Mutagenic action of a series of epoxides.

The mutagenicity of a series of 13 epoxide compounds was studied using a bacterial plate assay system. The histidine-dependent tester strains TA98 (for frameshift mutagens) and TA100 (for base-pair substitution mutagens) of Salmonella typhimurium were used. Mutagenicity was evaluated both with and without the additon of rat liver microsomal extract. Dieldrin, diglycidyl ether of bis phenol A and 3 of its homologues were not mutagenic. Allyl glycidyl ether, n-butyl glycidyl ether, vinly cyclohexene diepoxide, glycidol, glycidal-dehyde, diglycidyl ether, diepoxybutane and diglycidyl ether of substituted glycerine were mutagenic in the TA100 strain, causing reversion of the bacteria to histidine independence. Dose-reponse curves of the mutagenicity of the latter 4 compounds were obtained. On a molar basis, glycidaldehyde was about 20-50 times more potent in producing mutation that were the other 3 epoxides in the dose-response test. In general, the mutagenicity of the epoxides was not enhanced or diminished by the addition of microsomal extract.     

Comparative mutagenicity of aliphatic epoxides in Salmonella

37 aliphatic epoxides comprising 6 subclasses (unsubstituted aliphatic epoxides, halogenated aliphatic epoxides, glycidyl esters, glycidates, glycidyl ethers and diglycidyl ethers) were tested, under code, for mutagenicity in Salmonella strains TA98, TA100, TA1535 and TA1537 and/or TA97 with and without metabolic activation using a standardized protocol. The 4 halogenated aliphatic epoxides and the 4 diglycidyl ethers were all mutagenic. The 2 glycidates were negative in all strain/activation systems used while all 5 glycidyl esters were mutagenic. 3 of the 8 unsubstituted aliphatic epoxides and 11 of the 12 glycidyl ethers were mutagenic. Glycidol also was mutagenic whereas 9,10-epoxyoctadecanoic acid, 2-ethylhexyl ester was not mutagenic. Of the 28 mutagenic compounds, all but neodecanoic acid, 2,3-epoxypropyl ester and 2-ethylhexyl glycidyl ether were detected in TA100 without activation. The latter two were detected only with activation in TA100 and TA1535. The majority of the other 26 chemicals were also mutagenic in TA1535 without activation. Good intra- and interlaboratory reproducibility was seen in the results of each of the 4 chemicals tested in more than one set of experiments. The current results confirm and extend the observations of other investigators regarding structural effects on the mutagenicity of members of the aliphatic epoxide class of chemicals.     

Mutagenicity of aliphatic epoxides

The mutagenicity of 17 aliphatic epoxides was determined using the specially constructed mutants of Salmonella typhimurium developed by Ames. The activity of these epoxides together with those reported in the literature as mutagens in strains TA100 and TA1535 depended on the degree of substitution around the oxirane ring. Monosubstituted oxiranes were the most potent mutagens in both strains. 1,1-Disubstitution resulted in the complete loss or reduction of mutagenicity. trans-1,2-Disubstituted, and tetrasubstituted oxiranes all lacked mutagenicity, while the cis-1,2-disubstituted oxiranes tested were weakly mutagenic in strain TA100 only. For the monosubstituted compounds the presence of electron-withdrawing substituents increased mutagenicity.     

Mutagenicity of aliphatic epoxides.

The mutagenicity of 17 aliphatic epoxides was determined using the specially constructed mutants of Salmonella typhimurium developed by Ames. The activity of these epoxides together with those reported in the literature as mutagens in strains TA100 and TA1535 depended on the degree of substitution around the oxirane ring. Monosubstituted oxiranes were the most potent mutagens in both strains. 1,1-Disubstitution resulted in the complete loss or reduction of mutagenicity, trans-1,2-Disubstituted, and tetrasubstituted oxiranes all lacked mutagenicity, while the cis-1,2-disubstituted oxiranes tested were weakly mutagenic in strain TA100 only. For the monosubstituted compounds the presence of electron-withdrawing substituents increased mutagenicity.     

