Kegg Pathway: 1- and 2-Methylnaphthalene degradation

J Bacteriol. 2009 Oct 23;
Selesi D, Jehmlich N, von Bergen M, Schmidt F, Rattei T, Tischler P, Lueders T, Meckenstock RU

The highly enriched deltaproteobacterial culture N47 anaerobically oxidizes the polycyclic aromatic hydrocarbons naphthalene and 2-Methylnaphthalene with sulfate as electron acceptor. Combined genome sequencing and LC-MS/MS-based shotgun proteome analysis were performed to identify genes and proteins involved in anaerobic aromatic catabolism. Proteome analysis from 2-Methylnaphthalene-grown N47 cells resulted in the identification of putative enzymes catalyzing the anaerobic conversion of 2-Methylnaphthalene to 2-naphthoyl-CoA as well as the reductive ring cleavage of 2-naphthoyl-CoA leading to the formation of acetyl-CoA and CO2. The glycyl radical-catalyzed fumarate addition to the methyl group of 2-Methylnaphthalene is catalyzed by naphthyl-2-methyl-succinate synthase (Nms) composed of alphabetagamma-subunits that are encoded by the genes nmsABC. Upstream of nmsABC, nmsD is located encoding the Nms-activating enzyme which harbors the characteristic [Fe4S4] cluster sequence motifs of S-adenosylmethionine (SAM)-radical enzymes. The bns gene cluster, coding for enzymes involved in beta-oxidation reactions of naphthyl-2-methyl-succinate to 2-naphthoyl-CoA, was found four intervening open reading frames further downstream. It consists of eight genes (bnsABCDEFGH) corresponding to 8.1 kb, which are closely related to enzymes involved in anaerobic toluene degradation within the denitrifiers Aromatoleum aromaticum EbN1, Azoarcus sp. T, and Thauera aromatica. Another contiguous DNA sequence harbors the gene for 2-naphthoyl-CoA reductase (ncr) and 16 additional genes that were found to be expressed in 2-Methylnaphthalene-grown cells. These genes code for enzymes that were correlated to catalyze the dearomatization and ring cleavage reactions of 2-naphthoyl-CoA to acetyl-CoA and CO2. Comparative sequence analysis of the four encoding subunits (ncrABCD) showed the closest similarity to Azoarcus type of benzoyl-CoA reductase. The present work provides first insight into the genetic basis of anaerobic 2-Methylnaphthalene metabolism and delivers implications for understanding contaminant degradation.

Appl Biochem Biotechnol. 2009 Oct; 159(1): 1-10
Kim YB, Kim JY, Kim EK

Amphiphilic polyurethane (APU) nano-particle enhanced the mobilization of 2-Methylnaphthalene (2-MNPT) in soil. Significant increase in the solubility of 2-MNPT was achieved. The molar solubilization ratio was 0.4 (mole 2-MNPT/mole APU). Simple precipitation of APU particle by 2 N CaCl(2) recovered 95% of APU particle and 92% of 2-MNPT simultaneously. Also, 2-MNPT, which was entrapped inside the APU particle, was directly degraded by Acinetobacter sp. as same efficiency as without APU particle. These results showed the potentials of APU particle in the mobilization and biodegradation of hydrophobic compounds from soil.

Environ Microbiol. 2009 Jan; 11(1): 209-19
Musat F, Galushko A, Jacob J, Widdel F, Kube M, Reinhardt R, Wilkes H, Schink B, Rabus R

