Developing a standard spiking procedure for the introduction of hydrophobic organic compounds into field‐wet soil

Abstract

Abstract-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 highspeed blender. The relative standard deviations obtained by this procedure were 2.7 and 5.3% for 14 C-Phe and 14 C-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 ϫ 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.

Differential degradation of polycyclic aromatic hydrocarbon mixtures by indigenous microbial assemblages in soil

“…The soil contained trace levels of PAHs (4Á7 mg kg À1 dry soil), including those prioritized by the Environmental Protection Agency. Soil was manually sieved through a < 4 mm sieve, divided into four equal parts and the following treatments applied: (i) left unamended as a control; (ii) amended with a mixture of phenanthrene (200 mg kg À1 dry weight of soil) (Sigma-Aldrich, Dublin, Ireland) and fluoranthene (50 mg kg À1 dry weight of soil) (Sigma-Aldrich); (iii) amended with a mixture of phenanthrene (200 mg kg À1 dry weight of soil) and benzo(a)pyrene (50 mg kg À1 dry weight of soil) (Sigma-Aldrich); (iv) amended with a mixture of phenanthrene (200 mg kg À1 dry weight of soil), fluoranthene and benzo(a)pyrene (both 50 mg kg À1 dry weight of soil) using acetone as a carrier, following methods described in Northcott and Jones (2000). 50 AE 1 g of soil was placed into separate sterile PVC microcosms (40 mm diameter, 110 mm height), containing holes in the bottom to permit free passage of air.…”

Validation of Procedures to Quantify Nonextractable Polycyclic Aromatic Hydrocarbon Residues in Soil

“…The precision of total sample oxidation data was excellent with relative standard deviations (RSDs) of 2 to 3% obtained for six replicate measurements. The precision of the three extraction methods was determined by replicate subsampling and analysis of 14 C‐9‐Phe, 14 C‐4,5,9,10‐Pyr, and 14 C‐7‐B[ a ]P from sterile arable soil amended with sewage sludge that had been spiked and aged for 21 days (Northcott and Jones, 2000b). Triplicate samples were removed from three individually spiked and aged 250‐g soil microcosms for each PAH ( n = 9) and extracted with our extraction procedures.…”

“…Field‐wet grassland and arable crop soil that had been amended with concentrated sewage sludge solids were spiked with the appropriate 14 C radiolabeled and nonradiolabeled analog PAH using our previously evaluated and optimized procedure (Northcott and Jones, 2000b). Briefly, 250 g of field‐wet soil was added to a blender containing 10 mL of acetone and 250 μL of the appropriate PAH spiking standard.…”

“…Unspiked blanks containing arable soil amended with sewage sludge were prepared with the same spiking procedure and an equivalent volume of acetone. The prepared arable soil microcosms that were amended with sewage sludge were sterilized by γ irradiation (Northcott and Jones, 2000b).…”

Chapter 3. Determination of semivolatile organic compounds and polycyclic aromatic hydrocarbons in solids by gas chromatography/mass spectrometry

“…An amount equivalent to 1.5 µg per analyte is spiked at the laboratory into the customer requested matrix samples, and the spike recovery range (based on criteria from the initial method validation study) is expected to be 60 to 120 percent. However, some sediment matrices might not yield the anticipated recoveries because of inherent difficulties in producing a uniform, thoroughly mixed spike sample, or because equilibration times needed to incorporate the compounds of interest differ widely in diverse sediment matrices (Northcott and Jones, 2000). Analysis of duplicate samples also is encouraged for evaluating reproducibility of results at environmental concentrations.…”