Biodegradation Half-lives Research Articles

Biodegradability relationships among propylene glycol substances in the organization for Economic Cooperation and Development ready‐ and seawater biodegradability tests

Eight propylene glycol substances, ranging from 1,2-propanediol to a poly(propylene glycol) (PPG) having number-average molecular weight (M(n)) of 2,700 (i.e., PPG 2700), were evaluated in the Organization for Economic Cooperation and Development (OECD) ready- and seawater biodegradability tests. Uniformity in test parameters, such as inoculum source/density and test substance concentrations, combined with frequent measurements of O2 consumption and CO2 evolution, revealed unexpected biodegradability trends across this family of substances. Biodegradability in both tests decreased with increased number of oxy-propylene repeating units (n = 1, 2, 3, 4) of the oligomeric propylene glycols (PGs). However, this trend was reversed for the PPG polymers, and increased biodegradability was observed with increases of average n to seven, 17, and 34 (M(n) = 425, 1,000, and 2,000, respectively). This relationship between molecular weight and biodegradability was reversed again when average n was incremented from 34 (PPG 2000) to 46 (PPG 2700). Six of the tested substances (n = 1, 2, 3, 7, 17, and 34) met the OECD-specified criteria for "ready biodegradability," whereas the tetrapropylene glycol (n = 4) and PPG 2700 substances failed to meet these criteria. Biodegradation half-lives for these eight substances ranged from 3.8 d (PPG 2000) to 33.2 d (PPG 2700) in the ready test, and from 13.6 (PG) to 410 d (PPG 2700) in seawater. Biodegradation half-lives in seawater were significantly correlated with half-lives determined in the ready test. However, half-lives in both tests were correlated poorly with molecular weight, water solubility, and log K(ow). It is speculated that the molecular conformation of these substances, perhaps more so than these other physicochemical properties, has an important role in influencing biodegradability of the propylene glycol substances.

Biological degradation of triclocarban and triclosan in a soil under aerobic and anaerobic conditions and comparison with environmental fate modelling

Triclocarban and triclosan are two antimicrobial agents widely used in many personal care products. Their biodegradation behaviour in soil was investigated by laboratory degradation experiments and environmental fate modelling. Quantitative structure–activity relationship (QSAR) analyses showed that triclocarban and triclosan had a tendency to partition into soil or sediment in the environment. Fate modelling suggests that either triclocarban or triclosan “does not degrade fast” with its primary biodegradation half-life of “weeks” and ultimate biodegradation half-life of “months”. Laboratory experiments showed that triclocarban and triclosan were degraded in the aerobic soil with half-life of 108 days and 18 days, respectively. No negative effect of these two antimicrobial agents on soil microbial activity was observed in the aerobic soil samples during the experiments. But these two compounds persisted in the anaerobic soil within 70 days of the experimental period.

Developing Methods to Predict Chemical Fate and Effect Endpoints for Use Within REACH

With the pending implementation of REACH, both old and new chemicals will have to be registered and chemical safety reports will have to be compiled. Depending on the yearly tonnages produced or imported, (eco-) toxicological and chemical fate data of varying degrees of detail will have to be produced. It has been forecast that these new requirements will result in higher costs for registration and an increased need for animal testing. Some of this additional workload could be avoided by making use of in vitro or in silico prediction methods. At Eawag (Swiss Federal Institute of Aquatic Science and Technology) several research groups are working on the development and validation of quantitative structure–activity relationships (QSARs) and related methods to predict ecotoxicological and fate endpoints, such as reactivities in or partitioning between different environmental media, based on chemical structure or easily measurable physico-chemical properties. When developing such tools, special attention has to be paid to use only descriptors whose mechanistic significance for the modelled endpoint is well understood on a molecular level. In this article four examples of our work in the field of compound fate and effect predictions will be presented: i) the measurement of compound descriptors for use in linear-free-energy relationships to predict partition coefficients between environmental media; ii) the development of free-energy relationships for the prediction of indirect photolysis; iii) the evaluation of existing structure-biodegradability models to predict soil biodegradation half-lives; and iv) the application of mode-of-action-based test batteries to develop quantitative structure–activity relationships to classify chemicals according to their modes of toxic action.

