Simple Genomic Traits Predict Rates of Polysaccharide Biodegradation.

Natural and chemically modified polysaccharides are extensively employed across a wide array of industries, leading to their prevalence in the waste streams of industrialized societies. With projected increasing demand, a pressing challenge is to swiftly assess and predict their biodegradability to inform the development of new sustainable materials. In this study, we developed a scalable method to evaluate polysaccharide breakdown by measuring microbial growth and analyzing microbial genomes. Our approach, applied to polysaccharides with various structures, correlates strongly with well-established regulatory methods based on oxygen demand. We show that modifications to the polysaccharide structure decreased degradability and favored the growth of microbes adapted to break down chemically modified sugars. More broadly, we discovered two main types of microbial communities associated with different polysaccharide structures─one dominated by fast-growing microbes and another by specialized degraders. Surprisingly, we were able to predict biodegradation rates based only on two genomic features that define these communities: the abundance of genes related to rRNA (indicating fast growth) and the abundance of glycoside hydrolases (enzymes that break down polysaccharides), which together predict nearly 70% of the variation in polysaccharide breakdown. This suggests a trade-off, whereby microbes are either adapted for fast growth or for degrading complex polysaccharide chains, but not both. Finally, we observe that viral elements (prophages) encoded in the genomes of degrading microbes are induced in easily degradable polysaccharides, leading to complex dynamics in biomass accumulation during degradation. In summary, our work provides a practical approach for efficiently assessing polymer degradability and offers genomic insights into how microbes break down polysaccharides.

Exploring structure-activity relationships for polymer biodegradability by microorganisms.

Research on the environmental biodegradation or microbial biodegradation of polymers has substantially increased recently due to growing demand for biodegradable polymers for certain applications. Environmental biodegradation of a polymer depends on the intrinsic biodegradability of the polymer and the characteristics of the receiving environment. The intrinsic biodegradability of a polymer is determined by the chemical structure and resulting physical properties (e.g., glass transition temperature, melting temperature, modulus of elasticity, crystallinity, and crystal structure) of the polymer. Quantitative structure-activity relationships (QSARs) on biodegradability have been well-established for discrete (non-polymeric) organic chemicals, but not for polymers due to the absence of adequate biodegradability data based on consistent and standardized biodegradation tests with appropriate characterization and reporting of the polymers tested. This review summarizes empirical structure-activity relationships (SARs) for biodegradability of polymers in laboratory studies involving various environmental matrices. In general, polyolefins with carbon-carbon chain are not biodegradable, while polymers containing labile bonds such as ester, ether, amide, or glycosidic bonds in their polymer chain may be favorable for biodegradation. Under a univariate scenario, polymers with higher molecular weight, higher crosslinking, lower water solubility, higher degree of substitution (i.e., higher average number of substituted functional groups per monomer unit), and higher crystallinity may result in reduced biodegradability. This review paper also highlights some of the challenges that hamper QSAR development for polymer biodegradability, stresses the need for better characterization of polymer structures used in biodegradation studies, and emphasizes the necessity for consistent testing conditions for the ease of cross-comparison and quantitative modeling analysis during future QSAR development.

Knowledge Gaps in Polymer Biodegradation Research.

The environmental fate of polymers has attracted growing attention in the academic, industrial, and regulatory communities as well as in the general public as global production and use of polymers continue to increase. Biodegradable polymers especially have drawn significant interest. Polymer biodegradation literature published over the past decade was reviewed to compare test methods commonly used for evaluating polymer biodegradation, and to identify key areas for improvement. This paper examines key aspects of study design for polymer biodegradation such as physical form of the test material, use of appropriate reference materials, selection of test systems, and advantages and limitations of various analytical methods for determining biodegradation. Those aspects of study design are critical for determining the outcome of polymer biodegradation studies. This paper identifies several knowledge gaps for assessing polymer biodegradation and provides four key recommendations. (1) develop standardized guidelines for each specific environmental matrix (compost, activated sludge, marine environments, etc.) that can used for all polymer types, (2) develop accelerated biodegradation test methods and predictive methods for polymers, (3) develop an integrated analytical approach using multiple simple, and effective analytical methods, and (4) develop new frameworks for assessing the overall persistence of polymers and are accepted by the greater scientific community.

