Yoshitaka Yonezawa

Anaerobic transformation of chlorophenols in methanogenic sludge unexposed to chlorophenols

Transformation of all 19 chlorophenol (CP) isomers was investigated in a laboratory anaerobic methanogenic sludge that had not been exposed to synthetic chemicals. Concentration of CP was analyzed over time to calculate disappearance rate constants using first-order reaction kinetics and all possible CP degradation pathways were estimated. The rate constants ranged between 0.46 x 10(-3) and 0.161 day(-1). CPs were transformed via dechlorination. The chlorine atom at the ortho-position was the most easily dechlorinated, whereas dechlorination rate at the para-position was lowest. The overall pathways of CP transformation were much less diverse than that we previously found for contaminated sediment. The Dolfing hypothesis of microbial selection of the most thermodynamically favorable pathways was not applicable for CP transformation in this study as well as previous study performed by our group.

Transformations of chloronitrobenzenes in anaerobic sediment

Abstract The transformations of chloronitrobenzenes (CNBs) in anaerobic estuarine sediment were examined. The sediment had been preexposed to various anthropogenic chemicals from the surrounding industries. The sulfate content of the interstitial and overlaying waters was approximately 20 mmole/1 indicating that the sediment was sulfidogenic. All the CNBs tested transformed without any lag period. The kinetic data followed a first-order reaction mechanism with rate constants ranging from 0.216 to 0.866 day −1 or half-lives from 0.8 to 3.2 days. The intermediates detected in the experiment indicated that the reduction of the nitro group was the first stage in the transformation of chloronitro aromatic compounds, resulting in the formation of corresponding chloroanilines (CAs). The CAs further transformed via ortho and para dechlorination pathways.

Major substrates for microbial sulfate reduction in the sediments of Ise Bay, Japan

To clarify the anaerobic microbial interactions in the process of carbon mineralization in marine eutrophic environments, the microbial sulfate reduction and methane production rates were examined in coastal marine sediments of Ise Bay, Japan, in autumn 1990. Sulfate reduction rates (51–210 nmol ml−1 day−1 at 24°C) were much higher than the methane production ones (<1.78 nmol ml−1 day−1) in the surface sediments (top 2 cm) at the six stations surveyed (water depth: 10.7–23.3 m). Substrates for sulfate-reducing bacteria (SRB) were estimated after the addition of a specific inhibitor for SRB (20 mmol l−1 molybdate) into the sediment slurry, from the substrate accumulation rates. In the presence of the inhibitor, sulfate reduction was completely stopped and volatile fatty acids (mainly acetate) were accumulated, although hydrogen was not. Methane production occurred markedly accompanied by consumption of the accumulated acetate from the third day after the addition of molybdate. The maximum rate of methane production was 1.2–1.9 μmol ml−1 day−1, which was similar to those in highly polluted freshwater sediments such as the Tama River, Tokyo, Japan. These results show that acetate is a common major substrate for sulfate reduction and methane production, and SRB competitively inhibit potential acetoclastic methanogenesis in coastal sediments. Methanogens may potentially inhabit the sediments at low levels of population density and activity.

Degradation of tri-n-buytltin in Ise Bay sediment

The vertical distribution patterns of the transformation products of tri-n-butyltin (TBT) in sediment cores collected from 6 sites in Ise Bay, Japan indicated that TBT was transformed by two pathways: methylation and debutylation. Anaerobic incubation of sediment spiked with TBT showed that the methylation was mainly supported by sulfate reducing activity and debutylation was mainly supported by nitrate reducing activity. These results showed that contribution of the two transformation reactions of TBT varied according to the dominant microbial activities in the sediment. The two types of vertical distribution of butyltins observed in the sediment cores appear to be the result of different dominant microbial activity in the sediment.

The distribution of chlorobenzenes in the bottom sediments of Ise bay

Abstract The concentration of dichloro- to hexachlorobenzene in the surficial bottom sediments in Ise Bay were determined as a preliminary study of the behavior of these compounds in this coastal environment. The sediment samples were collected from 10 stations on the west coast and in Yokkaichi Port in March 1987 and from 44 stations all over the bay in October 1987. 1, 2- and 1, 3-Dichlorobenzene and 1, 2, 3- and 1, 2, 4-trichlorobenzene levels were highest in the vicinity of Yokkaichi Port and Tsu-Matsuzaka Port. Higher levels of these compounds were also found in the middle of the bay. The concentrations of tetrachlorobenzene isomers were generally low but they were also higher in the vicinity of the two ports. 1, 3, 5-Trichlorobenzene was higher only in the vicinity of Yokkaichi. The levels of these compounds were not higher around Nagoya City, the largest city in the bay. The stations with higher dichloro- and trichlorobenzenes concentrations in the middle of the bay covered the area where the sediment particle size was small. This was also the area where downward water flow was estimated to exit. These findings indicated that these congeners were adsorbed by suspended particulates and transported by water flow. The distribution patterns, therefore, could be explained by the following effects: the distance from the source, the horizontal transport caused by the river inflows and the sedimentation caused by downward water flow. Pentachlorobenzene concentration was very low and its distribution was not clear. Hexachlorobenzene had quite a different distribution pattern from other congeners, indicating that its sources were different.

