Turbidity matters: differential effect of a 2,4-D formulation on the structure of microbial communities from clear and turbid freshwater systems

LOZANO, V.L.; MIRANDA, C.E.; VINOCUR, A.L.; GONZÁLEZ, C.; UNREIN, F.; WOLANSKY, M.J.; PIZARRO, H.N.

Heliyon

ElSevier

Año: 2019 vol. 5

2405-8440

We evaluated the effect of AsiMax 50®, a commercial formulation of 2,4-D (2,4-dichlorophenoxyacetic acid), onthe structure of both micro þ nano phytoplankton (>2 μm; species composition and abundance) and cytometricpopulations (photosynthetic picoplankton (PPP, 0.2?2 μm), which included prokaryotic phycocyanin-rich picocyanobacteria(PC-Pcy), phycoerythrin-rich picocyanobacteria (PE-Pcy) and eukaryotic phototrophs (PEuk); andbacterioplankton (HB), heterotrophic bacteria), using a microcosms-based approach and a single 7-day exposure.Assays were performed on two different microbial assemblages sampled from freshwater bodies of two contrastingturbidity status: clear (chlorophyll a ¼ 7.6 μgL-1, turbidity ¼ 1 NTU) and organic turbid systems (chlorophylla ¼ 25.0 μgL-1, turbidity ¼ 9 NTU). For each system, the herbicide was applied to 500 mL-Erlenmeyerflasks, at seven concentration levels of the active ingredient (a.i.): 0 (control ¼ no addition), 0.02, 0.2, 2, 20,200 and 2,000 mg a.i.L1. The impact of AsiMax 50® seemed to be greater in the turbid system. In this system,total abundance of living (live) micro þ nano phytoplankton showed a significant increase at lower concentrationsand data were fitted to a humped-shaped curve. For both clear and organic turbid systems, micro þ nanophytoplankton decreased in species richness and abundance at higher herbicide concentrations. These resultssuggest that 2,4-D may mimic hormonal function. Some species, such as Ochromonas sp. and Chlamydomonas sp.,showed different responses to herbicide exposure between water systems. In the turbid system, the increase inabundance of the PPP fraction observed at 7-d exposure was probably due to either an increase in PE-Pcy (thussuggesting the existence of auxin pathways) or a reduction in competitive pressure by micro þ nano plankton. Ourresults provide some evidence of the importance of using community-scale approaches in ecotoxicological studiesto predict changes in freshwater ecosystems exposed to a 2,4-D-based formulation. However, caution must betaken when extrapolating these effects to real scenarios, as assays were based on a laboratory microcosmexperiment.