Mutagenicity of aromatic glycidyl ethers with Salmonella

6 aromatic glycidyl ethers containing naphthyl, biphenyl or benzylphenyl substituents were synthesized. These epoxides together with the commercially available compounds 2-biphenylyl glycidyl ether were examined for dose-mutagenicity relationships using the plate incorporation Ames test with Salmonella typhimurium strains TA100 and TA1535. Structure-mutagenicity relationships were further examined for these compounds and 3 phenyl glycidyl ethers by concurrent testing at a single dose with strain TA100. Meaningful correlations could not be established for the mutagenicity of these epoxides to their molecular volumes, partition values, nor to their reactivities with the model nucleophile, 4-(4-nitrobenzyl) pyridine. However, it was noted that increased conjugated aromatic unsaturation with its resulting planarity led to increased mutagenicity and that this effect decreased when it was further removed from the epoxide moiety.     

Bacterial mutagenicity investigation of epoxides: drugs,drug metabolites,steroids and pesticides

Although it has been observed that many epoxides are ultimate mutagens, surprisingly little is known about epoxides to which man may be extensively exposed, e.g., physiological compounds, drugs, drug metabolites and pesticides. We have now investigated 35 such and related epoxides for mutagenicity, using reversion of his^?Salmonella typhimurium TA98 and TA100 as biological end-point. None of the tested steroids (12 compounds), vitamin K epoxides (3 compounds) and pesticides (dieldrin, endrin, HEOM (1,2,3,4,9,9-hexachloro-6,7-epoxy-1,4,4a5,6,7,8,8a-octahydro-1,4-methanonaphthalene), heptachlor epoxide) showed any mutagenic activity. Negative results were also obtained with the antibiotics oleandomycin, anti-capsin and asperlin, the cardiotonic drug resibufogenin, the widely used parasympatholytic drugs butylscopolamine and scopolamine, the sedatives valtratum, didovaltratum and acevaltratum, the tranquilizer oxanamide as well as with the drug metabolites carbamazepine 10,11-oxide and diethylstilbestrol α,β-oxide. Three barbiturate epoxides, formed by metabolism of allobarbital, alphenal and secobarbital, caused weak but reproducible mutagenic effects at high concentrations. The cytostatic agent ethoglucide was the only drug having substantial mutagenic activity. Its mutagenic potency was similar to those of the control epoxides styrene 7,8-oxide, p-bromostyrene 7,8-oxide and m-bromostyrene 7,8-oxide, but much lower than those of benzo[a]pyrene 4,5-oxide, benzo[e]pyrene 4,5-oxide and 7,12-dimethylbenz[a]-anthracene 5,6-oxide.Some epoxides were also tested in other Salmonella typhimurium strains or in the presence of rat-liver S9 mix. Positive results were only obtained with compounds that had already been detected as mutagens in the direct test with strain TA100.     

The genotoxicity of enantiomeric aliphatic epoxides

The (R)- and (S)-optical isomers of 9 epoxides, benzyloxymethyloxirane, epichlorohydrin, glycidol, glycidyl 3-nitrobenzenesulfonate, glycidyl 4-nitrobenzoate, glycidyl tosylate, styrene oxide, glycidyl 1-naphthyl ether and glycidyl 4-nitrophenyl ether, have been compared for their in vivo and in vitro genotoxicity. The in vitro short-term test employed was the Ames mutagenicity assay with Salmonella strain TA100. The in vivo tests were chromosomal aberrations (CA) as well as sister-chromatid exchange (SCE) in bone-marrow cells of mice following intraperitoneal administration of these epoxides. Differences in mutagenicity between isomers were established with TA100 for all the compounds. While 13 of the isomers were genotoxic compared to a negative control by CA measurements, only in the case of glycidyl 4-nitrobenzoate could a significant difference be found between isomers by this test. However, with SCE evaluations, differences were detected between the (R)- and (S)-isomers for all the pairs of compounds with the exception of those for benzyloxymethyloxirane and glycidyl 4-nitrophenyl ether. At least in part, differences in the patterns of genotoxicity among compounds can be related to their differences in reaction pathways.     

