Esters Dimethyl Phthalate Research Articles

Photocatalytic degradation mechanisms of dimethyl phthalate esters by MWCNTs-anatase TiO2 nanocomposites using the UHPLC/Orbitrap/MS technique

Dimethyl phthalate esters (DMPEs) have been identified as endocrine disrupting plastisizers and emerging contaminants which can be released readily upon exposure to the environment. In this study, MWCNTs/TiO2 nanocomposites, which possess the potential application for the photocatalytic degradation of DMPEs under UV irradiation, were prepared via simple one-pot sol-gel reaction using titanium isopropoxide (TTIP) as titania precursor and multiwalled carbon nanotubes (MWCNTs). The MWCNTs/TiO2 nanocomposites was calcined in air for 2 h at the temperatures ranging from 350 to 750 °C. As a result, the MWCNTs/TiO2 nanocomposites synthesized at calcination temperature of 450 °C demonstrated the highest photodegradation efficiency of 97% after 180 min UV irradiation and its degraded products were evaluated using the ultra high performance liquid chromatography (UHPLC) coupled with a high resolution (HR) Orbitrap mass spectrometry (MS). A primary degradation mechanism was proposed and it was noteworthy that some new intermediates were discovered and reported. This work has developed a simple method for qualitative determination of DMPEs based on HPLC with UV detection.

New insights into the photocatalytic endocrine disruptors dimethyl phathalate esters degradation by UV/MWCNTs-TiO2 nanocomposites

Dimethyl phthalate esters (DMPEs) are considered to be endocrine disruptors and environmentally hazardous materials in plastic industries wastewater because of its low solubility and accumulated persistent toxicity. In the present study, MWCNTs/TiO2 nanocomposites were fabricated by modified sol-gel technique using titanium isopropoxide as titanium oxide sources and purified MWCNTs, to degrade DMPEs through photocatalysis using UV irradiation. The effect of MWCNTs loading (3–15 wt %) on TiO2 and the photocatalytic performance of DMPEs in aqueous solution by UV/MWCNTs/TiO2 nanocomposites were investigated. For experiments conducted with the same illumination time, the photodegradration of DMPEs was enhanced with increasing the MWCNTs contents from 3 to 10 wt % and then decreased with a further enhancement to 15 wt %. Basically, the presence of MWCNTs in the nanocomposites can lead to the decrease in the relative amount of TiO2 in the photocatalyst and then to the decrease of the photogenerated carriers. This is because the same amount of photocatalyst was added for the photoreaction, and hence, the photodegradation of DMPEs decreases especially for the nanocomposites containing MWCNTs exceed than 10 wt %. The presence of functional group (COOH) on the MWCNTs surface would help the achievement of direct chemical bonding between MWCNTs and the TiO2 nanoparticles, resulting in the synergistic effect of MWCNTs and TiO2 where the flow of photogenerated electrons in the space charge region to the MWCNTs surface. A method based on high-performance liquid chromatography (HPLC) was developed to study the degraded DMPEs samples produced after exposure to UV light.

Estimated daily intake and cumulative risk assessment of phthalates in Taiwan military personnel

Background: Phthalate esters (PAEs), which may have potential adverse health effects, are widely used in industrial and consumer products. The public raised concerns of exposure to PAEs after di-2-ethylhexyl PAE (DEHP) had been illegally used in food products in Taiwan in 2011. However, there is little information regarding the exposure levels of PAEs among Taiwanese military personnel. Objective: Health risk assessment indicators, including daily intake (DI), hazard quotient (HQ), and hazard index (HI), were used to assess the distribution and trends of PAEs and cumulative risk in Taiwanese military personnel. Materials and Methods: We recruited 503 participants who participated in northern voluntary military service from June to August 2017. We calculated the DI of five PAEs, namely dimethyl PAE, diethyl PAE, dibutyl PAE (DBP), benzyl butyl phthalate, and DEHP, and selected the reference dose (RfD) described by the US Environmental Protection Agency (EPA) as an acceptable exposure reference value to compute the HQ and HI. We used statistical analysis to examine the differences and trends of PAE metabolites in urine and investigated the possible primary sources of PAEs with principal component analysis. Results: The detection rates of 7 PAE metabolite concentrations were ≥72.2%. All DIs, HQRfDs, and HIRfDs were not over the standard EPA RfD. For all participants, two principal components (PC) were extracted. Three DEHP metabolites and MBP were correlated with PC1, and MiBP and MnBP were correlated with PC2. Conclusions: The main potential sources of PAE exposure for Taiwanese military personnel are DEHP and DBP. Efforts to reduce exposure to environmental PAEs are necessary to maintain health within the military.

