High Throughput Biodegradation-Screening Test To Prioritize and Evaluate Chemical Biodegradability

Design of greener drugs: aligning parameters in pharmaceutical R&D and drivers for environmental impact

Active pharmaceutical ingredients (APIs) in the environment, primarily resulting from patient excretion, are of concern because of potential risks to wildlife. This has led to more restrictive regulatory policies. Here, we discuss the 'benign-by-design' approach, which encourages the development of environmentally friendly APIs that are also safe and efficacious for patients. We explore the challenges and opportunities associated with identifying chemical properties that influence the environmental impact of APIs. Although a straightforward application of greener properties could hinder the development of new drugs, more nuanced approaches could lead to drugs that benefit both patients and the environment. We advocate for an enhanced dialogue between research and development (R&D) and environmental scientists and development of a toolbox to incorporate environmental sustainability in drug development.

Remarkably and stable catalytic activity in reduction of 4-nitrophenol by sodium sesquicarbonate-supporting Fe2O3@Pt

Reasonable design of bimetallic nanomaterials with support is beneficial to improve catalytic performance. This work reports a new kind of sodium sesquicarbonate-supporting Fe₂O₃@Pt via etching Fe₃O₄@Pt@SiO₂, which exhibits highly efficient and stable catalytic reduction performance towards 4-NP. Sodium sesquicarbonate-supporting Fe₂O₃@Pt has an interconnected one-dimensional network structure that provides sufficient channels for mass transfer. At the same time, a large amount of Fe₂O₃@Pt is exposed on its surface, which hinders the aggregation of pt clusters and Fe₂O₃ nanoparticles, and facilitates the direct contact of Fe₂O₃@Pt reaction sites with reactant molecules, thus improving the catalytic rate of 4-NP reduction reaction. Moreover, the introduction of non-metallic Fe can not only reduce the consumption of precious metal Pt, but also improve the catalytic efficiency due to the synergistic effect. This study opens up a new avenue to develop robust catalysts for heterogeneous catalytic reactions.

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).

Classification and Regression Machine Learning Models for Predicting Aerobic Ready and Inherent Biodegradation of Organic Chemicals in Water

Machine learning (ML) is viewed as a promising tool for the prediction of aerobic biodegradation, one of the most important elimination pathways of organic chemicals from the environment. However, available models only have small datasets (<3200 records), make binary classification predictions, evaluate ready biodegradability, and do not incorporate experimental conditions (e.g., system setup and reaction time). This study addressed all these limitations by first compiling a large database of 12,750 records, considering both ready and inherent biodegradation under different conditions, and then developing regression and classification models using different chemical representations and ML algorithms. The best regression model (R² = 0.54 and root mean square error of 0.25) and classification model (the prediction accuracy from 85.1%) achieved very good performance. The model interpretation indicated that the models correctly captured the effects of chemical substructures, following the order of C═O > O═C-O > OH > CH₃ > halogen > branching > N > 6-member ring. The consideration of chemical speciation based on pK_a and α notations did not affect the regression model performance but significantly improved the classification model performance (the accuracy increased to 87.6%). The models also showed large applicability domains and provided reasonable predictions for more than 98% of over 850,000 environmentally relevant chemicals in the Distributed Structure-Searchable Toxicity database. These robust, trustable models were finally made widely accessible through two free online predictors with graphical user interface.

Assessment of leachable and persistent dissolved organic carbon in sludges and biosolids from municipal wastewater treatment plants

Environmental regulation of organic pollutants has not kept pace with the growth in the number and diversity of legacy and emerging organic substances now in use. Simpler and cheaper tools and methodologies are needed to quickly assess the organic pollutant risks in waste materials applied to land such as municipal wastewater treatment sludges and biosolids. This study attempts to provide these, using an approach that consists of chemical leaching and analysis of dissolved organic carbon and determination of its biodegradability by measuring persistent dissolved organic carbon. Primary and secondary sludges, dewatered sludge cake, and anaerobically and thermally treated biosolids obtained from various types of municipal wastewater treatment plants were used in the study. The study found little variability in the levels of dissolved organic carbon leached from primary sludges obtained from different municipal wastewater treatment plants but found significant differences for secondary sludges based on levels of nitrification at the municipal wastewater treatment plants. As predicted treated biosolids leached less dissolved organic carbon than untreated dry sludges but had relatively higher proportions of persistent or poorly biodegradable dissolved organic carbon. Across all tested sludges and biosolids persistent dissolved organic carbon ranged from 14 to 39%, with biosolids that have undergone anaerobic digestion and thermal treatment more likely to contain greater relative proportion of persistent dissolved organic carbon than untreated sludges. The approach presented in this study will be useful in assessing the effectiveness of current and widely employed sludge treatment methods in reducing persistent organic pollutants in biosolids disposed on land.