The anaerobic biodegradation of naphthalene, an aromatic hydrocarbon in tar and petroleum, has been repeatedly observed in environments but scarcely in pure cultures. To further explore the relationships and physiology of anaerobic naphthalene-degrading microorganisms, sulfate-reducing bacteria (SRB) were enriched from a Mediterranean sediment with added naphthalene. Two strains (NaphS3, NaphS6) with oval cells were isolated which showed naphthalene-dependent sulfate reduction. According to 16S rRNA gene sequences, both strains were Deltaproteobacteria and closely related to each other and to a previously described naphthalene-degrading sulfate-reducing strain (NaphS2) from a North Sea habitat. Other close relatives were SRB able to degrade alkylbenzenes, and phylotypes enriched anaerobically with benzene. If in adaptation experiments the three naphthalene-grown strains were exposed to 2-Methylnaphthalene, this compound was utilized after a pronounced lag phase, indicating that naphthalene did not induce the capacity for 2-Methylnaphthalene degradation. Comparative denaturing gel electrophoresis of cells grown with naphthalene or 2-Methylnaphthalene revealed a striking protein band which was only present upon growth with the latter substrate. Peptide sequences from this band perfectly matched those of a protein predicted from genomic libraries of the strains. Sequence similarity (50% identity) of the predicted protein to the large subunit of the toluene-activating enzyme (benzylsuccinate synthase) from other anaerobic bacteria indicated that the detected protein is part of an analogous 2-Methylnaphthalene-activating enzyme. The absence of this protein in naphthalene-grown cells together with the adaptation experiments as well as isotopic metabolite differentiation upon growth with a mixture of d(8)-naphthalene and unlabelled 2-Methylnaphthalene suggest that the marine strains do not metabolize naphthalene by initial methylation via 2-Methylnaphthalene, a previously suggested mechanism. The inability to utilize 1-naphthol or 2-naphthol also excludes these compounds as free intermediates. Results leave open the possibility of naphthalene carboxylation, another previously suggested activation mechanism.

Toxicol Lett. 2008 May 30; 178(3): 146-51
Kim D, Farthing MW, Miller CT, Nylander-French LA

The objective of this research was to develop a mathematical description of uptake of aromatic and aliphatic hydrocarbons into the stratum corneum of human skin in vivo. A simple description based on Fick's laws of diffusion was used to predict the spatiotemporal variation of naphthalene, 1- and 2-Methylnaphthalene, undecane, and dodecane in the stratum corneum of human volunteers. The estimated values of the diffusion coefficients for each chemical were comparable to values predicted using in vitro skin systems and biomonitoring studies. These results demonstrate the value of measuring dermal exposure using the tape-strip technique and the importance of quantifying of dermal uptake.

Environ Sci Technol. 2006 Jul 1; 40(13): 4165-73
Safinowski M, Griebler C, Meckenstock RU

The sulfate-reducing enrichment culture N47 can grow on naphthalene or 2-Methylnaphthalene as the sole carbon and energy source. Here we show that the culture can furthermore cometabolicallytransform a variety of polycyclic and heteroaromatic compounds with naphthalene or methylnaphthalene as the auxiliary substrate. Most of the cosubstrates were converted to the corresponding carboxylic acids, frequently to several isomers. The mass spectra of specific metabolites that were extracted from supernatants of cultures containing the cosubstrates benzothiophene, benzofuran, and 1-methylnaphthalene resembled known intermediates of the anaerobic naphthalene and 2-Methylnaphthalene degradation pathways (i.e., naphthyl-2-methylsuccinic acid and naphthyl-2-methylenesuccinic acid). This indicates that some of the tested compounds were first methylated and then transformed to the corresponding methylsuccinic acids by a fumarate addition to the methyl group. For some of the cosubstrates, a partial or total inhibition of growth on the auxiliary substrate was observed. This was not caused by the toxicity of the individual cosubstrate itself, but by a specific combination of auxiliary substrate and cosubstrate. None of the cosubstrates tested could be utilized as the sole carbon source and electron donor by the enrichment culture N47. Field investigations at the tar-oil-contaminated aquifer, where strain N47 originated, revealed the presence of a number of metabolites similar to the ones identified in batch culture supernatants. Our findings suggest that aromatic hydrocarbons and heterocyclic compounds can be converted by aquifer organisms and produce a variety of polar compounds that become mobile in groundwater.

Environ Toxicol Chem. 2006 Jul; 25(7): 1746-56
Knightes CD, Peters CA

Biodegradation kinetics were studied for binary and complex mixtures of nine polycyclic aromatic hydrocarbons (PAHs): Naphthalene, 1-methylnaphthalene, 2-Methylnaphthalene, 2-ethylnaphthalene, phenanthrene, anthracene, pyrene, fluorene, and fluoranthene. Discrepancies between the observed biodegradation rates and those predicted by a sole-substrate model indicate that significant substrate interactions occurred in both the binary and complex-mixture experiments. For all compounds except naphthalene, biodegradation was enhanced. The observations were compared to predictions from two multisubstrate biodegradation kinetic models: One that accounts for competitive inhibition, and one that does not. Both models are fully predictive in that parameters had been determined from an independent set of sole-substrate experiments. In the binary experiments, the major multisubstrate effect was biomass enhancement as a result of growth on naphthalene. Substrate interactions were orders of magnitude larger for most compounds in the complex mixtures, but significant competitive inhibition effects counteracted some of the biomass enhancement effect. The present study has demonstrated that the sole-substrate model is inadequate to describe multisubstrate biodegradation kinetics for a broad range of PAH mixtures. Whereas the multisubstrate model without inhibition did an adequate job of predicting the observed effects in some cases, we advocate the use of the multisubstrate model with inhibition for similar modeling efforts in light of the evidence that the model was correct more often than not. Theory supports its use because of the common enzyme pathways for biodegradation of PAHs.

