Trace level detection of melamine and cyanuric acid extracted from pet liquid food (milk) using a SERS Au nanogap substrate

This study reported an application of Au nanogap substrates for surface-enhanced Raman scattering (SERS) measurements to quantitatively analyze melamine and its derivative products at trace levels in pet liquid food (milk) combined with a waveband selection approach, namely variable importance in projection (VIP). Six different concentrations of melamine, cyanuric acid, and melamine combined with cyanuric acid were created, and SERS spectra were acquired from 550 to 1620cm-1. Detection was possible up to 200 pM for melamine-contaminated samples, and 400 pM concentration detection for other two groups. The VIP-PLSR models obtained correlation coefficient (R2) values of 0.997, 0.985, and 0.981, with root mean square error of prediction (RMSEP) values of 18.492 pM, 19.777 pM, and 15.124 pM for prediction datasets. Additionally, partial least square discriminant analysis (PLS-DA) was used to classify both pure and different concentrations of spiked samples. The results showed that the maximum classification accuracy for melamine was 100%, for cyanuric acid it was 96%, and for melamine coupled with cyanuric acid it was 95%. The results obtained clearly demonstrated that the Au nanogap substrate offers low-concentration, rapid, and efficient detection of hazardous additive chemicals in pet consuming liquid food.

Environmental exposure to melamine and its derivatives and kidney outcomes in children

Melamine caused acute nephrotoxicity in a past food adulteration incident, but it is unclear whether and how widespread ambient exposure to melamine and related compounds might affect pediatric kidney health. We assessed cross-sectional associations between childhood exposure to melamine and its derivatives and biomarkers of kidney injury and health and explored potential heterogeneity by sex suggested by sex-dependent differences in renal physiology. We measured melamine and its derivatives ammeline, ammelide, and cyanuric acid (CYA) in spot urine samples collected from 192 children from an urban site (Seattle, WA) and 187 children from a rural site (Yakima, WA) aged 4-8 years in the Global Alliance to Prevent Prematurity and Stillbirth (GAPPS) Study. In addition, biomarkers of kidney injury were measured in the same urine samples, including albumin, total protein, KIM-1, NAG, NGAL, and EGF. We utilized linear regressions to examine associations between individual chemical exposures and kidney biomarkers. Interaction terms examined association modification by sex, as well as potential interactions between melamine and CYA. Despite comparable exposures, girls had higher levels of many kidney injury biomarkers compared to boys. A ten-fold higher melamine concentration was associated with a 18% (95% CI: 5.6%, 31%) higher EGF in the full sample, while ten-fold higher melamine was associated with a 76% (14.1%, 173%) higher KIM-1 in boys but not in girls (-10.1% (-40.6%, 36.1%), interaction p = 0.026). Melamine exhibited significant negative interactions with CYA in association with total protein and NAG that appeared to be specific to girls. Our results suggest possible associations between melamine exposure and markers of kidney injury that may be more pronounced in boys. These findings provide novel insights into melamine and related derivative compound health effects at low levels of exposure in children and emphasize the role of sex in mediating the relationship between nephrotoxicant exposure and kidney injury.

Nanoflower-like graphitic carbon nitride aerogel: Artful cyanuric acid-controlled synthesis and enhanced photocatalytic hydrogen evolution activity

The previously reported studies on cyanuric acid-assembly strategy usually ignores the promoting function of cyanuric acid in the production of g-C3N4, limiting the development of molecular assembly strategies. In this study, a cyanuric acid-controlled synthesis strategy involving the pre-assembly of cyanuric acid with melamine and subsequent one-step calcination was developed to produce a three-dimensional (3D) nanoflower-like graphitic carbon nitride (g-C3N4) aerogel. Some cyanuric acid molecules underwent a polycondensation reaction with melamine during the pre-assembly process and finally polymerized into the g-C3N4 structure during subsequent calcination. Meanwhile, the remaining cyanuric acid molecules assembled with melamine via hydrogen-bond interactions and underwent incomplete decomposition during subsequent calcination, which not only promoted the production of 3D nanoflower-like aerogel structures, but also introduced the carbonyl (CO) and hydroxyl (-OH) groups onto the g-C3N4 surface, resulting in the successful generation of a 3D nanoflower-like oxygen-modified g-C3N4 aerogel. Moreover, the fabricated g-C3N4 aerogel exhibited a greatly enhanced H2 production rate (1573 μmol h-1 g-1), which is ∼ 6.6 times higher than that of bulk g-C3N4 (239 μmol h-1 g-1) owing to the synergistic promotion function of ultrathin nanoflower-like aerogel and oxygen modification structures. This strategy provides a theoretical basis for the development of highly efficient g-C3N4 photocatalysts via molecular assembly.

