Extraction procedures for the study of phytotoxicity and degradation processes of selected triketones in a water ecosystem

Seasonal distribution of multiclass pesticide residues in the surface waters of northwest Croatia

As part of our OPENTOX project, we evaluated the incidence and mass concentrations of multiclass pesticide residues in 23 river/stream water samples collected in urban and agricultural areas of northwest Croatia at various points of the pesticide application season in 2015. The study included 16 compounds of five herbicide classes and seven compounds of three insecticide classes. Pesticide residues were accumulated from water by solid-phase extraction and analysed using high performance liquid chromatography with UV-diode array detection and/or gas chromatography-mass spectrometry. Herbicide residues were more common than the insecticide ones, and, as expected, they peaked in the middle of the application season. Metolachlor showed the highest concentrations and was found in 91 % of all samples, followed by terbuthylazine, found in 70 % of the samples. The highest total mass concentration of detected pesticides was measured in the water samples of the Krapina (3992 ng/L) and Sutla (3455 ng/L) collected in rural areas with intensive agriculture. Our findings strongly speak in favour of continued monitoring of surface waters and possibly extending the list of priority water pollutants.

Metabolic profiles in the course of the shikimic acid pathway of Raphanus sativus var. longipinnatus exposed to mesotrione and its degradation products

The influence of pesticides on the metabolism of edible plants has not been fully investigated. Moreover, once introduced into the environment, pesticides are degraded to many compounds with undefined bioactivity. In presented work, under experimental conditions, model edible plant (Raphanus sativus var. longipinnatus) was exposed to herbicide stress by application of a herbicide (mesotrione, 2-(4-methanesulfonyl-2-nitrobenzoyl)cyclohexane-1,3-dione, MES) or its degradation products (amino-4-(methylsulfonyl)benzoic acid, AMBA; 4-(methylsulfonyl)-2-nitrobenzoic acid MNBA; cyclohexane-1,3-dione, CHD). Metabolic profiles of plants were employed to estimate the plant's defence response to MES and its metabolites. The intensity of herbicide stress was determined by measuring the changes in chlorophyll and catecholamines concentration formed in the shikimic acid pathway. Non-target analysis was conducted by LC-MS/MS, determination of catecholamines by LC-FL, chlorophyll by spectrophotometry. The highest phytotoxicity is characterized by MES (2000%-fold increase in the content of herbicide stress marker (normetanephrine) compared to a blank), followed by CHD (500%) combined with 15% increase in chlorophyll concentration. AMBA and MNBA as stress factors caused the increase in the content of catecholamines in the plant (86-160%). Simultaneously, an increase in chlorophyll content was observed (26-50%). Such diversity of the organism's defence response, also visible on metabolic profiles, can be associated with the chemical structure of compounds that are stress factors. MES and CHD, in contrast to AMBA and MNBA, have cyclohexano-1,3-moiety in their structure, which seems to be responsible for herbicidal properties.

Potential application of Pistia stratiotes for the phytoremediation of mesotrione and its degradation products from water

The aim of the present work is to estimate remediation potential of Pistia stratiotes, its ability to uptake mesotrione (MES) - one of the most frequently used herbicides, and its main degradation products: 2-amino-4-methylsulfonyl benzoic acid (AMBA) and 4-methylsulfonyl-2-nitrobenzoic acid (MNBA). This research focuses on model experiments performed under laboratory conditions. The results show that Pistia stratiotes can uptake up to 75% of degradation products from 1 L of surface water samples polluted with 0.4 µg/L of each analyte during 7 days without significant phytotoxic effect. Under the same experimental conditions, the effectiveness of mesotrione sorption is in the range of 42-58%. The phytotoxicity of this compound is higher in comparison to its degradation products (decrease of chlorophyll concentration in plant tissues exposed to MES 27-32% vs 4-13% in case of exposition to AMBA and MNBA). The adequate nutrition of the plants is crucial to their well-being and thus the sorption of pollutants.

Enhanced disappearance of mesotrione and fomesafen by water hyacinth (Eichhornia crassipes) in water

This study aimed to investigate the potential use of water hyacinth (Eichhornia crassipes) in removing two herbicides (mesotrione and fomesafen) with long degradation cycles in water. The relative growth rate (RGR) of water hyacinth in the presence of 100-mg/L mesotrione and fomesafen was significantly lower than that in their absence, particularly with fomesafen. Moreover, the RGR_FW and RGR_DW with treatment with fomesafen were 1.47- and 1.58-fold lower than those with treatment with mesotrione, respectively. The disappearance rate constants of mesotrione and fomesafen in natural water were, respectively, 0.1148 and 0.0276 d^-1 with plants and 0.0038 and 0.0005 d^-1 without plants. The disappearance rate constants with and without plants were significantly different, indicating that uptake by plants combined with degradation by plant-associated bacteria account for 96.7% and 98.2% of the removal of mesotrione and fomesafen, respectively. The bioconcentration factor for mesotrione and fomesafen in living water hyacinth plants ranged 0.38-16.97 and 1.05-3.50 L/kg, respectively, whereas the residues of mesotrione and fomesafen in water decreased by 70-92 and 22-34%, respectively, after the plants were grown for 14 d in culture solution with 100-mg/L mesotrione and fomesafen. These results show that uptake by plants combined with degradation by plant-associated bacteria may be the dominant process in the removal of mesotrione and fomesafen from water by plants. Water hyacinth may be applied as an efficient, economical, and ecological alternative to accelerate the removal and degradation of agro-industrial waste water polluted with mesotrione and fomesafen.

