Removal Kinetics of Four Leacher Herbicides Through Solar Heterogeneous Photocatalysis as Influenced by Water Matrix Components.

This work focuses on the effect of dissolved substances on the photocatalytic degradation of four herbicides, metribuzin and terbuthylazine (triazine) and chlorotoluron and isoproturon (phenylurea) in three different water matrix (deionized, mineral and leaching water). To study the effect of heterogeneous photocatalysis on their degradation, TiO2 and ZnO were used as photocatalysts in tandem with an oxidant (Na2S2O8). Results show that the addition of both semiconductor materials significantly enhances degradation of the herbicides although in different proportions. Similar effectivity of both photocatalyst, assessed as a function of the mean half-lives calculated, was observed (85 and 87 min for TiO2 and Zn, respectively), while the mean half-life in the photolytic experiment was markedly higher (265 min). The degradation rate was in the order: metribuzin > chlorotoluron ≈ isoproturon > terbuthylazine. A faster degradation was observed in all cases in deionized water as compared to mineral and leaching water indicating that the presence of dissolved salts and organic matter considerably slows down the effectiveness of the treatment. Although after 180 min of treatment, total mineralization was not achieved in mineral and leaching water, this technology considerably reduces the pollutant load in complex water matrices. Therefore, solar heterogeneous photocatalytic processes, especially those involving ZnO and TiO2 as photocatalysts, offers a valuable tool for surface and groundwater remediation, especially in those areas receiving a large number of hours of sunshine per year.

Leaching behaviour appraisal of eight persistent herbicides on a loam soil amended with different composted organic wastes using screening indices.

The addition of organic wastes is a common agronomic practice in some Mediterranean regions to increase soil organic matter. In addition, they consume high amounts of agrochemicals. Hand-packed soil columns were used to evaluate the effect of three different composted organic soil amendments (agro-forestry, agro-industrial and animal manure) on the leachability of eight persistent herbicides. A new leaching index based on the amounts recovered from leachates and referred as Experimental Leaching Index (ELI) is proposed according to the mean annual precipitation in a specific place. This index is compared with others such as Groundwater Ubiquity Score (GUS), Relative Leaching Potential Index (RLPI) and Leachability Index (LIX), which only include degradation (DT50) and sorption (KOC) parameters. According to ELI, metribuzin is very mobile in all cases, while terbuthylazine, chlorotoluron and isoproturon present high leachability only in unamended soil reducing their leaching potential in amended soils. Aclonifen, oxyfluorfen, trifluralin and pendimethalin behave in all cases as immobile (non-leacher) compounds.