ASTM D7363-13a

1.1 The U.S. Environmental Protection Agency (USEPA) narcosis model for benthic organisms in sediments contaminated with polycyclic aromatic hydrocarbons (PAHs) is based on the concentrations of dissolved PAHs in the interstitial water or “pore water” in sediment. This test method covers the separation of pore water from PAH-impacted sediment samples, the removal of colloids, and the subsequent measurement of dissolved concentrations of the required 10 parent PAHs and 14 groups of alkylated daughter PAHs in the pore water samples. The “24 PAHs” are determined using solid-phase microextraction (SPME) followed by Gas Chromatography/Mass Spectrometry (GC/MS) analysis in selected ion monitoring (SIM) mode. Isotopically labeled analogs of the target compounds are introduced prior to the extraction, and are used as quantification references.

1.2 Lower molecular weight PAHs are more water soluble than higher molecular weight PAHs. Therefore, USEPA-regulated PAH concentrations in pore water samples vary widely due to differing saturation water solubilities that range from 0.2 µg/L for indeno[1,2,3-cd]pyrene to 31 000 µg/L for naphthalene. This method can accommodate the measurement of microgram per litre concentrations for low molecular weight PAHs and nanogram per litre concentrations for high molecular weight PAHs.

1.3 The USEPA narcosis model predicts toxicity to benthic organisms if the sum of the toxic units (ΣTU_c) calculated for all “34 PAHs” measured in a pore water sample is greater than or equal to 1. For this reason, the performance limit required for the individual PAH measurements was defined as the concentration of an individual PAH that would yield ¹/₃₄ of a toxic unit (TU). However, the focus of this method is the 10 parent PAHs and 14 groups of alkylated PAHs (Table 1) that contribute 95 % of the toxic units based on the analysis of 120 background and impacted sediment pore water samples.³ The primary reasons for eliminating the rest of the 5-6 ring parent PAHs are: (1) these PAHs contribute insignificantly to the pore water TU, and (2) these PAHs exhibit extremely low saturation solubilities that will make the detection of these compounds difficult in pore water. This method can achieve the required detection limits, which range from approximately 0.01 µg/L, for high molecular weight PAHs, to approximately 3 µg/L for low molecular weight PAHs.

TABLE 1 Target PAHs, Toxic Unit Factors and Performance Limits^A

Analyte	Added d-PAH Internal Standard	d-PAH Internal Std. for Calculation	Conc. for One Toxic Unit, Ctu, (ng/mL)	Performance Limit (ng/mL)	Basis for Performance LimitB
Naphthalene	A	A	193.47	5.69	B
2-Methylnaphthalene		B	81.69	2.40	B
1-Methylnaphthalene	B	B	81.69	2.40	B
C2-Naphthalenes		A	30.24	0.89	B
C3-Naphthalenes		A	11.10	0.33	B
C4-Naphthalenes		A	4.05	0.12	C
Acenaphthylene		C	308.85	9.03	B
Acenaphthene	C	C	55.85	1.64	B
Fluorene	D	D	39.30	1.16	B
C1-Fluorenes		D	13.99	0.41	B
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