Degradation of dimethyl phthalate esters by a filamentous fungus Aspergillus versicolor isolated from deep-sea sediments

AbstractDimethyl phthalate esters (DMPEs), which belong to phthalate esters (PAEs), are widely distributed environmental pollutants with endocrine-disrupting toxicity. The present study focused on a filamentous fungus capable of degrading DMPEs isolated from deep-sea sediments of the Indian Ocean at a water depth of 3300 m using an enrichment culture technique. The filamentous fungus was identified as

Transformation of dimethyl phthalate esters (DMPEs) by a marine red yeast Rhodotorula mucilaginosa isolated from deep sea sediments of the Atlantic Ocean

A marine red yeast capable of degrading dimethyl phthalate esters (DMPEs) was isolated from deep-sea sediments of the Atlantic Ocean using enrichment culture technique. The yeast was identified as Rhodotorula mucilaginosa Mar-Y3 based on internal transcribed spacer (ITS) gene sequence analysis. The biochemical degradation pathways of three DMPE isomers, namely dimethyl phthalate (DMP), dimethyl isophthalate (DMI), and dimethyl terephthalate (DMT), were investigated using this yeast. The yeast cannot completely mineralize DMPEs, but can transform them to respective phthalate monoester or phthalic acid. R. mucilaginosa Mar-Y3 also degraded different DMPE isomers through varied metabolism pathways and biodegradation rates. The yeast performed one-step ester hydrolysis with a relatively low degradation rate to transform DMP and DMI to the respective monoester; however, monomethyl phthalate (MMP) and monomethyl isophthalate (MMI) were the dead-end products and further metabolism did not proceed. The yeast carried out sequential ester hydrolysis with a relatively high degradation rate to transform DMT to terephthalic acid (TA) via monomethyl terephthalate (MMT), but TA was resistant to further metabolism. These results suggested that phthalate esterases produced by the deep-sea yeast R. mucilaginosa Mar-Y3 had a very high substrate specificity for different DMPE isomers, and that the degradation of DMPEs by this yeast involved distinct esterases responsible for the hydrolysis of two identical carboxylic ester bonds.

Biodegradation of dimethyl phthalate ester using free cells, entrapped cells of Variovorax sp. BS1 and cell free enzyme extracts: A comparative study

Whole cells of Variovorax sp. BS1 had the ability to biodegrade up to 600 mg L−1 (3.08 mM) of dimethyl phthalate (DMP) at the end of 30 h of incubation at 30 °C. The total organic carbon analyses suggested mineralization of DMP using isolated bacterial strain. The cell-free extracts of Variovorax sp. BS1 contained mixture of enzymes required for the complete biodegradation of DMP, diethyl phthalate (DEP) and dibutyl phthalate (DBP). Transient intermediates or end products were not detected by HPLC and LC-MS analyses during or after biodegradation of DMP by Variovorax sp. BS1. Addition of Zn+2 to assay mixture containing DMP and cell free extract resulted in the accumulation of detectable quantity of metabolite, ortho-phthalate thereby suggesting that DMP biodegradation proceeded via de-esterification reactions. Cells of Variovorax sp. BS1 entrapped in calcium alginate beads could be re-used for atleast ten sequential cycles in plain water with diminutive loss of DMP biodegradation activity. Results suggested that whole cells, alginate entrapped cells of Variovorax sp BS1 and enzymes present in the cell free extracts may be used for efficient biodegradation of dimethyl phthalate.

