Non-target effects of a glyphosate-based herbicide on Common toad larvae (Bufo bufo, Amphibia) and associated algae are altered by temperature.
BACKGROUND
Glyphosate-based herbicides are the most widely used pesticides in agriculture, horticulture, municipalities and private gardens that can potentially contaminate nearby water bodies inhabited by amphibians and algae. Moreover, the development and diversity of these aquatic organisms could also be affected by human-induced climate change that might lead to more periods with extreme temperatures. However, to what extent non-target effects of these herbicides on amphibians or algae are altered by varying temperature is not well known.


METHODS
We studied effects of five concentrations of the glyphosate-based herbicide formulation Roundup PowerFlex (0, 1.5, 3, 4 mg acid equivalent glyphosate L-1as a one time addition and a pulse treatment of totally 4 mg a.e. glyphosate L-1) on larval development of Common toads (Bufo bufo, L.; Amphibia: Anura) and associated algae communities under two temperature regimes (15 vs. 20 °C).


RESULTS
Herbicide contamination reduced tail growth (-8%), induced the occurrence of tail deformations (i.e. lacerated or crooked tails) and reduced algae diversity (-6%). Higher water temperature increased tadpole growth (tail and body length (tl/bl) +66%, length-to-width ratio +4%) and decreased algae diversity (-21%). No clear relation between herbicide concentrations and tadpole growth or algae density or diversity was observed. Interactive effects of herbicides and temperature affected growth parameters, tail deformation and tadpole mortality indicating that the herbicide effects are temperature-dependent. Remarkably, herbicide-temperature interactions resulted in deformed tails in 34% of all herbicide treated tadpoles at 15 °C whereas no tail deformations were observed for the herbicide-free control at 15 °C or any tadpole at 20 °C; herbicide-induced mortality was higher at 15 °C but lower at 20 °C.


CONCLUSIONS
These herbicide- and temperature-induced changes may have decided effects on ecological interactions in freshwater ecosystems. Although no clear dose-response effect was seen, the presence of glyphosate was decisive for an effect, suggesting that the lowest observed effect concentration (LOEC) in our study was 1.5 mg a.e. glyphosate L-1water. Overall, our findings also question the relevance of pesticide risk assessments conducted at standard temperatures.
Institute of Zoology, University of Natural Resources and Life Sciences Vienna (BOKU) , Vienna , Austria.
Fabian
F
Baier
Institute of Zoology, University of Natural Resources and Life Sciences Vienna (BOKU) , Vienna , Austria.
Edith
E
Gruber
Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences Vienna (BOKU), Vienna, Austria; WasserCluster Lunz-Biologische Station GmbH, Lunz am See, Austria.
Thomas
0000-0002-7767-4607
T
Hein
Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences Vienna (BOKU), Vienna, Austria; WasserCluster Lunz-Biologische Station GmbH, Lunz am See, Austria.
Elisabeth
E
Bondar-Kunze
Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences Vienna (BOKU) , Vienna , Austria.
Marina
M
Ivanković
Institute of Soil Research, University of Natural Resources and Life Sciences Vienna (BOKU) , Vienna , Austria.
Axel
A
Mentler
Institute for Environmental Sciences, Universität Koblenz-Landau , Landau , Germany.
Carsten A
CA
Brühl
Institute of Applied Statistics and Computing, University of Natural Resources and Life Sciences Vienna (BOKU) , Vienna , Austria.
Bernhard
B
Spangl
Institute of Zoology, University of Natural Resources and Life Sciences Vienna (BOKU) , Vienna , Austria.
Johann G
0000-0001-7744-7378
JG
Zaller
Agrochemicals; Agroecology; Algae; Amphibia; Aquatic organisms; Climate change; Ecotoxicology; Herbicides; Non-target effects; Pesticides