Investigation of melamine and cyanuric acid concentration in several brands of liquid milk and its non-carcinogenic risk assessment in adults and infants

In this study, the melamine and cyanuric acid concentration of widely used milk brands and the probability of non-carcinogenic risk of the brands for adults and infants were investigated. These values were 1.37 mg/L, 1.10 mg/L, and 1.09 mg/L, which corresponded to creamy sterilized sample, high-fat (creamy) pasteurized sample, and low-fat (less-creamy) pasteurized sample, respectively. Similarly, the highest amount of cyanuric acid occurred in brand A with the values of 0.79 mg/L, 0.65 mg/L, and 0.64 mg/L, which was reported in the same samples mentioned for melamine. The HQ (Hazard Quotient) of melamine in the brands of A, B, C and D for adults was 0.0025, 0.0011, 0.0006 and 0.0008 respectively. These values for infants were reported as 2.2280, 0.9444, 0.5714 and 0.6714 respectively. The risk probability of melamine for adults was less than 1. However, the HQ in brand A for infants was greater than 1 (2.380), which indicate the high probability of non-carcinogenic risk. Furthermore, the HI (Hazard Index) values of the brands of A, B, C and D for infants were 2.7913, 1.1737, 0.7067 and 0.838, respectively. The simultaneous melamine and cyanuric acid in the brands A and B in for infants increase the non-carcinogenic risk probability by approximately 2.8 and 1.2 times, respectively. The results revealed that the melamine and cyanuric acid concentrations in creamy milk samples (0.5%) were higher than in less-creamy milk samples (2.5%). Moreover, the amount of the compounds in sterilized milk samples was higher than pasteurized. In this study, a conversion factor (0.7) was proposed in order to find out the concentration of cyanuric acid in milk sample with the amount of melamine is known but the cyanuric acid concentration is unknown.

Twenty-four-hour temporal trend of melamine and its derivatives in urine in association with meal consumption: a panel study in Shanghai, China

Timing of sampling is important for the exposure assessment of melamine (MEL) and its derivatives. This study aimed to investigate whether MEL and its derivatives in spot urine can effectively represent individual exposure levels throughout the day in adults and to explore their temporal trend before and after meal consumption for helping understand the timing of sampling and for assessing the potential exposure risk. This is a 2-day panel study with 43 college students being enrolled to provide urine specimens in 24 h (from the morning of the first day to the second day) and to answer a questionnaire on demographic characteristics, physical measurements, and time of having meal. Spearman correlation and Wilcoxon rank-sum test were used to examine the associations of the urinary concentrations of MEL and its derivatives in different sampled times and compare the concentrations' differences before and after meal consumption. Urinary concentrations of MEL and its derivatives (ammeline (AMN), ammelide (AMD), and cyanuric acid (CYA)) in the first-morning urine at the second day and randomly selected spot urine were positively associated with the average concentrations in the previous 24-h urine (all P ≤ 0.002). Urinary MEL concentration increased rapidly after meal consumption, reaching a maximum at approximately 3 h and then decreased gradually towards baseline (P = 0.006). Two subjects (4.65%) had a cumulative daily intake exceeding the severest tolerable daily intake. MEL and its three derivatives in spot urine can effectively represent the average concentrations in the previous 24-h urine in adults. Meal consumption is still a notable source of exposure to MEL for humans. These findings are important for choosing a better sampling strategy of performing exposure assessment. Meanwhile, the acute elevation in urinary MEL concentration following meal consumption may pose a potential health risk.

Effects of melamine and cyanuric acid on placental and fetal development in rats

Melamine or cyanuric acid alone has low toxicity, but combined exposure to melamine and cyanuric acid was reported to cause unexpected toxicological effects. This study investigated the potential effects and toxic mechanism of combined exposure to melamine and cyanuric acid on placental and fetal development in rats. Exposure to melamine and cyanuric acid caused maternal toxicity manifested by increased abnormal symptoms and decreased body weight gain. Developmental toxic effects included a decrease in placental and fetal weights with increased fetal deaths and post-implantation loss. Melamine and cyanuric acid induced oxidative stress in the developing placenta and fetus. The placentas from rats treated with melamine and cyanuric acid showed shortening of the placental layers with histological changes, decreased cell proliferation, increased apoptotic changes, and decreased insulin-like growth factor (IGF)/IGF-binding proteins (IGFBPs) and placental lactogen (PL) expression levels. Fetuses from melamine- and cyanuric acid-treated dams showed increased apoptotic changes and suppressed cellular proliferation in their livers and vertebrae. Consequently, combined exposure to melamine and cyanuric acid resulted in high levels of oxidative stress and impaired placental development associated with impairment of the IGF/IGFBP and PL systems, resulting in increased apoptotic changes and reduced fetal cell proliferation.

