Degradation Of Chemicals Research Articles

Peroxide Pre-Oxidation of Recalcitrant Toxic Waste to Enhance Biodegradation

Land disposal is required for industrial chemicals which are not readily biodegraded. Such compounds lead to adverse effects on the environment if they escape containment. Recalcitrant and persistent hydrocarbons and chlorinated chemicals are inherently resistant to any degree of biodegradation and cause a growing threat to underground aquifer quality. Hydrogen peroxide is a potentially economical method of pre-oxidation utilized to enhance the biodegradation of persistent and recalcitrant organics in contaminated soil systems. This pre-oxidation technology was examined in a laboratory respirometer using three model toxic organic chemicals: toluene, trichloroethylene and pentachlorophenol. Microbial cultures were selected from contaminated sites for the degradation of each model organic chemical. The rate at which the microbes degraded the organic chemicals in unoxidized aqueous systems was compared to the rate of degradation in peroxide pre-oxidized aqueous systems. Results indicated that pre-oxidation enhanced the biodegradation of trichloroethylene and pentachlorophenol. Toluene, in contrast, was not significantly oxidized by pretreatment with hydrogen peroxide, and its biodegradation rate was not enhanced by the oxidation pre-treatment process.

Simulation Test Method for Degradation of Chemicals by Microorganisms in Water. TOC Die-Away Method.

A simulation test method was developed to study biodegradation of chemical compounds by monitoring the decrease in total organic carbon (TOC) of a test medium during incubation with river water microorganisms. Artificial river water containing the test chemical as the sole carbon source with 20 ppm of carbon was used as the growth medium and river water microorganisms which were trapped by membrane filtration (0.45 um) were dispersed in the medium by sonication. The test medium was incubated for 28 d with shaking in the dark. Samples were drawn periodically and biodegradation was determined by measuring the remaining TOC. Biodegradation of 13 chemicals was studied by this TOC die-away method and compared these results with that of cultivation method which was reported earlier. The change in dominating populations during incubation was found to depend significantly on the test chemical when their colony morphology was examined periodically.

Transport systems encoded by bacterial plasmids

A variety of bacterial functions are encoded on plasmids, extrachromosomal elements. Examples of plasmid-borne functions are antibiotic production and resistance, degradation of recalcitrant chemicals, virulence factors, and plant symbiotic properties. Several transport systems with diverse functions have recently been found to be carried on plasmids. These systems serve to either accumulate or extrude a compound from a cell. The focus of this review is to present a survey on several of these novel plasmid-borne transport systems emphasizing functions, components, and molecular genetics.

Supplemental Substrate Enhancement of 2,4-Dinitrophenol Mineralization by a Bacterial Consortium

A Janthinobacterium sp. and an actinomycete, both capable of mineralizing 2,4-dinitrophenol (DNP), were used to construct a consortium to mineralize DNP in nonaxenic bench-scale sequencing batch reactors (SBRs). Average K(m) values for DNP mineralization by pure cultures of the Janthinobacterium sp. and the actinomycete were 0.01 and 0.13 mug/ml, respectively, and the average maximum specific growth rate (mu(max)) values for them were 0.06 and 0.23/h, respectively. In the presence of NH(4)Cl, nitrite accumulation in pure culture experiments and in the SBRs was stoichiometric to initial DNP concentration and the addition of nitrogen enhanced DNP mineralization in the SBRs. Mineralization of 10 mug of DNP per ml was further enhanced in SBRs by the addition of glucose at concentrations of 100 and 500 mug/ml but not at 10 mug/ml. Possible mechanisms for this enhanced DNP mineralization in SBRs were suggested by kinetic analyses and biomass measurements. Average mu(max) values for DNP mineralization in the presence of 0, 10, 100, and 500 mug of glucose per ml were 0.33, 0.13, 0.42, and 0.59/h, respectively. In addition, there was greater standing biomass in reactors amended with glucose. At steady-state operation, all SBRs contained heterogeneous microbial communities but only one organism, an actinomycete, that was capable of mineralizing DNP. This research demonstrates the usefulness of supplemental substrates for enhancing the degradation of toxic chemicals in bioreactors that contain heterogeneous microbial communities.

