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At least 199 records · Page 11Linked to original sources

PubMed2002

Hydrogen isotopic enrichment: an indicator of biodegradation at a petroleum hydrocarbon contaminated field site.

Compound-specific carbon and hydrogen isotope analysis was used to investigate biodegradation of benzene and ethylbenzene in contaminated groundwater at Dow Benelux BV industrial site. delta13C values for dissolved benzene and ethylbenzene in downgradient samples were enriched by up to 2+/-0.5 per thousand, in 13C, compared to the delta13C value of the source area samples. delta2H values for dissolved benzene and ethylbenzene in downgradient samples exhibited larger isotopic enrichments of up to 27+/-5 per thousand for benzene and up to 50+/-5 per thousand for ethylbenzene relative to the source area. The observed carbon and hydrogen isotopic fractionation in downgradient samples provides evidence of biodegradation of both benzene and ethylbenzene within the study area at Dow Benelux BV. The estimated extents of biodegradation of benzene derived from carbon and hydrogen isotopic compositions for each sample are in agreement, supporting the conclusion that biodegradation is the primary control on the observed differences in carbon and hydrogen isotope values. Combined carbon and hydrogen isotope analyses provides the ability to compare biodegradation in the field based on two different parameters, and hence provides a stronger basis for assessment of biodegradation of petroleum hydrocarbon contaminants.

Biodegradation, Environmental↗

PubMed2003

Soil column evaluation of factors controlling biodegradation of DNT in the vadose zone.

High concentrations of 2,4-dinitrotoluene (2,4-DNT) and 2,6-dinitrotoluene (2,6-DNT) are present in vadose zone soils at many facilities where explosives manufacturing has taken place. Both DNT isomers can be biodegraded under aerobic conditions, but rates of intrinsic biodegradation observed in vadose zone soils are not appreciable. Studies presented herein demonstrate that nutrient limitations control the onset of rapid 2,4-DNT biodegradation in such soils. In column studies conducted at field capacity, high levels of 2,4-DNT biodegradation were rapidly stimulated by the addition of a complete mineral medium but not by bicarbonate-buffered distilled deionized water or by phosphate-amended tap water. Biodegradation of 2,6-DNT was not observed under any conditions. Microcosm studies using a DNT-degrading culture from column effluent suggest that, after the onset of 2,4-DNT degradation, nitrite evolution will eventually control the extent of degradation achieved by two mechanisms. First, high levels of nitrite (40 mM) were found to strongly inhibit 2,4-DNT degradation. Second, nitrite production reduces the solution pH, and at pH levels below 6.0, 2,4-DNT degradation slows rapidly. Under conditions evaluated in laboratory-scale studies, 2,4-DNT biodegradation enhanced the rate of contaminant loss from the vadose zone by a factor of 10 when compared to the washout due to leaching.

Biodegradation, Environmental↗

PubMed2005

Enrichment of stable carbon and hydrogen isotopes during anaerobic biodegradation of MTBE: microcosm and field evidence.

The conventional approach to evaluate biodegradation of organic contaminants in groundwater is to demonstrate an increase in the concentration of transformation products. This approach is problematic for MTBE from gasoline spills because the primary transformation product (TBA) can also be a component of gasoline. Compound-specific stable isotope analysis may provide a useful alternative to conventional practice. Changes in the delta13C and deltaD of MTBE during biodegradation of MTBE in an anaerobic enrichment culture were compared to the delta13C and deltaD of MTBE in groundwater at nine gasoline spill-sites. The stable isotopes of hydrogen and carbon were extensively fractionated during anaerobic biodegradation of MTBE. The stable isotope enrichment factor for carbon (epsilonC) in the enrichment cultures was -13 (-14.1 to -11.9 at 95% confidence level), and the hydrogen enrichment factor (epsilonH) was -16 (-21 to -11 at 95% confidence level). The isotope enrichment factors for carbon and hydrogen during anaerobic biodegradation indicate that the first reaction is enzymatic hydrolysis of the O-Cmethyl bond. The ratio of epsilonH to epsilonC was consistent between the enrichment culture and the field site that provided the inoculum, and with the other eight sites, suggesting a common degradation pathway. Compound-specific isotope evidence is discussed in terms of its utility for monitoring in situ biodegradation, in particular, for measuring how much MTBE was degraded. For the studied field sites, significant biodegradation of the original mass of MTBE is suggested, in some cases exceeding 90%.

