METALAXYL-M LEACHING FROM DIFFERENT SUBSTRATES AND DRAINAGE SYSTEMS IN INTENSIVE GREEN ROOFS

Contemporary urban areas are characterized by the lack of green spaces due to the overwhelming presence of structured surfaces. In such cases green roofs are an effective alternative. However, there is a lack of research evidences concerning the leaching potential of the applied agrochemicals on the green roofs that might reach the sewage systems. The aim of the present study was to investigate the leaching potential of metalaxyl-m (mefenoxam), a highly soluble fungicide, used in turfgrass management. Fifty four lysimeters were constructed and filled with different substrates using two different drainage systems: a) a tri-layered sand/lava system (S) and b) a geotextile/lava (G) system. For the first trial (A) the substrates were SL₆₀-P₄₀, SL₆₀-P₂₀-PER₂₀, SL₆₀-PER₄₀, SL₃₀-P₄₀-PER₃₀, SL₃₀-PER₇₀. The substrates for the second trial (B) were SL₃₀-P₂₀-PER₃₀-L₂₀, SL₃₀-P₂₀-PER₃₀-PV₂₀, SL₃₀-P₂₀-PER₃₀-LV₂₀, SL₃₀-PER₄₀-PV₃₀, SL₃₀-PER₇₀, (SL=Sandy Loam Soil, P=Peat, PER=Perlite, L=Greek Lava, PV=Italian Pumice, LV=Italian Lava). All lysimeters were seeded with Festuca arundinacea. Metalaxyl-m leaching was determined by high performance liquid chromatography-mass spectrometry (LC/MS). It was found that metalaxyl-m leaching rate was greater in the substrates that did not include peat, regardless of the drainage system. In addition metalaxyl-m concentration in the leachate was reduced, as the peat participation in the substrate increased from 0 to 20 and then to 40%. However it was noticed that despite the observed differences in-between substrates, all the detected concentrations exceeded the maximum permitted residues level (MRL) of 0,1 μg L^-1 indicating the need for caution during pesticide application in intensive type green roofs.