Integration of biodegradation half-life model and oil toxicity model into a diagnostic tool for assessing biorernediation technology

An integration of a natural biodegradation half-life model and oil toxicity model has resulted in a precise, fine-tuned science-based technology for evaluating success of bioremediation strategies, particularly for crude oil-contaminated soil. By extension, this mathematical tool can be applied for impact assessment of crude oil on land at a given time. This Methods paper focuses on both the use of diazotrophic bacteria in evaluating toxicity of a given crude oil and natural biodegradation half-life of the petroleum hydrocarbon in the given ecosystem, the ultimate goal being the development of a diagnostic tool for best decision making in the allocation of limited financial resources and best options for bioremediation strategies.

Estimating biodegradation half-lives for use in chemical screening

Biodegradation half-lives are needed for many applications in chemical screening, but these data are not available for most chemicals. To address this, in phase one of this work we correlated the much more abundant ready and inherent biodegradation test data with measured half-lives for water and soil. In phase two, we explored the utility of the BIOWIN™ models (in EPI Suite™) and molecular fragments for predicting half-lives. BIOWIN™ model output was correlated directly with measured half-lives, and new models were developed by re-regressing the BIOWIN™ fragments against the half-lives. All of these approaches gave the best results when used for binary (fast/slow) classification of half-lives, with accuracy generally in the 70–80% range. In the last phase, we used the collected half-life data to examine the default half-lives assigned by EPI Suite™ and the PBT Profiler™ for use as input to their level III multimedia models. It is concluded that estimated half-lives should not be used for purposes other than binning or prioritizing chemicals unless accuracy improves significantly.

A new biodegradation prediction model specific to petroleum hydrocarbons

A new predictive model for determining quantitative primary biodegradation half-lives of individual petroleum hydrocarbons has been developed. This model uses a fragment-based approach similar to that of several other biodegradation models, such as those within the Biodegradation Probability Program (BIOWIN) estimation program. In the present study, a half-life in days is estimated using multiple linear regression against counts of 31 distinct molecular fragments. The model was developed using a data set consisting of 175 compounds with environmentally relevant experimental data that was divided into training and validation sets. The original fragments from the Ministry of International Trade and Industry BIOWIN model were used initially as structural descriptors and additional fragments were then added to better describe the ring systems found in petroleum hydrocarbons and to adjust for nonlinearity within the experimental data. The training and validation sets had r2 values of 0.91 and 0.81, respectively.

Natural Attenuation Rate Clarifications: The True Picture is in the Details

The term “Natural Attenuation” (NA) has been defined as naturally occurring processes in soil and groundwater environments that act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in those media. Monitored natural attenuation (MNA) protocols generally involve the collection of biogeochemical data from groundwater monitoring wells at sites. The data are correlated in time and space with the various chemicals of concern (COC's) to establish predominant biodegradation mechanisms. Modelers using the first-order decay expression typically use the rate coefficient as a calibration parameter and adjust it until the transport model results match field data. With this approach, uncertainties with a number of parameters (e.g., dispersion, sorption, biodegradation, etc.) are lumped together in a single calibration parameter. The problems associated with the lumped parameter approach are illustrated using two commonly used models, BIOSCREEN and Buscheck/Alcantar Analytical Solution, in a variety of practical examples. The natural attenuation decay rate estimated using the lumped parameter approach is distinguished from a biodegradation rate established by isolating processes and examining biodegradation lines of evidence. The half-life determined from empirical data using the lumped parameter approach is often mistakenly interchanged with a biodegradation half-life when it is an all-encompassing half-life based on the interaction of numerous processes. Isolation of the processes, as they are represented in the governing transport equation, and a rationale approach at parameter estimation to avoid the potential pitfalls of the all-inclusive “attenuation rate,” are provided.In closing, it is imperative to implement the following steps to dissern lumped process degradation rates from biodegradation half-lives: (a) be sure the rate/half-life processes are clarified as to what they encompass, (b) establish exactly how the rate/half-life was determined, (c) make certain other processes, such as dispersion, were estimated correctly, and (d) if the half-life is presented as a first-order biodegradation rate, examine the available lines of evidence to substantiate it.

