Polyester biodegradability: importance and potential for optimisation.

To reduce global CO2 emissions in line with EU targets, it is essential that we replace fossil-derived plastics with renewable alternatives. This provides an opportunity to develop novel plastics with improved design features, such as better reusability, recyclability, and environmental biodegradability. Although recycling and reuse of plastics is favoured, this relies heavily on the infrastructure of waste management, which is not consistently advanced on a worldwide scale. Furthermore, today's bulk polyolefin plastics are inherently unsuitable for closed-loop recycling, but the introduction of plastics with enhanced biodegradability could help to combat issues with plastic accumulation, especially for packaging applications. It is also important to recognise that plastics enter the environment through littering, even where the best waste-collection infrastructure is in place. This causes endless environmental accumulation when the plastics are non-(bio)degradable. Biodegradability depends heavily on circumstances; some biodegradable polymers degrade rapidly under tropical conditions in soil, but they may not also degrade at the bottom of the sea. Biodegradable polyesters are theoretically recyclable, and even if mechanical recycling is difficult, they can be broken down to their monomers by hydrolysis for subsequent purification and re-polymerisation. Additionally, both the physical properties and the biodegradability of polyesters are tuneable by varying their building blocks. The relationship between the (chemical) structures/compositions (aromatic, branched, linear, polar/apolar monomers; monomer chain length) and biodegradation/hydrolysis of polyesters is discussed here in the context of the design of biodegradable polyesters.

Relationship between Composition and Environmental Degradation of Poly(isosorbide-co-diol oxalate) (PISOX) Copolyesters.

To reduce the global CO2 footprint of plastics, bio- and CO2-based feedstock are considered the most important design features for plastics. Oxalic acid from CO2 and isosorbide from biomass are interesting rigid building blocks for high Tg polyesters. The biodegradability of a family of novel fully renewable (bio- and CO2-based) poly(isosorbide-co-diol) oxalate (PISOX-diol) copolyesters was studied. We systematically investigated the effects of the composition on biodegradation at ambient temperature in soil for PISOX (co)polyesters. Results show that the lag phase of PISOX (co)polyester biodegradation varies from 0 to 7 weeks. All (co)polyesters undergo over 80% mineralization within 180 days (faster than the cellulose reference) except one composition with the cyclic codiol 1,4-cyclohexanedimethanol (CHDM). Their relatively fast degradability is independent of the type of noncyclic codiol and results from facile nonenzymatic hydrolysis of oxalate ester bonds (especially oxalate isosorbide bonds), which mostly hydrolyzed completely within 180 days. On the other hand, partially replacing oxalate with terephthalate units enhances the polymer's resistance to hydrolysis and its biodegradability in soil. Our study demonstrates the potential for tuning PISOX copolyester structures to design biodegradable plastics with improved thermal, mechanical, and barrier properties.

Simultaneous detection of pesticides and pharmaceuticals in three types of bio-based fertilizers by an improved QuEChERS method coupled with UHPLC-q-ToF-MS/MS.

Bio-based fertilizers (BBFs) have the potential to contain both pesticides and pharmaceutical residues, which may pose a threat to soils, crops, and human health. However, no analytical screening method is available currently to simultaneously analyze a wide range of contaminants in the complex origin-dependent matrices of BBFs. To fill this gap, our study tested and improved an original QuEChERS method (OQM) for simultaneously analyzing 78 pesticides and 18 pharmaceuticals in BBFs of animal, plant, and ashed sewage sludge origin. In spiked recovery experiments, 34-58 pharmaceuticals and pesticides were well recovered (recovery of 70-120%) via OQM at spiking concentrations levels of 10 ng/g and 50 ng/g in these three different types of BBFs. To improve the extraction efficiency further, ultrasonication and end-over-end rotation were added based on OQM, resulting in the improved QuEChERS method (IQM) that could recover 57-79 pesticides and pharmaceuticals, in the range of 70-120%. The detection limits of this method were of 0.16-4.32/0.48-12.97 ng/g, 0.03-11.02/0.10-33.06 ng/g, and 0.06-5.18/0.18-15.54 ng/g for animal, plant, and ash-based BBF, respectively. Finally, the IQM was employed to screen 15 BBF samples of various origins. 15 BBFs contained at least one pesticide or pharmaceutical with ibuprofen being frequently detected in at concentration levels of 4.1-181 ng/g. No compounds were detected in ash-based BBFs.