Investigating differential binding of polychlorinated dibenzo-p-dioxins/dibenzofurans in soil and soil components using selective supercritical fluid extraction.

Supercritical fluid extraction (SFE) with pure carbon dioxide was performed at increasingly strong conditions to investigate differential binding of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) in two impacted soils, in their sieved size fractions, and in small (a few mg) samples of industry-related waste products separated from impacted soil. The binding strengths of PCDD/Fs were shown to be different in the two soils, and in their different soil particle size fractions. As might be expected based on surface area considerations, one soil showed the strongest binding in the smallest (<5µm) sieved fraction. However, the other soil showed the strongest binding in the larger sized fractions, possibly indicating that process-related particles could be controlling PCDD/F binding. Selective SFE of various types of particles including black carbon and charcoal (separated from soil), and from a suspected process anode residue did show different PCDD/F binding behavior ranging from quite weak binding (charcoal) to very strong binding (anode particles). Shifts to the stronger SFE fractions in the soils after activated carbon treatment agreed well with the decreases previously found in the uptake of PCDD/Fs by earthworms, as well as decreases in their freely-dissolved aqueous concentrations in soil/water slurries. These results show that, as previously demonstrated for PAHs and PCBs, selective SFE can be a useful tool to investigate differences in PCDD/F binding behaviors in impacted soils and sediments and their component parts, as well as a rapid tool for estimating the effectiveness of activated carbon treatments on decreasing the bioavailability of PCDD/Fs in soils and sediments.

Effectiveness of activated carbon and biochar in reducing the availability of polychlorinated dibenzo-p-dioxins/dibenzofurans in soils.

Five activated carbons (ACs) and two biochars were tested as amendments to reduce the availability of aged polychlorinated dibenzo-p-dioxin/dibenzofurans (PCDD/Fs) in two soils. All sorbents (ACs and biochars) tested substantially reduced the availability of PCDD/Fs measured by polyoxymethylene (POM) passive uptake and earthworm (E. fetida) biouptake. Seven sorbents amended at a level of 0.2 × soil total organic carbon (0.2X) reduced the passive uptake (physicochemical availability) of total PCDD/Fs in POM by 40% to 92% (or toxic equivalent by 48% to 99%). Sorbents with finer particle sizes or more macropores showed higher reduction efficiencies. The powdered regenerated AC and powdered coconut AC demonstrated to be the most effective and the two biochars also performed reasonably well especially in the powdered form. The passive uptake of PCDD/F in POM increased approximately 4 to 5 fold as the contact time between POM and soil slurry increased from 24 to 120 d while the efficacy of ACs in reducing the physicochemical availability remained unchanged. The reduction efficiencies measured by POM passive uptake for the regenerated AC were comparable to those measured by earthworm biouptake (bioavailability) at both dose levels of 0.2X and 0.5X. The biota-soil accumulation factor (BSAF) values for unamended soil ranged from 0.1 for tetra-CDD/F to 0.02 for octa-CDD/F. At both dose levels, the regenerated AC reduced the BSAFs to below 0.03 with the exception of two hexa-CDD/Fs. The reduction efficiencies measured by earthworm for coconut AC and corn stover biochar were generally less than those measured by POM probably due to larger particle sizes of these sorbents that could not be ingested by the worms.

Aerobic biodegradation of amines in industrial saline wastewaters.

