Application of Twisselmann extraction, SPME, and GC-MS to assess input sources for organophosphate esters into soil.

Although the ubiquitous distribution of organophosphate esters (OPEs) in the environment has been documented very thoroughly, data on their occurrence in soil is so far sparse. In this study, an analytical method was developed to determine six OPEs in soil. The method consists of a combination of Twisselmann extraction and solid-phase microextraction (SPME), followed by gas chromatography-mass spectrometry (GC-MS). To develop the method, spiked soil was extracted using a Twisselmann extractor after freeze-drying. The extract was evaporated to dryness, redissolved, and filtered. A volume of 7 mL was then analyzed by SPME, followed by GC-MS. The effects of different parameters on analyte recoveries during sample preparation, e.g., solvent for Twisselmann extraction, solvent for redissolving the extract, addition of copper, and filtration of the extract, were systematically investigated. Under optimum conditions, 10 g soil samples were extracted using toluene, and the extract was redissolved in methanol/water (1:14) and filtered. It was not necessary to add copper. For TnBP, TBEP, TCPP, and TCEP, recoveries ranged from 77.0% to 89.6%. Those for TPP and TDCP were much lower, at 31.5% and 42.0%, respectively (addition level 22.9-45.8 ng g(-1)). The variability of recoveries under these conditions was between 0.3 and 16.2% (n = 3). Limits of detection (LOD) were 0.002-3 ng g(-1). When ultrasonication was used in place of Twisselmann extraction in the developed method, recoveries were three to four times lower (27.4% to 30.6%), but the variability of recoveries was below 3% (n = 3). The method was applied to quantify OPEs in soil collected from the university campus in Osnabrueck (Germany). Average concentrations (n = 6) in soil samples ranged from 1.23 ng g(-1) to 4.96 ng g(-1) (dry weight) for TCPP, TPP, and TCEP. The results demonstrate for the first time that atmospheric deposition leads to soil contamination by OPEs.