Table 3. Comparison of the freely dissolved concentrations (ng/L) of DDTs from Eq-SPME and PRC-SPME in PV8C sediments (amended without and with 0.5, 2, and 5% sand or activated carbon.

	o,p′-DDD		o,p′-DDE		p,p′ -DDD		p,p′-DDE
	Eq-SPME	PRC-SPME	Eq-SPME	PRC-SPME	Eq-SPME	PRC-SPME	Eq-SPME	PRC-SPME
PV8C	8.7 ± 0.16	8.8 ± 0.68	16 ± 1.5	31 ± 11	108 ± 21	70 ± 6.0	57 ± 8.1	71 ± 16
PV8C + 0.5% sand	9.6 ± 0.26	8.7 ± 0.04	17 ± 0.63	25 ± 3.3	74 ± 22	71 ± 2.6	58 ± 5.1	69 ± 11
PV8C + 2% sand	9.0 ± 0.38	8.3 ± 0.37	17 ± 0.11	24 ± 2.6	65 ± 20	63 ± 3.3	61 ± 0.87	70 ± 8.3
PV8C + 5% sand	8.0 ± 0.06	8.6 ± 0.73	16 ± 0.09	22 ± 0.42	65 ± 11	72 ± 1.9	58 ± 0.30	58 ± 0.14
PV8C + 0.5% AC	6.4 ± 0.21	5.2 ± 0.35	13 ± 0.46	16 ± 5.6	45 ± 7.8	38 ± 2.1	49 ± 1.7	51 ± 20
PV8C + 2% AC	1.5 ± 0.08	1.2 ± 0.41	4.5 ± 0.01	3.5 ± 0.1	23 ± 12	7.1 ± 0.85	18 ± 0.85	13 ± 0.32
PV8C + 5% AC	0.27 ± 0.07	0.2 ± 0.02	0.93 ± 0.09	0.74 ±0.11	3.0 ± 0.95	1.4 ± 0.02	4.2 ± 0.28	2.9 ± 0.5

Eq-SPME = solid-phase microextraction with equilibrium method; PRC-SPME = reference compound–calibrated solid-phase microextraction; PV8C = Palos Verdes Shelf, California, USA; o,p′-DDD = 1,1-dichloro-2,4-bis-(chlorophenyl)ethane; o,p′-DDE = 1,1-dichloro-2,4-bis-(chlorophenyl)ethylene; p,p′-DDD = 1,1-dichloro-2,2-bis-(chlorophenyl)ethane; p,p′-DDE = 1,1-dichloro-2,2-bis-(chlorophenyl)ethylene; AC = active carbon.