The treatment of hypersaline wastewaters represents a challenge since high salt concentrations disrupt bacteria present in normal biological treatments. This study was conducted to determine the fate of amines in two hypersaline wastewaters obtained from an industrial treatment plant processing influents with 3% and 7% of NaCl. The compounds were aniline (ANL), 4,4'-methylenedianiline (4,4'-MDA), cyclohexylamine (CHA), N-(2-aminoethyl)ethanolamine (AEA), N,N-diethylethanolamine (DEA), N,N-bis(2-hydroxyethyl)methylamine (MDEA), and tris(2-hydroxyethyl)amine (TEA). Mixtures of these chemicals with a mixed liquor suspended solids concentration of 1000 mg L(-1) were prepared at two salinities (3% and 7% NaCl). Ethanolamines were readily biodegraded at both salinities, following first-order kinetics with half-lives ranging between 10 and 58 h. Hydroxyl groups present in the ethanolamines had a positive impact on the biodegradation. Salinity did not affect the biodegradation rate of TEA and MDEA, whereas AEA and DEA degraded faster in 3% NaCl. After 48h, CHA was metabolized within a 24-h period in 3% NaCl, while no degradation was observed in 7% NaCl. ANL exhibited lag phases in both salinities and, in the following 24-h period, ANL concentrations dropped 40% and disappeared after 48 h. 4,4'-MDA degraded in 3% NaCl (half-life of 123 h) and remained unaltered after 120 h in 7% NaCl.

Role of black carbon in the distribution of polychlorinated dibenzo-p-dioxins/dibenzofurans in aged field-contaminated soils.

Floodplain soils containing elevated levels of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) were collected from several locations along the Tittabawassee River (Michigan, USA). The PCDD/F profiles of these soils exhibited distinct congener patterns consistent with byproducts from either chloralkali manufacturing or chlorophenols productions. Black carbon (BC) particles were isolated for the first time from floodplain soil impacted by PCDD/Fs. Petrographic analysis showed that BC particles, including coal, oxidized coal, metallurgical coke, depositional carbon, coal tar/pitch, cenosphere, and charcoal, comprised approximately 30% by volume of the organic fraction with size range of 250µm-2000µm from a typical floodplain soil. The BC particles with anthropogenic origin such as pitch and coke associated with the chloralkali production process served as both the source and subsequent transporter for the highly hydrophobic PCDD/Fs. These anthropogenic BC particles were enriched with high levels of PCDFs, containing approximately 1000-fold the concentration found in the bulk soil. The strong association of PCDD/Fs with anthropogenic BC directly impacts the physicochemical and biological availability thus the risk associated with these hydrophobic organochlorines in soils and sediments.

Bioaccumulation of polychlorinated dibenzo-p-dioxins/dibenzofurans in E. fetida from floodplain soils and the effect of activated carbon amendment.

Laboratory studies were conducted to evaluate the bioaccumulation of aged polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in soil near the base of the terrestrial food chain using earthworms (E. fetida) as a model organism. This research also assessed the effect of activated carbon (AC) addition to soil on PCDD/F bioaccumulation in earthworms and passive uptake in polyoxymethylene (POM) samplers. Two soils taken from a wetland and a levee along the Tittabawassee River floodplain downstream of Midland, MI were used in this study. In the untreated soils, biota sediment accumulation factors (BSAFs) ranged from 0.17 for 2,3,7,8-TCDD to 0.02 for some of the higher chlorinated congeners, which were substantially lower than would be predicted using a conventional equilibrium partitioning model. The addition of AC to the floodplain soils generally reduced the BSAF values to lower than 0.02. Amendment of the wetland soil (having a high organic content) with 2% and 5% AC resulted in a 78 and 91% reduction of toxicity equivalent (TEQ) in earthworms, respectively. More strikingly, amendment of the natural levee soil (having a low organic content) with 2% and 5% AC showed >99% reduction of TEQ in earthworms. Also, freely dissolved aqueous concentrations of PCDD/Fs in soil slurries, as measured by equilibrium passive samplers, decreased up to 99% with AC treatment. Results of this study indicate that bioaccumulation of PCDD/Fs in earthworms from historically impacted floodplain soils is low and can be further reduced by amending with a strong sorbent.

