Aflatoxins (AFs) are toxic fungal secondary metabolites that are commonly detected in food commodities. Currently, there is a lack of generic methods capable of determining AFs both at postharvest stages in agricultural products and preharvest stages, namely, the agricultural soil. Here, we present a simple and reliable method for quantitative analysis of AFs in soil and food matrices at environmentally relevant concentrations for the first time, using the same extraction procedure and chromatography, either by HPLC-FLD or LC–MS. AFs were extracted from matrices by ultrasonication using an acetonitrile/water mixture (84:16, v + v) without extensive and time-consuming cleanup procedures. Food extracts were defatted with n-hexane. Matrix effects in terms of signal suppression/enhancement (SSE) for HPLC-FLD were within ±20% for all matrices tested. For LC–MS, the SSE values were mostly within ±20% for soil matrices but outside ±20% for all food matrices. The sensitivity of the method allowed quantitative analysis even at trace levels with quantification limits (LOQs) between 0.04 and 0.23 μg kg–1 for HPLC-FLD and 0.06–0.23 μg kg–1 for LC–MS. The recoveries ranged from 64 to 92, 74 to 101, and 78 to 103% for fortification levels of 0.5, 5, and 20 μg kg–1, respectively, with repeatability values of 2–18%. The validation results are in accordance with the quality criteria and limits for mycotoxins set by the European Commission, thus confirming a satisfactory performance of the analytical method. Although reliable analysis is possible with both instruments, the HPLC-FLD method may be more suitable for routine analysis because it does not require consideration of the matrix.

<p>Grape pomace (GP) can be legally applied as an organic fertilizer in the vineyards in Germany. Some risks are associated with this common practice, since grape pomace is observed to have a high carbon to nitrogen ratio and contains bioactive secondary metabolites. Despite these concerns, up to date little is known about the mobility of substances in the vineyard soil. In this study, our goal was to investigate the mobility of the macronutrient content of GP, derived from four Rhineland palatinate grape varieties, in three different soils in a column model. We used a three-step lab-scale approach that included the analysis of total carbon (C), nitrogen (N) and polyphenolic content (TPC) to analyse the mobility in:</p> <p>1) the GP, representing the maximum total amount</p> <p>2) the rainwater, representing the aqueous extractable fraction of the total amount</p> <p>3) the soil column, as the soil-mobile fraction, as well as the leachate</p> <p>Our results showed that up to 4 % of the total polyphenolic content of the pomace is leached into the soil. The recovery in the soil strongly depends on the combination of soil type and grape variety investigated. Generally, sandy and acidic soils showed an even distribution of phenolics with a high recovery rate (up to 92 %) of the water extractable amount. Most polyphenols could be recovered from the upper soil layer (0-10 cm). Despite the low pH of GP, there was no effect on soil pH. The same holds true for the C/N ratio. These results give a first impression of the mobility of macronutrients in the soil using a column model, supporting the need for incubation experiments that aim for the effect of the application on biogeochemical processes.</p>

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Grape pomace (GP) has an added value because of its contribution to carbon (C) and nitrogen (N) in soils when applied as an organic fertilizer. Macronutrients from GP are translocated into the soil after amendment, but little is known about the factors that may influence the mobility of C, N and bioactive molecules, i.e., polyphenols, in the soil column. We investigated the mobility of the macronutrient content of GP, derived from two red (Dornfelder and Pinot noir) and two white grape varieties (Riesling and Pinot blanc). For that, three different soils (loamy sand RefeSol01A, silt loam RefeSol02A and a vineyard soil) were evaluated in a column model using a GP application rate of 30 t ha−1. The three-step lab-scale approach included the analysis of total C, N and polyphenols expressed as total polyphenolic content (TPC) in: (a) the fresh GP, representing the total amount of C, N and TPC; (b) the mobility with rainwater, representing the aqueous extractable fraction and (c) the mobility in the soil column and leaching potential. Our results showed that total C/N ratios were wider in the white GP varieties compared with the red ones. Higher TPC values were measured in Dornfelder and Pinot noir compared with white varieties. Analysis of the water-extractable fraction showed that the C recovery may reach up to 48% in Pinot blanc, which also corresponds to the highest N contribution. Extractable polyphenols were higher in the red compared with the white varieties by a factor of 2.4. C and N were mobilized with rainwater from the GP through the soil column. However, the application rate used in the experiment was not indicative of an accumulation in the soil. Compared with the control (no GP application), C values were significantly higher in the leachates from GP-treated soils, in contrast to N values. Up to 10% of the TPC of the pomace was leached into the soil. The TPC recovery in the soils strongly depended on the combination of soil type and GP variety. Generally, the sandy and more acidic soil showed an even distribution of phenolics with a high recovery rate (up to 92%) compared with more neutral and silty soil. Most of the polyphenol content could accumulate in the upper soil layer (0–10 cm). These results provide the first insights on the mobility of macronutrients in the soil using a column model and point out the need to relate those experiments to soil and GP properties in order to avoid the accumulation of nutrients in soil or mobility to adjacent ecosystems.

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