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

Abstract

We evaluated the effect of AsiMax 50®, a commercial formulation of 2,4-D (2,4-dichlorophenoxyacetic acid), on the structure of both micro + nano phytoplankton (>2 μm; species composition and abundance) and cytometric populations (photosynthetic picoplankton (PPP, 0.2–2 μm), which included prokaryotic phycocyanin-rich picocyanobacteria (PC-Pcy), phycoerythrin-rich picocyanobacteria (PE-Pcy) and eukaryotic phototrophs (PEuk); and bacterioplankton (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 contrasting turbidity status: clear (chlorophyll a = 7.6 μgL -1 , turbidity = 1 NTU) and organic turbid systems (chlorophyll a = 25.0 μgL -1 , turbidity = 9 NTU). For each system, the herbicide was applied to 500 mL-Erlenmeyer flasks, at seven concentration levels of the active ingredient (a.i.): 0 (control = no addition), 0.02, 0.2, 2, 20, 200 and 2,000 mg a.i.L −1 . The impact of AsiMax 50® seemed to be greater in the turbid system. In this system, total abundance of living (live) micro + nano phytoplankton showed a significant increase at lower concentrations and data were fitted to a humped-shaped curve. For both clear and organic turbid systems, micro + nano phytoplankton decreased in species richness and abundance at higher herbicide concentrations. These results suggest 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 in abundance of the PPP fraction observed at 7-d exposure was probably due to either an increase in PE-Pcy (thus suggesting the existence of auxin pathways) or a reduction in competitive pressure by micro + nano plankton. Our results provide some evidence of the importance of using community-scale approaches in ecotoxicological studies to predict changes in freshwater ecosystems exposed to a 2,4-D-based formulation. However, caution must be taken when extrapolating these effects to real scenarios, as assays were based on a laboratory microcosm experiment.

Freshwater dissolved oxygen dynamics: changes due to glyphosate, 2,4-D and their mixture, both under clear and turbid-organic conditions

“…The fourth hypothesis that the impact of herbicides is stronger at high herbicide doses was supported by our results because the greatest variations in both DO% and abundance were observed in the treatments at high concentration. A dose-dependent impact of these herbicides on structural features of microbial communities has also been found previously (Lozano et al, 2018(Lozano et al, , 2019.…”

“…The network correlation revealed that the turbid system showed more correlations among the abundance of microbial fractions and DO%, suggesting that it is less resilient than the clear system for all herbicide treatments. A greater stability of the clear system under herbicide stress was also found by Lozano et al (2019), who analyzed the impact of AsiMax 50 ® on clear and turbid systems using a laboratory microcosms approach. The fact that in the clear system DO% was highly correlated with M+N phytoplankton abundances, while in the turbid one it was correlated with Pcy abundances may reflect different community responses to the herbicide (Cottingham et al, 1998) and supports the fifth hypothesis of this work.…”

“…There is very little information on the impact of AsiMax 50 ® on freshwaters (Lozano et al, 2019) and only a few records concerning the effects of its active ingredient, 2,4-D, are available. The impact of 2,4-D on freshwater in general and on algal photosynthesis in particular is currently controversial, with some authors reporting stimulation (Kobraei & White, 1996;Boyle, 1980;Relyea, 2009) and others inhibition (Singh & Shrivastava, 2016;Zhu et al, 2016).…”

Activated Carbon from Yam Peels Modified with Fe3O4 for Removal of 2,4-Dichlorophenoxyacetic Acid in Aqueous Solution

“…2,4-dichlorophenoxyacetic acid (2,4-D) is a common herbicide with high efficiency and low cost which has been widely used in agribusiness for the neutralization of weeds in different crops [5]. 2,4-D is labeled by different international agencies as a non-biodegradable carcinogenic and mutagenic compound [6], and it has been found in the water sources of different countries [7] such as Argentina (1.9 mg/L) [8], Colombia (0.001 mg/L) [9], Canada (0.002775 mg/L), Iran (0.016 mg/L), and Ireland (1 × 10 −6 mg/L) [10]. 2,4-D is among the 10 most used active agents in pesticides in the United States, and it is often used for essential crops such as sugarcane, corn, wheat, oats, and barley [11].…”

Hidden impacts of environmental stressors on freshwater: Cytoscape® correlation networks for community ecotoxicology analysis

“…(Havens, 1994). Running correlation networks using an interface as Citoscape® (Shannon et al 2003) could help us understand the impact of a stressor on the relationships between the different components of a community (Lozano et al 2019), and elucidate ecological mechanisms of mitigation or exacerbation. A new mode of response to a stressor at the community-level -or higher-could arise by studying the correlations of the changes in the abundances of the different components of a system.…”