When irradiated in paddy-field water, propanil (PRP) undergoes photodegradation by direct photolysis, by reactions with OH and CO, and possibly also with the triplet states of chromophoric dissolved organic matter. Irradiation also inhibits the nonphotochemical (probably biological) degradation of PRP. The dark- and light-induced pathways can be easily distinguished because 3,4-dichloroaniline (34DCA, a transformation intermediate of considerable environmental concern) is produced with almost 100% yield in the dark but not at all through photochemical pathways. This issue allows an easy assessment of the dark process(es) under irradiation. In the natural environment, we expect PRP photodegradation to be important only in the presence of elevated nitrate and/or nitrite levels, e.g., [NO] approaching 1 mmol L (corresponding to approximately 60 mg L). Under these circumstances, OH and CO would play a major role in PRP phototransformation. Because flooded paddy fields are efficient denitrification bioreactors that can achieve decontamination of nitrate-rich water used for irrigation, irrigation with such water would both enhance PRP photodegradation and divert PRP dissipation processes away from the production of 34DCA, at least in the daylight hours.
Among the advanced oxidation processes (AOPs), the Fenton reaction has attracted much attention in recent years for the treatment of water and wastewater. This review provides insight into a particular variant of the process, where soluble Fe(II) salts are replaced by zero-valent iron (ZVI), and hydrogen peroxide (H2O2) is replaced by persulfate (S2O82−). Heterogeneous Fenton with ZVI has the advantage of minimizing a major problem found with homogeneous Fenton. Indeed, the precipitation of Fe(III) at pH > 4 interferes with the recycling of Fe species and inhibits oxidation in homogeneous Fenton; in contrast, suspended ZVI as iron source is less sensitive to the increase of pH. Moreover, persulfate favors the production of sulfate radicals (SO4•−) that are more selective towards pollutant degradation, compared to the hydroxyl radicals (•OH) produced in classic, H2O2-based Fenton. Higher selectivity means that degradation of SO4•−-reactive contaminants is less affected by interfering agents typically found in wastewater; however, the ability of SO4•− to oxidize H2O/OH− to •OH makes it difficult to obtain conditions where SO4•− is the only reactive species. Research results have shown that ZVI-Fenton with persulfate works best at acidic pH, but it is often possible to get reasonable degradation at pH values that are not too far from neutrality. Moreover, inorganic ions that are very common in water and wastewater (Cl−, HCO3−, CO32−, NO3−, NO2−) can sometimes inhibit degradation by scavenging SO4•− and/or •OH, but in other cases they even enhance the process. Therefore, ZVI-Fenton with persulfate might perform unexpectedly well in some saline waters, although the possible formation of harmful by-products upon oxidation of the anions cannot be ruled out.
Microplastics are of rising health concerns because they have been detected even in remote and pristine environments, from the Artic snow to the Marianne Trench. The occurrence and impact of nanoplastics in ecosystems is almost unknown, in particular due to analytical limitations such as very small sizes that fall below detection limits of current techniques. Here we take advantage of a common interference in analytical flow cytometry to develop a method for the quantification of the number of plastic particles in the 0.6–15 µm size range. Plastic particles are stained with the lipophilic dye Nile-Red then detected by flow cytometry, a method regularly used in biology for rapid quantification of fluorescent cells. We found that sample analysis lasts 90 s, which is hundreds of times faster than the analysis of filter portions by micro-Raman and other spectroscopic techniques. Our method is highly efficient in detecting polyethylene, with staining efficiency higher than 70% and signal linearity with concentration. Staining efficiency up to 96% was observed for polyvinylchloride and for polystyrene.
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