Organic contaminants in bio-based fertilizer treated soil: Target and suspect screening approaches.

Using bio-based fertilizer (BBF) in agricultural soil can reduce the dependency on chemical fertilizer and increase sustainability by recycling nutrient-rich side-streams. However, organic contaminants in BBFs may lead to residues in the treated soil. This study assessed the presence of organic contaminants in BBF treated soils, which is essential for evaluating sustainability/risks of BBF use. Soil samples from two field studies amended with 15 BBFs from various sources (agricultural, poultry, veterinary, and sludge) were analyzed. A combination of QuEChERS-based extraction, liquid chromatography quadrupole time of flight mass spectrometry-based (LC-QTOF-MS) quantitative analysis, and an advanced, automated data interpretation workflow was optimized to extract and analyze organic contaminants in BBF-treated agricultural soil. The comprehensive screening of organic contaminants was performed using target analysis and suspect screening. Of the 35 target contaminants, only three contaminants were detected in the BBF-treated soil with concentrations ranging from 0.4 ng g-1 to 28.7 ng g-1; out of these three detected contaminants, two were also present in the control soil sample. Suspect screening using patRoon (an R-based open-source software platform) workflows and the NORMAN Priority List resulted in tentative identification of 20 compounds (at level 2 and level 3 confidence level), primarily pharmaceuticals and industrial chemicals, with only one overlapping compound in two experimental sites. The contamination profiles of the soil treated with BBFs sourced from veterinary and sludge were similar, with common pharmaceutical features identified. The suspect screening results suggest that the contaminants found in BBF-treated soil might come from alternative sources other than BBFs.

Risk reductions during pyrene biotransformation and mobilization in a model plant-bacteria-biochar system.

The productive application of motile microorganisms for degrading hydrophobic contaminants in soil is one of the most promising processes in modern remediation due to its sustainability and low cost. However, the incomplete biodegradation of the contaminants and the formation of the intermediary metabolites in the process may increase the toxicity in soil during bioremediation, and motile inoculants may mobilize the pollutants through biosorption. Therefore, controlling these factors should be a fundamental part of soil remediation approaches. The aim of this study was to evaluate the sources of risk associated with the cometabolism-based transformation of 14C-labeled pyrene by inoculated Pseudomonas putida G7 and identify ways to minimize risk. Our model scenario examined the increase in bioaccessibility to a distant source of contamination facilitated by sunflower (Helianthus annuus L.) roots. A biochar trap for mobilized pollutant metabolites and bacteria has also been employed. The experimental design consisted of pots filled with a layer of sand with 14C-labeled pyrene (88 mg kg-1) as a contamination focus located several centimeters from the inoculation point. Half of the pots included a biochar layer at the bottom. The pots were incubated in a greenhouse with sunflower plants and P. putida G7 bacteria. Pots with sunflower plants showed a higher biodegradation of pyrene, its mobilization as metabolites through the percolate and the roots, and bacterial mobilization toward the source of contamination, also resulting in increased pyrene transformation. In addition, the biochar layer efficiently reduced the concentrations of pyrene metabolites collected in the leachates. Therefore, the combination of plants, motile bacteria and biochar safely reduced the risk caused by the biological transformation of pyrene.

Anaerobic degradation of benzene and other aromatic hydrocarbons in a tar-derived plume: Nitrate versus iron reducing conditions.