An examination of the physical properties, fate, ecotoxicity and potential environmental risks for a series of propylene glycol ethers.

Propylene glycol ethers (PGEs) are comprised of mono-, di- and tri-PGEs and several of their acetate esters. The nature of the range of applications that use PGEs suggests that there is a potential for both intentional and unintentional entry of the materials into the environment. Selected physical/chemical properties, fate characteristics, aquatic toxicity data and calculated environmental concentrations were used to assess potential risks from the manufacture, handling, use, and disposal of PGEs. In general, the PGEs are low to moderately volatile, have high aqueous solubilities, low octanol-water partition coefficients (Kow), and bioconcentration factor values of <10, which indicate they are unlikely to accumulate in aquatic food chains. Both abiotic and biological degradation processes reduce environmental concentrations of PGEs. In air, vapor-phase PGEs react with photo-chemically produced hydroxyl radicals and have half-lives ranging from 5.5 to 34.4 h. A variety of ready and inherent biodegradation test methods, as well as tests that simulate biodegradation in wastewater treatment plants, surface water and soil have been conducted on PGEs. Significant aerobic biodegradation was generally observed, with a range of biodegradation half-lives on the order of 5-25 d. Acute aquatic toxicity studies with PGEs resulted in LC50 values ranging from approximately >100 to >20,000 mg/l for freshwater fish, the pelagic invertebrate Daphnia magna, green algae Selenastrum capricornutum (now called Pseudokirchneriella capricornutum) and bacteria. Level 3 multi-media modeling (EQC model of Mackay) was used to simulate regional-scale concentrations of PGEs in air, soil, water, and sediment. Toxicity thresholds were then compared with regional-scale water, soil and sediment concentrations to determine hazard quotients. Based upon this analysis, concentrations of PGEs are unlikely to pose adverse risks to the environment.

Biodegradability of Di(2-Ethylhexyl) Phthalate by Pseudomonas Fluorescens FS1

Di(2-ethylhexyl)phthalate (DEHP), one of high-molecular weight phthalate esters (PAEs), is used in the manufacturing of polyvinylchloride (PVC) resins, polyvinyl acetate, cellulosics, and polyurethanes, and contributes to environmental pollution. In this article, the characteristics of DEHP biodegradation by an effective degradation bacterium, Pseudomonas fluorescens FS1 that isolated from the activated sludge at a petrochemical factory, was capable of using phthalate esters as the sole carbon and energy source, were investigated. Experimental results showed that the biodegradation of DEHP by P. fluorescens FS1 could be described by the first-order reaction model, which could be expressed as: lnC = -0.0688t + A, and the half-life of DEHP biodegradation was 10.07 d when the initial concentrations of DEHP were less than 50 mg L −1 . The inhibition effects of DEHP as a substrate had become predominant above the concentration of 50 mg L −1 . The PAEs-degrading enzyme of P. fluorescens FS1, mainly located in the soluble part and the particle of cytoplasm, was an intracellular enzyme. The metabolites of DEHP degradation by P. fluorescens FS1, which monoester, phthalic acid, benzonic acid, phenol, were extracted using dichloromethane at different time intervals and identified by the GC-MS. The tentative pathway proposed for degradation of DEHP by P. fluor- escens FS1 under aerobic condition is monoester in the beginning, further enzymatic degradation of the monoester produces phthalic acid, benzonic acid, phenol and finally CO2 and H2O.

