Co-occurrence, toxicity, and biotransformation pathways of metformin and its intermediate product guanylurea: Current state and future prospects for enhanced biodegradation strategy

Accumulation of metformin and its biotransformation product "guanylurea" are posing an increasing concern due to their low biodegradability under natural attenuated conditions. Therefore, in this study, we reviewed the unavoidable function of metformin in human body and the route of its release in different water ecosystems. In addition, metformin and its biotransformation product guanylurea in aquatic environments caused certain toxic effects on aquatic organisms which include neurotoxicity, endocrine disruption, production of ROS, and acetylcholinesterase disturbance in aquatic organisms. Moreover, microorganisms are the first to expose and deal with the release of these contaminants, therefore, the mechanisms of biodegradation pathways of metformin and guanylurea under aerobic and anaerobic environments were studied. It has been reported that certain microbes, such as Aminobacter sp. and Pseudomonas putida can carry potential enzymatic pathways to degrade the dead-end product "guanylurea", and hence guanylurea is no longer the dead-end product of metformin. However, these microbes can easily be affected by certain geochemical cycles, therefore, we proposed certain strategies that can be helpful in the enhanced biodegradation of metformin and its biotransformation product guanylurea. A better understanding of the biodegradation potential is imperative to improve the use of these approaches for the sustainable and cost-effective remediation of the emerging contaminants of concern, metformin and guanylurea in the near future.

The elevated toxicity of the biodegradation product (guanylurea) from metformin and the antagonistic pattern recognition of combined toxicity: Insight from the pharmaceutical risk assessment and the simulated wastewater treatment

The emerging contaminants metformin (MET) and its degradation product guanylurea (GUA) are released into aquatic environments through wastewater treatment plants (WWTPs). Thus, the environmental risks of wastewater with more treatments may be underestimated due to the lower effect concentration of GUA and the higher detected concentration of GUA in treated wastewater in comparison with MET. In this study, we aimed to investigate the combined toxicity mode of MET and GUA to Brachionus calyciflorus by simulating the degrees of wastewater treatments through adjustments to the ratio of MET and GUA in medium. The results showed that the 24 h-LC₅₀ of MET, GUA, their mixtures of equal concentrations and the mixtures of equal toxic units to B. calyciflorus were 907.44, 544.53, 1185.82 and 940.52 mg/L, respectively, demonstrating GUA is significantly more toxic than MET. An antagonistic interaction between MET and GUA was found in mixture toxicity assessments. Compared with the control, MET treatments only significantly affected the intrinsic rate of population increase of rotifers (r_m), while all life-table parameters were significantly affected by GUA. In addition, at medium and high concentrations (120 and 600 μmol/L), the net reproductive rate (R₀) and r_m of rotifers under GUA were significantly lower than those under MET. Notably, increased proportion of GUA relative to MET in binary-mixture treatments resulted in increased survival risk and reduced fecundity of rotifers. Moreover, the responses of population dynamics to exposures of MET and GUA were mainly attributed to the reproduction of rotifer, indicating that an improved wastewater treatment process is necessary to protect aquatic ecosystems. The study highlights the importance of considering the combined toxicity of emerging contaminants and degradation product in environmental risk assessment, especially the unintentional transformations of parent compound in treated wastewater.

Environmental Concentrations of the Type 2 Diabetes Medication Metformin and its Transformation Product Guanylurea in Surface Water and Sediment in Ontario and Quebec, Canada