Environ Sci Technol. 2005 May 1; 39(9): 3077-82
Yang J, Lu M

Diesel particulate matter (DPM) has been recognized as carcinogenic due to its respirable sizes and toxic compositions. It is essential to understand its formation mechanisms to effectively reduce DPM emissions. Studies have indicated that resonance stabilize radicals can result in more soot and PAC (polycyclic aromatic compounds) formation in combustion processes. As the largest single polycyclic aromatic constituent in petroleum fuels, 1- and 2-Methylnaphthalenes can readily form resonance-stabilized radicals in combustion, and yet the reaction mechanisms are not well understood. In this paper, product formation mechanisms of these compounds are experimentally investigated in a flow reactor. The pyrolysis of 1- and 2-Methylnaphthalene was studied from 800 to 1000 degrees C, and the oxidation of 2-Methylnaphthalene was studied from 650to 950 degrees C. The PACs were quantified by GC/MS and HPLC, and soot was quantified gravimetrically. Naphthalene is the most abundant product and is formed from methyl loss by H displacement. Isomerization in pyrolytic conditions results in the second most abundant product. The methyl radicals recombine with the reactants to form ethylnaphthalenes and dimethylnaphthalenes. 2-Naphthaldehyde is formed from the oxidation of the naphthylmethyl radicals. 1-Methylnaphthalene is of slightly higher reactivity in comparison to its isomer. The experimental results indicate that the PAC formation from the pyrolysis and oxidation of the two methylnaphthalenes are likely to be governed by similar mechanisms. The lack of carbon dimerization products in significant quantities may be due to their further growth into soot.

Chem Commun (Camb). 2005 Feb 28; 1090-1
Wang Y, Wu JJ, Wang YF, Qin LP, Jin WJ

Using sodium deoxycholate as a protective medium, the selective recognition of Cu(II) at ng ml(-1) level is realized through dynamic phosphorescence quenching of 1-bromo-2-Methylnaphthalene (BMN) without deoxygenation. The limit of detection is 4.32 ng ml(-1), and the relative standard deviation is 1% at 10 microM, linear up to 1 x 10(-5) M.

FEMS Microbiol Lett. 2004 Nov 1; 240(1): 99-104
Safinowski M, Meckenstock RU

The upper pathway of anaerobic degradation of 2-Methylnaphthalene was studied with a sulphate-reducing enrichment culture, which is able to grow with naphthalene or 2-Methylnaphthalene as sole carbon source and electron donor. Anaerobic degradation of 2-Methylnaphthalene is initiated by an addition of fumarate to the methyl-group producing the first intermediate, naphthyl-2-methyl-succinate. In a subsequent beta-oxidation of the original methyl atom, the central metabolite 2-naphthoic acid is generated. In the following pathway, the aromatic ring system is reduced, cleaved, and finally oxidised to CO(2). Here, we present two new enzymatic reactions of the 2-Methylnaphthalene degradation pathway that were measured in crude cell extracts. All metabolites were identified with HPLC by co-elution with synthesised reference substances. The first enzyme, succinyl-CoA:naphthyl-2-methyl-succinate CoA-transferase, catalyses the activation of naphthyl-2-methyl-succinic acid to the corresponding CoA ester. The average specific activity of this enzyme was 19.6 nmol x min(-1) x mg of protein(-1). The CoA-transfer was not inhibited by sodium borohydride and only partially by hydroxylamine, indicating that this enzyme belongs to the family III of CoA-transferases like the corresponding enzyme in the anaerobic toluene degradation pathway. The product of this CoA-transfer reaction, naphthyl-2-methyl-succinyl-CoA is then oxidised in a reaction to naphthyl-2-methylene-succinyl-CoA by the enzyme naphthyl-2-methyl-succinyl-CoA dehydrogenase. The specific activity of this enzyme was 0.115 nmol x min(-1) x mg of protein(-1). The enzymatic activity could only be detected using phenazine methosulphate as electron acceptor. No activity was observed with natural electron acceptors such as nicotinamide adenine dinucleotide or flavin adenine dinucleotide. The two novel reactions presented here demonstrate that the original methyl-group of 2-Methylnaphthalene is oxidised to the carboxyl group of 2-naphthoic acid in the upper part of the anaerobic degradation pathway.

