Developing a standard spiking precedure for the introduction of hydrophobic organic compounds into field-wet soil

The purpose of this study was to reevaluate a number of spiking procedures we had previously investigated for spiking dry soil, determine their suitability for spiking radiolabeled hydrophobic organic compounds in field-wet soil, and identify the optimal spiking procedure. In the first part of this study, two radiolabeled polycyclic aromatic hydrocarbons (PAHs), phenanthrene (Phe) and benzo[a]pyrene (BaP), were introduced into field-wet soil by four different spiking procedures and the recovery and homogeneity of compound distribution assessed by analysis of replicate subsamples. The identified optimal spiking procedure involved adding an acetone spike solution to 10 ml acetone in a blender base, adding 250 g field-wet soil, and mixing with a high-speed blender. The relative standard deviations obtained by this procedure were 2.7 and 5.3% for 14C-Phe and 14C-7-BaP, respectively, and were comparable to those we obtained in a previous study for spiking dry soil. The persistence of acetone used as a carrier solvent in the optimal spiking procedure was assessed at various times after spiking to identify a suitable equilibration time to allow for solvent volatilization. The equilibration time, together with the identified optimal spiking procedure, were combined to develop a standard spiking procedure. The standard spiking procedure was used to prepare multiple soil microcosms individually spiked with radiolabeled Phe, pyrene, and BaP for a long-term aging study on the formation of PAH-bound residues in arable soil. The mean spike activity and homogeneity of spike distribution in 54 sterilized microcosms (3 x 18) stored over 525 d was determined. Mean spike recovery and relative standard deviations (RSDs) for the three radiolabeled PAHs in the individually spiked and prepared microcosms were very good. However, this data illustrates the importance of determining the concentration and homogeneity of spikes within all individual test portions in experiments where organic compounds are spiked into soil or sediment.