Biodegradation of bisphenol a in aquatic environments: River die‐away

The biodegradability of bisphenol A (BPA) was assessed in surface waters from seven different rivers across the United States and Europe. Rapid biodegradation of BPA was observed in all rivers following lag phases ranging from 2 to 4 d. Biodegradation half-lives for BPA were typically less than 2 d following the lag phase. Mineralization of BPA was observed in all river waters, with average carbon dioxide yields of approximately 76% of the theoretical maximum (range 59-103%) at the end of the incubation period (< or = 18 d). Short half-lives (0.5 to 3 d) were noted for BPA biodegradation in river waters regardless of geographic location, sampling site (i.e., upstream vs downstream of wastewater outfalls), sediment addition (< or = 0.05%), and initial test chemical concentration (50-5,500 microgram/L). Subsequent studies conducted at environmentally relevant concentrations (0.05 and 0.5 microgram/L) also indicated short half-lives (3-6 d) for BPA and support the extrapolation of the half-lives measured in this study over a wide range of environmental concentrations. The fact that BPA was degraded rapidly in surface waters taken from diverse locations in the United States and Europe as well as in studies recently conducted in Japan suggests that BPA degrading microorganisms are widely distributed in nature. These observations provide clear evidence that BPA is not persistent in the aquatic environment.

Seasonal factors affecting surfactant biodegradation in Antarctic coastal waters: comparison of a polluted and pristine site

This report is the first seasonal study of anthropogenic pollutant biodegradation rates in Antarctic coastal waters. The capacity of surface waters from Rothera Research Station, Adelaide Island, Antarctica, to biodegrade the anionic surfactant sodium dodecyl sulphate (SDS) was quantified in biodegradation tests from April 1988 to January 1999. Large temporal differences in the persistence of SDS were observed. In mid-winter (July), the SDS-biodegradation half life was twice that measured in mid-summer (January), despite small temperature differences (up to 2.45 °C). Comparisons between water from a pristine site and a site receiving grey-waste water from the station showed that some acclimation to SDS was occurring in the contaminated water. This resulted in SDS half lives up to ∼80 h shorter in the polluted water compared with the pristine site in the summer months when a large population of SDS-degrading bacteria had developed. Biodegradation half lives in Antarctic coastal waters (160–460 h) were generally far higher than those observed in temperate waters.

Ultimate biodegradation of alkylphenol ethoxylate surfactants and their biodegradation intermediates

The ultimate biodegradation of the commercial products nonylphenol ethoxylates (NPE9), octylphenol ethoxylates (OPE9), and their biodegradation intermediates, NPE1.5, OPE1.5, NP, and OP, was measured using conventional methods. The extent of biodegradation was also determined by gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography (HPLC) analysis of metabolites and measurement of dissolved organic carbon. Optimized pseudo-first order degradation rate constants and half-lives were calculated from these data and from previously published data, using Larson's equation for surfactant degradation kinetics. Ultimate aerobic biodegradation of alkylphenol ethoxylates and their biodegradation intermediates has now been examined using acclimated wastewater treatment plant sludge as the microbial seed, household wastewater treatment systems, and unacclimated fresh water, seawater, and soil. Ultimate biodegradation half-lives ranged from about one to four weeks and provide definitive evidence for the extensive biodegradability of alkyphenol ethoxylates (APE) surfactants and their metabolites and their lack of persistence in the environment.

Sensitivity analysis of a soil leachability model for petroleum fate and transport in the vadose zone

Risk-based assessment methods are commonly used at petroleum-contaminated sites. In South Carolina, the Soil Leachability Model (SLM) is used to calculate site-specific target levels (SSTLs) for soils that may leach contaminants to groundwater. The SLM is a series of analytical equations that is based upon the Green and Ampt equation to predict infiltration rates and accounts for equilibrium partitioning and first-order biodegradation of the contaminant as it travels to groundwater. To reduce costs, many soil property inputs to the model are estimated using regression equations that relate textural classification to these physical properties. It was not known what effect errors in these inputs might have on the SSTLs computed with the SLM. Thus, a sensitivity analysis was performed to determine the influence of parameter variability on benzene and naphthalene SSTLs computed for three soil types and two groundwater depths. The results of this study indicate that SSTLs computed with the SLM are very sensitive to organic carbon content and biodegradation half-lives for sand, loam, and clay, saturated hydraulic conductivity for loam and clay and most soil input parameters for clay. Overestimation of organic carbon content or underestimation of biodegradation half-lives in sand, loam or clay, or underestimation of the saturated hydraulic conductivity in loam or clay can result in SSTLs that are orders of magnitude too large, and therefore, potentially unconservative.

Bioremediation of MTBE: a review from a practical perspective.