Exposure to nitrogenous based flame retardants in Chinese population: Evidence from a national-scale study

Extensive use of nitrogen-based flame retardants (NFRs) has resulted in their widespread environmental occurrence. To investigate human exposure to NFRs on a national scale, the abundance and spatial distribution of NFRs were assessed in urine specimens collected from 13 cities in China. Six out of eight target NFRs were detectable in more than half of the urine samples, and the total concentrations of NFRs ranged from 3.22 to 880 ng/mL with a median of 46.7 ng/mL. Cyanuric acid was the most abundant chemical, accounting for 66.2%, followed by melamine (16.3%), ammelide (10.8%), and ammeline (6.11%). Regional differences in concentrations and composition profiles of NFRs were observed within China as a result of different production and application profiles. In addition, we found that urinary NFRs levels were much higher than but statistically correlated with that of organophosphates (r² = 0.69, p < 0.05), another class of phosphorus-based flame retardant, implying similar emission sources and/or human exposure pathways. Furthermore, the estimated daily intakes and hazard quotients revealed that the Chinese population's exposure to NFRs is within safe limits. To the best of our knowledge, this is the first study to document the ubiquitous occurrence and region-specific variations of human exposure to NFRs in China.

Associations of exposure to melamine, cyanuric acid, phthalates with markers of early kidney impairment, and their interactions in US adults: analyses of NHANES 2003-2004 data

Melamine (MEL), cyanuric acid (CYA), and phthalates have kidney toxicity, respectively. Still, no study has explored whether there is an interaction of co-exposure to MEL, CYA, and phthalates on early kidney impairment, including cystatin C (CYST), beta 2-microglobulin (β2-MG), albumin creatinine ratio (ACR), and estimated glomerular filtration rate (eGFR). Urine samples were collected from 333 adults in the National Health and Nutrition Examination Survey (NHANES) 2003-2004, and urinary MEL, CYA, and ten metabolites of phthalates were quantified. The multiple markers of early kidney impairment were also measured, including serum CYST, β2-MG, urinary ACR, and eGFR. Their associations were explored by multiple linear and multivariate logistic regression models. Meanwhile, the interactions of co-exposure to MEL, CYA, and phthalates on early kidney impairment were analyzed by Wilcoxon rank-sum test combined with the LSD test. In the multiple linear regression model, urinary concentrations of monobenzyl phthalate (MBzP), mono(3-carboxypropyl) phthalate (MCPP), mono(2-ethyl-5-carboxypentyl) phthalate (MECPP), and mono(2-ethylhexyl) phthalate (MEHP) were positively associated with urinary ACR, serum β2-MG, and CYST, respectively. Urinary concentrations of MBzP and MCPP were negatively associated with eGFR. In the multivariate logistic regression model, increased urinary CYA concentration was the risk factor of CYST abnormality with an odds ratio (OR) (95% confidence interval, 95% CI) of 2.38 (1.01, 5.60) (P = 0.047) and increased urinary MBzP concentration was the risk factor of ACR abnormality with an OR of 2.59 (1.41, 4.75) (P = 0.002). The co-exposure to MEL, CYA, and four phthalate metabolites (MEHP, MBzP, MCPP, and MECPP) presented significantly interactive effects on the markers of early kidney impairment, respectively. There were the independent and interactive effects of exposure to MEL, CYA, and specific phthalate metabolites on early kidney impairment. Due to co-exposure to multiple environmental chemicals in our daily life, more attention should be paid to the health damage raised by the synergistic effects of environmental chemicals.

Prenatal cyanuric acid exposure disrupts cognitive flexibility and mGluR1-mediated hippocampal long-term depression in male rats

Cyanuric acid is one of the most widely used classes of industrial chemicals and is now well known as food adulterant and contaminant in pet food and infant formula. Previously, it was reported that animals prenatally exposed to cyanuric acid showed neurotoxic effects that impaired memory consolidating and suppressed long-term potentiation (LTP) in the hippocampus. However, it is not clear if prenatal exposure to cyanuric acid induces deficits in reversal learning and long-term depression (LTD), which is required for the developmental reorganization of synaptic circuits and updating learned behaviors. Here, pregnant rats were i.p. injected with cyanuric acid (20 mg/kg) during the whole of gestation, and male offspring were selected to examine the levels of hippocampal mGluR1 and mGluR2/3 in young adulthood. The LTD at the Schaffer collateral-CA1 pathway was induced by low-frequency stimulation (LFS) and recorded. Reversal learning and hippocampus-dependent learning strategy were tested in Morris-water maze (MWM) and T-maze tasks, respectively. To further confirm the potential mechanism, selective agonists of mGluR1 and mGluR2/3 and antagonists of mGluR were intra-hippocampal infused before behavioral and neuronal recording. We found the levels of alkaline phosphatase were markedly increased in the maternal placenta and fetal brain following prenatal exposure. The expression of mGluR1 but not mGluR2/3 was significantly decreased and mGluR1-mediated LTD was selectively weakened. Prenatal cyanuric acid impaired reversal learning ability, without changing place learning strategy. The mGluR1 agonist could effectively enhance LFS-induced LTD and mitigate reversal learning deficits. Meanwhile, the reductions in the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPAR)-mediated spontaneous excitatory postsynaptic currents (sEPSCs) amplitude and frequency of cyanuric acid offspring were simultaneously alleviated by mGluR1 agonist infusions. Therefore, the results indicate the cognitive and synaptic impairments induced by prenatal cyanuric acid exposure are attributed to the disruption of the hippocampal mGluR1 signaling. Our findings provided the first evidence for the deteriorated effects of cyanuric acid on synaptic depression and advanced cognitive performance.

