Pesticide Mixtures Cause Short‐Term, Reversible Effects on the Function of Autotrophic Periphyton Assemblages

Abstract

In a laboratory experiment we investigated the effects of pesticide mixtures on the structure and function of freshwater biofilms, with focus on their photoautotrophic component. We identified 6 herbicides and 1 fungicide commonly found in Swedish streams at relatively high concentrations and created 3 ternary mixtures that were tested in concentration series ranging from observed environmental concentrations to up to 100 times higher. Biofilms were exposed to these pesticide mixtures for 8 d and then allowed to recover for another 12 d. Our results show a rapid and consistent inhibition of photosynthesis after just 24‐h exposure to the highest test concentration of pesticides, as well as in some treatments with lower concentrations (i.e., 10 times the environmental level), on exposure. Interestingly, the observed effects were reversible because biofilm photosynthesis recovered rapidly and completely in clean media in all but one treatment. In contrast to the functional response, no effects were observed on the algal assemblage structure, as assessed by diagnostic pigments. We conclude that the pesticide mixtures induce a rapid but reversible inhibition of photosynthesis, without short‐term effects on biofilm structure. Environ Toxicol Chem 2020;39:1367–1374. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Interactions with freshwater biofilms cause rapid removal of common herbicides through degradation – evidence from microcosm studies

“…close to the Redeld ratio, 38 whereas the continuous aeration of the test vessels guaranteed a constant supply of atmospheric CO 2 . Earlier studies have also shown that recovery from herbicideinduced photosynthetic inhibition can be fast, 15 i.e. through rapid, adaptive evolution (cf.…”

“…Ahlgren et al 1990 26 ). Aer 9 weeks of growth, biolms were well-established, and microscopic analysis showed that green algae made up 90% of the total biovolume, while diatoms and cyanobacteria accounted for 8% and 1%, respectively (detailed in 15 ). These biolms were used for exposure to pesticides as described below.…”

“…12 For example, pesticides negatively affect the abundance of invertebrates, 13 as well as the density, antioxidant defence and photosynthetic efficiency of diatoms, 14 although the latter may reect shortterm inhibition. 15 Herbicides are commonly more watersoluble than insecticides and fungicides and thus comprise a large fraction of the pesticides frequently detected in surface water monitoring. 16,17 Herbicides in surface waters are submitted to both abiotic (e.g., photolysis, hydrolysis) and biotic (microbial) degradation, the latter usually being quantitatively more important.…”

Distribution and risk assessment of pesticide residues in sediment samples from river Ganga, India

“…The other problem usually discussed is the impact by mixture of different pesticides present at a time. Thus, there is a need to establish the real impact of these mixtures (pesticides) on biota communities of the ecosystem [35][36][37], which can be predicted by the independent action of the pesticide or by concentration addition impact. Consumers assume the different action of pesticides, therefore ignoring the agonistic/antagonistic action of mixture and overestimating the effect [38][39][40].…”

Combining Polar Organic Chemical Integrative Samplers (POCIS) with Toxicity Testing on Microalgae to Evaluate the Impact of Herbicide Mixtures in Surface Waters

“…Although the impact of insecticides on macroinvertebrates has been documented in several field studies (Liess & Von der Ohe, 2005 ; Liess et al, 2021 ), primary producer impairment proves difficult to relate to herbicide exposure. On the one hand, effects from pulsed exposures on periphyton seem to be rapidly reversible (Bighiu et al, 2020 ); on the other hand, macrophytes are more responsive to factors that are independent of anthropogenic pressures (Bucior et al, 2021 ; Demars et al, 2012 ). Algae tests involving photosystem II (PSII) inhibition and growth are an alternative to evaluate pesticide mixture impact in grab samples (De Baat et al, 2018 ; Glauch & Escher, 2020 ) as well as in passive sampler extracts (Vermeirssen et al, 2010 ).…”