Environ Toxicol Chem. 2004 Jun; 23(6): 1538-48
Jonsson G, Bechmann RK, Bamber SD, Baussant T

Sheepshead minnows (Cyprinodon variegatus) were continuously exposed to two concentrations of polycyclic aromatic hydrocarbons (PAHs) dissolved in seawater (sigma PAH = 7.57 and 72.31 microg/L) for 36 d, followed by 8 d of depuration. The PAHs studied were naphthalene (NPH or C0-NPH), phenanthrene (PHE or C0-PHE), pyrene (PYR), 2-Methylnaphthalene (C1-NPH), 1,3-dimethylnaphthalene (C2-NPH), 2-isopropylnaphthalene (C3-NPH), 9-methylphenanthrene (C1-PHE), and 9-ethylphenanthrene (C2-PHE). Uptake rate constants (k1) for NPHs increased with increasing degree of alkylation and log value of the octanol/water partition coefficient (Kow), whereas k1 values for three- and four-ring PAHs were lower despite their high log Kow values. Elimination rate constants (k2) for the homologue series of NPHs and PHEs generally increased with decreasing degree of alkylation and log Kow values. However, the depuration time did not directly correlate with the molecular size for nonalkylated PAHs. Bioconcentration factors (BCFs) were estimated from the ratio of k1 to k2 and also directly from PAH concentrations in fish tissue and water samples, and the factors generated by the two methods were very similar. A significant positive correlation was determined between log BCFs and log Kow values for the series of C0- through C3-NPH at both low (r2 = 0.985, p = 0.0077) and high (r2 = 0.956, p = 0.022) exposures, although this correlation was not determined for all the PAHs studied. As a result of increased metabolism and/ or reduced bioavailability with increasing lipophilic character, the estimated BCFs for C0- through C2-PHE and PYR were generally lower than those for C0- through C3-NPH. The two exposure levels revealed minor variations in k1 and k2 values for parent PAHs and in the temporal pattern of PAH metabolite concentrations in bile. The present results indicate that the presence and nature of alkyl groups have a significant influence on the kinetics and metabolism of PAHs in fish.

Photochem Photobiol Sci. 2004 Sep; 3(9): 898-905
Bergamini G, Ceroni P, Maestri M, Balzani V, Lee SK, Vogtle F

The photochemical and photophysical behaviour of two dendrimers consisting of a benzophenone core and branches that contain four (4) and eight (5) naphthalene units at the periphery has been investigated in CH(2)Cl(2) solution (298 K) and in CH(2)Cl(2)/CHCl(3) 1:1 v/v rigid matrix (77 K). For comparison purposes, the photophysical properties of dimethoxybenzophenone (1), 2-Methylnaphthalene (2) and of a dendron containing four naphthalene units (3) have also been studied. In both dendrimers 4 and 5, excitation of the peripheral naphthalene units is followed by fast (1.1 x 10(9) s(-1) at 298 K, > 2.5 x 10(9) s(-1) at 77 K for 5; 2.9 x 10(8) s(-1) at 298 K, 7 x 10(5) s(-1) at 77 K for 5) singlet-singlet energy transfer to the benzophenone core. On a longer time scale (>1 x 10(6) s(-1) at 298 K, >6 x 10(3) s(-1) at 77 K for 4; 3.1 x 10(7) s(-1) at 298 K, ca. 3 x 10(2) s(-1) at 77 K for 5) a back energy transfer process takes place from the triplet state of the benzophenone core to the triplet state of the peripheral naphthalene units. Selective excitation of the benzophenone unit is followed by intersystem crossing and triplet-triplet energy transfer to the peripheral naphthalene units. In hydrogen donating solvents, the benzophenone core is protected from degradation by the presence of the naphthalene units. In solutions containing Tb(CF(3)SO(3))(3), sensitization of the green Tb(3+) luminescence is observed on excitation of both the peripheral naphthalene units and the benzophenone core of 5. Upon excitation of the naphthalene absorption band (266 nm) with a laser source, intradendrimer triplet-triplet annihilation of naphthalene excited states leads to delayed naphthalene fluorescence (lambda(max)= 335 nm), that can also be obtained upon excitation at 355 nm (benzophenone absorption band). The results obtained show that preorganization of photoactive units in a dendritic structure can be exploited for a variety of useful functions, including photosensitized emission, protection from undesired photoreactions, and energy up-conversion.