E-waste dismantling-related occupational and routine exposure to melamine and its derivatives: Estimating exposure via dust ingestion and hand-to-mouth contact

Melamine (MEL) and its derivatives are increasingly applied as nitrogenous flame retardants in consumer products. Nevertheless, limited information is available on their environmental occurrence and subsequent human exposure via multiple exposure pathways. In this study, we analysed MEL and its derivatives in dust (indication of the dust ingestion route) and hand wipe samples (indication of the hand-to-mouth route) collected in various microenvironments. The levels of ∑MELs in both dust (median: 24,100 ng/g) and participant hand samples (803 ng/m²) collected in e-waste dismantling workshops were significantly higher than those in samples collected in homes (15,600 ng/g and 196 ng/m², respectively), dormitories (13,100 ng/g and 227 ng/m², respectively) and hotel rooms (11,800 ng/g and 154 ng/m², respectively). Generally, MEL dominated in dust samples collected in e-waste dismantling workshops, whereas cyanuric acid dominated in hand wipe samples. This may occur partly because the latter is an ingredient in disinfection products, which are more frequently employed in daily lives during the COVID-19 pandemic. Exposure assessment suggests that dust ingestion is an important exposure pathway among dismantling workers and the general population, whereas hand-to-mouth contact could not be overlooked in certain populations, such as children and dismantling workers not wear gloves at work.

Green detection of trace cyanuric acid and free chlorine together via ion chromatography

Chlorinated cyanurates (CCAs) are a type of disinfectants currently used worldwide for fight of Coronavirus. However, CCAs upon dosed into water can release not only free chlorine (FC), a strong disinfectant, but also cyanurate (CYA), a persistent compound potentially harmful to human and environment. Therefore, detecting CYA and FC in water are very important not only for ensuring sufficient disinfection but also for monitoring the impacts of FC and CYA on receiving watershed. However, conventional analytical methods for them are mostly based on colorimetric methods, which have high method detection limits (MDLs) and rely on chemical reactions that are likely sensitive to coexisting chemicals. To overcome these issues, we herein proposed a facile and reaction-free method to detect CYA and FC together in just one run by ion chromatography (IC) equipped with both conductivity and ultraviolet absorbance detectors. The method features obvious advantages over colorimetric methods in being lower MDLs (3.6 μg/L for CYA and 9.0 μg/L for FC), environmental-friendly (i.e., no organic solvent involved), and more resistant to alkaline solution. With this method, trace levels of CYA (i.e., 34-44 μg/L), which were nondetectable by conventional method, were found in two river water samples, implying that the local environment was already polluted by CCAs during the pandemic period. Overall, this study demonstrates a robust tool that may assist better understanding and monitoring the fate and transport of trace CCA derivatives in water.

Prenatal cyanuric acid exposure depresses hippocampal synaptic plasticity and induces spatial learning and memory deficits

The infant and fetus may be exposed to cyanuric acid (CA) via several different routes into the diet or milk product as well as deliberate contamination. Previous findings indicated chronic CA treatment caused neurotransmission and synaptic impairment in the early developing hippocampus. This study was designed to characterize the effects of different doses (10 mg/kg, 20 mg/kg and 40 mg/kg) of CA exposure on the developing fetus. Pregnant rats were intraperitoneally exposed to CA during the entire period of gestation and male offspring were selected for water maze task, neural recording and N-methyl-d-aspartate (NMDA) receptor detection around the eighth postnatal week. We found that CA exposure impaired the learning and memory function in a dose-dependent manner. The paired-pulse ratio (PPR) and GluN2A-dependent long-term potentiation (LTP) at the Schaffer collateral-CA1 pathway were affected in CA-exposed rats. Remarkably, hippocampal levels of NMDA-GluN2A, but not NMDA-GluN2B, were significantly decreased. Meanwhile, the spine density of hippocampal CA1 neurons was not altered by the CA exposure. Our findings are consistent with the hypothesis that CA treatment during the prenatal period produces deficits in spatial cognition by disrupting hippocampal synaptic function.