Fecal mutagens from subjects consuming a mixed-western diet

Because of potential significance of fecal mutagens (presumptive carcinogens) in the pathogenesis of colon cancer, feces from 99 healthy subjects from the New York metropolitan area were studied. The diet histories indicate that all participants were consuming a mixed-western diet which is high in total fat and low in fiber. Fecal samples that were incubated under anaerobic conditions at 37 degrees C for 96 h or frozen without incubation, were extracted with hexane: peroxide-free diethyl ether (1:1), partially purified on a silica Sep-pak cartridge and assayed for mutagenicity using the Salmonella typhimurium/mammalian microsome system. Aliquots of fecal samples incubated anaerobically showed a higher frequency of mutagenic activity (per cent samples showing activity) in strains TA98 and TA100 with and without microsomal (S9) activation. In addition, the mutagens requiring S9 activation, were more frequently inactivated when the fecal samples were frozen immediately after defecation and transported to the laboratory. Compared with hexane: ether, extraction of fecal samples with acetone increased the mutagenic activity mostly with TA98 with S9 activation. The HPLC fractionation of hexane: ether extract with methanol: water gradient using reverse phase C-18 column and UV detector at 254 nm indicated that the mutagenic activity (TA98 with S9 activation) is concentrated in several peaks. This is the first demonstration of HPLC profile of fecal samples that are active in TA98 with S9 activation. HPLC profile of fecal extracts and mutagenic activity of these extracts in strains TA98 and TA100 suggest the presence of several types of mutagens in the feces of healthy subjects consuming a high-fat, low-fiber mixed-western diet.     

Mutagenic effect of furocoumarin monoadducts and cross-links on bacteriophage lambda

The mutagenicities of 17 closely related oxiranes were determined in 4 tester strains (Salmonella typhimurium TA98, TA100, TA1535, TA1537). The test compounds comprised all possible oxides of benzene and its partially hydrogenated congeners. In TA100 and TA1535, 12 of the tested oxiranes were weak to moderate mutagens. 4 of these were also active in TA98. No mutagenicity was observed with the remaining 5 compounds in any of the 4 strains.The presence of a double bond in formal conjugation with the epoxide ring increased the mutagenicity relative to that of the saturated oxirane. Interestingly, additional epoxide rings within the same molecule did not markedly increase the mutagenic activity, and for the oxiranes that are not activated by a double bond, the relationship between mutagenic activity and the number of epoxide rings in the molecule was even inverse.The influence of bromo and hydroxyl substitution on oxirane mutagenicity is discussed. Most notably, a compound having a 4-hydroxyl group in syn position to a 1,2-epoxide ring fused to the cyclohexane ring, a structure which has been suggested to increase the electrophilic reactivity of dihydrodiol epoxides through hydrogen bonding, was almost inactive.     

Mutagenicity and chemical analysis of sequential organic extracts of airborne particulates

To obtain insight into the identity of chemicals associated with the mutagenicity of United States National Institute of Standards and Technology (NIST) Standard Reference Materials SRM 1649 (urban dust) and SRM 1650 (diesel particulate), parallel mutagenicity tests and chemical analyses were performed on dichloromethane and sequential organic extracts of these samples. SRM 1649 and 1650 were sequentially extracted with five organic solvents of increasing polarity, in order to partition mutagenic components into discrete fractions. The solvents (with associated polarity index) were as follows: (1) hexane (0.0); (2) hexane:diethyl ether 9:1 (0.29); (3) hexane:diethyl ether 1:1 (1.45); (4) diethyl ether (2.9); (5) methanol (6.6). 0.9270 g of SRM 1649, and 0.0510 g of SRM 1650 were each extracted three times with 8 ml of each of the solvents, the three aliquots were pooled, and analysed for target organics or solvent-exchanged into DMSO for mutagenicity testing in Salmonella typhimurium strains TA98 and TA100.The dichloromethane extracts of SRM 1649 and SRM 1650 contained direct-actin mutagens in Salmonella strains TA98 and TA100; SRM 1650 was significantly more potent than SRM 1649 in either strain. Addition of S9 caused a large decrease in mutagenicity of each extract, although SRM 1650 remained more potent. An interesting pattern of mutagenicity was observed for the sequential extracts of SRM 1649 and SRM 1650: the mutagenic potency of SRM 1649 extracts increased with increasing polarity of the extraction solvent while the response of the SRM 1650 extracts was the opposite. This suggests that the direct-acting mutagens in SRM 1650 are unlike those in SRM 1649. The response, though diminished, was largely unchanged when S9 was included in the test mixture.Chemical analyses on the various extracts were performed using a Hewlett-Packard model 5890 gas chromatograph equipped with a model 5970B mass selective detector (GC-MSD), and a 0.3 μm film thickness cross-linked methyl silicone capillary column (HP 1909A-101). Selected ion monitoring (SIM) methods were used to analyze for 105 target compounds including PAHs and nitro-PAHs. Chemical analysis of the dichloromethane extracts of SRM 1649 and SRM 1650 identified three main classes of compounds: polyaromatic hydrocarbons (PAH), vitro-polyaromatic hydrocarbons (NO₂-PAHs) and heterocyclics. The concentration of target compounds and the proportion of vitro-PAHs and heterocyclic compounds were considerably greater in SRM 1650 than in SRM 1649, consistent with the observed differences in their mutagenic potency. However, the different responses of the dichloromethane extracts in TA98 and TA100 suggest the presence of different (unidentified) compounds.Many of the target compounds were detected at least once in the sequential extracts from SRM 1649 and SRM 1650. There was no evident relationship between the occurrence of extracted organics, or classes of organics, and the polarity of solvents, except that, generally, the largest amount and variety of compounds were recovered in the first and second extracts (hexane; hexane:diethyl ether, 9:1). Preliminary examination of the chemical analysis results did not provide an explanation of the observed trends in mutagenic response. No single class of chemicals or individual compound was found to account for the observed pattern of mutagenicity. Compounds other than those identified must also contribute to the observed mutagenicity of any of the SRM 1649 and SRM 1650 extracts.     