Accidents↗

PubMed2005

Polycyclic aromatic hydrocarbon biodegradation rates: a structure-based study.

This study was designed to examine the role of molecular structure in determining the biodegradation rates of polycyclic aromatic hydrocarbons (PAHs). Laboratory experiments were performed in aqueous systems, and data were analyzed in a manner that allowed determination of first-order biodegradation rates independent of bioavailability limitations from physical-chemical processes. An aerobic mixed culture was used, which had been enriched on a broad range of PAHs. The 22 PAHs included in this study ranged in size from two to four rings and included compounds with 5-carbon rings and alkyl substituents. The range of observed biodegradation rates was only 1 order of magnitude, which is much less than that which is typically observed in the field. This supports the findings of other types of studies, which conclude that most of the observed variation in environmental PAH biodegradation rates comes from processes controlling the bioavailability of the compounds and not processes controlling uptake or biotransformation. Rate differences that were observed were attributable either to the presence of a 5-carbon ring or an alkyl substituent in an alpha position. Various molecular descriptors that might be expected to correlate with rate-limiting steps in the biodegradation process were used in an attemptto develop a quantitative structure-activity relationship for the PAH biodegradation rates. No significant correlations were found, but rate limitation from interactions with the relevant enzymes remains a possibility.

Aerobiosis↗

PubMed2005

New evaluation scheme for two-dimensional isotope analysis to decipher biodegradation processes: application to groundwater contamination by MTBE.

Compound-specific analysis of stable carbon and hydrogen isotopes was used to assess the fate of the gasoline additive methyl tert-butyl ether (MTBE) and its major degradation product tert-butyl alcohol (TBA) in a groundwater plume at an industrial disposal site. We present a novel approach to evaluate two-dimensional compound-specific isotope data with the potential to identify reaction mechanisms and to quantify the extent of biodegradation at complex field sites. Due to the widespread contaminant plume, multiple MTBE sources, the presence of numerous other organic pollutants, and the complex biogeochemical and hydrological regime atthe site, a traditional mass balance approach was not applicable. The isotopic composition of MTBE steadily changed from the source regions along the major contaminant plume (-26.4% to +40.0% (carbon); -73.1% to +60.3% (hydrogen)) indicating substantial biodegradation. Constant carbon isotopic signatures of TBA suggest the absence of TBA degradation at the site. Published carbon and hydrogen isotope fractionation data for biodegradation of MTBE under oxic and anoxic conditions, respectively, were examined and used to determine both the nature and the extent of in-situ biodegradation along the plume(s). The coupled evaluation of two-dimensional compound-specific isotope data explained both carbon and hydrogen fractionation data in a consistent way and indicate anaerobic biodegradation of MTBE along the entire plume. A novel scheme to reevaluate empiric isotopic enrichment factors (epsilon) in terms of theoretically based intrinsic carbon (12k/13k) and hydrogen (1k/2k) kinetic isotope effects (KIE) is presented. Carbon and hydrogen KIE values, calculated for different potential reaction mechanisms, imply that anaerobic biodegradation of MTBE follows a SN2-type reaction mechanism. Furthermore, our data suggest that additional removal process(es) such as evaporation contributed to the overall MTBE removal along the plume, a phenomenon that might be significant also for other field sites at tropic or subtropic climates with elevated groundwater temperatures (25 degrees C).

Bacteria, Anaerobic↗

PubMed2005

Biodegradability, DBP formation, and membrane fouling potential of natural organic matter: characterization and controllability.