Purification and characterization of an intracellular esterase from a marine Fusarium fungal species showing phthalate diesterase activity

An intracellular esterase was isolated from a marine fungus Fusarium sp. DMT-5-3 with dimethyl isophthalate (DMI) as the inducing substrate. The purified esterase is a dimeric protein consisting of two identical subunits. The molecular mass of the enzyme is about 76 kDa. The optimal temperature and pH for the esterase activity was 50 °C and 8.0, respectively. The enzyme remained stable between pH 6.0–12.0 and under 40 °C. The esterase activity was particularly activated by Mg2+ and inhibited by Cr3+, Cu2+, Hg2+, Zn2+, Ni2+, Co2+, Cd2+, and Mn2+. Substrate specificity analysis showed that the enzyme was capable of hydrolyzing DMI and dimethyl terephthalate (DMT), but not dimethyl phthalate (DMP) and three isomers of monomethyl phthalate esters (MMPEs). Compared with previously reported DMT esterase isolated from tested fungus, this DMI esterase showed smaller molecular mass but broader substrate specificity. These results suggested that phthalate esterases produced by Fusarium sp. DMT-5-3 are highly substrate-specific and there are distinct esterases involved in hydrolysis of two carboxylic ester bonds of dimethyl phthalate esters (DMPEs).

Electrochemical degradation of the dimethyl phthalate ester on a fluoride-doped Ti/β-PbO2 anode

The electrooxidation of the dimethyl phthalate (DMP) ester was galvanostatically carried out in a filter-press reactor using a fluoride-doped lead dioxide (β-PbO2,F) film electrodeposited on a Ti substrate. The variables investigated were the nature of the supporting electrolyte (NaCl and Na2SO4), pH (3, 7, and 10), current density (10, 20, 40, 60, and 80mAcm−2), and temperature (10, 20, 30, 40, and 50°C). The removal of DMP was monitored through high performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis. The best conditions were obtained using Na2SO4 and at low current densities, independent of the solution pH or temperature. These conditions led to the highest levels of current efficiencies and complete combustion. However, the TOC removal levels were low, due to the generation of highly oxidized intermediates, which was confirmed by the intermediates detected by HPLC.

Photo-assisted electrochemical degradation of the dimethyl phthalate ester on DSA® electrode

Phthalic acid esters are synthetic compounds used as additives in plastic structures. As these chemicals are physically bound, they can contaminate humans affecting the endocrine system. The present study focused on the photo-assisted electrochemical (PAE) method to degrade a phthalic acid ester, such as dimethyl phthalate – DMP, using a one-compartment filter press flow cell and a commercial DSA® electrode. The variables investigated to optimize the DMP compound removal were NaCl concentration, current density, and temperature. The efficiency toward the DMP concentration abatement and total organic carbon (TOC) removal was the analytical parameters analyzed. The highest rates of DMP and TOC removals were attained at high NaCl concentrations and current densities, due to the generation of high reactive oxidants in the PAE method that seemed to suppress mass transport limitations. The temperature had no significant influence on the DMP removal. Moreover, depending on the nature of the intermediate compounds generated, the PAE method could enable a rapid treatment option before disposal of contaminated effluents containing DMP, and possibly other endocrine disruptors. Despite the high levels of current efficiency attained, more work is required to optimize the electrical energy consumption, especially with respect to the choice of the UV lamp.

