Effect of Pesticide Inoculation, Duration of Composting, and Degradation Time on the Content of Compost Fatty Acids, Quantified Using Two Methods

Abstract

Compost biobeds can promote biodegradation of pesticides. The microbial community structure changes during the composting process, and simple methods can potentially be used to follow these changes. In this study the microbial identification (MIDI) and ester-linked (EL) procedures were used to determine the composition of fatty acid methyl esters (FAMEs) in composts aged 3 and 12 months, inoculated with 3 recalcitrant pesticides (azoxystrobin, chlorotoluron, and epoxyconazole and a coapplication of all three) after 0, 56, and 125 days of degradation. Pesticide persistence was high, and after 125 days the residue was 22 to 70% of the applied amount depending mostly on the composting age. Seventy-one FAMEs belonging to nine groups were detected. The EL method provided three times as many detections as did the MIDI method and was more sensitive for all FAME groups except alcohol. Thirty-six and five FAMEs were unique to the EL and MIDI methods, respectively. The extraction method was of importance. The EL method provided a higher number of detections for 57 FAMEs, and the MIDI method provided a higher number for 9 FAMEs, while the two methods were equal for 5 FAMEs; thus, the EL method provided a more uniform overall FAME profile. Effects of the other factors were not always clear. Inoculation with pesticide did not influence the FAME profile with the MIDI method, while it influenced cyclopropane and monounsaturated content with the EL method. Composting age and degradation time had an effect on some groups of FAMEs, and this effect was greater with the EL method. The use of some FAMEs as biomarkers to follow microbial community succession was likely influenced by the type of compost and other factors.Plant protection has become a key factor in intensive agriculture, but the widespread use of pesticides can be toxic to nontarget organisms and can lead to ecosystem alterations. Formulated chlorotoluron (a herbicide), azoxystrobin (a fungicide), and epoxyconazole (a fungicide) are commonly used at the postemergence stage mainly for cereals, to control broadleaved weeds and grasses and to control some foliar and soilborne diseases, respectively.Most information on pesticide persistence is derived from registration documents, few studies appear in the scientific literature, and independent research is always suggested. A recent pesticide database (Footprint, 2007; http://www.eu -footprint.org/ppdb.html, accessed April 2010) reports half-life values (days) in soil, derived from laboratory studies at 20°C, of 73.5 for azoxystrobin, 59 for chlorotoluron, and 226 for epoxyconazole. However, a certain variability exists, and in other research half-lives are longer, i.e., more than 2 years (at 10°C) for epoxyconazole (4), 62 to 107 days for azoxystrobin (10), and 30 to 200 days for chlorotoluron (36), showing that significant degradation should be measured on a time scale of months or years (8, 9) according to the results of a recent review on pesticide persistence (3).The use of such persistent pesticides on agricultural fi...

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

“…Relative amounts of hydroxylated and cyclopropane FAMEs were greater in MIDI extracts, whereas EL extracts contained relatively greater amounts of iso and anteiso branching FAMEs. This is consistent with the results found previously in compost [ 10 , 31 , 32 ]. Overall, our results confirmed that EL had a higher number of distinguishing FAMEs than MIDI.…”

“…In fact, the pesticide half-life reduces 2.1 fold when comparing 12M with S. Pesticide degradation also depended on the compost age. Indeed, persistence decreased with the reduction in compost age, as resulted from comparing 12M with 3M, in accordance with our previous work [ 10 ]. However, if less mature compost is better able than mature compost to degrade pesticides, probably due to the greater carbon sources for microorganisms [ 29 ], the abundance of functional groups in a mature compost might increase the number of interactions with a pesticide and thus its persistence, as shown between a humic acid and a herbicide [ 30 ].…”

“…The procedures used derived from a previous similar study with slight modifications necessary for compost. The EL and MIDI procedures are explained in detail elsewhere [ 10 ].…”

“…Although the soil type and organic carbon content greatly influence the mobility of pesticides through leaching [ 6 ], the microbial community has been reported to be usually reduced after the application of pesticides [ 7 , 8 , 9 ]. A modification in the microbial community structure, towards one more adapted to breaking down complex molecules, has been found to be induced by the addition of three pesticides (i.e., azoxystrobin, chlorotoluron and epoxiconazole) to a compost mixture [ 10 ], although compost amendment on its own might induce changes in the soil microbial community [ 11 , 12 ]. Differences in the microbial community structure were also found after the application of azoxystrobin, fludioxonil and penconazole in biobed organic substrates with changes mostly attributed to an inhibition of fungi [ 13 ].…”

“…For a better understanding of the dynamics of microbial community structures after pesticide application it is necessary to elucidate the changes induced in microbial communities that influence the pesticide biodegradation. In a previous study [ 10 ], we investigated the effect of three pesticides (azoxystrobin, chlorotoluron and epoxiconazole) on the microbial community structure in a compost biomixture by extracting the fatty acid methyl ester derivatives (FAMEs) profiles with the microbial identification system (MIDI) and ester-linked method (EL). The main results were that FAMEs profile was mostly affected by the extraction method and to a lesser extent by compost age.…”