A liquid chromatography-electrospray ionization-tandem mass spectrometry study of ethanolamines in high salinity industrial wastewaters.

The detection and quantitation of four ethanolamines, tris(2-hydroxyethyl)amine (triethanolamine, TEA), N,N-bis(2-hydroxyethyl)methylamine (methyldiethanolamine, MDEA), N-(2-aminoethyl)ethanolamine (AEA), and N,N-diethylethanolamine (DEA), were achieved in wastewaters from two aerobic activated sludge bioreactors located in an industrial wastewater treatment plant. The streams had salt concentrations of approximately 3% and 7% by weight in Reactor 1 and Reactor 2, respectively. The use of liquid chromatography-electrospray ionization-tandem mass spectrometry avoided the need for some sample preparation steps such as extraction, concentration, and derivatization. Ion suppression in the electrospray, attributable to the presence of sodium clusters, was attenuated by a 10-fold dilution of the wastewaters with acetonitrile. A matrix-matched calibration model averted other potential interferences. For the compounds analyzed in selected reaction monitoring mode (TEA, MDEA, and DEA), the calibration curves presented linearity in a range of 10-1000microg/L with corresponding detection limits ranging from 2 to 11microg/L, depending upon the specific analyte and aqueous matrix. AEA was calibrated in selected ion monitoring mode (100-1000microg/L), with corresponding detection limits in the two wastewaters of 74.6 and 85.3microg/L, respectively. Overall good precision (<10%) and accuracy (97-110%) were achieved for both matrices, which fell within-laboratory reproducibility. Finally, the amines were introduced into six mixed liquor samples from both reactors and quantified following the reported protocol. Again, recoveries were close to 100% with a relative standard deviation of less than 10% in all cases.

Effects of aging and sediment composition on hexachlorobenzene desorption resistance compared to oral bioavailability in rats.

Studies were conducted to assess the effects of black carbon, clay type and aging (1-1.5yr) on desorption and bioavailability of hexachlorobenzene (HCB) in spiked artificial sediments. Tenax (a super sorbent)-mediated desorption was used to examine the effects of these parameters on the physicochemical availability of HCB. The Tenax-mediated desorption of HCB from the four aged artificial sediments exhibited biphasic kinetics. The fast desorbing fractions ranged from 64.8% to 22.3%, showing reductions of 4.0-18.9% compared with freshly-spiked sediments. Statistical analysis on the fast desorbing fractions showed that all three treatment effects (i.e., montmorillonite clay, black carbon content, and aging) were significant. Two sediments with higher black carbon content exhibited much greater aging effects (i.e., greater reduction in fast desorbing fraction) than the other two sediments without the addition of black carbon. For both freshly-spiked and aged sediments, the desorption resistant sediment-bound HCB (i.e., slow desorbing fraction) correlated reasonably well to previously reported rat fecal elimination of HCB, which is a measure of the non-bioavailable fraction of sediment-bound HCB. A similar correlation was also observed between fast desorbing fraction and previously reported accumulation of HCB in the rat body (carcass+skin). These observations suggest that physicochemical availability, as defined by the desorption of HCB from sediments, provides a reasonable prediction of the oral bioavailability of sediment-bound HCB to rats. These results showed that montmorillonite clay, black carbon and aging reduced physicochemical availability and ultimately bioavailability of sediment-bound HCB.

Effect of organic carbon content, clay type, and aging on the oral bioavailability of hexachlorobenzene in rats.