Purification and characterization of an intracellular esterase from a Fusarium species capable of degrading dimethyl terephthalate

Esterase is the key enzyme involved in microbial degradation of phthalate esters (PAEs). In this study, an intracellular esterase was purified from a coastal sediment fungus Fusarium sp. DMT-5-3 capable of utilizing dimethyl terephthalate (DMT) as a substrate. The purified enzyme is a polymeric protein consisting of two identical subunits with a molecular mass of about 84kDa. The enzyme showed a maximum esterase activity at 50°C and was stable below 30°C. The optimal pH was 8.0 and the enzyme was stable between pH 6.0 and 10.0. The esterase activity was inhibited by Cr3+, Hg2+, Cu2+, Zn2+, Ni2+, and Cd2+. Substrate specificity analysis showed that the enzyme was specific to DMT hydrolysis, but had no effect on other isomers of dimethyl phthalate esters (DMPEs) or monomethyl phthalate esters (MMPEs). These findings suggest that the phthalate esterase produced by Fusarium sp. DMT-5-3 is inducible and distinctive esterases involved in hydrolysis of the two carboxylic ester linkages of DMPEs.

Comparison of initial hydrolysis of the three dimethyl phthalate esters (DMPEs) by a basidiomycetous yeast, Trichosporon DMI-5-1, from coastal sediment

Dimethyl phthalate esters (DMPEs) are a group of plasticizers commonly detected in the environment with potential adverse human health impact. The degradation of DMPEs by fungal systems has been studied to a limited extent, particularly by yeasts. In this study, a basidiomycetous yeast Trichosporon DMI-5-1 capable of degrading DMPEs was obtained and the degradation pathways were investigated. A DMPE-degrading yeast was isolated from costal sediment by enrichment culture technique and was identified as Trichosporon sp. DMI-5-1 based on microscopic morphology and 18S rDNA sequence. Comparative investigations on biodegradation of three isomers of DMPEs, namely dimethyl phthalate (DMP), dimethyl isophthalate (DMI), and dimethyl terephthalate (DMT), were carried out with this yeast strain. Trichosporon sp. DMI-5-1 could not mineralize DMPEs completely but transform them to respective monomethyl phthalate or phthalic acid. Biochemical degradation pathways for the three DMPE isomers by Trichosporon sp. DMI-5-1 were apparently different. The yeast carried out one-step ester hydrolysis of DMP and DMI to respective monoesters (monomethyl phthalate and monomethyl isophthalate, respectively) and no further metabolism of these two monoesters. Meanwhile, DMT was transformed by the yeast to monomethyl terephthalate and subsequently to terephthalic acid by stepwise hydrolysis of the two ester bonds. This study shows that different catalytic processes are involved in the transformation of DMPEs by the basidiomycetous yeast Trichosporon sp. DMI-5-1 and suggests that its esterases, responsible for the initial hydrolyzing the two ester bonds of DMPEs, are highly substrate specific.

Degradability of the three dimethyl phthalate isomer esters (DMPEs) by a Fusarium species isolated from mangrove sediment