The anaerobic degradation of aromatic hydrocarbons in a plume originating from a Pintsch gas tar-DNAPL zone was investigated using molecular, isotopic- and microbial analyses. Benzene concentrations diminished at the relatively small meter scale dimensions of the nitrate reducing plume fringe. The ratio of benzene to toluene, ethylbenzene, xylenes and naphthalene (BTEXN) in the fringe zone compared to the plume zone, indicated relatively more loss of benzene in the fringe zone than TEXN. This was substantiated by changes in relative concentrations of BTEXN, and multi-element compound specific isotope analysis for δ2H and δ13C. This was supported by the presence of (abcA) genes, indicating the presumed benzene carboxylase enzyme in the nitrate-reducing plume fringe. Biodegradation of most hydrocarbon contaminants at iron reducing conditions in the plume core, appears to be quantitatively of greater significance due to the large volume of the plume core, rather than relatively faster biodegradation under nitrate reducing conditions at the smaller volume of the plume fringe. Contaminant concentration reductions by biodegradation processes were shown to vary distinctively between the source, plume (both iron-reducing) and fringe (nitrate-reducing) zones of the plume. High anaerobic microbial activity was detected in the plume zone as well as in the dense non aqueous phase liquid (DNAPL) containing source zone. Biodegradation of most, if not all, other water-soluble Pintsch gas tar aromatic hydrocarbon contaminants occur at the relatively large dimensions of the anoxic plume core. The highest diversity and concentrations of metabolites were detected in the iron-reducing plume core, where the sum of parent compounds of aromatic hydrocarbons was greater than 10 mg/L. The relatively high concentrations of metabolites suggest a hot spot for anaerobic degradation in the core of the plume downgradient but relatively close to the DNAPL containing source zone.

Scientific concepts and methods for moving persistence assessments into the 21st century.

The evaluation of a chemical substance's persistence is key to understanding its environmental fate, exposure concentration, and, ultimately, environmental risk. Traditional biodegradation test methods were developed many years ago for soluble, nonvolatile, single-constituent test substances, which do not represent the wide range of manufactured chemical substances. In addition, the Organisation for Economic Co-operation and Development (OECD) screening and simulation test methods do not fully reflect the environmental conditions into which substances are released and, therefore, estimates of chemical degradation half-lives can be very uncertain and may misrepresent real environmental processes. In this paper, we address the challenges and limitations facing current test methods and the scientific advances that are helping to both understand and provide solutions to them. Some of these advancements include the following: (1) robust methods that provide a deeper understanding of microbial composition, diversity, and abundance to ensure consistency and/or interpret variability between tests; (2) benchmarking tools and reference substances that aid in persistence evaluations through comparison against substances with well-quantified degradation profiles; (3) analytical methods that allow quantification for parent and metabolites at environmentally relevant concentrations, and inform on test substance bioavailability, biochemical pathways, rates of primary versus overall degradation, and rates of metabolite formation and decay; (4) modeling tools that predict the likelihood of microbial biotransformation, as well as biochemical pathways; and (5) modeling approaches that allow for derivation of more generally applicable biotransformation rate constants, by accounting for physical and/or chemical processes and test system design when evaluating test data. We also identify that, while such advancements could improve the certainty and accuracy of persistence assessments, the mechanisms and processes by which they are translated into regulatory practice and development of new OECD test guidelines need improving and accelerating. Where uncertainty remains, holistic weight of evidence approaches may be required to accurately assess the persistence of chemicals. Integr Environ Assess Manag 2022;18:1454-1487. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Biodegradability of novel high Tg poly(isosorbide-co-1,6-hexanediol) oxalate polyester in soil and marine environments.

