Andrei L. Barkovskii

Dechlorination of PCDD/F by organic and inorganic electron transfer molecules in reduced environments

The dechlorination of octa- and pentachlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) was investigated using organic and inorganic electron shuttles relevant to anaerobic sediments. OctaCDD was dechlorinated to hexaCDD in the presence of resorcinol, catechol, and 3,4-dichlorobenzoate, resulting in an increase of 2,3,7,8-substituted hepta- and hexaCDD. Vitamin B12 mediated the dechlorination of octaCDD to tetraCDD, octaCDF to hexaCDF, and 1,2,3,7,8-pentaCDD to at least two tetraCDD, including 2,3,7,8-TCDD. Zerovalent zinc stoichiometrically dechlorinated octaCDD to hexa- and pentaCDD under basic and neutral conditions, respectively. Thus, abiotically-mediated dechlorination reactions may contribute significantly to the fate of PCDD/F in reduced environments.

Dioxin cycling in aquatic sediments: the Passaic River Estuary

The contribution of dechlorination reactions to the transformation of dioxins in river sediments was evaluated under a range of geochemical conditions mimicking freshwater, estuarine and marine environments, and interpreted in the light of recent evidence for their accumulation at the air-water interface. The yield of dechlorinated products increased with salinity, but never exceeded 20% of the initial dioxins present. Among the homologue groups in saline conditions, diCDDs were dominant at 32-47 mol% (8-16 nM). The production of 2,3,7,8-TCDD increased with decreasing salinity and in the presence of dissolved organic matter, exhibiting a maximum ratio (2,3,7,8-TCDD:non-2,3,7,8-TCDD) of 0.5. These differences in patterns may be related to the dominant microbial respiratory processes responsible for carbon turnover under the imposed conditions, and are strongly affected by the presence of organic matter. Based on these results, a conceptual dechlorination and carbon turnover model is proposed to help explain the likely reactivity of dioxins in the Passaic River Estuary.

Origins and environmental mobility of antibiotic resistance genes, virulence factors and bacteria in a tidal creek's watershed.

To compare bacterial compositions of watershed run‐offs released by a human settlement and a forested area, and to evaluate their role as carriers of antibiotic resistance and virulence genes.

Polychlorinated Dibenzo-p-Dioxins in Anaerobic Soils and Sediments

Significant differences have been observed in the 2,3,7,8-substituted residue patterns of polychlorinated dibenzo-p-dioxins (PCDD) in freshwater, estuarine and marine sediments. Whereas these patterns can, to some degree, be explained by source identification, PCDD at environmental concentrations were recently found to be dechlorinated via microbial and chemical processes. Both peri- (1,4,6,9-substituted chlorines) and lateral (2,3,7,8-substituted chlorines) dechlorination patterns, as well as differences in extent of dechlorination were found to be correlated to specific abiotic and biotic catalytic activities. Qualitative relationships were based on isomer-specific analysis and the appearance of selective congeners under different conditions. The relevance of these processes to sediment biogeochemistry indicates that microbial dechlorination contributes significantly to the natural weathering of these types of pollutants. Whereas the lack of knowledge on the catalytic nature of the dechlorination reaction precludes the establishment of QSARs, characterization of microbial activities in combination with geochemical indicators may eventually present a means to describe the potential for microbial PCDD dechlorination in a given sediment environment and allow for a scientifically justified interpretation of patterns observed.

NEW METHOD USING GROWTH DYNAMICS TO QUANTIFY MICROBIAL CONTAMINATION OF KAOLINITE SLURRIES

The early and sensitive detection of microbial contamination of kaolinite slurries is needed for timely treatment to prevent spoilage. The sensitivity, reproducibility, and time required by current methods, such as the dip-slide method, do not meet this challenge. A more sensitive, reproducible, and efficient method is required. The objective of the present study was to develop and validate such a method. The new method is based on the measured growth kinetics of indigenous kaolinite-slurry microorganisms. The microorganisms from kaolinite slurries with different contamination levels were eluted and quantified as colony-forming units (CFUs). Known quantities of E. coli (ATCC 11775) were inoculated into sterilized kaolinite slurries to relate kaolinite-slurry CFUs to true microbial concentrations. The inoculated slurries were subsequently incubated, re-extracted, and microbial concentrations quantified. The ratio of the known inoculated E. coli concentration to the measured concentration was expressed as the recovery efficiency coefficient. Indigenous microbial communities were serially diluted, incubated, and the growth kinetics measured and related to CFUs. Using the new method, greater optical densities (OD) and visible microbial growth were measured for greater dilutions of kaolinite slurries with large microbial-cell concentrations. Growth conditions were optimized to maximize the correlation between contamination level, microbial growth kinetics, and OD value. A Standard Bacterial Unit (SBU) scale with five levels of microbial contamination was designed for kaolinite slurries using the experimental results. The SBU scale was validated using a blind test of 50 unknown slurry samples with various contamination levels provided by the Imerys Company. The validation tests revealed that the new method using the SBU scale was more time efficient, sensitive, and reproducible than the dip-slide method.