Transport of pesticides via macropores (IUPAC Technical Report)

Abstract

Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the need for formal IUPAC permission on condition that an acknowledgment Transport of pesticides via macropores (IUPAC Technical Report)Abstract: This report provides an overview of the transport of solutes via macropores focusing on the practical relevance of the phenomenon. After a description of matrix flow and preferential flow in soil, information related to macropores, including their formation and measurement techniques, is briefly presented. Then, the influence of experimental conditions and of environmental and agricultural factors and pesticide properties is discussed, based on a statistical evaluation of all published studies offering sufficient quantitative information. Most of the analyzed parameters do not significantly influence the experimental pesticide losses. The groundwater ubiquity score (GUS) index turned out to be the most important compound property to describe substance losses through macropore flow.In a third section, tools for modeling pesticide transport through macropores are presented and critically evaluated. Results of the computer model MACRO, which is also used in the EU pesticide registration process, are compared with experimental losses. For five out of seven investigated pesticides (A-D, F), the simulated losses are in agreement with the experimental data. However, for two compounds with very low K OC values, MACRO overestimated the losses.Finally, the significance of pesticide transport via macropores for contamination of ground and surface water is assessed. Losses caused by macropore transport may considerably exceed losses caused by matrix transport at a specific site. Therefore, a site-specific assessment of pesticide leaching is needed.

Adsorbing vs. Nonadsorbing Tracers for Assessing Pesticide Transport in Arable Soils

“…It is commonly accepted that high precipitation or irrigation shortly after application increases the losses through macropores (Kördel et al, 2008), as was observed in the present experiments. Accordingly, detection of pesticides and non-conservative tracers in leachate within a few hours or days after irrigation has been previously observed at the laboratory and field scales and attributed to preferential flow (Kladivko et al, 1991;Kanwar et al, 1997;Kung et al, 2000;Haws et al, 2004).…”

“…The flow of water and solutes through soil is largely determined by the size and connectivity of the water-filled pores (Jarvis, 2007). In addition to transport through the porous matrix, pesticides may be rapidly leached below the root zone by advective transport through macropores (e.g., cracks, earthworm channels, root holes, fissures, and interaggregate packing voids), largely bypassing the soil matrix (Bouma and Dekker, 1978;Beven and Germann, 1982;Jarvis, 2007), reducing the potential for pollutant adsorption and degradation and thus increasing the threat of groundwater contamination (Kördel et al, 2008). This preferential flow is recognized as prevalent under a wide range of conditions in soils with unstable, poor structure as well as those containing cracks Core Ideas • Atrazine preferential flow shortly after application was governed by soil type.…”

Effects of Wood Amendments on the Degradation of Terbuthylazine and on Soil Microbial Community Activity in a Clay Loam Soil

“…Moreover, although the soil studied had a fine texture, which is known to limit the diffusion and transport of contaminants, the groundwater beneath has been found to be contaminated by triazines. This fact can be ascribed to preferential flow pathways (Flury et al 1996;Kördel et al 2008) occurring when large and discontinuous macropores operate and cause rapid movement of chemicals through the unsaturated zone. The transport of pesticides via macropores has been frequently found in fine textured soils and herbicides may contaminate groundwater especially if the degradation phenomena in surface soil do not significantly reduce their concentration (Guzzella et al 2003(Guzzella et al , 2006, as in the case of our soil.…”

Model-based estimation of pesticides and transformation products and their export pathways in a headwater catchment

“…The total export fraction via preferential flow to tile drains was in the same order of magnitude (0.02-0.07 %) for all substances although their K OC values differed by a factor 30 and their DT50 by a factor 13. Thus, the importance of the intrinsic pesticide properties seemed to be reduced for vertical preferential flow (Larsson and Jarvis, 2000;Kördel et al, 2008), but total tile drain export increased more for stronger sorbing substances.…”