In order to reduce the plastic accumulation in the environment, biodegradable plastics are attracting interest in the plastics market. However, the low thermal stability of most amorphous biodegradable polymers limits their application. With the aim of combining high glass transition temperature (Tg), with good (marine) biodegradation a family of novel fully renewable poly(isosorbide-co-diol) oxalate (PISOX-diol) copolyesters was recently developed. In this study, the biodegradability of a representative copolyester, poly(isosorbide-co-1,6-hexanediol) oxalate (PISOX-HDO), with 75/25 mol ratio IS/HDO was evaluated at ambient temperature (25 °C) in soil and marine environment by using a Respicond system with 95 parallel reactors, based on the principle of frequently monitoring CO2 evolution. During 50 days incubation in soil and seawater, PISOX-HDO mineralised faster than cellulose. The ready biodegradability of PISOX-HDO is related to the relatively fast non-enzymatic hydrolysis of polyoxalates. To study the underlying mechanism of PISOX-HDO biodegradation, the non-enzymatic hydrolysis of PISOX-HDO and the biodegradation of the monomers in soil were also investigated. Complete hydrolysis was obtained in approximately 120 days (tracking the formation of hydrolysis products via 1H NMR). It was also shown that (enzymatic) hydrolysis to the constituting monomers is the rate-determining step in this biodegradation mechanism. These monomers can subsequently be consumed and mineralised by (micro)organisms in the environment much faster than the polyesters. The combination of high Tg (>100 °C) and fast biodegradability is quite unique and makes this PISOX-HDO copolyester ideal for short term applications that demand strong mechanical and physical properties.

Moving persistence assessments into the 21st century: A role for weight-of-evidence and overall persistence.

Assessing the persistence of chemicals in the environment is a key element in existing regulatory frameworks to protect human health and ecosystems. Persistence in the environment depends on many fate processes, including abiotic and biotic transformations and physical partitioning, which depend on substances' physicochemical properties and environmental conditions. A main challenge in persistence assessment is that existing frameworks rely on simplistic and reductionist evaluation schemes that may lead substances to be falsely assessed as persistent or the other way around-to be falsely assessed as nonpersistent. Those evaluation schemes typically assess persistence against degradation half-lives determined in single-compartment simulation tests or against degradation levels measured in stringent screening tests. Most of the available test methods, however, do not apply to all types of substances, especially substances that are poorly soluble, complex in composition, highly sorptive, or volatile. In addition, the currently applied half-life criteria are derived mainly from a few legacy persistent organic pollutants, which do not represent the large diversity of substances entering the environment. Persistence assessment would undoubtedly benefit from the development of more flexible and holistic evaluation schemes including new concepts and methods. A weight-of-evidence (WoE) approach incorporating multiple influencing factors is needed to account for chemical fate and transformation in the whole environment so as to assess overall persistence. The present paper's aim is to begin to develop an integrated assessment framework that combines multimedia approaches to organize and interpret data using a clear WoE approach to allow for a more consistent, transparent, and thorough assessment of persistence. Integr Environ Assess Manag 2022;18:868-887. © 2021 ExxonMobil Biomedical Sciences, Inc. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Independent mode sorption of perfluoroalkyl acids by single and multiple adsorbents.

Infinite dilution partition coefficients, Kp,0, of a series of unbranched perfluoralkylacids, PFAAs with 3 to 8 CF2 units between water and commercially available weak anion exchange (WAX) and strong anion exchange (MAX) polymers, C18-modified silica, hydrophilic-lipophilic balance polymer (HLB), and Al2O3 sorbents were determined with self-packed columns using an HPLC-MS/MS setup. The anionic WAX sorbent shows a much higher adsorption affinity (about 450 fold) for PFBA than was observed for the applied hydrophobic sorbent HLB. Since the incremental value for each CF2 group is smaller when the electrostatic adsorption process is observed, the hydrophobic partition coefficient of HLB supersedes the electrostatic one of WAX at around PFTeDA. Adsorption of PFAAs to Al2O3 was weak and did not show a clear chain length dependency. A recently developed independent mode (IM) adsorption model is a more accurate model to combine the electrostatic and hydrophobic interaction terms. This model predicts the correct behaviour of especially short chain PFAAs in soil or sediment sorption experiments. Factors increasing sorption efficiency of well- and ill-defined single and multiple adsorbents towards PFAAs are discussed. The IM model provides a method to optimise sorption remediation strategies of PFAAs in contaminated waters and proposes a two-step strategy, a starting hydrophobic step followed by an electrostatic one to remove more efficiently the short chain PFAAs.

