Trace analysis of pesticides and an assessment of their occurrence in surface and drinking waters from the State of São Paulo (Brazil)

Abstract

An efficient method based on solid phase extraction (SPE) and determination by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for simultaneous determination of 12 pesticides at trace levels in surface and drinking waters from the State of São Paulo (Brazil), which are likely to be contaminated due to the widespread use of these products. Several parameters that affect SPE and the analysis were studied, such as conditioning and elution solvents, sample pH, breakthrough volume and matrix effects. Method development was validated by several figures of merit. Recoveries from synthetic samples spiked at 150 ng L⁻¹ and 1000 ng L⁻¹ levels with difenoconazole, epoxiconazole, tebuconazole, atrazine, azoxystrobin, pyraclostrobin, picoxystrobin, trifloxystrobin, profenofos and fipronil varied from 73 to 99%, with intraday precision in the 5–24% range. A lower fortification level (10 ng L⁻¹), close to detection limits, led to recoveries from 86–155%, which was considered acceptable for the purpose of trace analysis of environmental samples. Low detections limits (1–50 ng L⁻¹) and quantification limits (2–180 ng L⁻¹) were obtained. The method was applied for the determination of pesticide residues at the nanogram per liter level in samples of drinking water from 9 cities and in surface waters from 13 rivers of the State of São Paulo, Brazil. The results showed that the investigated waters are highly impacted with carbendazim and atrazine, which were the most frequently determined compounds.