The biodegradation of aromatic hydrocarbons by bacteria.

Aromatic compounds of both natural and man-made sources abound in the environment. The degradation of such chemicals is mainly accomplished by microorganisms. This review provides key background information but centres on recent developments in the bacterial degradation of selected man-made aromatic compounds. An aromatic compound can only be considered to be biodegraded if the ring undergoes cleavage, and this is taken as the major criteria for inclusion in this review (although the exact nature of the enzymic ring-cleavage has not been confirmed in all cases discussed). The biodegradation of benzene, certain arenes, biphenyl and selected fused aromatic hydrocarbons, by single bacterial isolates, are dealt with in detail.

A convenient model and program for the assessment of abiotic degradation of chemicals in natural waters

A convenient model for the estimation and comparison of rates of various degradation processes of chemicals in natural waters is described. The estimates are determined by combining physicochemical properties of the chemicals with properties of natural waters and solar photon irradiancies.

Influence of Alternate Electron Acceptors on the Metabolic Fate of Hydroxybenzoate Isomers in Anoxic Aquifer Slurries

The biodegradation of hydroxybenzoate isomers was investigated with samples obtained from two sites within a shallow anoxic aquifer. The metabolic fates of the substrates were compared in denitrifying, sulfate-reducing, and methanogenic incubations. Under the latter two conditions, phenol was detected as a major intermediate of p-hydroxybenzoate, but no metabolites were initially found with m- or o-hydroxybenzoate. However, benzoate accumulation was noted when metabolic inhibitors were used with these samples. About 9 to 17 days was required for >95% removal of the parent isomers under these conditions. When aquifer slurries were amended with nitrate, the equivalent removal of the hydroxybenzoates occurred within 4 days. In the denitrifying incubations, phenol was formed from all three hydroxybenzoates and accounted for about 30% of the initial substrate amendment. No benzoate was measured in these samples. All metabolites were identified by chromatographic mobility, mass spectral profiles, or both. Autoclaved controls were uniformly incapable of transforming the parent substrates. These results suggest that the anaerobic fate of hydroxybenzoate isomers depends on the relative substitution pattern and the prevailing ecological conditions. Furthermore, since these compounds are central metabolites formed during the breakdown of many aromatic chemicals, our findings may help provide guidelines for the reliable extrapolation of metabolic fate information from diverse anaerobic environments.

Microbial Enzymes for Oxidation of Organic Molecules

Enzymatic systems employed by microorganisms for oxidative transformation of various organic molecules include laccases, ligninases, tyrosinases, monooxygenases, and dioxygenases. Reactions performed by these enzymes play a significant role in maintaining the global carbon cycle through either transformation or complete mineralization of organic molecules. Additionally, oxidative enzymes are instrumental in modification or degradation of the ever-increasing man-made chemicals constantly released into our environment. Due to their inherent stereo- and regioselectivity and high efficiency, oxidative enzymes have attracted attention as potential biocatalysts for various biotechnological processes. Successful commercial application of these enzymes will be possible through employing new methodologies, such as use of organic solvents in the reaction mixtures, immobilization of either the intact microorganisms or isolated enzyme preparations on various supports, and genetic engineering technology.

Testing of the abiotic degradation of chemicals in the atmosphere: The smog chamber approach

Methods for measuring the hydroxyl-, ozone-, and direct photochemical reactivity of a substance in one specially designed medium size smog chamber are described. Rate coefficients for the reaction of OH with n-hexane, n-heptane, ethene, ethyne, chloroform, trichloroethene, methanol, 2-propanol, benzene, o-xylene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, p-chloroaniline, naphthalene, acenaphthene, 1,4-dichloronaphthalene, biphenyl, and fluorenone are given and discussed. An upper limit of 5 × 10 −13 cm 3/sec is given for the sum penta- and hexachlorobiphenyls (PCB). Rate coefficients for the ozone reaction are given for β-pinene, limonene, Δ 3-carene, cineol, vinyl chloride and 1,3-butadiene. In cases where the literature data are available for comparison, the rate coefficients ( k OH and k O 3 ) reported here compare favorably with the best data reported. The direct photochemical reactivity has been shown to be measurable if the chamber is cleaned carefully. Preliminary results on benzophenone are reported. The methods described here, except that of direct photochemical reactivity, are in agreement with those proposed to OECD. Moreover, part of the Draft OECD Test Guideline (Berlin 1987) on “Photochemical-Oxidative Degradation in the Atmosphere” is based on work described here and on closely related work in other laboratories (Becker et al., 1984) .

