Fatty Acid Methyl Ester (FAME) Succession in Different Substrates as Affected by the Co-Application of Three Pesticides

INTRODUCTION: In intensive agriculture areas the use of pesticides can alter soil properties and microbial community structure with the risk of reducing soil quality. MATERIALS AND METHODS: In this study the fatty acid methyl esters (FAMEs) evolution has been studied in a factorial lab experiment combining five substrates (a soil, two aged composts and their mixtures) treated with a co-application of three pesticides (azoxystrobin, chlorotoluron and epoxiconazole), with two extraction methods, and two incubation times (0 and 58 days). FAMEs extraction followed the microbial identification system (MIDI) and ester-linked method (EL). RESULTS AND DISCUSSION: The pesticides showed high persistence, as revealed by half-life (t(1/2)) values ranging from 168 to 298 days, which confirms their recalcitrance to degradation. However, t(1/2) values were affected by substrate and compost age down to 8 days for chlorotoluron in S and up to 453 days for epoxiconazole in 12M. Fifty-six FAMEs were detected. Analysis of variance (ANOVA) showed that the EL method detected a higher number of FAMEs and unique FAMEs than the MIDI one, whereas principal component analysis (PCA) highlighted that the monosaturated 18:1ω9c and cyclopropane 19:0ω10c/19ω6 were the most significant FAMEs grouping by extraction method. The cyclopropyl to monoenoic acids ratio evidenced higher stress conditions when pesticides were applied to compost and compost+soil than solely soil, as well as with final time. CONCLUSION: Overall, FAMEs profiles showed the importance of the extraction method for both substrate and incubation time, the t(1/2) values highlighted the effectiveness of solely soil and the less mature compost in reducing the persistence of pesticides.