High biodiversity in a benzene-degrading nitrate-reducing culture is sustained by a few primary consumers.

A key question in microbial ecology is what the driving forces behind the persistence of large biodiversity in natural environments are. We studied a microbial community with more than 100 different types of species which evolved in a 15-years old bioreactor with benzene as the main carbon and energy source and nitrate as the electron acceptor. Using genome-centric metagenomics plus metatranscriptomics, we demonstrate that most of the community members likely feed on metabolic left-overs or on necromass while only a few of them, from families Rhodocyclaceae and Peptococcaceae, are candidates to degrade benzene. We verify with an additional succession experiment using metabolomics and metabarcoding that these few community members are the actual drivers of benzene degradation. As such, we hypothesize that high species richness is maintained and the complexity of a natural community is stabilized in a controlled environment by the interdependencies between the few benzene degraders and the rest of the community members, ultimately resulting in a food web with different trophic levels.

Effects of salinity on the treatment of synthetic petroleum-industry wastewater in pilot vertical flow constructed wetlands under simulated hot arid climatic conditions.

Petroleum-industry wastewater (PI-WW) is a potential source of water that can be reused in areas suffering from water stress. This water contains various fractions that need to be removed before reuse, such as light hydrocarbons, heavy metals and conditioning chemicals. Constructed wetlands (CWs) can remove these fractions, but the range of PI-WW salinities that can be treated in CWs and the influence of an increasing salinity on the CW removal efficiency for abovementioned fractions is unknown. Therefore, the impact of an increasing salinity on the removal of conditioning chemicals benzotriazole, aromatic hydrocarbon benzoic acid, and heavy metal zinc in lab-scale unplanted and Phragmites australis and Typha latifolia planted vertical-flow CWs was tested in the present study. P. australis was less sensitive than T. latifolia to increasing salinities and survived with a NaCl concentration of 12 g/L. The decay of T. latifolia was accompanied by a decrease in the removal efficiency for benzotriazole and benzoic acid, indicating that living vegetation enhanced the removal of these chemicals. Increased salinities resulted in the leaching of zinc from the planted CWs, probably as a result of active plant defence mechanisms against salt shocks that solubilized zinc. Plant growth also resulted in substantial evapotranspiration, leading to an increased salinity of the CW treated effluent. A too high salinity limits the reuse of the CW treated water. Therefore, CW treatment should be followed by desalination technologies to obtain salinities suitable for reuse. In this technology train, CWs enhance the efficiency of physicochemical desalination technologies by removing organics that induce membrane fouling. Hence, P. australis planted CWs are a suitable option for the treatment of water with a salinity below 12 g/L before further treatment or direct reuse in water scarce areas worldwide, where CWs may also boost the local biodiversity. Graphical abstract.

Comparison of the aerobic biodegradation of biopolymers and the corresponding bioplastics: A review.

Biodegradable plastics made from biopolymers (made in nature) or from bio-based polymers (made in a factory) are becoming increasingly important in replacing the massive amounts of conventional, non-degradable fossil-based plastics that have been produced and disposed over the past decades. In this review we compare the biodegradation rates and mechanisms of the bioplastics thermoplastic starch, cellulose acetate and lignin based bioplastics with the biodegradation rates and mechanisms of starch, cellulose and lignin, which are the unmodified biopolymers from which these bioplastics are produced. With this comparison we aim to determine to what extent the extensive knowledge on unmodified biopolymer biodegradation can be applied to the biodegradation of bioplastics (modified biopolymers) in the terrestrial environment. This knowledge is important, since it can be of great help in giving direction to the future research and development of bioplastics and for the development of bioplastic waste assessments and policies. We found that the similarities and differences in biodegradation are dependent on the structural changes imposed on a biopolymer during the bioplastic production process. A change in higher level structure, as found in thermoplastic starch, only resulted in a limited number of differences in the biodegradation process. However, when the chemical structure of a polymer is changed, as for cellulose acetate, different microorganisms and enzymes are involved in the biodegradation. Based on the cellulose acetate biodegradation process, a conceptual model was proposed that can be used as a starting point in predicting biodegradation rates of other chemically modified biopolymers used as bioplastics. Future bioplastic biodegradation research should focus on conducting long-term field experiments, since most studies are conducted in a laboratory setting and do not capture all processes occurring in the field situation. This applies even more to lignin based bioplastics, since very little experimental data were available on modified lignin biopolymer biodegradation.