Dimethyl phthalate esters (DMPEs) are common plasticizersand additives to improve flexibility and softness of plastic products(Cartwright et al., 2000; Wang et al., 2004; Xu et al., 2005). ThreeDMPE-isomers, namely dimethyl phthalate (ortho-DMP; ortho-arrangement of the two carboxyl groups), dimethyl isophthalate(DMI; meta-) and dimethyl terephthalate (DMT; para-), display dif-ferent physical and chemical properties and are used in differentindustrial applications. DMP is used as a plasticizer in cellulose es-ter-based plastics (cellulose acetate and cellulose butyrate; Stapleset al., 1997). In polyester-based products, such as tape for VCR cas-settes, synthetic textile fibers etc., DMI and DMT are used as inter-mediates for their synthesis (Lee et al., 1999; Wang and Gu,2006a,b). Phthalate esters (PAEs) occur ubiquitously in both aqua-tic and terrestrial environments (Gu et al., 2005), and foods (Peter-sen and Breindahl, 2000). Because they do not bond covalentlywith the resin, leaching and migration of PAEs from plastic materi-als into the environment are of major concern for the potentialhealth problems associated with these chemicals. PAEs may actas endocrine disruptors affecting the normal function of the repro-ductive system and development of humans and animals at verylow concentrations (Jobling et al., 1995; Colon et al., 2000; Guet al., 2005; Xu et al., 2005). As a result, six PAEs including DMPare listed as priority pollutants by the United States EnvironmentalProtection Agency (Gu et al., 2005).It is suggested that complete degradation of PAEs in the envi-ronment is via microbial mineralization (Staples et al., 1997; Guet al., 2005). Degradation of PAEs has been well documented inbacteria. Various PAE-degrading bacteria have been isolated fromactivated sludge, mangroves, soils, rivers, and the marine environ-ment (Vegaand Bastide, 2003; Changet al., 2004; Gu et al., 2005; Liet al., 2005a,b; Xu et al., 2005; Wang and Gu 2006a,b; Fang et al.,2007). Both Gram-positive and Gram-negative bacteria are respon-sible for the aerobic degradation of phthalic acid (PA) via differentpathways (Chang and Zylstra, 1998; Stingley et al., 2004). Severalfunctional operons involved in the metabolism of PA have beenidentifiedand characterizedin Arthrobacter keyseri12B, Mycobacte-rium vanbaaleniiPYR-1, Burkholderia cepacia DBO1 and other bacte-rial strains (Chang and Zylstra, 1998; Eaton, 2001; Stingley et al.,2004). However, degradation of PAEs by fungi has rarely beenshown. Fungi have been demonstrated to be potential degradersof a wide range of recalcitrant compounds, including polycyclicaromatic hydrocarbons (PAHs), benzene–toluene–ethylbenzene–xylenes (BTEX), chlorophenols, polychlorinated biphenyl, muni-tions waste, and pesticides (Tortella et al., 2005). Nevertheless,degradation of PAEs by fungi has been studied only to a limited ex-tent with Aspergillus niger and Sclerotium rolfsii (Sivamurthy et al.,1991; Ganji et al., 1995; Pradeepkumar et al., 2000). The role offungi on the environmental fate of PAEs remains largely unknown.Coastal wetlands, such as mangroves, are usually sinks of pollu-tants from the aquatic system (Tam et al., 2001; Ke et al., 2005).Mangrove microorganisms may play an important role in the fateoforganicpollutantsinaquaticenvironments.Anumberofbacterialspecies capable of degrading PAEs have been isolated from man-grove sediments, such as Pseudomonas fluorescens, Rhodococcus ru-ber, Pasturella multocida, and Sphingomonas paucimobilis (Li et al.,2005a,b;Xuetal.,2005;LiandGu,2006).However,therearenore-ports concerned with the degradation of PAEs by mangrove fungi.The Futain Mangrove Nature Reserve of Shenzhen, China, is on thesouthern border of Shenzhen, one of the cities with the most rapideconomic development in China. The Reserve is under increasingpollution pressure derived from intense urbanization of the city,The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only thosepapers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 42, 703–704).

Degradation of the endocrine-disrupting dimethyl phthalate carboxylic ester by Sphingomonas yanoikuyae DOS01 isolated from the South China Sea and the biochemical pathway

Bacteria capable of using dimethyl phthalate (DMP) as the sole carbon and energy source were isolated from the sediments collected at a depth of 1340 m from the South China Sea. Sphingomonas yanoikuyae DOS01, identified based on 16S rRNA gene sequence, utilized DMP from an initial level of 180 mg l −1 to non-detectable in 35 h at 30 °C, the optical density (OD 600) values increased over the time of incubation. Degradation intermediate monomethyl phthalate (MMP) accumulated up to 21.3 mg l −1 and then disappeared in the culture medium. When MMP or another intermediate phthalate (PA) was used as the sole substrate, this strain was only capable of degrading MMP, but not PA. Total organic carbon (TOC) analysis of the culture medium suggested that both DMP and MMP were mineralized, but not PA. This strain from the deep-ocean sediment transforms DMP to MMP using a common biochemical pathway for DMP as reported before. Further esterase activity assays indicated that the enzyme induced by MMP has higher affinity than that by DMP for the substrate p-nitrophenyl acetate. Our results indicated that complete degradation of DMP by this marine microorganism may involve a new biochemical pathway.