FEMS Microbiol Ecol. 2004 Jul 1; 49(1): 27-36
Meckenstock RU, Safinowski M, Griebler C

Polycyclic aromatic hydrocarbons (PAHs) are among the most important contaminants of groundwater. The 2- and 3-ring PAHs are of particular concern because they are water soluble in the 1-200 mug/l range and are transported with the groundwater over significant distances. Anaerobic degradation of PAH has been demonstrated in several microcosm studies with nitrate, ferric iron, or sulfate as electron acceptors and under methanogenic conditions. The biochemical degradation pathways were studied with naphthalene-degrading pure and enrichment cultures and revealed that 2-naphthoic acid is a central metabolite. Naphthalene is activated by addition of a C(1)-unit to generate 2-naphthoic acid, whereas methylnaphthalene is activated by addition of fumarate to the methyl group and further degraded to 2-naphthoic acid. In the central 2-naphthoic acid degradation pathway the ring system is reduced prior to ring cleavage generating e.g. 5,6,7,8-tetrahydro-2-naphthoic acid. The ring cleavage produces metabolites such as 2-carboxycyclohexylacetic acid indicating that further degradation goes via cyclohexane derivatives and not via aromatic compounds. Anaerobic degradation of PAH has also been demonstrated in situ in contaminated aquifers by identification of compound specific metabolites and using stable isotope fraction studies. Detection of specific metabolites of anaerobic PAH degradation such as naphthyl-2-methylsuccinate indicated anaerobic degradation of 2-Methylnaphthalene in situ whereas 2-naphthoic acid was indicative of naphthalene and 2-Methylnaphthalene degradation. Other carboxylic acids that were detected in groundwater indicated anaerobic degradation of a wide range of PAH and heterocyclic compounds. degradation of naphthalenes in contaminated aquifers could also be confirmed by carbon stable isotope shifts in the residual substrate fraction.

Mar Pollut Bull. 2004 Mar; 48(5-6): 504-13
Franson JC, Hollmén TE, Flint PL, Grand JB, Lanctot RB

In 2000, we collected blood from long-tailed ducks (Clangula hyemalis) and blood and eggs from common eiders (Somateria mollissima) at near-shore islands in the vicinity of Prudhoe Bay, Alaska, and at a reference area east of Prudhoe Bay. Blood was analyzed for trace elements and egg contents were analyzed for trace elements, organochlorine pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. Except for Se (mean=36.1 microg/g dry weight (dw) in common eiders and 48.8 microg/g dw in long-tailed ducks), concentrations of trace elements in blood were low and, although several trace elements differed between areas, they were not consistently higher at one location. In long-tailed ducks, Se in blood was positively correlated with activities of two serum enzymes, suggestive of an adverse effect of increasing Se levels on the liver. Although common eiders had high Se concentrations in their blood, Se residues in eggs were low (mean=2.28 microg/g dw). Strontium and Ni were higher in eggs near Prudhoe Bay than at the reference area, but none of the other trace elements or organic contaminants in eggs differed between locations. Concentrations of Ca, Sr, Mg, and Ni differed among eggs having no visible development, early-stage embryos, or late-stage embryos. Residues of 4,4'-DDE, cis-nonachlor, dieldrin, hexachlorobenzene, oxychlordane, and trans-nonachlor were found in 100% of the common eider eggs, but at low concentrations (means of 2.35-7.45 microg/kg wet weight (ww)). The mean total PCB concentration in eggs was 15.12 microg/kg ww. Of PAHs tested for, residues of 1- and 2-Methylnaphthalene and naphthalene were found in 100% of the eggs, at mean concentrations of 0.36-0.89 microg/kg ww.