Biodegradation and Non-Enzymatic Hydrolysis of Poly(Lactic-co-Glycolic Acid) (PLGA12/88 and PLGA6/94).

The predicted growth in plastic demand and the targets for global CO2 emission reductions require a transition to replace fossil-based feedstock for polymers and a transition to close- loop recyclable, and in some cases to, biodegradable polymers. The global crisis in terms of plastic littering will furthermore force a transition towards materials that will not linger in nature but will degrade over time in case they inadvertently end up in nature. Efficient systems for studying polymer (bio)degradation are therefore required. In this research, the Respicond parallel respirometer was applied to polyester degradation studies. Two poly(lactic-co-glycolic acid) copolyesters (PLGA12/88 and PLGA6/94) were tested and shown to mineralise faster than cellulose over 53 days at 25 °C in soil: 37% biodegradation for PLGA12/88, 53% for PLGA6/94, and 30% for cellulose. The corresponding monomers mineralised much faster than the polymers. The methodology presented in this article makes (bio)degradability studies as part of a materials development process economical and, at the same time, time-efficient and of high scientific quality. Additionally, PLGA12/88 and PLGA6/94 were shown to non-enzymatically hydrolyse in water at similar rates, which is relevant for both soil and marine (bio)degradability.

Pilot-scale hybrid constructed wetlands for the treatment of cooling tower water prior to its desalination and reuse.

Cooling towers are responsible for a large part of the industrial fresh water withdrawal, and the reuse of cooling tower water (CTW) effluents can strongly lower industrial fresh water footprints. CTW requires desalination prior to being reused, but various CTW components, such as total organic carbon (TOC), conditioning chemicals and total suspended solids (TSS) hamper physico-chemical desalination technologies and need to be removed from the CTW. A cost-efficient and robust pre-treatment is thus required, which can be provided by constructed wetlands (CWs). The present study is the first study that determined the CTW pre-treatment efficiency of hybrid-CWs and the impact of winter season and biocides in the CTW on the pre-treatment efficiency. The most efficient CW flow type and dominant removal mechanisms for CW components hampering physico-chemical desalination were determined. Subsurface flow CWs removed PO43-, TSS and TOC as a result of adsorption and filtration. Vertical subsurface flow CWs (VSSF-CW) excelled in the removal of benzotriazole as a result of aerobic biodegradation. Horizontal subsurface flow CWs (HSSF-CW) allowed the denitrification of NO3- due to their anaerobic conditions. Open water CWs (OW-CWs) did not contribute to the removal of components that hamper physico-chemical desalination technologies, but do provide water storage options and habitat. The biological removal processes in the different CW flow types were negatively impacted by the winter season, but were not impacted by concentrations of the biocides glutaraldehyde and DBNPA that are relevant in practice. For optimal pre-treatment, a hybrid-CW, consisting of an initial VSSF-CW followed by an OW-CW and HSSF-CW is recommended. Future research should focus on integrating the hybrid-CW with a desalination technology, e.g. reverse osmosis, electrodialysis or capacitive ionization, to produce water that meets the requirements for use as cooling water and allow the reuse of CTW in the cooling tower itself.

Benzotriazole removal mechanisms in pilot-scale constructed wetlands treating cooling tower water.