Metformin, used to treat Type 2 Diabetes, is the active ingredient of one of the most prescribed drugs in the world, with over 120 million yearly prescriptions globally. In wastewater treatment plants (WWTPs), metformin can undergo microbial transformation to form the transformation product guanylurea, which could have toxicological relevance in the environment. Surface water samples from 2018-2020 and sediment samples from 2020 were collected from 6 mixed-use watersheds in Quebec and Ontario, Canada and analyzed to determine the metformin and guanylurea concentrations at each site. Metformin and guanylurea were present above their limits of quantification in 51.0 and 50.7% of all water samples, and in 64% and 21% of all sediment samples, respectively. In surface water, guanylurea was often present at higher concentrations than metformin, while the inverse was true in sediment, with metformin frequently detected at higher concentrations than guanylurea. Additionally, at all sites influenced solely by agriculture, concentrations of metformin and guanylurea were lower than 1 µg/L in surface water, suggesting that agriculture is not a significant source of these compounds in the investigated watersheds. These data suggest that WWTPs and potentially septic system leaks are the most likely sources of the compounds in the environment. Guanylurea was detected at many of these sites above environmental concentrations of concern, where critical processes in fish may be affected. Due to the scarcity of available ecotoxicological data and the prominence of guanylurea across all sample sites, there is a need to perform more toxicological investigations of this transformation product and revisit regulations. This report will help provide toxicologists with environmentally relevant concentration ranges in Canada.

Efficacy of activated carbon filtration and ozonation to remove persistent and mobile substances - A case study in two wastewater treatment plants

Persistent and mobile (PM) substances are able to spread quickly in the water cycle and were thus identified as potentially problematic for the environment and water quality. If also toxic (PMT) or very persistent and very mobile (vPvM) their regulation under REACH as substances of very high concern is foreseen. Yet, knowledge on the effectiveness of advanced wastewater treatment in removing PM-substances from WWTP effluents is limited to few rather well-known chemicals. The occurrence and behavior of 111 suspected and known PM-substances was investigated in two wastewater treatment plants employing either powdered activated carbon (PAC, full-scale) or ozonation with subsequent sand/anthracite filtration (pilot-scale) and an additional granular activated carbon (GAC) filtration was investigated. 72 of the 111 PM-substances analyzed were detected at least once in the secondary effluent of either wastewater treatment plant, resulting in total concentrations of 104 μg/L and 40 μg/L, respectively. While PAC removed 32 % of PM-substances well, the total PM burden in the effluent was only reduced from 103 μg/L to 87 μg/L. Ozonation and the subsequent sand/anthracite filtration was able to reduce the PM burden in wastewater from 40 μg/L to 19 μg/L, showing a higher removal efficacy than PAC in this study. The additional GAC filtration further reduced the total PM-concentration to 13 μg/L. Among the investigated PM-chemicals detected were constituents of ionic liquids: The anion hexafluorophosphate was one of few chemicals that was detected in effluent concentrations >1 μg/L and could not be removed by the processes studied, showing that for some chemicals preventive actions may be required.

Chronic exposure to environmentally relevant concentrations of guanylurea induces neurotoxicity of Danio rerio adults

Recent studies have shown guanylurea (GUA) alters the growth and development of fish, induces oxidative stress, and disrupts the levels and expression of several genes, metabolites, and proteins related to the overall fitness of fish. Nonetheless, up to date, no study has assessed the potential neurotoxic effects that GUA may induce in non-target organisms. To fill the current knowledge gaps about the effects of this metabolite in the central nervous system of fish, we aimed to determine whether or not environmentally relevant concentrations of this metabolite may disrupt the behavior, redox status, AChE activity in Danio rerio adults. In addition, we also meant to assess if 25, 50, and 200 μg/L of GUA can alter the expression of several antioxidant defenses-, apoptosis-, AMPK pathway-, and neuronal communication-related genes in the brain of fish exposed for four months to GUA. Our results demonstrated that chronic exposure to GUA altered the swimming behavior of D. rerio, as fish remained more time frozen and traveled less distance in the tank compared to the control group. Moreover, this metabolite significantly increased the levels of oxidative damage biomarkers and inhibited the activity of acetylcholinesterase of fish in a concentration-dependent manner. Concerning gene expression, environmentally relevant concentrations of GUA downregulated the expression GRID2IP, PCDH17, and PCDH19, but upregulated Nrf1, Nrf2, p53, BAX, CASP3, PRKAA1, PRKAA2, and APP in fish after four months of exposure. Collectively, we can conclude that GUA may alter the homeostasis of several essential brain biomarkers, generating anxiety-like behavior in fish.