Degradation of dimethyl carboxylic phthalate ester by Burkholderia cepacia DA2 isolated from marine sediment of South China Sea

Burkholderia cepacia DA2, isolated from marine sediment of the South China Sea, is capable of utilizing dimethyl phthalate (DMP) as the sole source of carbon and energy. During the transformation of DMP in batch culture, its corresponding degradation intermediates were identified as monomethyl phthalate (MMP) and phthalate acid (PA) sequentially over the time of incubation. The biodegradation biochemical pathway of DMP was DMP to MMP and then to PA before mineralization. Degradation of DMP by B. cepacia DA2 was also dependent upon DMP-induction, and the initial concentrations of DMP affected the degradation rate. Degradation kinetics fit well with the modified Gompertz model. The optimum pH and salinity was 6.0 and < 5 per thousand, respectively, for DMP degradation by B. cepacia DA2. This study showed that the indigenous microorganisms of the deep-ocean sediments are capable of DMP degradation completely.

Photocatalytic degradation of dimethyl phthalate ester using novel hydrophobic TiO2 pillared montmorillonite photocatalyst

TiO2 pillared montmorillonites were prepared by introducing Ti4+ into a layer of montmorillonite modified with or without cetyltrimethylammonium bromide. The components and texture of the prepared composites were characterized by thermogravimetric analysis, X-ray powder diffraction and scanning electron misroscopy. The adsorption and photocatalytic degradation performance of a model environmental endocrine disruptor, dimethyl phthalate ester, were investigated using this newly prepared hydrophobic TiO2 pillared montmorillonite photocatalyst. The adsorption of dimethyl phthalate ester from water varied from 9% to 28% on the prepared hydrophobic photocatalyst. Although the experimental results showed that the photocatalytic activity of the hydrophobic photocatalyst was slightly lower than that of hydrophilic one, electron spin resonance verified that hydroxyl radicals were also generated in hydrophobic TiO2 pillared montmorillonite photocatalyst under UV irradiation. To elucidate the decomposition mechanism of dimethyl phthalate ester, 12 main photocatalytic intermediates were identified during the photocatalytic degradation process, and a plausible degradation mechanism was also proposed.

Determination of micelle/water partition coefficients and associated thermodynamic data for dialkyl phthalate esters

Micelle/water partition coefficients for three dialkyl phthalate esters — dimethyl phthalate ester (DMP), diethyl phthalate ester (DEP) and dipropyl phthalate ester (DPP) were obtained by micellar liquid chromatography (MLC). Experiments were conducted over a temperature range which led to calculation of a Gibbs free energy, enthalpy and entropy of transfer for the phthalate esters. In addition, small angle neutron scattering (SANS) experiments were conducted with no substantial change observed in micelle size before and after phthalate ester incorporation.

Environmental fate of endocrine-disrupting dimethyl phthalate esters (DMPE) under sulfate-reducing condition

Dimethyl phthalate esters (DMPE) can easily be released into the environment from plastic products. As endocrine disruptors, DMPE mimic estrogenic activities in animals and humans. The metabolites of DMPE are suspected to cause even more serious health problems. Among the common sterilization techniques adopted in the study of DMPE degradation, the average loss of the parent DMPE compounds after autoclaving was as high as 21.26%. In contrast, the loss after 0.2 microm filtration was significantly lower at 2.28%. It is suggested that filtration should be used over autoclaving for sterilizing DMPE. The environmental fate of DMPE under sulfate-reducing condition was simulated and studied in microcosm system. It was observed that dimethyl phthalate (DMP), dimethyl isophthalate (DMI) and dimethyl terephthalate (DMT) could not be mineralized over an extended period of 6 months, but with the transformation to the respective monomethyl phthalate and/or phthalic acid. The dominant species of microorganisms utilizing individual DMPE isomer as the sole carbon source were isolated and identified as facultative anaerobe Thauera sp., Xanthobacter sp. and Agrobacterium sp. for DMP, DMI and DMT, respectively. This study illustrates that the detrimental DMPE and their natural metabolites may accumulate in the sulfate-reducing environment. Accordingly, proper surveillance program should be devised to monitor both the parent compounds and degradation intermediates of DMPE in order to protect the aquatic ecosystem and human health.