The reuse of discharged cooling tower water (CTW) in the cooling tower itself could reduce fresh water intake and help mitigating fresh water scarcity problems. However, this requires desalination prior to its reuse, and hindering fractions, such as conditioning chemicals, should be removed before desalination to obtain a higher desalination efficiency. Constructed wetlands (CWs) can provide such a pre-treatment. In this study, the mechanisms underlying the removal of conditioning chemical benzotriazole (BTA) in CWs was studied using an innovative approach of differently designed pilot-scale CWs combined with batch removal experiments with substrate from these CWs. By performing these combined experiments, it was possible to determine the optimal CW design for BTA removal and the most relevant BTA removal processes in CWs. Adsorption yielded the highest contribution, and the difference in removal between different CW types was linked to their capability to aerobically biodegrade BTA. This knowledge on the main removal mechanisms for BTA allows for a CW design tailored for BTA removal. In addition, the outcomes of this research show that performing batch experiments with CW substrate allows one to determine the relevant removal mechanisms for a given compound which results in a better understanding of CW removal processes.

An examination of the role of biochar and biochar water-extractable substances on the sorption of ionizable herbicides in rice paddy soils.

The application of biochar as a soil amendment can increase concentrations of soil organic matter, especially water-extractable organic substances. Due to their mobility and reactivity, more studies are needed to address the potential impact of biochar water-extractable substances (BWES) on the sorption of herbicides in agricultural soils that are periodically flooded. Two paddy soils (100 and 700 years of paddy soil development), unamended or amended with raw (BC) or washed biochar (BCW), were used to test the influence of BWES on the sorption behavior of the herbicides azimsulfuron (AZ) and penoxsulam (PE). The adsorption of AZ to biochar was much stronger than that to the soils, and it was adsorbed to a much larger extent to BC than to BCW. The depletion of polar groups in the BWES from the washed biochar reduced AZ adsorption but had no effect on PE adsorption. The adsorption of AZ increased when the younger soil (P100) was amended with BC and decreased when it was amended with BCW. In P700, which has lower dissolved organic carbon (DOC) content than P100, the adsorption of AZ increased regardless of whether biochar was raw or washed. The adsorption of PE slightly decreased when P100 was amended with BC or BCW and slightly increased when P700 was amended with BC or BCW. In order to evaluate compositional differences in the biochar and BWES before and after the washing treatment, we performed solid-state 13C NMR spectroscopy of BC and BCW, and high resolution mass spectrometry of BWES. Our observations stress the importance of proper consideration of soil and biochar properties before their incorporation into paddy soils, since biochar may reduce or increase the mobility of AZ and PE depending on soil properties and time of application.

Long-term exposure of activated sludge in chemostats leads to changes in microbial communities composition and enhanced biodegradation of 4-chloroaniline and N-methylpiperazine.

Exposure history and adaptation of the inoculum to chemicals have been shown to influence the outcome of ready biodegradability tests. However, there is a lack of information about the mechanisms involved in microbial adaptation and the implication thereof for the tests. In the present study, we investigated the impact of a long-term exposure to N-methylpiperazine (NMP) and 4-chloroaniline (4CA) of an activated sludge microbial community using chemostat systems. The objective was to characterize the influence of adaptation to the chemicals on an enhanced biodegradation testing, following the OECD 310 guideline. Cultures were used to inoculate the enhanced biodegradability tests, in batch, before and after exposure to each chemical independently in chemostat culture. Composition and diversity of the microbial communities were characterised by 16s rRNA gene amplicon sequencing. Using freshly sampled activated sludge, NMP was not degraded within the 28 d frame of the test while 4CA was completely eliminated. However, after one month of exposure, the community exposed to NMP was adapted and could completely degrade it. This result was in complete contrast with that from the culture exposed for 3 months to 4CA. Long term incubation in the chemostat system led to a progressive loss of the initial biodegradation capacity of the community, as a consequence of the loss of key degrading microorganisms. This study highlights the potential of chemostat systems to induce adaptation to a specific chemical, ultimately resulting in its biodegradation. At the same time, one should be critical of these observations as the dynamics of a microbial community are difficult to maintain in chemostat, as the loss of 4CA biodegradation capacity demonstrates.