An 'omics approach to investigate the growth effects of environmentally relevant concentrations of guanylurea exposure on Japanese medaka (Oryzias latipes)

Metformin is a widely prescribed pharmaceutical used in the treatment of numerous human health disorders, including Type 2 Diabetes, and as a results of its widespread use, metformin is thought to be the most prevalent pharmaceutical in the aquatic environment by weight. The removal of metformin during the water treatment process is directly related to the formation of its primary degradation product, guanylurea, generally present at higher concentrations in surface waters relative to metformin. Growth effects observed in 28-day early life stage (ELS) Japanese medaka exposed to guanylurea were found to be similar to growth effects in 28-day ELS medaka exposed to metformin; however, effect concentrations were orders of magnitude below those of metformin. The present study uses a multi-omics approach to investigate potential mechanisms by which low-level, 1 ng · L-1 nominal, guanylurea exposure may lead to altered growth in 28-day post hatch medaka via shotgun metabolomics and proteomics and qPCR. Specifically, analyses show 6 altered metabolites, 66 altered proteins and 2 altered genes. Collectively, metabolomics, proteomics, and gene expression data (using qPCR) indicate that developmental exposure to guanylurea exposure alters a number of important pathways related to the overall health of ELS fish, including biomolecule metabolism, cellular energetics, nervous system function/development, cellular communication and structure, and detoxification of reactive oxygen species, among others. To our knowledge, this is the first study to both report the molecular level effects of guanylurea on non-target aquatic organisms, and to relate molecular-level changes to whole organism effects.

Biodegradation of metformin and its transformation product, guanylurea, by natural and exposed microbial communities

Metformin (MET) is a pharmaceutical product mostly biotransformed in the environment to a transformation product, guanylurea (GUA). In ready biodegradability tests (RBTs), however, contrasting results have been observed for metformin. The objective of this study was to measure the biodegradation of MET and GUA in RBTs, using activated sludge from the local wastewater treatment plant, either directly or after pre-exposure to MET, in a chemostat. The activated sludge community was cultivated in chemostats, in presence or absence of MET, for a period of nine months, and was used in RBT after one, three and nine months. The results of this study showed that the original activated sludge was able to completely remove MET (15 mg/l) and the newly produced GUA (50% of C_0MET) under the test conditions. Inoculation of the chemostat led to a rapid shift in the community composition and abundance. The community exposed to 1.5 mg/l of MET was still able to completely consume MET in the RBTs after one-month exposure, but three- and nine-months exposure resulted in reduced removal of MET in the RBTs. The ability of the activated sludge community to degrade MET and GUA is the result of environmental exposure to these chemicals as well as of conditions that could not be reproduced in the laboratory system. A MET-degrading strain belonging to the genus Aminobacter has been isolated from the chemostat community. This strain was able to completely consume 15 mg/l of MET within three days in the test. However, community analysis revealed that the fluctuation in relative abundance of this genus (<1%) could not be correlated to the fluctuation in biodegradation capacity of the chemostat community.

Developmental and Full-Life Cycle Exposures to Guanylurea and Guanylurea-Metformin Mixtures Results in Adverse Effects on Japanese Medaka (Oryzias latipes)

Metformin is currently thought to be the highest drug by weight released into the aquatic environment, as a direct result of its widespread use in the treatment of a number of human health disorders. The removal of metformin from wastewaters is directly related to the formation of guanylurea (metformin's only known persistent degradation product), which is generally present at higher concentrations in surface waters than the parent compound. With metformin use rising steadily, it is important to characterize the effects of guanylurea on nontarget aquatic organisms. We recently demonstrated the effects of developmental exposure to environmentally relevant concentrations of metformin on the growth of early life stage (ELS) medaka as well as effects on the body weight of adult male fish following full-life cycle exposures. In the present study, we describe similar effects of guanylurea exposure on these endpoints and life stages. Guanylurea led to effects on growth in a 28-d ELS assessment that were similar to those of metformin; however, these effects occurred at concentrations in the ng/L range compared with the μg/L range for metformin. A possible sex-dependent association with body weight changes was also observed in adults following a 165-d full-life cycle exposure to guanylurea alone or in a mixture with metformin. To our knowledge, the present is the first study to report the toxicity of guanylurea to nontarget aquatic organisms. Environ Toxicol Chem 2019;00:1-6. © 2019 SETAC.