The addition of methyl tert-butyl ether (MTBE) to gasoline has resulted in public uncertainty regarding the continued reliance on biological processes for gasoline remediation. Despite this concern, researchers have shown that MTBE can be effectively degraded in the laboratory under aerobic conditions using pure and mixed cultures with half-lives ranging from 0.04 to 29 days. Ex-situ aerobic fixed-film and aerobic suspended growth bioreactor studies have demonstrated decreases in MTBE concentrations of 83% and 96% with hydraulic residence times of 0.3 hrs and 3 days, respectively. In microcosm and field studies, aerobic biodegradation half-lives range from 2 to 693 days. These half-lives have been shown to decrease with increasing dissolved oxygen concentrations and, in some cases, with the addition of exogenous MTBE-degraders. MTBE concentrations have also been observed to decrease under anaerobic conditions; however, these rates are not as well defined. Several detailed field case studies describing the use of ex-situ reactors, natural attenuation, and bioaugmentation are presented in this paper and demonstrate the potential for successful remediation of MTBE-contaminated aquifers. In conclusion, a substantial amount of literature is available which demonstrates that the in-situ biodegradation of MTBE is contingent on achieving aerobic conditions in the contaminated aquifer.

Environmental risk assessment for the polycyclic musks AHTN and HHCB in the EU: I. Fate and exposure assessment

For the environmental exposure assessment of the fragrance ingredients 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN) and 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-γ-2-benzopyran (HHCB) the following properties were determined: vapour pressure 0.0682 and 0.0727 Pa; water solubility 1.25 and 1.75 mg/l; log K ow 5.7 and 5.9; log K oc 4.80 and 4.86; bioconcentration factor in fish: 597 and 1584 (fresh weight) for AHTN and HHCB, respectively. Both substances are degraded to more polar metabolites in fish, in soil and during sewage treatment. A review is made of concentrations measured in sludge, in freshwater and marine systems including suspended matter, sediment and fish. The 90th-percentile in more than 200 surface water samples is 0.3 μg/l for AHTN and 0.5 μg/l for HHCB. The 90th-percentile of the concentrations in fish is 0.12 mg/kg fresh weight for both substances ( n=27). These concentrations are lower by a factor of 5–15 than predicted on the basis of the yearly use volumes in Europe, 585 tonnes for AHTN and 1482 tonnes for HHCB. Concentrations in sludge-amended soils and in earthworms are predicted based on concentrations measured in sludge. For AHTN, the predicted values are: PEC soil, 0.029 mg/kg and PEC worm, 0.065 mg/kg while for HHCB the corresponding figures are 0.032 and 0.099 mg/kg. These concentrations assume a biodegradation half-life in the soil of 180 days based on preliminary soil biodegradation data.

Water-Resistant Film from Polyurethane/Nitrocellulose Coating to Regenerated Cellulose

Water-resistant films were obtained from polyurethane (PU)/nitrocellulose coating to regenerated cellulose films, which were prepared by coagulating cellulose cuoxam solution. The PU/nitrocellulose coating layer was cured at 80 °C for 2 min and formed semi-interpenetrating polymer networks (semi-IPNs) structure. The tensile strength (σb), water resistivity (R), water vapor permeability (P), and light transmittance of the coated films changed with nitrocellulose content in the coating, and the best values (such as σb, 679 kg·cm-2; R, 53%; P, 0.004 g·cm-2·day-1) were attained at 33 wt % nitrocellulose. The TEM, EPMA, DTA, IR, and UV results showed that the coated films have strong interfacial bonding, which is caused by covalent and hydrogen bonds between the cellulose film and the semi-IPNs coating. The biodegradation half-life t1/2 of the coated films in soil at 20−30 °C was given to be 58 days, and after about 6 months the coated films were almost completely decomposed by microorganisms. SEM and the kine...