Environ Sci Technol. 2004 Jan 15; 38(2): 617-31
Griebler C, Safinowski M, Vieth A, Richnow HH, Meckenstock RU

To evaluate the intrinsic bioremediation potential in an anoxic tar oil-contaminated aquifer at a former gasworks site, groundwater samples were qualitatively and quantitatively analyzed by compound-specific isotope analysis (CSIA) and signature metabolites analysis (SMA). 13C/12C fractionation data revealed conclusive evidence for in situ biodegradation of benzene, toluene, o-xylene, m/p-xylene, naphthalene, and 1-methylnaphthalene. In laboratory growth studies, 13C/12C isotope enrichment factors for anaerobic degradation of naphthalene (epsilon = -1.1 +/- 0.4) and 2-Methylnaphthalene (epsilon = -0.9 +/- 0.1) were determined with the sulfate-reducing enrichment culture N47, which was isolated from the investigated test site. On the basis of these and other laboratory-derived enrichment factors from the literature, in situ biodegradation could be quantified for toluene, o-xylene, m/p-xylene, and naphthalene. Stable carbon isotope fractionation in the field was also observed for ethylbenzene, 2-Methylnaphthalene, and benzothiophene but without providing conclusive results. Further evidence for the in situ turnover of individual BTEX compounds was provided by the presence of acetophenone, o-toluic acid, and p-toluic acid, three intermediates in the anaerobic degradation of ethylbenzene, o-xylene, and p-xylene, respectively. A number of groundwater samples also contained naphthyl-2-methylsuccinic acid, a metabolite that is highly specific for the anaerobic degradation of 2-Methylnaphthalene. Additional metabolites that provided evidence on the anaerobic in situ degradation of naphthalenes were 1-naphthoic acid, 2-naphthoic acid, 1,2,3,4-tetrahydronaphthoic acid, and 5,6,7,8-tetrahydronaphthoic acid. 2-Carboxybenzothiophene, 5-carboxybenzothiophene, a putative further carboxybenzothiophene isomer, and the reduced derivative dihydrocarboxybenzothiophene indicated the anaerobic conversion of the heterocyclic aromatic hydrocarbon benzothiophene. The combined application of CSIA and SMA, as two reliable and independent tools to collect direct evidence on intrinsic bioremediation, leads to a substantially improved evaluation of natural attenuation in situ.

Environ Sci Technol. 2004 Jan 15; 38(2): 609-16
Steinbach A, Seifert R, Annweiler E, Michaelis W

The aquifer of a former manufactured gas plant site, highly contaminated by dissolved monocyclic, heterocyclic, and polycyclic aromatic hydrocarbons, was studied to evaluate the applicability of carbon and hydrogen isotope fractionation to prove ongoing biodegradation of these compounds even in complex aquifer settings. The loss of toluene, o-xylene, p,m-xylene, and 2-Methylnaphthalene was accompanied by a considerable carbon isotope fractionation. Additionally, a strong 2H enrichment in residual o-xylene was detected. All isotope fractionations observed could be related to established biochemical degradation mechanisms, each involving a C-H bond cleavage in the rate-determining step. In contrast, other compounds such as 1-methylnaphthalene, methylbenzofuran, and acenaphthene exhibited a uniform stable carbon isotope composition. However, a decrease in concentration for these compounds was observed in the flowpath of the aquifer. High threshold concentrations of acenaphthene downgradient indicate that this contaminant is, if at all, only marginally biodegraded. Detailed analyses of xylenes provided support that compound specific isotope analyses and subsequent application of the Rayleigh model may provide a valuable basis to distinguish between different biodegradation mechanisms as well as dissolution processes in heterogeneous aquifers.

Chemosphere. 2003 Aug; 52(5): 869-81
Dimitriou-Christidis P, Harris BC, McDonald TJ, Reese E, Autenrieth RL