Modelling degradation kinetics of metformin and guanylurea in soil microcosms to derive degradation end-points

The degradation of metformin (MET) and guanylurea (GUA) fortified separately in freshly collected two top soils (0-10 cm) from New Zealand's pastoral region was studied under controlled laboratory conditions. Incubation studies were carried at 30 °C under aerobic conditions at 60% of maximum water holding capacity and at two (0.5 mg/kg and 5 mg/kg) nominal soil concentrations. Degradation profiles revealed a bi-phasic pattern of both the compounds with an initial rapid degradation followed by slow dissipation rate, resulting in poor fits by simple first order kinetics. However, the use of three non-linear mathematical models sufficiently described the measured data and well supported by an array of statistical indices to judge model's ability to fit the measured datasets. Further evaluation using box-whisker plots showed that double first-order in parallel (DFOP) and first-order two-compartment (FOTC) models best fitted the data points followed by the Bi-exponential (BEXP) model. Mechanistic assumptions from DFOP and FOTC suggest that degradation of MET and GUA proceeds at two different rates, possibly in two compartments. The calculated DT₅₀ using both models were in the range of 2.7-15.5 days and 0.9-4 days, while 90% dissipation time (DT₉₀) varied between 91 and 123 days and 44 and 137 days for MET and GUA, respectively. Degradation of both compounds were dependent on soil types and properties, incubation conditions and initial substrate concentration. Formation of GUA with decrease in MET concentration over time confirmed that GUA is a transformation product concomitantly formed from aerobic degradation of MET in soil.

Environmental risk assessment of metformin and its transformation product guanylurea. I. Environmental fate

Metformin (MET) is a pharmaceutical with very high use worldwide that is excreted in unchanged form, leading to concern about potential aquatic life impacts associated with MET, and its primary transformation product guanylurea (GUU). This study presents, in two companion papers, a risk assessment following internationally accepted guidelines of MET and GUU in surface water based on literature data, previously unpublished studies, and a new degradation test that resolves conflicting earlier results. Previous studies have shown that MET is removed during sewage treatment, primarily through transformation to GUU. In addition, measurements in WWTPs suggest that MET is not only transformed to GUU, but that GUU is further biodegraded. A prolonged inherent biodegradation test strongly suggests not only primary transformation of MET to GUU, but also subsequent full mineralization of GUU, with both degradation phases starting after a clear lag phase. MET may partition from surface water to sediment, where both transformation to GUU and in part mineralization is possible, depending on the presence of competent degrading microorganisms. In addition, MET may form non-extractable residues in sediments (12.8-73.5%). Both MET and GUU may be anaerobically degraded during sludge digestion, in soils or in sediments. Bioconcentration factor (BCF) values in crops and most plants are close to 1 suggesting low bioaccumulation potential, moreover, at least some plants can metabolize MET to GUU; however, in aquatic plants higher BCFs were found, up to 53. Similarly, neither MET nor GUU are expected to bioaccumulate in fish based on estimated values of BCFs ≤3.16.