Various natural organic matter (NOM) constituents were evaluated in terms of their biodegradability, disinfection byproduct (DBP) formation potentials, and membrane fouling. The biodegradability of NOM was evaluated with respect to biodegradable dissolved organic carbon (BDOC) and its inhibition control. NOM was divided into (i) colloidal and noncolloidal NOM, using a dialysis membrane with a molecular weight cutoff of 3500 Da and (ii) hydrophobic, transphilic, and hydrophilic NOM constituents, using XAD-8/4 resins. The colloidal, and noncolloidal hydrophilic, NOM were identified as being more problematic than the other components, exhibiting relatively higher biodegradability and reactivity toward DBP formation potential. A higher biodegradability especially can provide a high risk of membrane biofouling, if a membrane is fouled by highly biodegradable NOM. Colloidal, and noncolloidal hydrophilic, NOM constituents were also shown as major foulants of negatively charged membranes due to their high neutral fractions. Filter adsorber (F/A) types of activated carbons were evaluated in terms of removals of NOM, DBP formation potential, and BDOC and were compared to conventional processes and a nanofiltration membrane. The F/A process exhibited a comparatively good efficiency, especially in DBP and BDOC control, but was not so good at removing NOM. This suggests that F/A could potentially be combined with a membrane process to minimize the DBP formation potential and bio-/organic-fouling (i.e., F/A process as a pretreatment for a membrane process).

Biodegradation, Environmental↗

PubMed2003

Effect of expandable clays and cometabolism on PAH biodegradability.

Pyrene and phenanthrene degradation was examined in both single and binary slurry systems for three different natural soils. It was found that the amount of total expandable clays (smectite and vermiculite) was in a good agreement with the achieved rate and extent of biodegradation. For instance, the intrinsic phenanthrene biodegradation rate was 626 microg/L/day for the soil with the largest expandable clay and 3203 microg/L/day for the soil with the least. Similarly, the smallest total pyrene biodegradation (65%) was found for the soil rich in expandable clays, compared to an 82% pyrene reduction in the soil that had the lowest amount. Mass transfer limitation after compound sorption to the clays was more pronounced for the more hydrophobic pyrene. In the presence of phenanthrene, total pyrene biodegradation increased by 2 to 7% due to cometabolism, while the total phenanthrene biodegradation was only enhanced by 0.5 to 5% in the binary system. This research demonstrated that expandable clays might govern the substrate availability to microorganisms and microbial accessibility to substrates. Therefore, the contribution of organic matter and expandable clays to sorption, desorption and biodegradation should be taken equally into account in order to better understand complex bioremediation issues.

Aluminum Silicates↗

PubMed2002

Probabilistic assessment of biodegradability based on metabolic pathways: catabol system.

A novel mechanistic modeling approach has been developed that assesses chemical biodegradability in a quantitative manner. It is an expert system predicting biotransformation pathway working together with a probabilistic model that calculates probabilities of the individual transformations. The expert system contains a library of hierarchically ordered individual transformations and matching substructure engine. The hierarchy in the expert system was set according to the descending order of the individual transformation probabilities. The integrated principal catabolic steps are derived from set of metabolic pathways predicted for each chemical from the training set and encompass more than one real biodegradation step to improve the speed of predictions. In the current work, we modeled O2 yield during OECD 302 C (MITI I) test. MITI-I database of 532 chemicals was used as a training set. To make biodegradability predictions, the model only needs structure of a chemical. The output is given as percentage of theoretical biological oxygen demand (BOD). The model allows for identifying potentially persistent catabolic intermediates and their molar amounts. The data in the training set agreed well with the calculated BODs (r2 = 0.90) in the entire range i.e. a good fit was observed for readily, intermediate and difficult to degrade chemicals. After introducing 60% ThOD as a cut off value the model predicted correctly 98% ready biodegradable structures and 96% not ready biodegradable structures. Crossvalidation by four times leaving 25% of data resulted in Q2 = 0.88 between observed and predicted values. Presented approach and obtained results were used to develop computer software for biodegradability prediction CATABOL.