Bioavailability of lipophilic chemicals is influenced by the physicochemical properties of soils/sediment such as particle size, pH, clay, and organic carbon content. The present study investigated the effects of sediment composition and aging on the oral bioavailability of hexachlorobenzene (HCB) in rats. Formulated sediments were prepared using various ratios of kaolinite and montmorillonite clay, sand, peat moss, and black carbon, spiked with (14)C-HCB, and orally administered to rats prior to and after one year of aging in dark at 10 degrees C. In the nonaged sediments there was a 21 to 45% reduction in the oral bioavailability of HCB when compared to the corn oil standard without any clear pattern of the impact of the sediment clay and/or organic carbon content. One year of aging resulted in statistically significant (p = 0.049) reduction in the oral bioavailability of HCB from the sediments compared to the corn oil standard and nonaged sediment indicating stronger interactions between HCB and sediment contents with aging. The mean reduction in oral bioavailability after one year of aging ranged from approximately 5 to 14% greater than that observed for nonaged sediments. The fecal elimination of the HCB-derived radioactivity from the one-year-aged sediments was much higher than the nonaged sediments, consistent with the lower absorption from the gastrointestinal tract due to lower desorption of HCB from the aged sediments. Increase in the fecal elimination and decrease in oral bioavailability of (14)C-HCB was related to the increase in clay and black carbon.

The use of coarse, separable, condensed-phase organic carbon particles to characterize desorption resistance of polycyclic aromatic hydrocarbons in contaminated sediments.

Physical separations were employed to characterize the source of desorption-resistant behavior for polycyclic aromatic hydrocarbons (PAHs) in laboratory- and field-contaminated sediments. Size and density separation of laboratory-contaminated sediments did not effectively separate the amorphous-phase (volatile) and condensed-phase (nonvolatile) organic carbon as measured by thermal oxidation at 375 degrees C. These separations also did not result in sediment fractions with significantly different desorption characteristics as measured by apparent partition coefficients. Coarse particles from a field-contaminated sediment from Utica Harbor (UH; Utica, NY, USA), however, could be directly separated into sandy fractions and organic fractions that were composed of woody organic matter, charcoal or charred vegetative matter, and coal-like and coal-cinder particles. Chemical analysis showed that coal-like (glassy, nonporous) and coal-cinder (porous, sintered) particles exhibited very high PAH concentrations and high apparent partition coefficients. These particles also exhibited significantly higher condensed-phase (nonvolatile) organic carbon contents as defined by thermal oxidation at 375 degrees C. The apparent partition coefficients of PAHs in the coal-cinder particles were a good indication of the apparent partition coefficients in the desorption-resistant fraction of UH sediment, indicating that the coarse particles provided a reasonable characterization of the desorption-resistance phenomena in these sediments even though the coarse fractions represented less than 25% of the organic carbon in the whole sediment.

Effects of black carbon and montmorillonite clay on multiphasic hexachlorobenzene desorption from sediments.

The desorption kinetics of hexachlorobenzene (HCB) in four freshly spiked artificial sediments were determined using a polymeric adsorbent Tenax-mediated desorption. The sediments included a standard sediment (SS) prepared as per Organisation for Economic Cooperation and Development 218 guidelines and three derived artificial sediments prepared by supplementing the SS sediment with various levels of black carbon (lamp black soot) and/or montmorillonite clay. The desorption kinetics exhibited biphasic behavior, i.e., a fast desorbing fraction followed by a slow desorbing fraction. The addition of either lamp black soot or montmorillonite clay resulted in the reduction of the fast desorbing fraction (Ffast) of HCB in three derived sediments compared with SS sediment. Both black carbon and montmorillonite clay treatment effects on the fast desorbing fraction were statistically significant for the four artificial sediments. The black carbon treatment (i.e., addition of 0.5% wt/wt lamp black soot) effect was an average reduction of Ffast by approximately 11%, whereas the montmorillonite treatment (i.e., addition of 15% wt/wt montmorillonite clay) effect was an average reduction of Ffast by approximately 17%. The presence of soot black carbon particles reduced the desorption rate of HCB in sediments since black carbon exhibits very high sorption capacity and extremely slow diffusion rate compared with those of the natural organic matter in sediment.

Desorption resistance of polycyclic aromatic hydrocarbons and duration of exposure.