Chronic Cyanuric Acid Exposure Depresses Hippocampal LTP but Does Not Disrupt Spatial Learning or Memory in the Morris Water Maze

Exposure to cyanuric acid (CA) causes multiple organ failure accompanied by the involvement in kinds of target proteins, which are detectable and play central roles in the CNS. The hippocampus has been identified as a brain area which was especially vulnerable in developmental condition associated with cognitive dysfunction. No studies have examined the effects of CA on hippocampal function after in vitro or in vivo treatment. Here, we aimed to examine hippocampal synaptic function and adverse behavioral effects using a rat model administered CA intraperitoneally or intrahippocampally. We found that infusion of CA induced a depression in the frequency but not the amplitude of spontaneous excitatory postsynaptic currents (sEPSCs), miniature excitatory postsynaptic currents (mEPSCs), or N-methyl-D-aspartate (NMDA)-mediated excitatory postsynaptic currents (EPSCs) of the CA1 neurons in dose-dependent pattern. Both intraperitoneal and intrahippocampal injections of CA suppressed hippocampal LTP from Schaffer collaterals to CA1 regions. Paired-pulse facilitation (PPF), a presynaptic phenomenon, was enhanced while the total and phosphorylated expression of NMDA-GluN1, NMDA-GluN2A, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-GluA1 subunits were comparable between CA-treated and control groups. In Morris water maze test, both groups could effectively learn and retain spatial memory. Our studies provide the first evidence for the neurotoxic effect of CA and the insight into its potential mechanisms.

The pathologic lesions of liver caused by melamine alone or in combination with cyanuric acid in mice

The toxicity of melamine (MA) and its analogue cyanuric acid (CA) in multiple organs has been widely investigated. The purpose of this study was to characterize the pathological lesions of the liver caused by melamine alone or in combination with CA. Mice were oral administered 0, 25, 50, or 100 mg/kg/day MA and CA mixture (MC), or 25, 50, and 100 mg/kg/day MA alone for 7 days. We found MC caused increase of liver weight index and elevations of the serum concentrations of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and creatinine (Cr). Histopathologically, both MA and MC caused scattered necrosis and inflammation cell infiltration in liver. Notably, at 100 mg/kg/day MC, melamine-related crystals were observed in hepatic sinusoid. The liver at high-dose MA and MC groups were further examined by TEM. There were marked degeneration of the mitochondria, and crystal deposition in the Disse space or cytoplasm of hepatic cells and Kupffer cells. TUNEL staining revealed that MA and MC caused apoptosis of hepatocytes and Kupffer cells. Western blotting showed the expression of Bcl-2 decreased, and Bax and caspase-3 increase in liver. The analysis of oxidative stress showed that the expression and activities of two key antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPX) decreased, and the concentration of malondialdehyde (MDA) elevated in MA- and MC-treated mice. These results from this study demonstrated that both MA and MC caused pathological damage to the liver in mice, especially when ingested in high concentration.

Associations of melamine and cyanuric acid exposure with markers of kidney function in adults: Results from NHANES 2003-2004

Higher melamine exposure may increase the risk of kidney stone formation and kidney injury in infants, but little is known about the potential nephrotoxic effects of environmental low-dose melamine and its derivative exposure on kidney function of adults in the general population. Our objective was to assess associations between urinary concentrations of melamine and its derivative, cyanuric acid, and kidney function through analyzing the data from the National Health and Nutrition Examination Survey (NHANES) 2003-2004. Information on 298 participants aged ≥20 years was utilized. Urinary melamine and cyanuric acid levels were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Estimated glomerular filtration rate (eGFR) and urinary albumin-to-creatinine ratio (UACR) were calculated to reflect kidney function. Covariate-adjusted creatinine standardization concentrations accounting for sex, race, age, race/ethically, and body mass index, was employed to control potential confounding of kidney function. Multivariable linear regression models were conducted to estimate associations of covariate-adjusted creatinine standardization urinary melamine and cyanuric acid concentrations with eGFR and UACR. Log-binomial regression models were performed to estimate risks of impaired kidney function and hypertension associated with urinary melamine and cyanuric acid levels. The geometric mean values of urinary melamine and cyanuric acid concentrations were 1.51 μg/L [95% confidence interval (CI): 1.21 μg/L, 1.89 μg/L] and 5.86 μg/L (95% CI: 5.34 μg/L, 6.44 μg/L), respectively. The median value of estimated daily intake (EDI) for melamine was 0.06 (ranging from undetectable to 1.11) μg/kg body weight/day calculated by urinary concentration and creatinine excretion accounting for sex and body weight. Adults in the fourth quartile of melamine and cyanuric acid exposure had 0.142 mL/min/1.73 m² (95% CI: -0.271, -0.014) and 0.106 mL/min/1.73 m² (95% CI: -0.020, 0.006) lower eGFR for melamine and cyanuric acid, respectively, compared to participants in the first quartile of exposure with adjustment for potential confounders. To our best knowledge, this is the first study to report associations between melamine and its derivative and kidney function of the U.S. adults from NHANES 2003-2004. The suggestive evidence revealed that individuals with high melamine exposure had lower eGFR than those with low melamine exposure, although no significant association between melamine and cyanuric acid exposure and markers of kidney function was observed. These findings should be interpreted with caution regarding the possible reverse causality.