Mutagenicities of glycidyl ethers for Salmonella typhimurium: relationship between mutagenic potencies and chemical reactivity

The lethal and mutagenic effects of ethyl, benzyl, 1-naphthylmethyl, 2-naphthylmethyl, 1-naphthylethyl, 2-naphthylethyl and 9-anthrylmethyl glycidyl ethers on Salmonella typhimurium (TA100, TA1535, TA98 and TA1538) were investigated. LD30-value became smaller with an increase in compound hydrophobicity. The mutagenicities of these compounds in TA100 increased in the order: 1-naphthylethyl glycidyl ether less than 2-naphthylethyl glycidyl ether less than benzyl glycidyl ether less than 2-naphthylmethyl glycidyl ether less than 1-naphthylmethyl glycidyl ether less than 9-anthrylmethyl glycidyl ether. 1-Naphthylmethyl and 2-naphthylmethyl glycidyl ethers were mutagenic toward TA1535. In TA98, 1-naphthylmethyl and 9-anthrylmethyl glycidyl ethers showed mutagenic activity and 9-anthrylmethyl glycidyl ether was more mutagenic than 1-naphthylmethyl glycidyl ether. 9-Anthrylmethyl glycidyl ether was also active in TA1538. In the reaction of glycidyl ethers with deoxyguanosine and related compounds, glycidyl ethers attacked at only N-7 of guanine. The alkylation rates of glycidyl ethers toward guanine residues in DNA were determined and the exciplex-formation ability of 7-substituted guanines was studied. The reactivity of glycidyl ethers with guanine residues in DNA has not provided a sufficient explanation for the variation in mutagenic potencies of glycidyl ethers.     

Mutagenicity and chemical analysis of sequential organic extracts of airborne particulates.

To obtain insight into the identity of chemicals associated with the mutagenicity of United States National Institute of Standards and Technology (NIST) Standard Reference Materials SRM 1649 (urban dust) and SRM 1650 (diesel particulate), parallel mutagenicity tests and chemical analyses were performed on dichloromethane and sequential organic extracts of these samples. SRM 1649 and 1650 were sequentially extracted with five organic solvents of increasing polarity, in order to partition mutagenic components into discrete fractions. The solvents (with associated polarity index) were as follows: (1) hexane (0.0); (2) hexane:diethyl ether 9:1 (0.29); (3) hexane:diethyl ether 1:1 (1.45); (4) diethyl ether (2.9); (5) methanol (6.6). 0.9270 g of SRM 1649, and 0.0510 g of SRM 1650 were each extracted three times with 8 ml of each of the solvents, the three aliquots were pooled, and analysed for target organics or solvent-exchanged into DMSO for mutagenicity testing in Salmonella typhimurium strains TA98 and TA100. The dichloromethane extracts of SRM 1649 and SRM 1650 contained direct-acting mutagens in Salmonella strains TA98 and TA100; SRM 1650 was significantly more potent than SRM 1649 in either strain. Addition of S9 caused a large decrease in mutagenicity of each extract, although SRM 1650 remained more potent. An interesting pattern of mutagenicity was observed for the sequential extracts of SRM 1649 and SRM 1650: the mutagenic potency of SRM 1649 extracts increased with increasing polarity of the extraction solvent while the response of the SRM 1650 extracts was the opposite. This suggests that the direct-acting mutagens in SRM 1650 are unlike those in SRM 1649. The response, though diminished, was largely unchanged when S9 was included in the test mixture. Chemical analyses on the various extracts were performed using a Hewlett-Packard model 5890 gas chromatograph equipped with a model 5970B mass selective detector (GC-MSD), and a 0.3 microns film thickness cross-linked methyl silicone capillary column (HP 1909A-101). Selected ion monitoring (SIM) methods were used to analyze for 105 target compounds including PAHs and nitro-PAHs. Chemical analysis of the dichloromethane extracts of SRM 1649 and SRM 1650 identified three main classes of compounds: polyaromatic hydrocarbons (PAH), nitro-polyaromatic hydrocarbons (NO2-PAHs) and heterocyclics. The concentration of target compounds and the proportion of nitro-PAHs and heterocyclic compounds were considerably greater in SRM 1650 than in SRM 1649, consistent with the observed differences in their mutagenic potency. However, the different responses of the dichloromethane extracts in TA98 and TA100 suggest the presence of different (unidentified) compounds.(ABSTRACT TRUNCATED AT 400 WORDS)     

