Influence of biochar on the enantioselective behavior of the chiral fungicide metalaxyl in soil

Comunicación oral presentada en la EGU General Assembly 2015, held 12-17 April, 2015 in Vienna, Austria. Id.15367Chiral pesticides comprise an emerging and important class of organic pollutants currently, accounting for more than a quarter of used pesticides. Consequently, the contamination problems caused by chiral pesticides are concern matter and factors affecting enantioselective processes of chiral pesticides in soil need to be understood. For example, certain soil management practices, such as the use of organic amendments, can affect the enantioselective behavior of chiral pesticides in soils. Recently, biochar (BC), i.e. organic matter subjected to pyrolysis, has been proposed as organic amendment due to beneficial properties such as its high stability against decay in soil environments and its apparent ability to influence the availability of nutrients. BC is considered to be more biologically inert as compared to otherforms of organic carbon. However, its side-effects on the enantioselectivity of processes affecting the fate of chiral pesticides is unknown. The aim of this study was to assess the effect of biochar (BC) on the enantioselectivity of sorption, degradation, and leaching of the chiral fungicide metalaxyl in an agricultural soil. Amending the soil with BC (2% w/w) resulted in 3 times higher sorption of metalaxyl enantiomers compared to unamended soil, but no enantioselectivity in the process was observed. Moreover, both enantiomers showed some resistance to be desorbed in BC-amended soil compared to unamended soil. Dissipation studies revealed that the degradation of metalaxylwas more enantioselective in the unamended soil than in BC-amended soil. In unamended soil, R-metalaxyl(biologically active) and S- metalaxyl had half-lives (t1/2) of 3 and 34 days, respectively. BC enhanced the persistence of both enantiomers in the soil, with R-metalaxyl being degraded faster (t1/2=43 days) than S-metalaxyl (t1/2= 100 days). The leaching of both S-and R-metalaxyl was almost suppressed after amending the soil with BC; less than 10% of the fungicide applied to soil columns was recovered in leachates, in contrast to significantly higher percentages leachedin unamended soil, being the process more enantioselective in the latter case. Finally, total recoveries of both enantiomers were greater for BC-amended soil columns than for unamended soil columns, indicating reduced degradation in BC- amended soil. Our findings illustrated the ability of biochar to modify the enantioselectivity behavior of metalaxyl in soil by its high sorption capacity. BC could contribute to reduce the current agronomic doses used for chiral pesticides to deplete the contamination problems associated with their use, and also to act as an immobilizing amendment in soil remediation strategies.MINECO (AGL2011-23779), FACCE-JPI (Designchar4food), JA (AGR-264) and FEDERF-SE (OP 2007-2013).Peer Reviewe

Participation of the Halogens in Photochemical Reactions in Natural and Treated Waters

Halide ions are ubiquitous in natural waters and wastewaters. Halogens play an important and complex role in environmental photochemical processes and in reactions taking place during photochemical water treatment. While inert to solar wavelengths, halides can be converted into radical and non-radical reactive halogen species (RHS) by sensitized photolysis and by reactions with secondary reactive oxygen species (ROS) produced through sunlight-initiated reactions in water and atmospheric aerosols, such as hydroxyl radical, ozone, and nitrate radical. In photochemical advanced oxidation processes for water treatment, RHS can be generated by UV photolysis and by reactions of halides with hydroxyl radicals, sulfate radicals, ozone, and other ROS. RHS are reactive toward organic compounds, and some reactions lead to incorporation of halogen into byproducts. Recent studies indicate that halides, or the RHS derived from them, affect the concentrations of photogenerated reactive oxygen species (ROS) and other reactive species; influence the photobleaching of dissolved natural organic matter (DOM); alter the rates and products of pollutant transformations; lead to covalent incorporation of halogen into small natural molecules, DOM, and pollutants; and give rise to certain halogen oxides of concern as water contaminants. The complex and colorful chemistry of halogen in waters will be summarized in detail and the implications of this chemistry for global biogeochemical cycling of halogen, contaminant fate in natural waters, and water purification technologies will be discussed

Repellency of Predator Urine to Woodchucks and Meadow Voles

Woodchucks (Marmota monax) and meadow voles (Microtus pennsylvanicus) can be serious pests in orchards where they damage young fruit trees by gnawing on main stems. Previous work indicated that topical application of bobcat (Lynx rufus) urine to apple trees could reduce woodchuck damage by an average of 98%. Here, we report on field trials designed to determine whether various fractions of bobcat urine could achieve comparable reductions in gnawing activity. Trials with smooth sumac (Rhus glabra) resulted in an average reduction in gnawing over a 4-week period, relative to controls, of 86% for undiluted urine, 56% for a methanol extract of urine, and 25% for a solution of 5 nitrogen-containing compounds (indole, phenylacetamide, 1-methylhydantoin, 2,6-dimethylpyrazine, 6-valerolactam) in the approximate concentrations they were found in urine. Trials with apple seedlings and cuttings resulted in an average reduction in gnawing over a period of 2-3 weeks, relative to controls, of 90% for undiluted urine, 49% for a methylene chloride extract of urine, 34% for a solution containing a single sulfur-containing compound extracted from urine (3-mercapto-3-methy l-butanol) , and 30 % when this compound was mixed with three additional sulfur volatiles from urine. Reductions due to the nitrogen- and sulfur-containing fractions were not significant. We also conducted laboratory trials in which we recorded the amount of time meadow voles spent in treated versus untreated halves of an arena. Preliminary trials indicated strong aversions (P\u3c0.01) to areas containing bobcat, red fox (Vulpes vulpes), or coyote (Canis latrans) urine, and no aversion (P = 0.56) to woodchuck urine. In subsequent trials, we tested various fractions of bobcat urine and found that the methylene chloride extract and solutions containing either 3-mercapto-3-methyl-butanol, P-mercaptoethanol, or thiophenol caused significant aversions, but the mixture of five nitrogen-containing compounds did not. Woodchucks and meadow voles respond aversively to predator urine, but we were unable to identify fractions of bobcat urine capable of eliciting aversions comparable in magnitude to those achieved with undiluted urine