Utilization of the zebrafish model to unravel the harmful effects of biomass burning during Amazonian wildfires.

Amazonian wildfires in 2019 have raised awareness about rainforest burning due to increased emissions of particulate matter and carbon. In the context of these emissions, by-products of lignin thermal degradation (i.e. methoxyphenols) are often neglected. Methoxyphenols entering the atmosphere may form intermediates with currently unknown reaction mechanisms and toxicity. This study for the first time provides a comprehensive insight into the impact of lignin degradation products [guaiacol, catechol], and their nitrated intermediates [4-nitrocatechol, 4,6-dinitroguaiacol, 5-nitroguaiacol] on zebrafish Danio rerio. Results revealed 4-nitrocatechol and catechol as the most toxic, followed by 4,6DNG > 5NG > GUA. The whole-organism bioassay integrated with molecular modeling emphasized the potential of methoxyphenols to inhibit tyrosinase, lipoxygenase, and carbonic anhydrase, consequently altering embryonic development (i.e. affected sensorial, skeletal, and physiological parameters, pigmentation formation failure, and non-hatching of larvae). The whole-organism bioassay integrated with in silico approach confirmed the harmful effects of lignin degradation products and their intermediates on aquatic organisms, emphasizing the need for their evaluation within ecotoxicity studies focused on aquatic compartments.

Toxicity evaluation of olive oil mill wastewater and its polar fraction using multiple whole-organism bioassays.

Olive mill wastewater (OMW) as a by-product of olive oil extraction process has significant polluting properties mainly related to high organic load, increased COD/BOD ratio, high phenolic content and relatively acidic pH. Raw OMW from Slovenian Istria olive oil mill and its polar fraction were investigated in this study. Chemical characterization of OMW polar fraction identified tyrosol as the most abundant phenolic product, followed by catechol. Lethal and sub-lethal effects of OMW matrix and its polar fraction were tested using a battery of bioassays with model organisms: bacteria Vibrio fischeri, algae Chlorella vulgaris, water fleas Daphnia magna, zebrafish Danio rerio embryos, clover Trifolium repens and wheat Triticum aestivum. Raw OMW sample was the most toxic to V. fischeri (EC50 = 0.24% of OMW sample final concentration), followed by D. magna (EC50 = 1.43%), C. vulgaris (EC50 = 5.20%), D. rerio (EC50 = 7.05%), seeds T. repens (EC50 = 8.68%) and T. aestivum (EC50 = 11.58%). Similar toxicity trend was observed during exposure to OMW polar fraction, showing EC50 values 2.75-4.11 times lower comparing to raw OMW. Tested samples induced also sub-acute effects to clover and wheat (decreased roots, sprouts elongation); and to zebrafish embryos (increased mortality, higher abnormality rate, decreased hatching and pigmentation formation rate). A comprehensive approach using a battery of bioassays, like those used in this study should be applied during ecotoxicity monitoring of untreated and treated OMW.

Acute toxicity of emerging atmospheric pollutants from wood lignin due to biomass burning.

Guaiacol (2-methoxyphenol) is an important atmospheric pollutant. It is the major component of wood lignin and is essentially emitted to the atmosphere during biomass burning. Its aging in the tropospheric aqueous phase leads to the generation of the following ring-retaining transformation products, also during nighttime: 4-nitroguaiacol, 6-nitroguaiacol, and dinitroguaiacol. This study presents the first toxicological data of guaiacol and its nitro derivatives and reveals their harmful potential for the ecosystem. Applying V. fischeri bioluminescence acute toxicity test, EC50 values range from 16.7 to 103mgL-1 after a 30-min incubation period, which classifies all investigated compounds as 'harmful' according to the European legislation. The investigation of environmentally relevant mixtures did not show significant joint actions between the four studied compounds. Therefore, their concentration addition can be considered for ecotoxicological purposes. However, a synergistic effect between guaiacol and a minor unidentified first-generation product of its aqueous-phase aging was observed and should be taken into account when assessing the reaction mixture toxicity. These results stress the need for further toxicological testing, including organisms of different trophic levels, to better evaluate the environmental hazard of guaiacol and especially its nitro derivatives.

Evaluation of the reaction artifacts in an annular denuder-based sampler resulting from the heterogeneous ozonolysis of naphthalene.

The heterogeneous ozonolysis of naphthalene adsorbed on XAD-4 resin was studied using an annular denuder technique. The experiments involved depositing a known quantity of naphthalene on the XAD-4 resin and then measuring the quantity of the solid naphthalene that reacted away under a constant flow of gaseous ozone (0.064 to 4.9 ppm) for a defined amount of time. All experiments were performed at room temperature (26 to 30 °C) and atmospheric pressure. The kinetic rate coefficient for the ozonolysis reaction of naphthalene adsorbed on XAD-4 resin is reported to be (10.1 ± 0.4) × 10(-19) cm(3) molecule(-1) s(-1) (error is 2σ, precision only). This value is five times greater than the currently recommended literature value for the homogeneous gas phase reaction of naphthalene with ozone. The obtained rate coefficient is used to evaluate reaction artifacts from field concentration measurements of naphthalene, acenaphthene, and phenanthrene. The observed uncertainties associated with field concentration measurements of naphthalene, acenaphthene, and phenanthrene are reported to be much higher than the uncertainties associated with the artifact reactions. Consequently, ozone reaction artifact appears to be negligible compared to the observed field measurement uncertainty results.

Heterogeneous oxidation of terbuthylazine by "dark" OH radicals under simulated atmospheric conditions in a flow tube.

In order to investigate the heterogeneous oxidation kinetics of the herbicide terbuthylazine (TERB), a stable and reproducible generation system of "dark" hydroxyl radical in the gas phase was developed and optimized using a PTR-MS. TERB was adsorbed on silica particles, which were coated on the walls of a flow tube. The hydroxyl radical was produced in the dark through the ozonolysis of 2,3-dimethyl-2-butene (DMB). The radical concentration was determined applying two different methods of calculation based on the monitoring of (i) a gaseous compound used as a tracer, m-xylene; (ii) one of the OH radical precursors, DMB. The obtained gaseous OH radical concentration in the reactor was (9.0 ± 4.0) × 10(7) radical cm(-3). Exposing TERB to the oxidant for 1-14 h, a heterogeneous kinetic constant of kOH = (1.5 ± 0.8) × 10(-13) cm(3) molecule(-1) s(-1) was found at 26 °C and RH < 1%. As a result, the heterogeneous oxidation of TERB by OH radicals seems to be much slower (by a factor of 63) when the organic compound is present in the particulate phase than when it reacts in homogeneous gas phase.