Establishing a ready biodegradability test system using OxiTop® to evaluate chemical fate in a realistic environment

The purpose of this study is to propose the use of OxiTop® for measuring biochemical oxygen demand (BOD) under the Japanese Chemical Substances Control Law in order to properly evaluate chemical fate in a real environment. In our previous study, the biodegradation of test chemicals was accelerated by both adsorbing the chemical to silica gel with chloroform and increasing the medium volume from 300 to 3900 mL in the OECD 301F test using a coulometer. However, the biodegradability of these chemicals could not be evaluated based on BOD due to chloroform residue in the silica gel, or the medium volume could not be increased further due to the oven size of the coulometer. In this study, we established an evaluation system using OxiTop® based on BOD by increasing the medium volume to 9000 mL. Based on triplicate testing, increasing the medium volume accelerated biodegradation and decreased variation in BOD.

Insight into the Morphology-Dependent Catalytic Performance of CuO/CeO2 Produced by Tannic Acid for Efficient Hydrogenation of 4-Nitrophenol

The construction of a heterogeneous nanocatalyst with outstanding catalytic performance via an environmentally benign and cost-effective synthetic category has long been one of the challenges in nanotechnology. Herein, we synthesized highly efficient and low-cost mesoporous morphology-dependent CuO/CeO₂ -Rods and CuO/CeO₂ -Cubes catalysts by employing a green and multifunctional polyphenolic compound (tannic acid) as the stabilizer and chelating agent for 4-nitrophenol (4-NP) reduction reaction. The CuO/CeO₂ -Rods exhibited excellent performance, of which the activity was 3.2 times higher than that of CuO/CeO₂ -Cubes. This can be connected with the higher density of oxygen vacancy on CeO₂ -Rods (110) than CeO₂ -Cubes (100), the oxygen vacancy favors anchoring CuO species on the CeO₂ support, which promotes the strong interaction between finely dispersed CuO and CeO₂ -Rods at the interfacial positions and facilitates the electron transfer from BH₄ ^- to 4-NP. The synergistic catalytic mechanism illustrated that 4-NP molecules preferentially adsorbed on the CeO₂ , while H₂ from BH₄ ^- dissociated over CuO to form highly active H* species, contributing to achieving efficient hydrogenation of 4-NP. This study is expected to shed light on designing and synthesizing cost-effective and high-performance nanocatalysts through a greener synthetic method for the areas of catalysis, nanomaterial science and engineering, and chemical synthesis.

Investigation of OECD 301F ready biodegradability test to evaluate chemical fate in a realistic environment

The OECD 301F ready biodegradability test has been approved for use under the Japanese Chemical Substances Control Law since 2018. This test uses activated sludge obtained from a sewage treatment plant instead of the standard activated sludge used for the 301C test. In addition, the test is allowed to add an inert support or emulsifying agent, and/or to change the volume of the test medium. In this study, we first confirmed that the standard sludge had lower biodegradation activities than the sludge taken from a sewage treatment plant. Second, we showed that biodegradation percentages were increased by adding suitable amounts of silica gel or Tween 80. Third, we found that the biodegradations were accelerated by only increasing the medium volume under the conditions that concentrations of chemical, silica gel, and sludge were held constant. These findings are expected to contribute to the appropriate evaluation of chemical fate in a realistic environment.