A convenient test method for photochemical transformation of pollutants in the aquatic environment

A test method, based on a modified Xenotest 1200, is described, and has been proved to be convenient for determination of the rate of photolytical degradation and by that it can make a valuable contribution to the evaluation of environmental stability of organic compounds. The test method was applied to testing of photochemical degradation of organic chemicals in aquatic media. Solutions of six chlorinated phenolic substances, 8-quinolinol and 9,10-anthraquinone were illuminated with filtered light, simulating daylight at controlled conditions. Quantum yields of photochemical degradation and half lifetimes (of conversion) were calculated using a sun spectrum at 60°N. Chlorophenols absorbing light at 295 – 350 nm were converted and theoretical half lifetimes of 0.75 –2.6 hours were obtained. The photochemical conversion of 8-quinolinol was slow. Anthraquinone was studied in ethanol/water and the degradation corresponded to a half lifetime of 2.8 hours.

Screening test method for degradation of chemicals in water. A simple and rapid method for biodegradation test (cultivation method).

A simple and rapid biodegradation test method (cultivation method) was developed for the screening of chemicals which were hard to be degradable by microorganisms in the natural water. Namely, a water, acetone or dimethyl-sulfoxide solution (0.1 ml) of the test chemicals was added to a mixture of river or sea water (4.9 ml) from unpolluted area and an autoclaved solution (5.0 ml) of 0.2% peptone (added by 3% NaCl for sea water) in a sterile test tube (25×200 mm) with a tight plug. After sealed with film and fixed at angle 30° in a dark box, test tubes were incubated at 30°C and shaked at 120 rpm. At appropriate times during cultivation, the remaining chemicals were determined for obtaining the degradation percentage by growing microorgaisms, which were examined by the measurement of turbidity (OD at 610 nm) of the mixture. This cultivation method gave considerably constant results on many chemicals tested, when degradability was judged from degradation percentage after 3 d-incubation as follows : 100-50% to be easy-, 50-15% to be moderate-, and 15-0% to be hard-of-degradability.

Screening test for degradation of chemicals in water - Degradation test by photoirradiation.

As one of the screening test methods for the degradation of chemicals in water, the photoirradiation test method was developed by using the equipment illustrated in Fig. 1. After quartz tubes (content : 13×100 mm) containing diluted solutions of test chemicals with water or ethanol/water (5 ml) are sealed with stoppers, they are fixed in the equipment at 1/4 slope at 30 cm distance from the light source (two fluorochemical lamps : 20 W×2) and irradiated with shaking at 25°C at 100 rpm (amplitude : 7 cm). At appropriate times during irradiation, the remaining amounts of chemicals in the tubes are determined. The degradability is judged from the time required for 50% degradation.

A smog chamber for studies of the photochemical degradation of chemicals in the presence of aerosols

A smog chamber, especially designed for the simulation of the tropospheric photochemical degradation of chemicals adsorbed on aerosol surfaces, is described. With optimum aerodynamic diameters of the aerosols (0.5 μm) and by special thermostatization of the chamber residence times of the aerosols up to 2 days in the dark and up to 1 day in the presence of simulated sun irradiation are achieved. Experiments on the degradation of simple alkanes (up to n-nonane) and aromatics in the absence and presence of aerosols (SiO 2 and TiO 2) are reported. Rate constants for the reactions of OH with n-alkanes from n-butane to n-tridecane are determined to be ( k ± 2 σ)/10 −12 cm 3 s −3 = 2.54 ± 0.04, 4.13 ± 0.05, 5.68 ± 0.04, 7.31 ± 0.08, 8.79 (reference value), 10.3 ± 0.2, 12.4 ± 0.2, 13.3 ± 0.2, 13.9 ± 0.2, 15.5 ± 0.2), respectively, at 300 K. These rate constant measurements and the observed concentrations of OH remain unaffected in the presence of SiO 2 aerosol at mass concentrations of l mg m −3. In the presence of TiO 2 at 2 mg m −3 mass concentration, the steady-state concentration of OH is enhanced by an order of magnitude. In addition, a heterogeneous photodegradation process of the hydrocarbons occurs on the surface of the TiO 2 aerosol.