Biodegradation pathway of o-cresol by heterogeneous culture Phenol acclimated activated sludge

Abstract The biodegradation process of o -cresol by heterogeneous culture is presented in this paper. Metabolic intermediates of o -cresol by phenol acclimated activated sludge were analyzed by GC-MS. o -Cresol was first transformed to three dihydroxytoluenes; 3-methylcatechol, 4-methylresorcinol and methylhydroquinone. Three dihydroxytoluene biodegradation experiments with 3-methylcatechol, 4-methylresorcinol and methylhydroquinone revealed that 3-methylcatechol was the main route, and 3-methylcatechol was further degraded through at least two meta cleavage pathways. Various hydroxylated toluenes, namely trihydroxytoluenes and tetrahydroxytoluene were also found among the metabolites from 3-methylcatechol, 4-methylresorcinol and methylhydroquinone. These results indicated that various metabolism with main and side pathways coexisted in the biodegradation process by the heterogeneous culture.

Reductive transformations of halogenated aromatics in anaerobic estuarine sediment : Kinetics, products and pathways

Abstract The transformation of different classes of halogenated aromatic compounds in sulfidogenic sediment slurries was examined in laboratory incubation experiments. The results indicated that several processes were shown to occur, leading to the formation of a number of intermediate metabolites. The kinetics of transformation followed a first-order reaction mechanism, with k values in the range of 1.67 and 0.0005 day −1 or half-lives of 0.4 and 1386 days. The order of transformation rates among different classes of compounds was: phenols > anilines > benzenes > pesticides. The pathway of transformation among single-ring aromatic compounds indicated that ortho and para halogen removal was the predominant compared to meta halogen removal.

Reductive Dehalogenation of Chloroanilines in Anaerobic Estuarine Sediment

The reductive dehalogenation of chloroanilines (CAs) was investigated in anaerobic sediment/water systems. The sulfate content of the interstitial and overlaying waters was approximately 20 mmoles l−1 and the sediment was apparently sulfidogenic. The CAs exhibited first-order disappearance kinetics with the rate constants ranging from 0.012–0.005 day−1 or half-lives between 40 and 672 days. Pentachloroaniline (PeCA), 2,3,4,5-tetrachloroaniline (2,3,4,5-TeCA) and 3,4,5-trichloroaniline (3,4,5-TCA) were transformed by the sequential removal of halogen from the para and ortho positions. The disappearance of the parent compound and accumulation of metabolites were simulated using a first-order branched kinetic model.

The behavior of chlorobenzenes in Ise bay, estimated from their concentrations in various environmental media

Abstract Field survey of pollutants in various environmental media is indispensable for modeling the behavior of organic compounds discharged into the coastal environment. In this study, the concentrations of chlorobenzenes were measured in Ise Bay where industrial wastewater enters. Some chlorobenzene congeners, 1, 3-dichlorobenzene and 1, 2, 4-trichlorobenzene, were detected in seawater, suspended particulate and bottom sediment samples and their behavior was analyzed. The horizontal distributions showed that these chlorobenzene concentrations in the surface water and sediments were higher in the area near the shore of the industrial area than in the offshore area. The soluble chlorobenzene concentrations in the bottom water were low at all stations. The vertical distribution survey at each sampling site showed that the soluble concentrations were high in the surface water and low in the bottom water, but that those in the suspended particulates and the bottom sediments (dry solid base) had relatively similar concentrations. This indicated that chlorobenzenes in the bottom suspended particulates and in the bottom sediments were not equilibrated with chlorobenzenes in the bottom seawater. This could be explained by the following chlorobenzene behavior: the chlorobenzenes were adsorbed by suspended particulates in the surface water and settled to the bottom swiftly through less polluted seawater in the lower water layer with little desorption. This caused the chlorobenzene concentration gradient in the bottom sediment which reflected the chlorobenzene concentration absorbed by suspended particulates in the surface water. The behavior of chlorobenzenes suggested in this study showed that the use of chemical fate models based on the assumption that the soluble fraction and the fraction adsorbed by suspended particulates are always in equilibrium may yield misleading results.

The microbial community in a 2,4-dinitrophenol-digesting reactor as revealed by 16S rDNA gene analysis.

The microbial community of a 2,4-dinitrophenol-digesting reactor was investigated using different molecular biological techniques based on 16S rDNA gene sequences. A PCR-denaturing gradient gel electrophoresis (DGGE) analysis of the bacterial community in the reactor showed that one strong and five minor bands were observed in the DGGE profile. The results of excising and sequencing DGGE bands suggested that members of Rhodococcus, Nocardioides, and Nitrospira species were present in the reactor. Partial sequencing of cloned 16S rDNAs revealed diversity among the six main divisions--the alpha, delta subclasses of Proteobacteria, Nitrospira, Cytophagal Flexibacter/Bacteroides, Verrucomicrobia, and Actinobacteria--in the reactor. Two cloned sequence types were not closely affiliated with any described bacterial divisions. The isolation and phylogenetic analysis of 2,4-DNP-degrading bacteria from the reactor revealed that isolated strains were classified into two types of bacteria having different 16S rDNA sequences. One of these strain types was identified as a relative of Rhodococcus koreensis, and the other was identified as a relative of Nocardioides simplex FJ21-A.