Robustness of anaerobes exposed to cyanuric acid contaminated wastewater and achieving efficient removal via optimized co-digestion scheme

The impact of various industrial pollutants on anaerobes and the biodegradation potentials need much emphasis. This study aims to investigate the response of anaerobic microbial systems to cyanuric acid (CA) exposure; CA is toxic and possible carcinogen. First, the long-term exposure of mixed culture bacteria (i.e., municipal sludge) to low-strength wastewater containing 20 mg/L CA was conducted in an up-flow anaerobic staged reactor. Stable performance and sludge granulation were observed, and the microbial community structure showed the progression of genus Acinetobacter known as CA degrader. Second, batch-mode experiment was performed to examine the CA biodegradability at higher doses (up to 250 mg/L of CA) in the absence and presence of glucose as a co-substrate; response surface-based optimization was used to design this experiment and to estimate the optimum CA-glucose combination. CA removal of 77-98% was achieved when CA was co-digested with glucose (250-1,000 mg/L), after 7 days-incubation at temperature of 37 °C, compared to 34% when CA was solely digested. Further, the obtained methane yield dropped when CA exceeded over 125 mg/L, though the deterioration was mitigated by addition of higher concentration of glucose. Overall, we conclude that CA is efficiently degraded under anaerobic conditions when being co-digested with readily assimilable substrate.

Rosette-shaped graphitic carbon nitride acts as a peroxidase mimic in a wide pH range for fluorescence-based determination of glucose with glucose oxidase

Rosette-shaped graphitic carbon nitride (rosette-GCN) is described as a promising alternative to natural peroxidase for its application to fluorescence-based glucose assays. Rosette-GCN was synthesized via a rapid reaction between melamine and cyanuric acid for 10 min at 35 °C, followed by thermal calcination for 4 h. Importantly, rosette-GCN possesses a peroxidase-like activity, producing intense fluorescence from the oxidation of Amplex UltraRed in the presence of H₂O₂ over a broad pH-range of, including neutral pH; the peroxidase activity of rosette-GCN was ~ 10-fold higher than that of conventional bulk-GCN. This enhancement of peroxidase activity is presumed to occur because rosette-GCN has a significantly larger surface area and higher porosity while preserving its unique graphitic structure. Based on the high peroxidase activity of rosette-GCN along with the catalytic action of glucose oxidase (GOx), glucose was reliably determined down to 1.2 μM with a dynamic linear concentration range of 5.0 to 275.0 μM under neutral pH conditions. Practical utility of this strategy was also successfully demonstrated by determining the glucose levels in serum samples. This work highlights the advantages of GCNs synthesized via rapid methods but with unique structures for the preparation of enzyme-mimicking catalysts, thus extending their applications to the diagnostics field and other biotechnological fields. Graphical abstract.

Determination of melamine and its derivatives in textiles and infant clothing purchased in the United States

Melamine-based resins are used extensively in fabrics to impart fire and heat resistance as well as wrinkle-free properties. Little is known, however, regarding the occurrence of melamine and its derivatives in textiles. In this study, concentrations of melamine, ammeline, ammelide, and cyanuric acid were determined in 77 textile samples and infant clothing purchased from Albany, New York, USA. All textile samples contained one or more target analytes, at concentration ranges of 1.19-81,800, 3.21-17,800, <1.20-25,700, and <0.50-550 ng/g for melamine, cyanuric acid, ammeline, and ammelide, respectively. Melamine was the predominant compound, accounting for 52% of the total concentrations of four analytes (i.e., ∑melamines). Significant positive correlations were found between the concentrations of melamine and its three derivatives (0.347 < r < 0.862, p < .01). The concentrations of ∑melamines were significantly higher in cotton fabrics (mean: 10,500 ng/g) and cotton clothes (10,200 ng/g) than in synthetic fabrics (1,380 ng/g) and socks (40.0 ng/g) (p < .01). Simulated laundry experiments suggested that a single round of washing with water removed 76-90% of melamine from clothing. The calculated dermal exposure doses of melamine and cyanuric acid were three to four orders of magnitude below the reference value. This study provides the first evidence of the occurrence of melamine derivatives in textiles and clothing purchased in the United States. CAPSULE: Melamine and cyanuric acid are widely distributed in textiles and infant clothing collected from the United States.