Household discharge of chemical products and its classification based on anaerobic biodegradability

Synthetic household chemical products (HCP) are used in various household activities. An average urban household was estimated to consume ~ 3 kg HCP per month while discarding 212-387 mg/L HCP in sewage comprising > 265 different chemical compounds. The high sorption properties of HCP and their antimicrobial resistance lead to their long-term persistence in the environment. The intrusion of HCPs and their breakdown products into food chain causes detrimental effects on health and ecology. HCPs comprise mostly of a mixture of xenobiotics, organic and inorganic compounds resulting in an impaired biodegradation. Yet, the biodegradability of HCPs is seldom assessed. Therefore, this research proposes a modified Gompertz model approach to analyze BMP data in order to classify commercially available HCPs into seven groups based on the observed levels of recalcitrance and is in turn coined "Anaerobic Biodegradability Index" (ABI, beginning from ABI-VI to ABI-0 wherein ABI-VI represents the highest degradability and ABI-0 the least). This approach emulates "Energy-Star" ratings of electrical appliances classified based on electrical efficiency. Results of such a classification indicated that HCPs containing ≥ 10% anionic surfactants such as laundry detergents, handwash gel, dishwasher chemicals, and creosote surface cleaner, exhibit lowered anaerobic degradability and were therefore categorized between ABI-0 and ABI-II. Whereas the highly degradable HCP such as toothpaste, shower gel, and hair shampoo were categorized in ABI-V and ABI-VI categories. We perceive that the weightages and concentrations can be used in the future to define the capability of various wastewater treatment systems and their tolerance to various ABI classes.

Assessment on biodegradability prediction of tannery wastewater using EPI Suite BIOWIN model

Biodegradation of organic compounds would reveal important information on the final fate of a chemical in the environment. However, establishing biodegradability and fate of a chemical is cumbersome. In this scenario, the use of multimedia models help in predicting the fate and half-life of any compound to establish biodegradability. The study commenced with collection of wastewater samples, after primary and secondary treatment, from a Common Effluent Treatment Plant (CETP) treating tannery wastewater. The samples were subjected to gas chromatography-mass spectrometry (GC-MS) analysis. The GC-MS analysis identified that polyphenolic compounds were detected after biological treatment. The identified compounds emanated from tanning, dyeing, and fatliquoring process of leather making. Estimation Program Interface (EPI) Suite BIOWIN 3 and BIOWIN 4 model prediction revealed that while the primary biodegradation time-frame ranged from days to weeks, the ultimate biodegradation took weeks in the case of all the detected compounds. This study established that BIOWIN model could be used as a screening tool to determine biodegradability of complex chemicals used in tanneries and help to design better treatment facility with enhanced efficiency for removal of polyphenolic compounds. This methodology can also be applied to other industrial wastewaters containing recalcitrant chemicals, and with the help of BIOWIN model, information on biodegradability of chemicals present in the wastewater can be obtained.

Self-supporting hierarchical PdCu aerogels for enhanced catalytic reduction of 4-nitrophenol

This work reports a new kind of self-assembled PdCu monolithic aerogels via a mild reduction process, which exhibits highly efficient catalytic reduction activity towards 4-nitrophenol. The enhanced catalytic reduction performance can be contributed the following unique features of PdCu aerogels: 1) the interconnected channels and three-dimensional network provide a platform for accelerating mass transfer during catalysis; 2) metallic aerogels combined with stretching ultrathin nanowires has a large surface area and good crystallinity affording sufficient reactive sites and high atom utilization; 3) the introduction of nonprecious Cu not only drastically cuts down the cost but also attains the excellent catalytic activity due to the bimetallic intrinsic synergetic effect; 4) the self-supporting feature is good for improving the durability of the catalyst. This study pushes a new avenue to develop robust catalysts for heterogeneous catalytic reactions.

Multi-laboratory Validation of a New Marine Biodegradation Screening Test for Chemical Persistence Assessment

Current biodegradation screening tests are not specifically designed for persistence assessment of chemicals, often show high inter- and intra-test variability, and often give false negative biodegradation results. Based on previous studies and recommendations, an international ring test involving 13 laboratories validated a new test method for marine biodegradation with a focus on improving the reliability of screening to determine the environmental degradation potential of chemicals. The new method incorporated increased bacterial cell concentrations to better represent the microbial diversity; a chemical is likely to be exposed in the sampled environments and ran beyond 60 days, which is the half-life threshold for chemical persistence in the marine environment. The new test provided a more reliable and less variable characterization of the biodegradation behavior of five reference chemicals (sodium benzoate, triethanolamine, 4-nitrophenol, anionic polyacrylamide, and pentachlorophenol), with respect to REACH and OSPAR persistence thresholds, than the current OECD 306 test. The proposed new method provides a cost-effective screening test for non-persistence that could streamline chemical regulation and reduce the cost and animal welfare implications of further higher tier testing.