Complete Degradation of the Endocrine-Disrupting Chemical Dimethyl Phthalate ester by Flavobacterium sp.

The complete microbial degradation of dimethyl phthalate ester (DMPE) is described. DMPE is thought to be an endocrine-disrupting chemical. A pure culture (strain No. A-9) from soil sample capable of utilizing DMPE as the sole source of carbon and energy was identified as Flavobacterium sp. Degradation patterns of DMPE were observed on the high-performance liquid chromatogram (HPLC) of the culture filtrates of this strain, and growth of bacteria was measured as protein by the Kennedy and Fewson method. The growth yield of this strain was about 5.9 g of protein per mole of carbon source of DMPE, and was similar to that in the case of glucose as a carbon source. Complete degradation of DMPE had been achieved (1000 mg/l) in less than 2 days using Flavobacterium sp. strain No. A-9. The transient intermediates of DMPE were not detectable on the HPLC of the culture filtrates of this strain. This strain also degraded phthalic acid (PA) but could not degrade phthalic anhydride.

Aerobic degradation of dimethyl phthalate ester and its isomers

The microbial degradative characteristics of three phthalate ester isomers (ortho-, meta-, and para- benzene dicarboxylic esters, DMP,DMI, and DMT respectively for short) by a degrading bacterium isolated from mangrove soil were investigated. The bacterium was identified as Rhodococcus ruber with 16S rDNA sequencing. Experimental results showed that as the sole source of carbon and energy, DMP could be degraded and the degradation intermediates were identified as mono-methyl phthalate(MMP) and phthalic acid (PA). The tentative pathway proposed for degradation of DMP by the bacterium under aerobic condition was through monoester initially, and further degradation of monoester produced phthalic acid, and finally CO_ 2 and H_ 2O. DMI and DMT at a concentration of 50mg·L -1 were degraded within 10 days by Rhodococcus ruber, but the intermediates accumulated in the culture medium. the results suggest that the degradation of phthalate ester isomers was related to the structures of chemicals.

Biochemical pathway and degradation of phthalate ester isomers by bacteria

Degradation of dimethyl isophthalate (DMI) and dimethyl phthalate ester (DMPE) was investigated using microorganisms isolated from mangrove sediment of Hong Kong Mai Po Nature Reserve. One enrichment culture was capable of utilizing DMI as the sole source of carbon and energy, but none of the bacteria in the enrichment culture was capable of degrading DMI alone. In co-culture of two bacteria, degradation was observed proceeding through monomethyl isophthalate (MMI) ester and isophthalic acid (IPA) before the aromatic ring opening. Using DMI as the sole carbon and energy source, Klebsiella oxytoca Sc and Methylobacterium mesophilicum Sr degraded DMI through the biochemical cooperation. The initial hydrolytic reaction of the ester bond was by K. oxytoca Sc and the next step of transformation was by M. mesophilicum Sr, and IPA was degraded by both of them. In another investigation, a novel bacterium, strain MPsc, was isolated for degradation of dimethyl phthalate ester (DMPE) also from the mangrove sediment. On the basis of phenotypic, biochemical and 16S rDNA gene sequence analyses, the strain MPsc should be considered as a new bacterium at the genus level (8% differences). This strain, together with a Rhodococcus zopfii isolated from the same mangrove sediment, was able to degrade DMPE aerobically. The consortium consisting of the two species degraded 450 mg/l DMPE within 3 days as the sole source of carbon and energy, but none of the individual species alone was able to transform DMPE. Furthermore, the biochemical degradation pathway proceeded through monomethyl phthalate (MMP), phthalic acid (PA) and then protocatechuate before aromatic ring cleavage. Our results suggest that degradation of complex organic compounds including DMI and DMPE may be carried out by several members of microorganisms working together in the natural environments.