Environmental risk assessment of metformin and its transformation product guanylurea: II. Occurrence in surface waters of Europe and the United States and derivation of predicted no-effect concentrations

Metformin (MET), CAS 1115-70-4 (Metformin hydrochloride), is an antidiabetic drug with high usage in North America and Europe and has become the subject of regulatory interest. A pharmaceutical industry working group investigated environmental risks of MET. Environmental fate and chronic effects data were collated across the industry for the present risk assessment. Predicted environmental concentrations (PECs) for MET were modeled for the USA and Europe using the PhATE and GREAT-ER models, respectively. PECs were compared with measured environmental concentrations (MECs) for the USA and Europe. A predicted no effect concentration (PNEC) of 1 mg/L for MET was derived by deterministic procedures, applying an assessment factor of 10 to the lowest no observed effect concentration (i.e., 10 mg/L) from multiple chronic studies with algae, daphnids and fish. The PEC/PNEC and MEC/PNEC risk characterization ratios were <1, indicating no significant risk for MET with high Margins of Safety (MOS) of >868. MET is known to degrade during wastewater treatment to guanylurea (GUU, CAS 141-83-3), which we have shown to further degrade. There are no GUU toxicity data in the literature; hence, chronic studies for GUU were conducted to derive a PNEC of 0.16 mg/L. PECs were derived for GUU as for MET, plus MECs were retrieved from the literature. The PEC/PNEC and MEC/PNEC risk characterization ratios for GUU were also <1, with an MOS of >6.5. Based on standard risk assessment procedures for both MET and its transformation product GUU, there is no significant risk to aquatic life.

Sorption and mobility of metformin and guanylurea in soils as affected by biosolid amendment: Batch and column tests

Recent classification of metformin as an emerging contaminant warrants assessment of its fate and behaviour in the natural environment especially with land-based application of potentially contaminated wastewaters and biosolids. The present study provided further insight into the sorption mechanisms of metformin and its transformation product guanylurea in soil and upon biosolid fortification. Decreased metformin sorption (12.4%) as measured by the effective distribution coefficient (K_d^eff) was observed with biosolids amendment while significant increase (2500%) in guanylurea sorption was calculated. Analysis of co-solute effects confirmed their contrasting sorption mechanisms with the absence of competitive effects in unamended soil. Results of the column tests were in good agreement with the batch sorption studies as the fitted values of retardation factors decreased and increased for metformin and guanylurea, respectively, upon addition of biosolids. The shapes of the breakthrough curves suggest slower desorption rates for both compounds in unamended soil resulting to non-equilibrium conditions and back-end tailings. However, in biosolid-amended soil columns, these tailings were less pronounced resembling equilibrium transport. Results also demonstrated enhanced mobility of both compounds upon biosolids fortification. The non-equilibrium chemical transport model fitted the measured data well (0.975 > r² > 0.988) especially for unamended soils which suggests the existence of non-equilibrium conditions and rate-limited sorption sites.

Insight into the sorption mechanism of metformin and its transformation product guanylurea in pastoral soils and model sorbents

Single solute sorption mechanisms of metformin (MET) and guanylurea (GUA) were investigated in six soils and three model sorbents (kaolinite, bentonite and humic acid) at varying initial pH and background electrolyte (Ca²⁺) concentrations. Electrostatic interaction and cation exchange were proposed as mechanisms of MET sorption. At initial solution pH between pKa₁ and pKa₂, electrostatic interaction is the dominating mechanism of MET sorption. However, as pH approaches pKa₁, cation exchange becomes a significant mechanism of sorption as evidenced by the increased distribution coefficient (K_d) values in Matawhero (130-fold) and Nelson (2000-fold) soils with high cation exchange capacities (CEC) and permanently negative charged sites and when equilibrium pH < pKa₁ where the divalent cationic form dominates in the solution. Furthermore, results showed higher sorption of MET on bentonite with effective distribution coefficient (K_d^eff) value of 14.92 L/kg with high permanent negative charges than on kaolinite (K_d^eff = 6.70 L/kg), a variable charge clay. Increased MET sorption at low equilibrium pH on kaolinite (K_d^eff = 2.3 × 10⁷ L/kg) and humic acid (K_d^eff = 20.86 L/kg) further suggest cation exchange is also possible at pH < pKa₁. On the other hand, two lines of evidence suggest cation exchange as an important mechanism of GUA sorption: (a) the positive correlation between cation exchange capacity and K_d^eff values and (b) decreased K_d^eff values as the Ca²⁺ concentration in solution was increased in all soils. Biosolids amendment of three soils resulted in contrasting effects on sorption affinities with a decrease for MET and increase for GUA, further confirming sorption mechanisms and significance of solution pH and CEC on the sorption of MET and GUA, respectively.