Bayesian Model for Fate and Transport of Polychlorinated Biphenyl in Upper Hudson River

Modelers of contaminant fate and transport in surface waters typically rely on literature values when selecting parameter values for mechanistic models. While the expert judgment with which these selections are made is valuable, the information contained in contaminant concentration measurements should not be ignored. In this full-scale Bayesian analysis of polychlorinated biphenyl (PCB) contamination in the upper Hudson River, these two sources of information are combined using Bayes’ theorem. A simulation model for the fate and transport of the PCBs in the upper Hudson River forms the basis of the likelihood function while the prior density is developed from literature values. The method provides estimates for the anaerobic biodegradation half-life, aerobic biodegradation plus volatilization half-life, contaminated sediment depth, and resuspension velocity of 4,400 d, 3.2 d, 0.32 m, and 0.02 m/yr, respectively. These are significantly different than values obtained with more traditional methods, and are shown to produce better predictions than those methods when used in a cross-validation study.

Quantitative application of biodegradation data to environmental risk and exposure assessments

AbstractBiodegradation is an important removal mechanism for natural and synthetic organic chemicals released to aquatic, benthic, and terrestrial ecosystems. It results in a decrease in the overall mass or load of chemicals present in the environment and is key in preventing the accumulation and persistence of chemicals in specific environmental compartments. Although biodegradation is an important process for minimizing potential adverse impacts on environmental systems, it has not been traditionally considered in a quantitative fashion in environmental risk assessments. This article outlines an approach and provides simple kinetic criteria for incorporating biodegradation rate data into environmental exposure and risk assessments. The approach is a generic one that relates biodegradation half‐lives to chemical residence times in specific environmental compartments. It is broadly applicable to any organic chemical in a range of environmental compartments and has potential use as a technical and regulatory tool to better quantify environmental exposure and risk.

Factors for intermedia extrapolation in biodegradability assessment

In screening-level biodegradability assessment for xenobiotic chemicals it is often necessary to extrapolate from one environmental medium or set of conditions to another, to derive an estimate of biotransformation rate in the medium of interest. To develop a basis for such extrapolation we conducted a comparative analysis of biodegradation data from grab sample studies, focusing on (i) relative rates of aerobic biodegradation in fresh water and surface soil; and (ii) relative rates of aerobic and anaerobic biodegradation in surface soil. The results of this data review are expressed as a series of factors that represent ratios of biodegradation half-lives under the respective conditions. These factors may be used in chemical screening and in setting priorities for further review.

Quantitative assessment of the effects of metals on microbial degradation of organic chemicals

Biodegradation inhibition of a benchmark chemical, 2,4-dichloro-phenoxyacetic acid methyl ester (2,4-DME), was used to quantify the inhibitory effects of heavy metals on aerobic microbial degradation rates of organic chemicals. This procedure used lake sediments and aufwuchs (floating mats) collected in the field or from laboratory microcosms. Effects of CuCl2, HgCl2, ZnCl2, Cd(NO3)2, and Cr(NO3)3 at initial concentrations ranging from 0.3 microM to 73 mM (approximately 0.1 to 10,000 mg liter-1) were investigated. In general, such metallic compounds appeared to be considerably more inhibitory to the biodegradation of an organic chemical than high concentrations of microbially toxic organics studied previously. Effects of various metal concentrations were evaluated based on the following: (i) estimated MICs, (ii) concentrations that caused a significant effect on biodegradation parameters (both a greater than 10% decrease in Vmax and a greater than 10% increase in t1/2 for 2,4-DME degradation), and (iii) concentrations that caused biodegradation half-life doublings (HLDs). The MICs of metals in sediment were lowest for Zn2+ (0.10 microM) and highest for Cd2+ and Cu2+ (0.9 and 1.2 microM, respectively). The MICs of metals in aufwuchs were lowest for Hg2+ (0.01 microM), intermediate for Cu2+ and Zn2+ (0.42 and 0.62 microM, respectively), and highest for Cr3+ and Cd2+ (3.4 and 5.6 microM, respectively). Compared with Cu2+ on aufwuchs, 70 times more Zn2+, 250 times more Cr3+, and 1,000 times more Cd2+ was required to significantly affect aufwuchs biodegradation rate parameters and coefficients (Vmax and t1/2). Aufwuchs was significantly affected by the lowest Hg2+ concentration tested (5 microM).(ABSTRACT TRUNCATED AT 250 WORDS)