. However, sethoxydim, the active ingredient, did not cause detrimental effects when applied along with mineral spirits, the primary solvent of the formulation. A synergistic or additive effect between sethoxydim and the formulation components cannot be ruled out. This data suggests that Poast has the potential to cause severe harm to unicellular phototrophs in the case of herbicide over application or runoff. •Poast exposure in C. vulgaris directly damages the oxygen-evolving complex of photosystem II.•Poast leads to significant changes in biochemical composition of photomixotrophically grown cells.•Sethoxydim in the presence of mineral spirits does not result in toxicity to C. vulgaris. [Display omitted]