Liquid aqueous solubility (S(w,L)), octanol/water partition coefficients (K(ow)), liquid vapor pressure (P(v,L)), and Henry's law constants (H(c)) were estimated for 20 methylated naphthalenes ranging from monomethyl to tetramethylnaphthalenes. Chromatographic methods were used for the estimation. Chromatographic retention measurements were conducted for 11 reference compounds and regressions were fit between the retention indices and the physicochemical properties. HPLC octadecylsilyl column with acetonitrile/water eluent was used for the estimation of S(w,L) and K(ow). Two GC columns, HP5-MS and a more hydrophobic HP-1, were tested for the estimation of P(v,L). Measured retention indices for the methylated naphthalenes were entered to the regression equations to calculate the physicochemical properties for these compounds. Literature values, where available, were used to validate the calculated values. The method accurately estimated the physicochemical properties. Estimated S(w,L) and P(v,L) decreased with the number of methyl groups. K(ow) increased with the number of methyl groups. There was no obvious relation between H(c) and the number of methyl groups. Log S(w,L) ranged from 0.885 for 1,2,5,6-tetramethylnaphthalene to 2.269 for 1-methylnaphthalene (mmol/m(3)). Log K(ow) varied from 3.89 for 1-methylnaphthalene to 4.95 for 1,2,5,6-tetramethylnaphthalene. Log P(v,L) ranged from -0.983 for 1,2,5,6-tetramethylnaphthalene to 0.789 for 2-Methylnaphthalene (Pa). Log H(c) varied from 1.03 for 1,4,5-trimethylnaphthalene to 1.73 for 2,6-dimethylnaphthalene (Pa m(3)/mol). There were no apparent effects of GC column hydrophobicity on the accuracy of the results. Estimation of S(w,L) and K(ow) based on GC retention indices was not as accurate as with HPLC. Comparison of the estimated values with values predicted by EPIWIN indicated that EPIWIN is useful in giving order-of-magnitude prediction of physicochemical properties.

J Contam Hydrol. 2003 Jun; 64(1-2): 59-72
Richnow HH, Meckenstock RU, Reitzel LA, Baun A, Ledin A, Christensen TH

Concentrations and isotopic compositions (13C/12C) of aromatic hydrocarbons were determined in eight samples obtained from the strongly anoxic part of the leachate plume downgradient from the Vejen Landfill (Denmark), where methanogenic, sulfate-reducing and iron-reducing conditions were observed. Despite the heterogeneous distribution of the compounds in the plume, the isotope fractionation proved that ethylbenzene and m/p-xylene were subject to significant biodegradation within the strongly anoxic plume. The isotope fractionation factors (alphaC) for the degradation of the m/p-xylene (1.0015) and ethylbenzene (1.0021) obtained from the field observations were similar to factors previously determined for the anaerobic degradation of toluene and o-xylene in laboratory experiments, and suggest that in situ biodegradation is one major process controlling the fate of these contaminants in this aquifer. The isotope fractionation determined for 1,2,4-trimethylbenzene and 2-ethyltoluene suggested in situ biodegradation; however, the isotopic composition did not correlate well with the respective concentration as expressed by the Rayleigh equation. Some other compounds (1,2,3-trimethylbenzene, o-xylene, naphthalene and fenchone) did not show significant enrichments in delta13C values along the flow path. The compound concentrations were too low for accurate isotope analyses of benzene, toluene, 1- and 2-Methylnaphthalene, while interferences in the chromatography made it impossible to evaluate the isotopic composition for 4-ethyltoluene, 1,3,5-trimethylbenzene and camphor. In addition to demonstrating the potential of assessing isotopic fractionation as a means for documenting the in situ biodegradation of complex mixtures of aromatic hydrocarbons in leachate plumes, this study also illustrates the difficulties for data interpretation in complex plumes and high analytical uncertainties for isotope analysis of organic compounds in low concentration ranges.

Appl Microbiol Biotechnol. 2003 Oct; 62(5-6): 579-85
Basu A, Dixit SS, Phale PS

Pseudomonas putida CSV86 metabolizes 1- and 2-Methylnaphthalene through distinct catabolic and detoxification pathways. In spite of the similarity in the steps involved in the methylnaphthalene detoxification and the toluene side-chain hydroxylation pathways, the strain failed to utilize toluene or xylenes. However, it could grow on benzyl alcohol, 2- and 4-hydroxybenzyl alcohol. Metabolic studies suggest that the benzyl alcohol metabolism proceeds via the benzaldehyde, benzoate, and catechol ortho-cleavage pathway, in contrast to the well established catechol meta-cleavage pathway. Carbon source-dependent enzyme activity studies suggest that the degradation of aromatic alcohol involves two regulons. Aromatic alcohol induces the upper regulon, which codes for aromatic alcohol- and aromatic aldehyde-dehydrogenase and converts alcohol into acid. The aromatic acid so generated induces the specific lower regulon and is metabolized via either the ortho- or the meta-cleavage pathway. CSV86 cells transform 1- and 2-Methylnaphthalene to 1- and 2-hydroxymethyl naphthalene, which are further converted to the respective naphthoic acids due to the basal level expression and broad substrate specificity of the upper regulon enzymes.

