Isotopic exchange on SPME fiber in sediment under stagnant conditions: Implications for field application of PRC calibration
An overlooked issue for field application of in situ performance reference compound (PRC) calibration methods is the validity of the assumption that both the sorption of a target compound and desorption of its corresponding PRC follow the first‐order kinetics with the same rate constants under stagnant conditions. In the present study, disposable polydimethylsiloxane fibers of two sizes (7‐ and 35‐µm) impregnated with eight 13C‐labeled or deuterated PRCs were statically deployed into different marine sediments, from which the kinetics for sorption of the target compounds and desorption of the PRCs were characterized. Non‐symmetrical profiles were observed for exchange of the target analytes and their corresponding PRCs in sediment under stagnant conditions. The hysteretic desorption of PRCs in the kinetic regime may be ascribed to the low chemical potential between the fiber and sediment porewater, which reflects the inability of water molecules to rapidly diffuse through sediment to solvate the PRCs in the aqueous layer around the fiber surface. A moderate correlation (r = 0.77 and r = 0.57, p < 0.05 for both regressions) between the PRC‐calibrated equilibrium concentrations of p,p′‐DDE and PCB‐153 and the lipid normalized levels in worms (Neanthes arenaceodentata) was obtained in co‐exposure tests under simulating field conditions, probably resulted from slightly overestimated bioavailability because of the hysteretic desorption of PRCs and toxic effects.