Occurrence and distribution of melamine and its derivatives in surface water, drinking water, precipitation, wastewater, and swimming pool water

The extensive use of melamine and its three derivatives (i.e., ammeline, ammelide, and cyanuric acid) resulted in their widespread occurrence in the environment. Nevertheless, limited information is available on their distribution in the aquatic environment. In this study, concentrations and profiles of melamine and its derivatives were determined in 223 water samples, comprising river water, lake water, seawater, tap water, bottled water, rain water, wastewater, and swimming pool water, collected from New York State, USA. The sum concentrations of melamine and its derivatives (∑₄MELs) decreased in the following order: swimming pool water (median: 1.5 × 10⁷ ng/L) ≫ wastewater (1240) > precipitation (739) > tap water (512) > river water (370) > lake water (347) > seawater (186) > bottled water (98). Cyanuric acid was the major compound, accounting for 60-100% of ∑₄MELs concentrations in swimming pool water, wastewater, precipitation, tap water, seawater, and bottled water, whereas melamine dominated in river and lake water (54-64% of ∑₄MELs). Significant positive correlations (0.499 < R < 0.703, p < 0.002) were found between the concentrations of melamine and atrazine (a triazine herbicide) in surface waters. The geographic distribution in the concentrations of ∑₄MELs in river, lake, and tap water corresponded with the degree of urbanization, suggesting that human activities contribute to the sources melamine and cyanuric acid in the aquatic environments. A preliminary hazard assessment of melamine and cyanuric acid in waters suggested that their ecological or human health risks were minimal. This is the first study to document the occurrence and spatial distribution of melamine and its derivatives in waters from the United States.

Development and Validation of a HPLC-UV Method for Urea and Related Impurities

Urea is used in biopharmaceutical manufacturing processes for the purification of therapeutic proteins, for cleaning columns, and for refolding proteins after purification. The urea used for such purposes is typically USP grade material obtained from commercial sources and further characterization is required prior to use, such as determination of purity and identity. For this purpose, a robust analytical method is needed that can characterize the known organic impurities of urea. However, the existing methods show high assay variability and are not able to resolve all known organic impurities as desired for accurate quantification. In the present manuscript we developed a new high-performance liquid chromatography method with UV detection for the separation of urea and its impurities (biuret, cyanuric acid, and triuret). The method performance characteristics evaluated for urea and biuret were specificity, linearity, accuracy, identity, precision, and robustness and the newly developed method met all predefined performance acceptance criteria.

Melamine and cyanuric acid in foodstuffs from the United States and their implications for human exposure

We determined the concentrations of melamine, ammeline, ammelide, and cyanuric acid in meat, fish and seafood, cereal products, beverages, cooking oil, and vegetables (n = 121) collected from Albany, New York, United States. In addition, food packaging (n = 24) and animal feed (n = 12) were analyzed to determine the sources of melamine and its derivatives in foods. Among the six categories of foods analyzed, median concentrations of ∑melamine (sum of melamine and its three derivatives) in meat (23.6 ng/g fresh weight; fw) and cereal products (20.9 ng/g fw) were significantly (p < 0.05) higher than those in other food categories (<5.03 ng/g fw). Cyanuric acid and melamine were the major compounds, accounting for 51% and 26% of the total ∑melamine concentrations, respectively. ∑melamine was found ubiquitously in food packaging (median: 36.2 ng/g fw) and animal feed (56.5 ng/g fw), which are two important sources of melamine found in foodstuffs. The median estimated daily dietary intakes (including concentrations reported for dairy products in our previous study) of melamine and cyanuric acid were in the ranges of 13.4-72.7 and 75.4-347 ng/kg body weight/day, respectively, for various age groups. Dairy products, cereal products, and meat were major sources of dietary melamine (~76%) and cyanuric acid (~95%) exposure. The calculated hazard quotients for dietary exposure to melamine and cyanuric acid were well below 1.0, which suggested minimal risk from current exposures.