Biodegradation of metformin and guanylurea by aerobic cultures enriched from sludge

Sewage sludge from a municipal wastewater treatment facility employing activated sludge process was pre-incubated with varying substrates and mixtures of substrates including metformin (MET), guanylurea (GUA) and glucose. The biomass from enriched cultures separately utilising MET and glucose/GUA was then used to investigate the kinetics of aerobic biodegradation of MET and GUA, respectively, as individual substrates in batch reactors. The results showed that GUA can be completely degraded as a nitrogen source when glucose is provided as a carbon and energy source. On the contrary, MET can be biodegraded as a sole carbon and energy source. However, formation of by-product GUA in solution, which acts as a nitrogen source, rapidly increased the degradation rate of MET resembling autocatalytic behaviour. At low starting concentration of 5 mg/L, the specific substrate utilisation rates of MET and GUA were 0.0033 day^-1 and 0.0013 day^-1, respectively, which is reported first time in this study. Out of the five biodegradation kinetic models used to describe substrate utilisation, the Quiroga-Sales-Romero (QSR) model was found to predict the measured MET and GUA degradation profile well supported by the goodness of fit parameters. Furthermore, the QSR model was able to describe the autocatalytic degradation of MET and the incomplete biodegradation of GUA in solution.

Occurrence, Impact, Analysis and Treatment of Metformin and Guanylurea in Coastal Aquatic Environments of Canada, USA and Europe

This review discusses the occurrence, impact, analysis and treatment of metformin and guanylurea in coastal aquatic environments of Canada, USA and Europe. Metformin, a biguanide in chemical classification, is widely used as one of the most effective first-line oral drugs for type 2 diabetes. It is difficult to be metabolized by the human body and exists in both urine and faeces samples in these regions. Guanylurea is metformin's biotransformation product. Consequently, significant concentrations of metformin and guanylurea have been reported in wastewater treatment plants (WWTPs) and coastal aquatic environments. The maximum concentrations of metformin and guanylurea in surface water samples were as high as 59,000 and 4502ngL^-1, respectively. Metformin can be absorbed in non-target organisms by plants and in Atlantic salmon (Salmo salar). Guanylurea has a confirmed mitotic activity in plant cells. Analysis methods of metformin are currently developed based on high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). The removal of metformin from aquatic environments in the target regions is summarized. The review helps to fill a knowledge gap and provides insights for regulatory considerations. The potential options for managing these emerging pollutants are outlined too.

Detailed sorption characteristics of the anti-diabetic drug metformin and its transformation product guanylurea in agricultural soils

Detection of metformin, an antidiabetic drug and its transformation product guanylurea in various environmental matrices such as surface water and groundwater, coupled with their effects on aquatic organisms warrant an understanding of the compounds fate and behaviour in the environment. Batch studies were conducted with the aim of evaluating the sorption of these two emerging contaminants in six New Zealand agricultural soils of contrasting physico-chemical properties. Kinetic studies revealed that metformin and guanylurea sorption in Te Kowhai soil was very rapid initially achieving 90% sorption within the first 4 and 13h, respectively. Fit of several isotherm models to the measured batch sorption data showed that the hybrid models Langmuir-Freundlich and Redlich-Peterson best described the isotherms. Freundlich isotherm showed higher linearity for guanylurea (n_F=0.58-0.93) in all soils compared to metformin (n_F=0.25-0.71). A linear isotherm was fitted at environmentally relevant low concentrations (< 3mg/L) of target compounds and calculated values of sorption distribution coefficient (K_d) were in the range of 8.97 to 53.49L/kg for metformin and between 10.6 and 37.51L/kg for guanylurea. Sorption of both metformin and guanylurea was dependent on the soil characteristics, however, no generalisation could be made as to which had higher affinity to soils studied. Pearson's correlation and multiple regression analyses indicate that Si/Al (p=0.042) and clay (p=0.015) significantly influenced metformin K_d values, whereas the soil's cation exchange capacity (p=0.024) is the single most significant factor determining guanylurea sorption in soils. It is likely that the type of minerals present in soils and its ion-exchange capacity could play an important role in metformin and guanylurea sorption, respectively.