Kinetic distribution model for chemicals based on results from a standard environmental system

In order to reduce potential hazards to the environment resulting from production and use of chemicals, some governments have enacted laws and corresponding regulations. Thus, for instance, the German “law on hazardous substances,” and the regulation regarding a.o. submission of test data on physicochemical properties of new substances, have been ratified by the Federal Republic of Germany legislation in 1980 and 1981, respectively. This implies that before production, marketing, and use of a new chemical, its potential hazard to human beings and the environment has to be checked. Therefore it is necessary to have available accurate information about the probable fate of this new chemical in the environment, i.e., its distribution among the different environmental compartments. To this end, the submission of basic physicochemical data of a new chemical, such as boiling point, vapor pressure, water solubility, fat solubility, and partition coefficient in the system n-octanol/water, is mandatory for its registration. These data are meant to be used by the official evaluating department as a basis for describing the distribution behavior of the substance in the environment. However, there is no generally accepted procedure yet which would allow the reliable prediction. Such a calculation procedure should comprise all factors decisive for distribution and degradation of chemicals in the environment, according to their significance. We have taken a first step in this direction by carrying out the following experiments, with the aim of developing such a distribution model as well as identifying the physicochemical properties of chemicals required for the prediction of distribution patterns. The distribution patterns of 12 selected substances, having significant differences with respect to their physicochemical properties, were determined via radiotracer technique, in a defined, standardized, terrestrial ecosystem. The results of the experiments were compared with one another as well as with values calculated by use of mathematical models from the literature. These comparisons show that there are certain correlations between the distribution patterns obtained by experiments and those calculated by the stationary distribution models. However, these also indicate that some of the experimental findings cannot be explained within the framework of stationary distribution models. Kinetic models represent a more universal approach toward predicting the distribution of chemicals in an ecological system. Various prototypes are described in the literature but we could not use them due to their mathematical shortcomings. Therefore, we developed a kinetic model which provides the prediction formulas representing the probable distribution of chemicals in a standardized, terrestrial ecosystem, consisting of the compartments soil, plants, and air. The observed distribution patterns of the substances tested by us can be represented by two additive terms. The first one is defined by the conditions existing at the start of the distribution experiment in the standard ecosystem. The second term is specified by the physicochemical properties influencing the time course of the distribution process of the substance. These model parameters (diffusion, partition, and mass transfer coefficients as well as the velocity constants of the degradation processes) were adjusted to the data obtained from distribution experiments. The numerical values of the model parameters correlate satisfactorily with particular physicochemical characteristics of the substances while the model equations reproduce the experimentally determined distribution patterns as well as their time slope property. In summary, the distribution pattern of a chemical in the standardized terrestrial ecosystem can be predicted by mathematical calculation, if in addition to the parameters of the particular ecological system, the physicochemical characteristics of the substance, particularly Ostwald's solubility, soil/water partition coefficient, and kinetic constants of degradation processes are known. Additionally it is shown that there is the possibility of generalizing the kinetic model for the purpose of predicting distribution patterns of chemicals in nonstandardized ecological systems.

Stream Modeling of Non-Convetional Water Quality Parameters: Phenol, Cyanide, Ammonia, Oil and Grease

Due to complexities in the water uses of the modern time, the water quality management often needs much information in addition to the traditional DO and BOD data, to impose any kind of control on the industrial and municipal discharges into natural streams. The simplistic Monod type of substrate limiting kinetics are not sufficient to express the fate of complex chemicals such as phenol, cyanide, ammonia, oil and grease. This paper presents the kinetics of physical and biological degradation and transformation of such chemicals in the natural waters. The kinetics were developed through the multiple regression analysis using the data monitored over a year from a river in Pennsylvania, USA. The conventional unidirectional hydraulic transport and mass balance equations were then combined with these kinetics to predict the steady state water qualities in various reaches of the river under a specific set of known external discharges. When compared to the monitored water quality data under that specific set of external discharges, the predictions were found to be satisfactory. Some disagreement was observed in cyanide concentrations in the most down stream section of the 25 mile stretch of river.

