Herbicide effects of metazachlor on duckweed (Lemna minor and Spirodela polyrhiza) in test systems with different trophic status and complexity

Chloroacetanilides inhibit photosynthesis and disrupt the thylakoid membranes of the dinoflagellate Prorocentrum minimum as revealed with metazachlor treatment

The chloroacetanilides are among the most commonly used herbicides worldwide, which contaminate aquatic environments and affect aquatic phototrophs. Their sub-lethal toxicity has been evaluated using freshwater algae; however, the modes of cellular toxicity and levels of toxicity to marine organisms are not fully understood. In the present study, we assessed the cellular and molecular effects of chloroacetanilides on marine phototrophs using the dinoflagellate Prorocentrum minimum and the herbicide metazachlor (MZC). The MZC treatment led to a considerable reduction in cell number and pigment, and the EC₅₀ of MZC was calculated to be 0.647 mg/L. The photosynthetic parameters, Fv/Fm and chlorophyll fluorescence significantly decreased with MZC exposure time in a dose-dependent manner. In addition, MZC significantly induced photosynthesis genes, including PmpsbA, PmpsaA, and PmatpB, and the antioxidant PmGST, but not PmKatG. These findings were well matched to reactive oxygen species (ROS) production in MZC-treated cells. Interestingly, we observed inflated vacuoles, undivided chloroplasts, and breakdown of thylakoid membranes in MZC-treated cells. These results support the hypothesis that MZC severely damages chloroplasts, resulting in dysfunction of the dinoflagellate photosynthesis and possibly marine phototrophs in the environment.

Ecotoxicological evaluation of fungicides used in viticulture in non-target organisms

The effect of fungicides, commonly used in vine cultures, on the health of terrestrial and aquatic ecosystems has been poorly studied. The objective of this study was to evaluate the toxicity of three viticulture fungicides (myclobutanil, cymoxanil, and azoxystrobin) on non-target organisms, the bacteria Rhodopirellula rubra, Escherichia coli, Pseudomonas putida, and Arthrobacter sp., the microalgae Raphidocelis subcapitata, and the macrophyte Lemna minor. Fungicide toxicity was performed in acute cell viability assay for bacteria; 72-h and 7-day growth inhibition tests for R. subcapitata and L. minor, respectively. Contents of photosynthetic pigments and lipid peroxidation in L. minor were evaluated. Arthrobacter sp. and P. putida showed resistance to these fungicides. Even though azoxystrobin affected R. rubra and E. coli cell viability, this effect was due to the solvent used, acetone. Cell viability decrease was obtained for R. rubra exposed to cymoxanil and E. coli exposed to myclobutanil (30 min of exposure at 10 mg/L and 240 min of exposure at 46 mg/L, respectively). R. subcapitata showed about 10-fold higher sensitivity to azoxystrobin (EC_50-72h = 0.25 mg/L) and cymoxanil (EC_50-72h = 0.36 mg/L) than L. minor to azoxystrobin and myclobutanil (EC_50-72h = 1.53 mg/L and EC_50-72h = 1.89 mg/L, respectively). No lipid peroxidation was observed in L. minor after fungicide exposure, while changes of total chlorophyll were induced by azoxystrobin and myclobutanil. Our results showed that non-target aquatic organisms of different trophic levels are affected by fungicides used in viticulture.

Time-Cumulative Toxicity of Neonicotinoids: Experimental Evidence and Implications for Environmental Risk Assessments

Our mechanistic understanding of the toxicity of chemicals that target biochemical and/or physiological pathways, such as pesticides and medical drugs is that they do so by binding to specific molecules. The nature of the latter molecules (e.g., enzymes, receptors, DNA, proteins, etc.) and the strength of the binding to such chemicals elicit a toxic effect in organisms, which magnitude depends on the doses exposed to within a given timeframe. While dose and time of exposure are critical factors determining the toxicity of pesticides, different types of chemicals behave differently. Experimental evidence demonstrates that the toxicity of neonicotinoids increases with exposure time as much as with the dose, and therefore it has been described as time-cumulative toxicity. Examples for aquatic and terrestrial organisms are shown here. This pattern of toxicity, also found among carcinogenic compounds and other toxicants, has been ignored in ecotoxicology and risk assessments for a long time. The implications of the time-cumulative toxicity of neonicotinoids on non-target organisms of aquatic and terrestrial environments are far reaching. Firstly, neonicotinoids are incompatible with integrated pest management (IPM) approaches and secondly regulatory assessments for this class of compounds cannot be based solely on exposure doses but need also to take into consideration the time factor.

Application of common duckweed (Lemna minor) in phytoremediation of chemicals in the environment: State and future perspective

Over the past 50 years, different strategies have been developed for the remediation of polluted air, land and water. Driven by public opinion and regulatory bottlenecks, ecological based strategies are preferable than conventional methods in the treatments of chemical effluents. Ecological systems with the application of microbes, fungi, earthworms, plants, enzymes, electrode and nanoparticles have been applied to varying degrees in different media for the remediation of various categories of pollutants. Aquatic macrophytes have been used extensively for the remediation of pollutants in wastewater effluents and aquatic environment over the past 30 years with the common duckweed (L. minor) as one of the most effective macrophytes that have been applied for remediation studies. Duckweed has shown strong potentials for the phytoremediation of organic pollutants, heavy metals, agrochemicals, pharmaceuticals and personal care products, radioactive waste, nanomaterials, petroleum hydrocarbons, dyes, toxins, and related pollutants. This review covers the state of duckweed application for the remediation of diverse aquatic pollutants and identifies gaps that are necessary for further studies as we find pragmatic and sound ecological solutions for the remediation of polluted environment for sustainable development.

Immediate and mid-term effects of pyrimethanil toxicity on microalgae by simulating an episodic contamination

Since pesticides can represent a threat for non-target aquatic communities, including microalgae, we looked at the effects of the fungicide pyrimethanil on the growth of the freshwater green microalgae Selenastrum capricornutum. Additionally, attenuation of the toxicity of pyrimethanil due to its dissipation in the water was assessed. Pyrimethanil-contaminated samples were taken from outdoor mesocosms one (1.4 mg L(-1) of pyrimethanil) and ten (0.78 mg L(-1) of pyrimethanil) days after pyrimethanil application. Different dilutions were prepared using both nutrient-rich culture medium (LC Oligo) and non-contaminated mesocosm samples, and cell growth inhibition was assessed. Reference mesocosm samples were also diluted with LC Oligo in order to verify how the nutrient concentration in the LC Oligo could improve cell growth. Comparing cell growth of population exposed to pyrimethanil-treated sample taken at day 1 with cells growing in reference sample and LC Oligo, the growth inhibition was 80% (± 6.5) and 95% (± 2.0), respectively. The toxicity of samples taken from contaminated mesocosms at day 10 was attenuated to 34% (± 15) (when compared with reference sample) and 88% (± 3.0) (when compared with LC Oligo), as pyrimethanil concentrations in the mesocosms decreased. In conclusion, (i) pyrimethanil can be an environmental disturber for the microalgae; (ii) the toxicity of pyrimethanil in water was reduced almost 2.4 times (when compared with the reference sample) at as short a period as 10d if assuming that pesticide entrance is not continuous; (iii) toxicity of an environmental sample could be underestimated if the sample/medium used in dilution presents different nutrient levels.