Δ1-Tetrahydrocannabinol and 1α,2α-epoxyhexahydrocannabinol: Mutagenicity investigation in the ames test

1,2-Epoxyhexahydrocannabinol is a metabolite of Δ¹-tetrahydrocannabinol. Because many epoxides are mutagens, we investigated 1,2-epoxyhexahydrocannabinol as well as Δ¹-tetrahydrocannabinol for mutagenicity with Salmonella typhimurium TA1535, TA1537, TA98 and TA100 in the presence and in the absence of S9 mix from liver homogenate of rats treated with Aroclor 1254. Additionally, an epoxide hydratase inhibitor was used in some experiments. Whereas several other epoxides and further positive controls, not requiring activation or activated under the same conditions, respectively, showed strong mutagenicity, no indications of a mutagenic hazard by 1,2-epoxyhexahydrocannabinol or by Δ¹-tetrahydrocannabinol were found.     

Relationship between mutagenic potency in Salmonella typhimurium and chemical structure of amino- and nitro-substituted biphenyls

All positional isomers of mononitro- and monoaminobiphenyls and those of dinitro-, diamino- and aminonitrobiphenyls, which have one substituent on each benzene ring, were assayed for mutagenicity in Salmonella typhimurium by the Ames method. The results suggest that the structural requirements favoring mutagenic activity are the presence of substituents at the 4-position and their absence at the 2'-position. The introduction of an amino group to the 3'- or 4'-position of 4-nitrobiphenyl or a nitro group to 3'- or 4'-position of 4-aminobiphenyl enhanced the mutagenicity. Among the mutagenic compounds, 4-nitro analogues were mutagenic in strains TA98 and TA100 in the absence of a microsomal metabolic activation system. Strain TA98NR was not reverted by the direct-acting mutagens, whereas strain TA98/1,8-DNP6 was as revertible as strain TA98; these results suggest that the direct-acting mutagenicity involves the reduction of the nitro group by bacterial nitroreductase but does not involve specific esterification enzymes.     

Screening for the mutagenicity of nitro-group containing hypoxic cell radiosensitizers using Salmonella typhimurium strains TA 100 and TA 98

A series of sixteen 2-, 4- and 5-nitroimidazoles, four nitrobenzenes, five nitrofurans, and a nitropyrrole, most of which have been studied previously as hypoxic cell specific radiosensitizers, have been screened for their mutagenicity using the Salmonella typhimurium strains TA 100 and TA 98 developed by Ames and co-workers. Most of these compounds were mutagenic and had a one to two order of magnitude greater mutagenicity towards TA 100 (base-pair substitution sensitive) than TA 98 (frame-shift sensitive). The spectrum of mutagenic efficiencies for the drugs which was observed could be correlated to some extent with the electron affinity of these compounds. Exceptions to this correlation may indicate drugs of interest for further studies both as mutagens and hypoxic cell radiosensitizers.     

delta 1-Tetrahydrocannabinol and 1 alpha, 2 alpha-epoxyhexahydrocannabinol: mutagenicity investigation in the Ames test.

1,2-Epoxyhexahydrocannabinol is a metabolite of delta 1-tetrahydrocannabinol. Because many epoxides are mutagens, we investigated 1,2-epoxyhexahydrocannabinol as well as delta 1-tetrahydrocannabinol for mutagenicity with Salmonella typhimurium TA1535, TA1537, TA98 and TA100 in the presence and in the absence of S9 mix from liver homogenate of rats treated with Aroclor 1254. Additionally, an epoxide hydratase inhibitor was used in some experiments. Whereas several other epoxides and further positive controls, not requiring activation or activated under the same conditions, respectively, showed strong mutagenicity, no indications of a mutagenic hazard by 1,2-epoxyhexahydrocannabinol or by delta 1-tetrahydrocannabinol were found.     

