C18 Disk Tests

ERDC TN-DOER-R3

September 2004

unit, 12 E. fetida specimens were placed on top of 1 L of the appropriate substrate mixture con-

tained in a 15-cm-diameter, 15-cm-high Plexiglass cylinder. Animals were allowed to grow for

28 days prior to harvesting (ASTM 1998).

C18 Disk Tests. The C18 disk test was conducted to assess the potential bioavailability

(desorbability) of the organic contaminants in the substrates. The C18 disk study included a total

of 15 units. For each unit, one preconditioned C18 disk (SPE disk ENVI 18 DSK, diameter

47 mm, Supelco, Burdick and Jackson, Muskegon, Michigan) was suspended in a 250-mL

Erlenmeyer containing 10 g DW test substrate and 50 mL Reversed Osmosis (RO) water. One

mL of a solution containing 7 mmol of HgCl2 L-1 was added to each bottle to reduce microbial

activity. Bottles were incubated for 28 days in the dark at 22 C and shaken gently every second

day prior to analysis. The organics reached near-equilibrium on the disks in 28 days, as was veri-

fied before the onset of the tests (Krauss and Wilcke 2001, Krauss et al. 2000).

Analyses. Prior to incubation, each DM mixture was analyzed for chemical and physical char-

acteristics, in triplicate. The concentrations of PCBs and PAHs were determined in all DM mix-

tures, following a modified Bligh-Dyer extraction procedure (Bligh and Dyer 1959) and Gas

Chromatography/Mass Spectrometry detection (GC-MS; EPA-method 8270C). For Arochlor-

1248, the PCBs with molecular weights of 222, 256, 292, and 326 were quantitated as represen-

tatives. No other Arochlors were present in the IHC extracts. For the PAHs, the following con-

stituents were quantitated:

Naphthalene (NAP)

Acenaphthalene (ACY)

Acenaphthene (ACE)

Fluorene (FLU)

Phenanthrene (PHE)

Anthracene (ANT)

Fluoranthene (FLA)

Pyrene (PYR)

Benz[a]anthracene (BAA)

Chrysene (CHR)

Benzo(b)fluoranthene (BBF)

Benzo(k)fluoranthene (BKF)

Benzo(a)pyrene (BAP)

Benzo(ghi)perylene (BGHI)

Indeno(1,2,3-cd)pyrene (INP)

Dibenzo(a,h)anthracene (DIB)

As internal standard for the PCB extraction, PCB No. 7 was used, which was spiked to the DM

samples prior to extraction. The total concentrations of As, Cd, Cr, Cu, Pb, Ni, V, and Zn were

also determined (USEPA 1991), as were the bioavailable metal concentrations, using the

diethyltriamine-pentaacetic (DTPA) extractable fraction as a measure (Lindsay and Norvell

1978). Moisture content was determined by drying at 105 C in a forced-air oven until constant

weight. Concentrations of organic matter were determined by loss on ignition at 550 C, and bulk

density volumetrically (Allen et al. 1974). Organic carbon in the substrates was calculated by

multiplying the organic matter concentration by a factor of 0.58 (Jackson 1964). pHKCl was

measured with a pH-meter (Beckman Model PHI40, Fullerton, CA) in a 1-M KCl solution in a