Soil constitutes a central environmental compartment that, due to natural and anthropogenic activities, is a recipient of several contaminants. Among them, organochlorine pesticides are of major concern, even though they have been banned decades ago in the European Union, due to their persistence and the health effects they can elicit. In the presented work, a gas chromatographic tandem mass spectrometric (GC-MS/MS) developed method was applied to soil samples after the suspected and potential use of formulations containing organochlorine active substance. One soil sample was positive to dieldrin at 0.018 mg kg−1. Predicted environmental concentration in soil (PECsoil) considering a single application of this active substance potentially attributed the finding in its past use. The subsequent health risk assessment showed negligible non-carcinogenic risk and tolerable carcinogenic risk. The latter signifies that repetitive and prolonged sampling can unveil the pragmatic projection of persistent chemicals’ residues in the soil.

The Carry over effect, i.e. the appearance of a peak in the chromatogram of a blank analysis due to sample remaining from the previous analysis, was studied. The study was conducted for pesticide residues analysis by LC-MS/MS. In total 128 pesticides that belong to 13 different chemical classes were analyzed in order to investigate the cases that the effect is significant; i.e. a peak higher than 1% of the peak of the previous chromatogram appears. Carry over was found for 32 of the 128 studied pesticides (25%), at concentration levels between the LOD and 0.167 μg/mL. For 28 out of the 32 substances, more than two injections of a blank sample were required, as to reduce the effect significantly. Compounds presenting Carry over effect were mainly non-polar with logkow values between 4 and 7, characterized with very low water solubility, between 0.001 mg/L and 2 mg/L. On the contrary, the vapor pressure did not seem to be obviously related to the effect, as the substances presenting Carry over had various vapor pressure values, from 10-12 to 0.2 mP.

ABSTRACT.The most common problems encountered in LC-MS/MS analysis of food are cases of compounds with low recovery, low sensitivity in one transition, common transition with matrix or other analytes, as well as solvent and matrix effects. The significance of each case was experimentally investigated in this study by the use of representative compounds. The QuEChERS approach was used for the extraction of pesticides. The study involved analysis of 128 pesticides representing various chemical classes, polarities and molecular masses, in 8 products representing different commodities of food matrices. Blank matrices fortified at 33.3 and 167 μg/kg, were analysed using different LC-MS/MS conditions in order to evaluate the significance of each parameter. Additionally long term LC-MS/MS system suitability data of 18 months were used to evaluate the variability of retention time and ion ratio at the limit of detection. This was assessed by the use of 6 representative compounds and the respective control charts. Keywords: pesticide residues, food, LC-MS/MSΠΕΡΙΛΗΨΗ. Μελετήθηκαν τα πιο κοινά προβλήματα που παρουσιάζονται στις αναλύσεις τροφίμων με τη χρήση της υγρής χρωματογραφίας -φασματομετρίας μάζας τριπλού τετραπόλου (LC-MS/MS). Αφορούσαν σε ενώσεις με χαμηλές ανακτήσεις, χαμηλή ευαισθησία στη μια από τις δυο μεταπτώσεις, μία κοινή μετάπτωση με το υπόστρωμα ή με άλλους

Soil can be contaminated by pesticide residues through agricultural practices, by direct application or through spray-drift in cultivations. The dissipation of those chemicals in the soil may pose risks to the environment and human health. A simple and sensitive multi-residue analytical method was optimized and validated for the simultaneous determination of 311 active substances of pesticides in agricultural soils. The method involves sample preparation with QuEChERS-based extraction, and determination of the analytes with a combination of GC-MS/MS and LC-MS/MS techniques. Calibration plots were linear for both detectors over the range of five concentration levels, using matrix-matched calibration standards. The obtained recoveries from fortified-soil samples ranged from 70 to 119% and from 72.6 to 119% for GC-MS/MS and LC-MS/MS, respectively, while precision values were <20% in all cases. As regards the matrix effect (ME), signal suppression was observed in the liquid chromatography (LC)-amenable compounds, which was further estimated to be negligible. The gas chromatography (GC)-amenable compounds showed enhancement in the chromatographic response estimated as medium or strong ME. The calibrated limit of quantification (LOQ) value was 0.01 μg g−1 dry weight for most of the analytes, while the corresponding calculated limit of determination (LOD) value was 0.003 μg g−1 d.w. The proposed method was subsequently applied to agricultural soils from Greece, and positive determinations were obtained, among which were non-authorized compounds. The results indicate that the developed multi-residue method is fit for the purpose of analyzing low levels of pesticides in soil, according to EU requirements.