Environ Sci Technol. 2003 Jan 15; 37(2): 308-13
Phousongphouang PT, Arey J

Naphthalene and its methyl-, ethyl-, and dimethyl-derivatives are semivolatile polycyclic aromatic hydrocarbons expected to be in the gas phase in ambient atmospheres and are subject to nighttime degradation by gas-phase reactions with the nitrate (NO3) radical. Using a relative rate method, rate constants for the gas-phase reactions of NO3 radicals with a series of alkylnaphthalenes have been measured at 298 +/- 2 K and atmospheric pressure of air. The compounds studied were 1- and 2-Methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN), and the 10 dimethylnaphthalene isomers (1,2-, 1,3-, 1,4-,1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,6-, and 2,7-DMN). Sampling in Riverside, CA showed that these alkylnaphthalenes were readily detected in ambient air, with the exception of 1,8-DMN. The reactions of naphthalene and the alkylnaphthalenes with NO3 radicals proceed by initial addition of the radical to form an aromatic-NO3 adduct (with rate constant k(a)) which either decomposes back to reactants (with rate constant kb) or reacts with NO2 to form products (with rate constant k(c). Using naphthalene as the reference compound, the values of (k(a)k(c)/k(b)) obtained for the NO3 radical reactions (in units of 10(-28) cm(6) molecule(-2) S(-1), indicated errors are two least-squares standard deviations) were as follows: 1-MN, 7.15 +/- 0.37; 2-MN, 10.2 +/- 1.0; 1-EN, 9.82 +/- 0.69; 2-EN, 7.99 +/- 0.99; 1,2-DMN, 64.0 +/- 2.3; 1,3-DMN, 21.3 +/- 1.2; 1,4-DMN, 13.0 +/- 0.5; 1,5-DMN, 14.1 +/- 1.3; 1,6-DMN, 16.5 +/- 1.8; 1,7-DMN, 13.5 +/- 0.7; 1,8-DMN, 212 +/- 59; 2,3-DMN, 15.2 +/- 0.5; 2,6-DMN, 21.2 +/- 1.6; 2,7-DMN, 21.0 +/- 1.5.

Appl Environ Microbiol. 2003 Jan; 69(1): 275-84
Eriksson M, Sodersten E, Yu Z, Dalhammar G, Mohn WW

The potential for biodegradation of polycyclic aromatic hydrocarbons (PAHs)at low temperature and under anaerobic conditions is not well understood, but such biodegradation would be very useful for remediation of polluted sites. Biodegradation of a mixture of 11 different PAHs with two to five aromatic rings, each at a concentration of 10 micro g/ml, was studied in enrichment cultures inoculated with samples of four northern soils. Under aerobic conditions, low temperature severely limited PAH biodegradation. After 90 days, aerobic cultures at 20 degrees C removed 52 to 88% of the PAHs. The most extensive PAH degradation under aerobic conditions at 7 degrees C,53% removal, occurred in a culture from creosote-contaminated soil. Low temperature did not substantially limit PAH biodegradation under nitrate-reducing conditions. Under nitrate-reducing conditions,naphthalene, 2-Methylnaphthalene, fluorene, and phenanthrene were degraded. The most extensive PAH degradation under nitrate-reducing conditions at 7 degrees C, 39% removal, occurred in a culture from fuel-contaminated Arctic soil. In separate transfer cultures from the above Arctic soil, incubated anaerobically at 7 degrees C, removal of 2-Methylnaphthalene and fluorene was stoichiometrically coupled to nitrate removal. Ribosomal intergenic spacer analysis suggested that enrichment resulted in a few predominant bacterial populations,including members of the genera Acidovorax,Bordetella, Pseudomonas, Sphingomonas, and Variovorax. Predominant populations from different soils often included phylotypes with nearly identical partial 16S rRNA gene sequences (i.e., same genus) but never included phylotypes with identical ribosomal intergenic spacers (i.e., different species or subspecies). The composition of the enriched communities appeared to be more affected by presence of oxygen, than by temperature or source of the inoculum.