FT-IR study and solvent-implicit and explicit effect on stepwise tautomerism of Guanylurea: M06-2X as a case of study

All 66 conformers of guanylurea were optimized and frequency calculations were performed at M06-2X/6-311++G(d,p) level of theory. Theses conformers were categorized into five tautomers, and the most stable conformer of each tautomer were found. Geometrical parameters indicated that these tautomers have almost planar structure. Complete stepwise tautomerism were studied through both intramolecular proton transfer routs and internal rotations. Results indicated that the proton transfer routs involving four-membered heterocyclic structures were rate-determining steps. Also, intramolecular proton movement having six-membered transition state structures had very low energy barrier comparable to the transition states of internal rotation routs. Differentiation of studied tautomers could easily be done through their FT-IR spectra in the range of 3200 to 3900cm^-1 by comparing absorption bands and intensity of peaks. Solvent-implicit effects on the stability of tautomers were also studied through re-optimization and frequency calculation in four solvents. Water, DMSO, acetone and toluene had stabilization effect on all considered tautomers, but the order of stabilization effect was as follows: water>DMSO>acetone>toluene. Finally, solvent-explicit, base-explicit and acid-explicit effect were also studied by taking place of studied tautomer nearside of acid, base or solvent and optimization of them. Frequency calculation for proton movement by contribution of explicit effect showed that formic acid had a very strong effect on proton transfer from tautomer A1 to tautomer D8 by lowering the energy barrier from 42.57 to 0.8kcal/mol. In addition, ammonia-explicit effect was found to lower the barrier from 42.57 to 22.46kcal/mol, but this effect is lower than that of water and methanol-explicit effect.

Occurrence and indicators of pharmaceuticals in Chinese streams: A nationwide study

Pharmaceutically active compounds (PhACs) are excreted by humans and animals and released into the aquatic environment through wastewater, which can have potential negative impacts on ecological systems. To conduct a nationwide investigation of the occurrence of PhACs in water resources in China, an analytical procedure based on solid-phase extraction (SPE) and LC-MS/MS was used to measure 45 PhACs in surface water samples from a network of 29 rivers across 31 provinces in China in 2014 and 2015. PhACs were prevalent in all sampled streams. The concentrations of commonly detected PhACs were comparable to those detected in other countries. High total concentrations (mean > 1 μg L^-1) of all tested PhACs were primarily detected in areas under extreme water stress, specifically northern and eastern coastal areas. Source apportionment based on the profiles of the target compounds found that 54% of the PhACs in China originated from freshly discharged untreated sewage. Metformin (MET) and its biodegradation product, guanylurea (GUL), were used as a pair of indicators to predict PhAC contamination levels and differentiate between biotreated and unbiotreated wastewater. High MET/GUL can be used to indicate untreated wastewater, whereas low MET/GUL values are a strong indicator of treated wastewater. Furthermore, wastewater biotreatment ratios were calculated. We estimated that the biotreatment ratios of most of the provinces in China were less than 50%. We conclude that more attention should be paid to untreated sewage water, especially water in rural areas rather than the existing concentration on urban sewage treatment-oriented management.