Increased cell numbers improve marine biodegradation tests for persistence assessment

Currently available OECD biodegradation screening tests (BSTs) are not particularly suited for persistence screening. Their duration can be much less than international half-life thresholds for persistence and they are variable and stringent, therefore prone to false negatives. The present study extended test durations beyond 28 days and increased biomass concentrations for marine BSTs to better represent the microbial diversity inherent in the sampled environment. For this so-called environmentally relevant BST (erBST) marine cell concentrations were nominally increased 100-fold by tangential flow filtration. The marine erBST was validated against a standard BST using five ¹⁴C labeled reference compounds with a range of biodegradation potentials (aniline, 4-fluorophenol, 4-nitrophenol, 4-chloroaniline and pentachlorophenol) in a modified OECD 301B test. A full mass balance was collated to follow chemical fate in the tests. The erBST was more accurate and less variable than the comparator BST in assigning the reference compounds to their expected biodegradation classifications (non-persistent or potentially persistent). According to the REACH non-persistence criterion of ≥60% biodegradation over 60 days, the erBST correctly classified 60% of chemical replicates according to their expected biodegradation classification and had a coefficient of variation of 21% between replicates. In contrast, the BST correctly assessed 40% of reference chemicals in regards to their expected biodegradation classification with a coefficient of variation of 36%. All non-persistent chemicals showed increased degradation in the erBST, except for 4-chloroaniline, which did not degrade in either BST or erBST. Both tests showed no false positive results, correctly classifying the negative control pentachlorophenol as potentially persistent. Next, it is recommended to further validate the marine erBST in an inter-laboratory study incorporating different seawater sources to fully assess its variability and reliability.

The experimental determination of reliable biodegradation rates for mono-aromatics towards evaluating QSBR models

Quantitative Structure Biodegradation Relationships (QSBRs) are a tool to predict the biodegradability of chemicals. The objective of this work was to generate reliable biodegradation data for mono-aromatic chemicals in order to evaluate and verify previously developed QSBRs models. A robust biodegradation test method was developed to estimate specific substrate utilization rates, which were used as a proxy for biodegradation rates of chemicals in pure culture. Five representative mono-aromatic chemicals were selected that spanned a wide range of biodegradability. Aerobic biodegradation experiments were performed for each chemical in batch reactors seeded with known degraders. Chemical removal, degrader growth and CO₂ production were monitored over time. Experimental data were interpreted using a full carbon mass balance model, and Monod kinetic parameters (Y, K_s, q_max and μ_max) for each chemical were determined. In addition, stoichiometric equations for aerobic mineralization of the test chemicals were developed. The theoretically estimated biomass and CO₂ yields were similar to those experimentally observed; 35% (s.d ± 8%) of the recovered substrate carbon was converted to biomass, and 65% (s.d ± 8%) was mineralised to CO₂. Significant correlations were observed between the experimentally determined specific substrate utilization rates, as represented by q_max and q_max/K_s, at high and low substrate concentrations, respectively, and the first order biodegradation rate constants predicted by a previous QSBR study. Similarly, the correlation between q_max and selected molecular descriptors characterizing the chemicals structure in a previous QSBR study was also significant. These results suggest that QSBR models can be reliable and robust in prioritising chemical half-lives for regulatory screening purposes.

Improving the biodegradability in seawater test (OECD 306)

Growth and extensive urbanisation of the human population has been accompanied by increased manufacture and use of chemical compounds. To classify the fate and behaviour of these compounds in the environment, a series of international standardised biodegradation screening tests (BSTs) were developed over 30 years ago. In recent years, regulatory emphasis (e.g. REACH) has shifted from measuring biodegradation towards prioritisations based on chemical persistence. In their current guise, BSTs are ineffective as screens for persistence. The marine BST OECD 306 in particular is prone to high levels of variation and produces a large number of fails, many of which can be considered false negatives. An ECETOC funded two-day workshop of academia, industry and regulatory bodies was held in 2015 to discuss improvements to the marine BSTs based on previous research findings from the Cefic LRI ECO11 project and other foregoing studies. During this workshop, methodological improvements to the OECD 306 test were discussed, in addition to clarifying guidance on testing and interpretation of results obtained from marine BSTs (such as pass criteria, lag phases, freshwater read across and complex substances). Methodologically: (i) increasing bacterial cell concentrations to better represent the bacterial diversity inherent in the sampled environments; and (ii) increasing test durations to investigate extended lag phases observed in marine assessments, were recommended to be validated in a multi-institutional ring test.

