Liquid chromatography - high-resolution quadrupole time-of-flight mass spectrometry analysis of pesticides in French agricultural soils

ABSTRACT

Agricultural soils are not controlled in France for the massive use of pesticides. The quadrupole mass spectrometer is used for targeted analysis of a few dozen pesticides, while the high-resolution time-of-flight quadrupole mass spectrometer (QTOF-MS) allows both targeted and non-targeted analysis of hundreds of pesticides. In this study, a targeted method was developed in soils using pressurised-liquid extraction (PLE) and liquid chromatography (LC) coupled with a QTOF-MS. This method development was necessary to carry out next suspect and non-target screening in soils and has been validated for triazines, phenylureas and emerging pesticides in soils. The internal calibration of pesticides was validated for low levels (0.5 to 12.5 µg L⁻¹) and high levels (12.5 to 400 µg L⁻¹) using labelled internal standards. The determination coefficient (R²) of calibration curve of each pesticide was greater than 0.99. Excepted DCPU and IPPU, the mean recoveries of pesticides in five reference soils spiked at 40 µg kg⁻¹ and 10 µg kg⁻¹ were greater than 93.5% and 106.2%, and the variation coefficients lower than 14.7% and 22.5%, respectively. So, multiplier factors were applied to the quantification results of DCPU and IPPU, respectively, 2.5 and 1.7 for correction. This validated method has been applied to a selection of 40 French soils of Centre-Val de Loire region. The limit of quantification (LOQ) of pesticides varied between 0.005 and 0.175 µg kg⁻¹ in soils. Seven pesticides were the most detected in soils. Seventeen pesticides were detected between 10 and 50% of cases and very low detection frequencies (<10%) were found for 10 pesticides in soils. The mean concentrations were 0.730 µg kg⁻¹ dw for triazines, 1.367 µg kg⁻¹ dw for phenylureas and 7.638 µg kg⁻¹ dw for emerging pesticides. DCPMU and epoxiconazole were detected in all the 40 soils.

KEYWORDS:

• Pesticides
• soil
• pressurised-liquid extraction
• liquid chromatography
• time-of-flight
• mass spectrometry

Acknowledgments

Colleagues of INRAE Info&Sols in Orléans (France), responsible for the French Soil Quality Monitoring Network (RMQS), are gratefully acknowledged for providing the soil samples and informations about their agricultural uses and phytosanitary treatments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by ‘AgroEcoSystem’, a scientific department of INRAE (National Research Institute for Agriculture, Food and Environment).