A global perspective on the use, occurrence, fate and effects of anti-diabetic drug metformin in natural and engineered ecosystems

Metformin is the most commonly used anti-diabetic drug in the world. When consumed, this unmetabolised pharmaceutical compound is excreted by the body and eventually enters the environment through a variety of pathways. Based on its high consumption and excretion rates, high concentrations of metformin have been detected in influents of wastewater treatment plants. Metformin and its transformation product, guanylurea, are also expected to be present in other aquatic environments based on their physico-chemical properties. Not surprisingly, guanylurea has also been detected in surface water, groundwater, and drinking water. Available information on ecotoxicological effects of metformin suggests that metformin is a potential endocrine disruptor and thus further emphasising the threat this drug could pose to our environment. This review provides a comprehensive overview of metformin and critically discusses available literature data with respect to its global use/demand, occurrence, fate and ecotoxicity in treatment facilities equipped with conventional and advanced treatment technologies, and its degradation/removal mechanisms. Final section highlights the existing knowledge gaps regarding its ultimate fate under the natural and engineered ecosystems and identifies some important research areas requiring urgent attention from regulatory makers and scientific community.

Comprehensive study of the antidiabetic drug metformin and its transformation product guanylurea in Greek wastewaters

Many pollutants such as pharmaceuticals and their transformation products (TPs) are not efficiently removed from wastewater treatment plants and enter into surface waters. The aim of this study was to investigate the occurrence and behavior of metformin, one of the most prescribed drugs worldwide, and its biological transformation product guanylurea, in eight wastewater treatment plants (WWTPs) of Greece. All WWTPs were equipped with conventional activated sludge treatment and the samples were taken from the influents and the effluents, over the four seasons of one year. The analytical method developed based on SPE followed by LC-UV/Vis-ESI/MS analysis, while positive findings were confirmed also by means of LTQ Orbitrap mass spectrometer. High polarity of both compounds led to the extraction with Oasis HLB and the use of the anionic surfactant SDS. The results showed that metformin dominated in the influents (bql-1167 ng/L), while guanylurea in the effluents (bql-627 ng/L) of the wastewater treatment plants, with Metformin/Guanylurea ratio ranging between 0.88 and 81.3 in the influents and between 0.005 and 0.78 in the effluents. Lack of a clear seasonal tendency in the occurrence and removal or formation was observed. Finally, an ecotoxicological risk assessment of metformin in effluent wastewaters took place by calculating the ratio between the environmental concentrations (MEC) and the predicted no effect concentrations (PNEC). Despite the fact that metformin presented low risk in all cases, an environmental concern is suspected for guanylurea since it is continuously released into the aquatic environment.

Effectively designed molecularly imprinted polymers for selective isolation of the antidiabetic drug metformin and its transformation product guanylurea from aqueous media

In the present study, two novel molecularly imprinted polymers (MIPs) with remarkable recognition properties for metformin and its transformation product, guanylurea, have been prepared for their selective, enrichment, isolation and removal from aqueous media. The prepared adsorbents were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and swelling experiments. The performance of the prepared MIPs was evaluated by various parameters including the influence of pH, contact time, temperature and initial compound concentration. The effects on the adsorption behavior of the removal process parameters were studied and the equilibrium data were fitted by the Langmuir and Freundlich models. Due to the imprinting effect, adsorption performance of MIPs was always superior to its corresponding NIP (non-imprinted polymer), with maximum adsorption capacity ∼80 mg g(-1) for both MIPs. Stability and reusability of the MIPs up to the 5th cycle meant that they could be applied repeatedly without losing substantial removal ability. In the next step, the prepared MIP nanoparticles were evaluated as sorbents in a dispersive solid phase extraction (D-SPE) configuration for selective enrichment and determination of metformin and guanylurea in different aqueous matrices. Under the working extraction conditions, the D-SPE method showed good linearity in the range of 50-1000 ng L(-1), repeatability of the extractions (RSD 2.1-5.1%, n=3), and low limits of detection (1.5-3.4 ng L(-1)). The expanded uncertainty of the data obtained was estimated following a bottom-up approach. The proposed method combined the advantages of MIPs and D-SPE, and it could become an alternative tool for analyzing the residues of METF and its transformation product GUA in complex water matrices, such as wastewaters.