Biodegradation, Environmental↗

PubMed2002

Effect and mechanism of inorganic carbon on the biodegradation of dimethyl phthalate by Chlorella pyrenoidosa.

The effect and mechanism of inorganic carbon (IC) on the biodegradation of dimethyl phthalate (DMP) by a green microalga Chlorella pyrenoidosa was investigated. It was indicated that DMP could be used as the sole carbon source to support the slow heterotrophic growth of C. pyrenoidosa, but both the growth of C. pyrenoidosa and the biodegradation rate of DMP were obviously increased when initial inorganic carbon concentration (IC) was increased from 0.6 to 23.7 mg/l. Phthalic acid (PA) was found to be an intermediate product of DMP biodegradation and accumulated in the culture solution, which caused a sharp decrease in pH of medium and inhibited both the growth of alga and the biodegradation of DMP. The role of IC for improving the biodegradation of DMP was both to supply a favorite carbon source to support the rapid growth of alga and to mitigate the decrease of pH because of the production of PA. A suggested second-order kinetic equation of organic pollutant biodegradation by microalgae (-dC/dt = KNr) fitted well with the experimental data and the correlation coefficients were all above 0.9. The second-order constant (K) apparently declined with the increase of initial IC because lower ratio between organic carbon from DMP and IC was used to support the growth of alga when initial IC increased.

Biodegradation, Environmental↗

PubMed1994

A comparative study of the effects of biodegradable and titanium plating systems on cranial growth and structure: experimental study in beagles.

An experimental study was conducted in beagles to assess the effects of biodegradable and titanium plating systems on cranial growth and structure. Forty-eight 9-week-old purebred beagles were used in this study. To avoid any effects of sexual dimorphism, we used only female beagles. The animals were divided in three groups: sham-operated controls, n = 16; beagles implanted with commercially available titanium plates and screws, n = 16; and beagles implanted with biodegradable plates and screws, n = 16. The biodegradable plating system developed by Storz Instrument Company (St. Louis, Mo.) for use in the craniofacial skeleton does not require another procedure to remove plates and screws once the healing process is completed. To assess the dynamics of changes in cranial growth under the influence of two different plating systems, we conducted two identical studies during two different time periods: 6 weeks and 12 weeks. Using two different time frames allowed us to assess changes in the biodegradable material and in the bone and soft tissue surrounding this material. Statistical analysis revealed no significant differences in the gross cranial structure among the three groups. This finding suggests that the biodegradable plating system has no adverse effect on cranial growth. The material does resorb and/or disintegrate between 6 and 12 weeks after insertion. The rate of resorption is approximately 5.3 microns per day. The bone and soft tissue surrounding the biodegradable implant exhibited very limited inflammation and foreign body reaction. Bony overgrowth was frequently found over the plating system.

Animals↗

PubMed1978

Distribution of hydrocarbon-utilizing microorganisms and hydrocarbon biodegradation potentials in Alaskan continental shelf areas.

Hydrocarbon-utilizing microorganisms were enumerated from Alaskan continental shelf areas by using plate counts and a new most-probable-number procedure based on mineralization of (14)C-labeled hydrocarbons. Hydrocarbon utilizers were ubiquitously distributed, with no significant overall concentration differences between sampling regions or between surface water and sediment samples. There were, however, significant seasonal differences in numbers of hydrocarbon utilizers. Distribution of hydrocarbon utilizers within Cook Inlet was positively correlated with occurrence of hydrocarbons in the environment. Hydrocarbon biodegradation potentials were measured by using (14)C-radiolabeled hydrocarbon-spiked crude oil. There was no significant correlation between numbers of hydrocarbon utilizers and hydrocarbon biodegradation potentials. The biodegradation potentials showed large seasonal variations in the Beaufort Sea, probably due to seasonal depletion of available nutrients. Non-nutrient-limited biodegradation potentials followed the order hexadecane > naphthalene >> pristane > benzanthracene. In Cook Inlet, biodegradation potentials for hexadecane and naphthalene were dependent on availability of inorganic nutrients. Biodegradation potentials for pristane and benzanthracene were restricted, probably by resistance to attack by available enzymes in the indigenous population.