The desorption-resistant fraction of laboratory-spiked phenanthrene in two Louisiana (USA) sediments was not observed to be significantly different, but the two sediments exhibited different condensed-phase organic carbon contents, as defined operationally by the organic carbon remaining after combustion of the sediment at 375 degrees C. Only 3% of the original saturated phenanthrene in the sediments was not readily removed by exposure to a nonpolar polymeric resin and sorbent XAD-2. Allowing the laboratory-spiked contaminants to age for periods of up to three years yielded little difference in the desorption-resistant characteristics of the sediments. Field-contaminated sediments from Utica Harbor (Utica, NY, U.S.A.) and Rouge River (Detroit, MI, USA) that had a lengthy (decades to a century) period of contamination, however, exhibited significantly different desorption-resistant contaminant fractions, consistent with the fractions of condensed-phase organic carbon in the sediments. Measurements of the fraction that could be rapidly desorbed using the XAD-2 sorbent also accounted for essentially all desorption to pore water and, thus, provided a good prediction of effective bulk partition coefficients. It was concluded that the condensed-phase organic carbon was a good indicator of the potential for desorption resistance in field-contaminated sediments and that the rapidly desorbing fraction provided a quantitative indicator of its significance.

Modeling biphasic sorption and desorption of hydrophobic organic contaminants in sediments.

A model was developed to predict biphasic sorption and desorption of hydrophobic organic compounds in contaminated sediments. The model was based on relatively rapid porous diffusion in amorphous organic carbon and slow solid-phase diffusion in condensed-phase organic carbon. The model was used to simulate measured solid-fluid phase desorption (rates and pore-water concentrations) for four polycyclic aromatic hydrocarbons exhibiting a range of hydrophobicities (phenanthrene, anthracene, pyrene, and benzo[a]pyrene) in two field-contaminated sediments from Utica Harbor (Utica, NY, USA) and Rouge River (Detroit, MI, USA). Pore-water concentrations have been related to bioavailability, indicating the potential usefulness of the model to predict bioavailability. Key model parameters included the fraction of condensed-phase carbon (estimated by combustion at 375 degrees C), partition coefficient to the condensed-phase carbon (estimated by desorption measurements on coal-like particles physically separated from Utica Harbor sediments), and diffusivity and ratio of volume to surface area of the condensed-phase organic matter (fitted to measured desorption data on both sediments and for the measured polycyclic aromatic hydrocarbons). Best fit for the diffusion coefficient in the condensed-phase organic matter was 8.5 x 10(-20) m2/s, and ratio of volume to surface area was 2 microm. These parameters estimated measured pore-water concentrations of all polycyclic aromatic hydrocarbons in both sediments with an average error of 46% and a correlation coefficient of 0.76 and the fast-desorbing fractions (as measured by the fraction removed with a nonpolar polymeric sorbent XAD-2) with an average error of approximately 30% and a correlation coefficient of 0.54 (14% and 0.76, respectively, for all but benzo[a]pyrene). Modeling results were relatively insensitive to the two fitted parameters, with changes of an order of magnitude or more being required to affect the correlation between the model and observations significantly.

Bioavailability of desorption-resistant phenanthrene to the oligochaete Ilyodrilus templetoni.

We investigated bioavailability, as measured by the biota-sediment accumulation factor (BSAF), of reversibly sorbed and desorption-resistant phenanthrene to the deposit-feeding freshwater tubificid oligochaete Ilyodrilus templetoni. Desorption-resistant, phenanthrene-contaminated sediments were prepared by a sequential batch desorption method by washing with an isopropanol solution. The BSAFs averaged 1.20 +/- 0.32 and 0.59 +/- 0.13 for reversibly sorbed phenanthrene and desorption-resistant phenanthrene, respectively, indicating a significantly reduced bioavailability of desorption-resistant phenanthrene. A generalized model assuming a linear relationship between pore-water concentration and normalized bioaccumulation described 91% of the variance for both measured and selected literature data of the BSAF. The reduced bioavailibility of desorption-resistant phenanthrene was thus well described by physical and chemical measures of partitioning between pore water and sediment.