Mutagenicities of the pyrolyzates of peptides and proteins.

Pyrolyzates of 10 peptides, 10 proteins and 5 naturally-occurring materials were tested for mutagenicity in the histidine-requiring mutants Salmonella typhimurium TA98 and TA100. Significant mutagenic activity was detected with pyrolyzates of most of these materials. The pyrolyzates requred a liver microsomal fraction, as representative of mammalian metabolism, for their detection as mutagens. Among the pyrolyzates tested, the highest mutagenic activity was observed with that of a tryptophan-containing peptide. The pyrolyzate of protein obtained from tobacco leaf also showed mutagenicity. The higher the protein content in the leaf the higher the mutagenic activity of the pyrolyzate. Protein in a tobacco leaf may be the principal precursor of mutagens in tobacco-smoke condensate.     

Structural specificity of aromatic compounds with special reference to mutagenic activity in Salmonella typhimurium — a series of chloro- or fluoro-nitrobenzene derivatives

The mutagenicity of 21 chloro- or fluoronitrobenzene compounds and 9 chloro- or fluorobenzene compounds in Salmonella typhimurium (strains TA98, TA1538, TA1537, TA100 and TA1535) was examined. The tests were carried out under the conditions of absence and presence of liver microsomal activation.15 nitro-group compounds had mutagenic activity; above all, compounds of fluoronitrobenzene were mutagenic for both types of strain. On the other hand, chloronitrobenzene compounds were mutagenic for base-pair substitution strains only. Mutagenic activity was exhibited by all compounds having a chloro or fluoro substituent at the para and ortho position in the nitrobenzene nucleus. All compounds without a nitro substituent showed no mutagenic activity.     

Biphenyl and fluorinated derivatives: liver enzyme-mediated mutagenicity detected in Salmonella typhimurium and Chinese hamster V79 cells.

Hepatocarcinogenic polychlorinated and polybrominated biphenyls usually show negative results in in vitro mutagenicity assays. Problems in their testing result from their low water solubility and their slow rate of metabolism. We therefore investigated better soluble model compounds, namely biphenyl and its 3 possible monofluorinated derivatives. In the direct test, these compounds proved to be nonmutagenic in Salmonella typhimurium TA98 and TA100 (reversion to histidine prototrophy) and in Chinese hamster V79 cells (acquisition of resistance to 6-thioguanine). However, when the exposure was carried out in the presence of NADPH-fortified postmitochondrial fraction of liver homogenate from Aroclor 1254-treated rats, all 4 compounds showed mutagenic activity in V79 cells. 3-Fluorobiphenyl produced strong mutagenic effects in S. typhimurium TA100 as well, whereas the other biphenyls were inactive. In strain TA98, 3- and 4-fluorobiphenyl showed mutagenic activity. This mutagenicity was enhanced in the presence of 1,1,1-trichloropropene 2,3-oxide, an inhibitor of microsomal epoxide hydrolase, thus suggesting that epoxides may be active metabolites.     

Assessment of the Mutagenicity of Sediments from Yangtze River Estuary Using Salmonella Typhimurium/Microsome Assay

Sediments in estuaries are of important environmental concern because they may act as pollution sinks and sources to the overlying water body. These sediments can be accumulated by benthic organisms. This study assessed the mutagenic potential of sediment extracts from the Yangtze River estuary by using the Ames fluctuation assay with the Salmonella typhimurium his (−) strain TA98 (frameshift mutagen indicator) and TA100 (baseshift mutagen indicator). Most of the sediment samples were mutagenic to the strain TA98, regardless of the presence or absence of exogenous metabolic activation (S9 induction by β-naphthoflavone/phenobarbital). However, none of the samples were mutagenic to the strain TA100. Thus, the mutagenicity pattern was mainly frameshift mutation, and the responsible toxicants were both direct (without S9 mix) and indirect (with S9 mix) mutagens. The mutagenicity of the sediment extracts increased when S9 was added. Chemical analysis showed a poor correlation between the content of priority polycyclic aromatic hydrocarbons and the detected mutagenicity in each sample. The concept of effect-directed analysis was used to analyze possible compounds responsible for the detected mutagenic effects. With regard to the mutagenicity of sediment fractions, non-polar compounds as well as weakly and moderately polar compounds played a main role. Further investigations should be conducted to identify the responsible components.