Alaska↗

PubMed1991

Effects of surfactant adsorption and biodegradability on the distribution of bacteria between sediments and water in a freshwater microcosm.

A microcosm containing resuspended river sediment was used to investigate the effect of anionic surfactants on the distribution of bacteria between planktonic and attached populations. Freshwater river sediment containing viable bacteria was preequilibrated in the microcosm, which was subsequently supplemented with biodegradable or recalcitrant surfactants and a non-surface-active carbon and energy source. Population dynamics of both free-living and attached bacteria were measured by epifluorescence microscopy with simultaneous analysis of the residual solution concentration of the xenobiotic carbon source. The addition of the readily biodegradable anionic surfactants sodium decyl sulfate and sodium dodecyl sulfate in separate experiments caused an increase in the number of attached bacteria and a concomitant decrease in the number of free-living bacteria. As biodegradation of the surfactants progressed, these trends reversed and the bacterial populations had returned to their preaddition values by the time when biodegradation was completed. In contrast, sodium tetradecyl sulfate or sodium dodecane sulfonate did not stimulate bacterial association with sediment, nor were they biodegraded in the microcosm. Sodium pyruvate, a non-surface-active carbon and energy source, was readily utilized but caused no bacterial attachment to the sediment. These results indicate that for an anionic surfactant to induce bacterial attachment to river sediment, it must be biodegradable. The bacterial attachment to the sediment appears to be reversible and may be dependent on the accumulation of the surfactant at the surface or as a result of alteration of the surface free energies.

Adsorption↗

PubMed1994

Effect of a Pseudomonas rhamnolipid biosurfactant on cell hydrophobicity and biodegradation of octadecane.

In this study, the effect of a purified rhamnolipid biosurfactant on the hydrophobicity of octadecane-degrading cells was investigated to determine whether differences in rates of octadecane biodegradation resulting from the addition of rhamnolipid to four strains of Pseudomonas aeruginosa could be related to measured differences in hydrophobicity. Cell hydrophobicity was determined by a modified bacterial adherence to hydrocarbon (BATH) assay. Bacterial adherence to hydrocarbon quantitates the preference of cell surfaces for the aqueous phase or the aqueous-hexadecane interface in a two-phase system of water and hexadecane. On the basis of octadecane biodegradation in the absence of rhamnolipid, the four bacterial strains were divided into two groups: the fast degraders (ATCC 15442 and ATCC 27853), which had high cell hydrophobicities (74 and 55% adherence to hexadecane, respectively), and the slow degraders (ATCC 9027 and NRRL 3198), which had low cell hydrophobicities (27 and 40%, respectively). Although in all cases rhamnolipid increased the aqueous dispersion of octadecane at least 10(4)-fold, at low rhamnolipid concentrations (0.6 mM), biodegradation by all four strains was initially inhibited for at least 100 h relative to controls. At high rhamnolipid concentrations (6 mM), biodegradation by the fast degraders was slightly inhibited relative to controls, but the biodegradation by the slow degraders was enhanced relative to controls. Measurement of cell hydrophobicity showed that rhamnolipids increased the cell hydrophobicity of the slow degraders but had no effect on the cell hydrophobicity of the fast degraders. The rate at which the cells became hydrophobic was found to depend on the rhamnolipid concentration and was directly related to the rate of octadecane biodegradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkanes↗

PubMed2002

Assessing the role of Pseudomonas aeruginosa surface-active gene expression in hexadecane biodegradation in sand.