A new tool for direct non-invasive evaluation of chlorophyll a content from diffuse reflectance measurements

Chlorophyll is a key biochemical component that is responsible for photosynthesis and is an indicator of plant health. The effect of stressors can be determined by measuring the amount of chlorophyll a, which is the most abundant chlorophyll, in vegetation in general. Nowadays, invasive methods and vegetation indices are used for establishing chlorophyll amount or an approximation to this value, respectively. This paper demonstrates that H-point curve isolation method (HPCIM) is useful for isolating the signal of chlorophyll a from non-invasive diffuse reflectance measurements of leaves. Spinach plants have been chosen as an example. For applying the HPCIM only the registers of both, a standard and the sample are needed. The results obtained by HPCIM and the invasive method were statistically similar for spinach leaves: 144±6mg/m² (n=5) and 155±40mg/m² (n=5), respectively. However, more precise values were achieved with the HPCIM, which also involved minimal experimental effort. The HPCIM method was applied to spinach plants stressed by the action of several pesticides and water scarcity, showing a decrease of chlorophyll a content with time, which is related with a loss of health. The results obtained were compared with those achieved by two different reflectance vegetation indices (Macc01 and NDVI). Although NDVI and HPCIM gave similar footprints for the plants tested, vegetation indices fail in the estimation of real content of the chlorophyll a. The HPCIM could contribute to improve the knowledge of the chlorophyll a content of vegetation like health indicator, by applying it to a much employed non-invasive technique such as diffuse reflectance, which can be used in place or in remote sensing mode.

Fate and ecotoxicological impact of new generation herbicides from the triketone family: An overview to assess the environmental risks

Triketones, derived chemically from a natural phytotoxin (leptospermone), are a good example of allelochemicals as lead molecules for the development of new herbicides. Targeting a new and key enzyme involved in carotenoid biosynthesis, these latest-generation herbicides (sulcotrione, mesotrione and tembotrione) were designed to be eco-friendly and commercialized fifteen-twenty years ago. The mechanisms controlling their fate in different ecological niches as well as their toxicity and impact on different organisms or ecosystems are still under investigation. This review combines an overview of the results published in the literature on β-triketones and more specifically, on the commercially-available herbicides and includes new results obtained in our interdisciplinary study aiming to understand all the processes involved (i) in their transfer from the soil to the connected aquatic compartments, (ii) in their transformation by photochemical and biological mechanisms but also to evaluate (iii) the impacts of the parent molecules and their transformation products on various target and non-target organisms (aquatic microorganisms, plants, soil microbial communities). Analysis of all the data on the fate and impact of these molecules, used pure, as formulation or in cocktails, give an overall guide for the assessment of their environmental risks.

Atrazine, triketone herbicides, and their degradation products in sediment, soil and surface water samples in Poland

The aim of this study was to monitor the sediment, soil and surface water contamination with selected popular triketone herbicides (mesotrione (MES) and sulcotrione(SUL)), atrazine (ATR) classified as a possible carcinogen and endocrine disrupting chemical, as well as their degradation products, in Silesia (Poland). Seventeen sediment samples, 24 soil samples, and 64 surface water samples collected in 2014 were studied. After solid-liquid extraction (SLE) and solid phase extraction (SPE), analytes were determined by high-performance liquid chromatography (HPLC) with diode array detection (DAD). Ten years after the withdrawal from the use, ATR was not detected in any of the collected samples; however, its degradation products are still present in 41 % of sediment, 71 % of soil, and 8 % of surface water samples. SUL was determined in 85 % of soil samples; its degradation product (2-chloro-4-(methylosulfonyl) benzoic acid (CMBA)) was present in 43 % of soil samples. In 17 % of sediment samples, CMBA was detected. Triketones were detected occasionally in surface water samples. The chemometric analysis (clustering analysis (CA), single-factor analysis of variance (ANOVA), N-Way ANOVA) was applied to find relations between selected soil and sediment parameters and herbicides concentration. In neither of the studied cases a statistically significant relationship between the concentrations of examined herbicides, their degradation products and soil parameters (organic carbon (OC), pH) was observed.