Effect of Spent Mushroom Substrate Amendment of Vineyard Soils on the Behavior of Fungicides: 2. Mobility of Penconazole and Metalaxyl in Undisturbed Soil Cores

Abstract

Mobility of fungicides penconazole and metalaxyl in unamended and amended vineyard soils with fresh and composted spent mushroom substrates (F-SMS and C-SMS) was studied. Experiments were performed in non-incubated and incubated (outdoors for 77 days) undisturbed soil cores under non-saturated flow conditions. Breakthrough curves (BTC) of metalaxyl leaching were delayed with regard to the tracer ion, and they showed an incomplete leaching in all soil cores after the addition of 2.5-4.5 pore volumes. A decrease of the maximum peak concentration in C-SMS soils with regard to unamended soils (up to 24-fold in Viana soil) and an increase in the fungicide retention by soils (up to 8-fold in the first segment of Viana soil core) was observed. However, a decrease (up to 2.6-fold in Sajazarra soil) or an increase (up to 1.4-fold in Aldeanueva soil) of the maximum peak concentration in F-SMS soils was observed. No leaching of penconazole was observed in all cases. After fungicide incubation in soil cores, the amounts of metalaxyl retained and leached decreased significantly by 1.24-37.8-fold and 1.17-302-fold, respectively, whereas no changes were observed for penconazole. Degradation of metalaxyl occurred in non-incubated soil and increased after incubation (two metalaxyl metabolites were detected in the leachates and the soil extracts), but it was not seen for penconazole in any case. In consequence, the addition of SMS as amendment to soil (especially C-SMS) enhanced adsorption of both fungicides, although metalaxyl could be available for degradation. This effect contributes to prevent groundwater contamination by metalaxyl, but it could contribute to increase the surface water contamination by penconazole, because adsorption protects this fungicide from degradation, increasing its persistence in soils.