Low pollutant substrate bioavailability limits hydrocarbon biodegradation in soils. Bacterially produced surface-active compounds, such as rhamnolipid biosurfactant and the PA bioemulsifying protein produced by Pseudomonas aeruginosa, can improve bioavailability and biodegradation in liquid culture, but their production and roles in soils are unknown. In this study, we asked if the genes for surface-active compounds are expressed in unsaturated porous media contaminated with hexadecane. Furthermore, if expression does occur, is biodegradation enhanced? To detect expression of genes for surface-active compounds, we fused the gfp reporter gene either to the promoter region of pra, which encodes for the emulsifying PA protein, or to the promoter of the transcriptional activator rhlR. We assessed green fluorescent protein (GFP) production conferred by these gene fusions in P. aeruginosa PG201. GFP was produced in sand culture, indicating that the rhlR and pra genes are both transcribed in unsaturated porous media. Confocal laser scanning microscopy of liquid drops revealed that gfp expression was localized at the hexadecane-water interface. Wild-type PG201 and its mutants that are deficient in either PA protein, rhamnolipid synthesis, or both were studied to determine if the genetic potential to make surface-active compounds confers an advantage to P. aeruginosa biodegrading hexadecane in sand. Hexadecane depletion rates and carbon utilization efficiency in sand culture were the same for wild-type and mutant strains, i.e., whether PG201 was proficient or deficient in surfactant or emulsifier production. Environmental scanning electron microscopy revealed that colonization of sand grains was sparse, with cells in small monolayer clusters instead of multilayered biofilms. Our findings suggest that P. aeruginosa likely produces surface-active compounds in sand culture. However, the ability to produce surface-active compounds did not enhance biodegradation in sand culture because well-distributed cells and well-distributed hexadecane favored direct contact to hexadecane for most cells. In contrast, surface-active compounds enable bacteria in liquid culture to adhere to the hexadecane-water interface when they otherwise would not, and thus production of surface-active compounds is an advantage for hexadecane biodegradation in well-dispersed liquid systems.

Aldose-Ketose Isomerases↗

PubMed1991

Biodegradation of pentachlorophenol in soil: the response to physical, chemical, and biological treatments.

The effects of physical, chemical, and biological treatments on biodegradation of pentachlorophenol (PCP) were studied in a silt-loam soil contaminated with 175 mg PCP/kg and uniformly 14C-labelled PCP. Biodegradation of 14C-labelled PCP and technical-grade PCP were monitored over 210 days incubation. Mineralization of labelled PCP was significantly (p=0.05) influenced by soil treatments. Negligible biodegradation occurred in either the sterile control soil or the uninoculated control soil, with less than 1% of added 14C recovered as 14 CO2. Inoculation of unamended soil with a strain of Flavobacterium (ATCC 39723) known to degrade PCP increased biodegradation of PCP; approximately 60% of the [14C]PCP was recovered as 14CO2. Increased soil water content (60% versus 30% w/w) enhanced biodegradation (67% recovery of 14C as CO2), while increased chloride ion concentration and anoxic conditions were inhibitory (20 and 1% recoveries, respectively). Residual soil PCP concentrations were also influenced by various treatments. In the sterile control soil and noninoculated control, after 210 days incubation, concentrations of PCP were 143 and 1223 mg/kg, respectively, while the PCP concentration in the inoculated soil was 21 mg/kg. When soil organic matter was increased by adding finely ground red clover leaf and stem material, the residual PCP concentration was reduced to 6 mg/kg after 210 days. Increased soil water content resulted in a residual PCP concentration of 5 mg/kg. High-pressure liquid chromatography of soil extracts revealed no accumulation of partial PCP degradation products. The results indicated that biodegradation of PCP in soil was significantly influenced by various soil amendments.

Biodegradation, Environmental↗

PubMed2004

Biodegradation of amino-acid-based poly(ester amide)s: in vitro weight loss and preliminary in vivo studies.

