TABLE I. Summary of Changes Observed in Polycyclic Aromatic Hydrocarbon and Polycyclic Aromatic Compound Levels Throughout the Bioremediation Treatment Compound Naphthalene Acenaphthylene Acenaphthene Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz[a]anthracene Chrysene Benzo[b]ﬂuoranthene Benzo[k]ﬂuoranthene Benzo[a]pyrene Indeno[1,2,3-cd]pyrene Dibenz[a,h]anthracene Benzo[ghi]perylene 9-Fluorenone 4-Oxapyrene-5-one Benzoﬂuorenones (3 peaks) Benzothiophene Carbazole Benzo[b]naphtho[2,1-d]thiophene Concentration in soil (lg/g dry soil) 17 29 2.4 44 330 70 420 290 190 180 160 130 120 100 28 84 26 27 32 Fraction left in soil after degradation (%) Day Day Day 3 7 24 95 83 76 78 74 81 22 14 0.3 27 19 4.1 34 18 8.7 63 52 24 93 84 47 101 94 65 101 101 62 102 98 70 102 93 103 104 102 103 102 97 104 101 94 105 102 95 104 101 94 106 56 37 24 112 107 149 101 101 80 104 75 53 46 29 22 102 100 61 Day 29 70 73 0.3 2.6 6.4 14 37 50 49 52 86 89 91 101 93 102 21 156 64 51 18 47 The results are normalized for the raw data obtained for anthracene; day 3: 82%, day 7: 100%, day 24: 79%, day 29: 107%. % degradation was determined by comparing peak areas to available reference standards; for complete data set see Lundstedt et al., 2003. discussion of the changes in the chemical proﬁles of the treated soil, the reader is referred to the original publication. Lundstedt et al. [2003] positively identiﬁed 117 com- pounds in the Husarviken soil and Table I highlights the degradation results for the 16 US EPA priority PAHs and selected PACs. Concentrations of priority PAHs ranged from 2.4 to 420 lg/g dry soil, and the chemical composi- tion is similar to that noted for soils from other gasworks sites [Wilson and Jones, 1993; Kilbane, 1998; Eriksson et al., 2000; Saponaro et al., 2002], which typically con- tain a variety of high and low molecular weight PAHs and O- and S-heterocyclic compounds [Haeseler et al., 1999]. Oxy-PAHs, such as ketones, were also found in the Husarviken soil. These compounds have also been detected in other soils from former gasworks sites [Brooks et al., 1998; Eriksson et al., 2000; Saponaro et al., 2002]. The general trends in PAH biodegradation observed by Lundstedt et al. were consistent with those observed in other studies [Cerniglia, 1992; Wilson and Jones, 1993; Eriksson et al., 2000]. The concentrations of most com- pounds decreased over the duration of the bioremediation Environmental and Molecular Mutagenesis. DOI 10.1002/em Mutagenicity of Soil During Bioremediation 407 treatment and, as expected, low molecular weight PAHs and heterocyclic compounds degraded more rapidly than high molecular weight PAHs. Also, alkyl-PAHs appeared to be more recalcitrant than the corresponding unsubsti- tuted PAHs. The Lundstedt et al. work highlighted an increase in the concentration of oxy-PAHs over the course of the treatment, and noted that this outcome may contribute to the toxicological hazard of the treated soil. In the Husar- viken soil, two oxy-PAHs, 1-acenaphthenone and 4-oxa- pyrene-5-one (5H-phenanthro[4,5-bcd]pyranone), were speciﬁcally highlighted, and found to increase by 30 and 60%, respectively, over the course of the bioremediation. The concentrations of some oxy-PAHs, such as benz[a] anthracene-7,12-dione and 9-ﬂuorenone, did not decrease as rapidly as their parent PAHs (i.e., benz[a]anthracene and ﬂuorene) [Lundstedt et al., 2003]. This was unex- pected, especially because oxy-PAHs have previously been found to be more bioavailable than their parent com- pounds [Matscheko et al., 2002], and are therefore expected to degrade more rapidly. Mutagenicity of Soil Fractions During Bioremediation This study employed the Salmonella reverse mutation assay to assess the mutagenicity of nonpolar neutral and semipolar aromatic fractions of dried slurry extracts from day 0, 3, 7, 24, and 29 of the bioremediation treatment (i.e., same as the samples analyzed by Lundstedt et al., [2003]). Figure 1 summarizes the observed changes in mutagenic potencies throughout the course of the biore- mediation. The combined values for the nonpolar neutral and semipolar aromatic fractions on TA98 indicate that the total mutagenic activity varies from 1.2 to 6.9 rever- tants per mg dry soil without S9 and 2.8 to 15 revertants per mg dry soil with S9. These values are consistent with heavily contaminated soils from industrial locations [White and Claxton, 2004]. Nonpolar Neutral Compounds The mutagenic activities of the nonpolar neutral frac- tions without S9 were relatively low compared to those of the semipolar aromatic fractions. Moreover, the mutage- nicity of the nonpolar neutral fractions was highly vari- able over the course of the bioremediation. Mutagenic potencies ranged from 0.3 to 5.3 revertants per mg dry soil without S9. This low, yet measurable, level of muta- genic activity indicates the presence of direct-acting sub- stances that may include PAH transformation products that elute in this fraction. In general, the mutagenic activ- ity of the nonpolar neutral fractions was enhanced with the addition of S9, and the mutagenic potency values with S9 ranged from 4.2 to 43 revertants per mg dry soil (Fig. 1). This increase in mutagenicity upon the addition