Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: A review

Photocatalytic degradation of polycyclic aromatic hydrocarbons on soil surfaces using TiO2 under UV light

NF-TiO2 photocatalysis of amitrole and atrazine with addition of oxidants under simulated solar light: Emerging synergies, degradation intermediates, and reusable attributes

The potential effects of adjuvants, including surfactants used in pesticide formulation, have been extensively studied for many small organic chemicals, but similar investigation on pesticides is limited in most cases. Solubilizing effects leading to the apparently increased water solubility of a pesticide are commonly known through the preparation of formulations, but fundamental profiles, especially for a specific monodisperse surfactant, are not fully studied. Reduced volatilization of a pesticide from the formulation can be explained by analogy of a very simple organic chemical, but the actual mechanism for the pesticide is still obscure. In contrast, from the point of view of avoiding groundwater contamination with a pesticide, adsorption/desorption profiles in the presence of surfactants and adjuvants have been examined extensively as well as pesticide mobility in the soil column. The basic mechanism in micelle-catalyzed hydrolysis is well known, and theoretical approaches including the PPIE model have succeeded in explaining the observed effects of surfactants, but its application to pesticides is also limited. Photolysis, especially in an aqueous phase, is in the same situation. The dilution effect in the real environment would show these effects on hydrolysis and photolysis to be much less than expected from the laboratory basic studies, but more information is necessary to examine the practical extent of the effects in an early stage of applying a pesticide formulation to crops and soil. Many adjuvants, including surfactants, are biodegradable in the soil environment, and thus their effects on the biodegradation of a pesticide in soil and sediment may be limited, as demonstrated by field trials. Not only from the theoretical but also the practical aspect, the foliar uptake of pesticide in the presence of adjuvants has been investigated extensively and some prediction on the ease of foliar uptake can be realized in relation to the formulation technology. However, effect on root uptake of pesticides is to be further investigated. In an aqueous environment more or less contaminated by various chemicals such as detergents and their degradates, it is necessary to investigate the effect of adjuvants on uptake, bioconcentration, and trophic transfer of pesticides for better understanding of pesticide contamination of aquatic species in the aquatic environment.

Surfactant effects on environmental behavior of pesticides.

Transformation and fate of polycyclic aromatic hydrocarbons (PAHs) are critically influenced by natural conditions, especially their interactions with various components of soils and sediments. In the present study, phenanthrene was employed as a model to explore the potential photocatalysis effect of various cation-modified clay minerals in the soil under visible-light irradiation. For five types of cation-modified smectite clays, the photodegradation rates of phenanthrene follow the order: Fe 3+  > Cu 2+  > >Ca 2+  > K +  > Na + , which is explained in terms of photo-Fenton-like catalysis. To further inspect the effect of clay type, additional two types of clays were paralleled. Among three types of Fe(III)-modified clays, Fe(III)-smectite shows the highest photodegradation rate followed by Fe(III)-vermiculite and Fe(III)-kaolinite. The photoactivity order is consistent with the iron content contained in the three clays, suggesting that Fe(III) content plays an important role in photocatalytic degradation of phenanthrene. The reactivity of iron species greatly depends on the interlayer microenvironment of smectite such as pH and water content. Moreover, phthalates, 9,10-phenanthrenequinone and alkanoic acids were identified by GC/MS analyses as the main intermediate compounds, and the organic compounds were mineralized finally. The overall results provide valuable insights on the transformation and fate of PAHs in the natural soil environment.

Fan Xiaozhen

Papers

Dynamics of solar light photodegradation behavior of atrazine on soil surface