A systematic in vitro biodegradation study of regular poly(ester amide)s (PEAs) composed of naturally occurring hydrophobic alpha-amino acids, fatty diols and dicarboxylic acids using gravimetric (weight loss) method was carried out in the presence of hydrolases like alpha-chymotrypsin, lipase and a complex of proteases of Papaya. The last enzyme was used for modeling the catalytic action of nonspecific proteases. It was found that the PEAs, in the presence of enzyme solutions, were biodegraded by surface chemical erosion mechanism, according to the first-order kinetics. Spontaneous immobilization (adsorption) of the enzymes onto the PEAs surfaces was observed. The surface immobilized enzyme can also catalyze the chemical erosion of the PEAs. The enzymes could also be impregnated into the PEAs to make PEAs biochemically biodegraded, i.e. 'self-destructive', at a target rate. A comparison of in vitro biodegradation data of the PEAs with polylactide (PDLLA) showed that PEAs exhibited a far more tendency toward enzyme catalyzed biodegradation than PDLLA. A preliminary in vivo biodegradation study of selected PEA films in rats with and without lipase-impregnation showed that those PEAs were completely absorbed within 1-2 months post-implantation (for the lipase-impregnated ones) and 3-6 months (for the lipase-free ones). These findings prompt us to suggest that these new PEAs may have a great potential for designing drug sustained/controlled release devices, as well as implantable surgical devices.

Absorbable Implants↗

PubMed2004

Using Biowin, Bayes, and batteries to predict ready biodegradability.

Whether or not a given chemical substance is readily biodegradable is an important piece of information in risk screening for both new and existing chemicals. Despite the relatively low cost of Organization for Economic Cooperation and Development tests, data are often unavailable and biodegradability must be estimated. In this paper, we focus on the predictive value of selected Biowin models and model batteries using Bayesian analysis. Posterior probabilities, calculated based on performance with the model training sets using Bayes' theorem, were closely matched by actual performance with an expanded set of 374 premanufacture notice (PMN) substances. Further analysis suggested that a simple battery consisting of Biowin3 (survey ultimate biodegradation model) and Biowin5 (Ministry of International Trade and Industry [MITI] linear model) would have enhanced predictive power in comparison to individual models. Application of the battery to PMN substances showed that performance matched expectation. This approach significantly reduced both false positives for ready biodegradability and the overall misclassification rate. Similar results were obtained for a set of 63 pharmaceuticals using a battery consisting of Biowin3 and Biowin6 (MITI nonlinear model). Biodegradation data for PMNs tested in multiple ready tests or both inherent and ready biodegradation tests yielded additional insights that may be useful in risk screening.

Bayes Theorem↗

PubMed2004

The enhanced biodegradation of fenamiphos in soils from previously treated sites and the effect of soil fumigants.

The application of fenamiphos either alone or in combination with soil fumigants is a common practice in greenhouses and potato-cultivation areas in Greece. However, repeated applications of fenamiphos in the same field for a number of years can lead to the development of enhanced biodegradation of the nematicide. Studies in previously treated greenhouse sites and potato field sites in Greece were employed in order to investigate the development of enhanced biodegradation of fenamiphos and the respective effect of soil fumigants on the development of the phenomenon. Enhanced biodegradation of fenamiphos in a soil from a previously treated greenhouse site from the area of Aggelohori in Northern Greece was observed using both incubation and bioassay studies with nematodes. Fumigation of the enhanced soil with methyl bromide (MeBr) only temporarily inhibited degradation of fenamiphos unlike metham sodium (MS) whose application significantly reduced microbial degradation of fenamiphos. Similarly, enhanced biodegradation of fenamiphos was evident in soil from potato fields that had a history of previous exposure to fenamiphos. The slow rates of fenamiphos degradation observed in soils from the previously treated sites after sterilization with broad-spectrum antibiotics and also in soils from previously untreated sites suggested that soil microorganisms were responsible for its rapid degradation. The inhibition of enhanced biodegradation of fenamiphos in soil from the previously treated greenhouse site caused by the antibiotic penicillin probably indicates that Gram+ or other bacteria sensitive to penicillin are responsible for the rapid degradation of fenamiphos in this soil. No cross-adaptation was observed between fenamiphos and other nematicides registered in Greece for the control of root-knot and potato cyst nematodes, including cadusafos, ethoprophos, and oxamyl. According to our results, applications of MS followed by fenamiphos or in rotation with other registered nematicides are the most promising means for minimizing the risk of development of enhanced biodegradation of fenamiphos in soils.

Adaptation, Biological↗