Ein Beitrag zur Photostabilität organischer Umweltchemikalien in Gegenwart von Wasserstoffperoxid in aquatischen Systemen

It is well documented that the photolysis of H 2O 2 generates OH radicals which play an important role in explaining the degradation of environmental chemicals in aqueous medium. In the following work relative reaction rate constants of some representative substances were determined with wavelengths above 290 nm in the presence of H 2O 2. The results show, that the used system is suitable to check the OH radical reactivity of organic compounds under natural conditions.

Degradation of organic chemicals at trace levels in seawater and marine sediment. The effect of concentration on the initial fractional turnover rate

The initial degradation rates of 14C-phenol, 14C-N, N-dimethyl formamide and 14C-MCPA was investigated in freshly collected (non-adapted) seawater and marine sediment. A rapid and sensitive tracer method was used to measure mineralization at the ppb — ppt level. For all three substances, the initial fractional turnover rate increased with decreasing concentration. This concentration effect did not follow Michaelis-Menten kinetics. The effect was largest for the degradation of phenol inmarine sediment, corresponding to a 500 times increase in the initial fractional turnover rate per 10 4 times decrease in the concentration with the lowest concentration being 500 ng/liter. It is concluded that • — The degradation kinetics for the substances tested considered a non-volume basis proceed most rapidly at small concentrations. • — Tests for biodegradation representing the natural environment should be carried out at concentrations very close to the environmentally relevant concentrations which are often below the ppb-level.

Ecochemical assessment of environmental chemicals: Draft guideline of the test procedure to evaluate metabolism and degradationof chemicals by plant cell cultures

A guideline is drafted describing the screening procedure in detail. The aim for this is to facilitate an adoption of this test by bodies supervising environmental chemicals. Successful introduction of this method into the respective laboratories will cause no problems, as the procedure has been collaboratively established and improved.

Geochemical induced degradation of environmental chemicals

Attempts to correlate the concentration of organic chemicals in the environment with their production figures have resulted in a large deficit; this includes environmental chemicals such as chlorinated hydrocarbons. It has been assumed that analytical errors accounted for this deficit. Another explanation, however, allows for reactions of compounds under biotic and abiotic conditions. Because of the biostability of many organic chemicals biological transformation mechanisms can bring about slight charge only. By contrast, abiotic environmental factors such as the UV-irradiation or decomposition on natural surfaces contribute considerably to the transformation of this substance class. An investigation of such abiotic charges of organic chemicals must therefore pay particular attention to dynamic and catalytic effects primarily attributable to the respective molecular state and interactions with the environment. This paper deals with the photoinduced reactions of organic substances adsorbed on natural surfaces and their significance for the degradability of environmental chemicals.

Pentachlorophenol and 3,4-dichloroaniline as models for photochemical reactions in seawater

Pentachlorophenol (PCP) and 3,4-dichloroaniline (DCA) were used as models to examine photochemical reactions in seawater. The photolysis of PCP in seawater differed in both rate and product distribution from that in distilled water; rates were slower in seawater due to the photonucleophilic interaction of PCP with chloride ions, demonstrated by the formation of 36Cl-labeled PCP in irradiated PCP solutions containing Na 36Cl. DCA showed no rate change and gave identical products in both systems. Both PCP and DCA yielded greater amounts of photoreduction products in seawater than in distilled water, and tetrachloromuconic acid was isolated and identified as a new and unstable PCP photoproduct resulting from ringfission. This study demonstrates the operation of photooxidation, photonucleophilic substitution, and photoreduction reactions which differ in detail between seawater and distilled water and suggests that photochemical reactions can be a major factor in the breakdown of organic pollutants and other chemicals in the marine environment.