Improving the ecological relevance of aquatic bacterial communities in biodegradability screening assessments

Concentrating cells from aqueous samples is a common requirement for the enumeration of biomass, investigations of microbial diversity and detection of relatively rare organisms in the environment. Accurately representing the initial sampled environments in the concentrated cells is of particular importance when the subsequent analyses have tangible environmental, economic and societal consequences, as is the case with environmental exposure and risk assessment of chemicals. This study investigated the potential use of four different cell concentration methods: centrifugation, membrane filtration, tangential flow filtration and column colonisation. These methods were assessed against a series of scientific and practical criteria, including: similarity of concentrated community to initial environmental sample; cell concentration achieved; biodegradation test outcome; sample throughput; and capital and maintenance costs. All methods increased cell concentration by as little as 10-fold to as much as 1000-fold. DGGE and 454 pyrosequencing analysis showed concentrated communities to have >60% similarity to each other, and the initial sample. There was a general trend for a more reliable assessment of 4-nitrophenol biodegradation in 96-well plate biodegradation assays, with increasing cell concentration. Based on the selection criteria, it is recommended that there is not one concentration method fit for all purposes, rather, the appropriate method should be selected on a case-by-case basis. Membrane filtration would be the most suitable method for low sample volumes; the increased throughput capacity of tangential flow filtration renders it most suitable for large volumes; and centrifugation is most suitable for samples with high initial biomass concentrations. The poor similarity in microbial community composition of the column colonised samples compared to the initial samples, suggested a concentration basis; this combined with its low sample throughput precluded this approach for future concentration studies of planktonic bacterial samples.

Assessing the suitability of a manometric test system for determining the biodegradability of volatile hydrocarbons

Manometric test systems, adapted from those used to measure biochemical oxygen demand (BOD), and the OxiTop^® test system in particular, are being increasingly used to determine the biodegradability of chemicals in accordance to OECD 301F guidelines. In this study, the suitability of the OxiTop^® test system for determining the biodegradability of volatile hydrophobic substances has been explored. Experiments in biotic and abiotic systems were conducted with readily biodegradable complex aliphatic hydrocarbons covering a range of volatilities. Results indicated that abiotic losses of test substances were occurring due to sorption of the test substance to plastic components used in the OxiTop^® system. A further 'plastic-free' biodegradation test system was designed using PreSens optical dissolved oxygen (DO) sensors. This significantly improved the measured biodegradation due to reduced abiotic losses and better retention of the test substance. These results highlight the importance of considering the physico-chemical properties of test substances when selecting test methods and equipment. They also highlight the value of incorporating chemical analysis and abiotic controls to improve the interpretation of biodegradation studies.

Determining Biodegradation Kinetics of Hydrocarbons at Low Concentrations: Covering 5 and 9 Orders of Magnitude of Kow and Kaw

A partitioning-based experimental platform was developed and applied to determine primary biodegradation kinetics of 53 hydrocarbons at ng/L to μg/L concentrations covering C8-C20, 11 structural classes, and several orders of magnitude in hydrophobicity and volatility: (1) Passive dosing from a loaded silicone donor was used to set the concentration of each hydrocarbon in mixture stock solutions; (2) these solutions were combined with environmental water samples in gastight auto sampler vials for 1-100 days incubation, and (3) automated solid phase microextraction (SPME) coupled to GC-MS was applied directly on these test systems for measuring primary biodegradation relative to abiotic controls. First order biodegradation kinetics were obtained for 40 hydrocarbons in activated sludge filtrate, 18 in seawater, and 21 in lake water. Water phase half-lives in seawater and lake water were poorly related to hydrophobicity and volatility but were, with a few exceptions, within a factor of 10 or shorter than BioHCwin predictions. The most persistent hydrocarbons, 1,1,4,4,6-pentamethyldecalin, perhydropyrene, 1,2,3,6,7,8-hexahydropyrene, and 2,2,4,4,6,8,8-heptamethylnonane, showed limited or inconsistent degradation in all three environmental media. This biodegradation approach can cover a large chemical space at low substrate concentrations, which makes it highly suited for optimizing predictive models for environmental biodegradation.