Long-term effects of the herbicide glyphosate and its main metabolite (aminomethylphosphonic acid) on the growth, chlorophyll a and morphology of freshwater benthic diatoms

Authors

Chéron S., Felten V., Venkataramanan A., Wetzel C.E., Heudre D., Pradalier C., Usseglio-Polatera P., Devin S., Laviale M.

Reference

Heliyon, vol. 11, n° 13, art. no. e43680, 2025

Description

Although glyphosate and its main degradation product, aminomethylphosphonic acid (AMPA), are frequently found in surface waters worldwide, their effects on surface waters’ ecological health remain difficult to identify. In this study we investigated the impact of these two compounds on freshwater benthic diatoms, a key biological compartment which has been rarely documented so far. Besides potential effects on growth and chlorophyll a, diatom morphology was also documented via the appearance of deformations but also more subtle, non-teratological changes. In a first experiment, the two common diatom species Nitzschia palea and Gomphonema gracile were exposed to a wide range of concentrations of glyphosate (0.41–84.27 mg/L) and AMPA (2.89–103.53 mg/L) in order to assess their effects on growth and physiology (chlorophyll a content) after 7 d of exposure. Our results show that both compounds inhibited diatom growth while chlorophyll a was not affected. Glyphosate was more toxic than AMPA for both species and N. palea was more sensitive than G. gracile regardless of the tested compound. In a second experiment, longer-term effects were assessed by exposing the diatom N. palea in semi-static conditions for 28 d to 4 concentrations including an environmental one (0.0035–4.77 mg/L of glyphosate and 0.16–41.79 mg/L of AMPA). In addition to growth and chlorophyll a, a machine-learning based methodology was developed in order to analyze individual diatom morphometric descriptors. At the highest tested concentration, both contaminants inhibited growth but also chlorophyll a content. Moreover, the tested compounds did not generate teratological forms, but AMPA favored longer and slimmer individuals while glyphosate restricted diatom morphology by eliminating intermediate sizes, creating two subpopulations with distinct morphologies, thus underlying the activation of different mechanisms at population level. Our results show that morphological features could prove useful to quantify on a routine basis in order to better document the subtle ecotoxicological effects of contaminants.

Link

doi:10.1016/j.heliyon.2025.e43680