Spatial and temporal trends of melamine and its derivatives in sediment from Lake Shihwa, South Korea

Occurrence, spatial distribution, and temporal trends of melamine and its derivatives (ammeline, ammelide, and cyanuric acid) were investigated in surface sediment and two sediment cores collected from Lake Shihwa, South Korea. ∑Melamine (sum of melamine and its three derivatives) was found in all surface sediment samples at concentrations that ranged from 16.6 to 4390 ng/g dry weight (dw), with an average value of 202 ng/g dw. ∑Melamine concentrations exhibited a clear spatial gradient, in decreasing order, as: creeks (mean: 577 ng/g dw) > inshore locations (41.9 ng/g dw) > offshore locations (24.3 ng/g dw). ∑Melamine concentrations were notably high in sediment collected near wastewater treatment plant (WWTP) outfalls. Melamine was the most prevalent compound in sediment collected from creeks (87%) and WWTP outfall locations (48%), whereas cyanuric acid was the dominant compound in sediment from inshore (51%) and offshore (63%) locations. The historical profiles of ∑Melamine in sediment cores corresponded with coastal development and environmental changes in this region. This is the first study to document the occurrence and temporal distribution of melamine in sediment cores, and this information is useful in understanding the fate of these relatively less-studied chemicals in the environment.

iTRAQ-based proteomics analysis reveals the deregulated proteins related to liver toxicity induced by melamine with or without cyanuric acid in mice

The administration of melamine alone or its combination with cyanuric acid was shown to have certain liver toxicity. However, the injury mechanism of melamine-related toxicity to liver remains poorly understood. In the present study, we investigated the deregulated proteins related to liver toxicity induced by melamine with or without cyanuric acid in mice using iTRAQ quantitative proteomics technique. A total of 166 proteins were significantly changed by the melamine treatment, of which, 36 proteins were up-regulated and 130 proteins were down-regulated. Whereas, 242 proteins were significantly changed by the combined treatment of melamine and cyanuric acid, of which 81 proteins were up-regulated and 161 proteins were down-regulated. The enriched analysis of GO terms and KEGG pathway on the altered proteins showed that both enriched main GO terms and KEGG pathways appear to be different between the two kinds of treatments: melamine and mixture of melamine and cyanuric acid. Based on western blotting technique, it was confirmed that the expression of three proteins: heat shock protein 70 (HSP70), protein disulphide isomerase 6 (PDIA6) and heat shock 70 kDa protein 4-like (HSPA4L) were agreement with the findings in iTRAQ-Based quantitative analysis. These identified proteins might participate in the regulation of a wide range of biological processes, such as immune and inflammatory function, unfolded proteins response in endoplasmic reticulum, DNA damage, and the apoptosis of liver cells. These results from this study provide a new way to gain insight into the mechanisms of melamine-related toxicity to liver in animals.

Melamine and cyanuric acid exposure and kidney injury in US children

BACKGROUND

Melamine and cyanuric acid, which are currently used in a variety of common consumer products and present in foods, have been implicated in the development of urolithiasis and acute kidney injury in Chinese children. To determine whether US children have measurable concentrations of these chemicals in their bodies and whether they are at greater risk of acute kidney injury, we measured melamine and cyanuric acid exposure in a cohort of US children and determined their relationship with markers of kidney injury.

METHODS

We measured urinary melamine and cyanuric acid in a convenience sample of 109 children (4 months - 8 years) from Seattle, WA and New York City, NY using liquid chromatography with tandem mass spectrometry. We measured several urinary markers of kidney injury: fatty acid binding protein 3 (FABP3), kidney injury molecule 1 (KIM1), neutrophil gelatinase-associated lipocalin (NGAL) using Luminex xMAP methods, and urine urea was measured using standard laboratory methods. We described urinary melamine and cyanuric acid concentrations and assessed predictors of the exposures. We used multivariable linear regression to assess relationships between melamine/cyanuric acid and kidney injury markers in unadjusted and adjusted (creatinine, age, sex) analyses.

RESULTS

Melamine and cyanuric acid were above the limit of detection (LOD) in 78% and 95% of all samples, respectively. The mean concentrations (SD) for melamine and cyanuric acid were 27.4 ng/ml (141.9 ng/ml) and 35.3 ng/ml (42.4 ng/ml). In unadjusted analyses, we observed statistically significant increases in the percentages of FABP3 and KIM1 in relation to a one log unit change in melamine and cyanuric acid, respectively. In adjusted analyses, we observed a 55% (95% CI 0, 141) increase in KIM1 in relation to a one log unit increase in cyanuric acid.

CONCLUSIONS

US children have detectable concentrations of melamine and cyanuric acid in urine, and these concentrations are higher than those reported in children from other countries. This is a novel finding that improves upon previous exposure estimates using questionnaires only and suggests widespread exposure in the population. Cyanuric acid is associated with increased KIM 1 concentrations, suggesting kidney injury. Given the potential widespread exposure, future analyses should examine melamine and cyanuric acid in relation to chronic kidney disease and markers of kidney injury in a larger cohort that is representative of the general population.

A nationwide survey of the occurrence of melamine and its derivatives in archived sewage sludge from the United States

Melamine-based resins are used extensively in laminates, plastics, coatings, glues, and dinnerware. Little is known, however, about the occurrence of melamine and its derivatives in the environment. In this study, a nationwide survey of melamine and its derivatives, namely ammeline, ammelide, and cyanuric acid, was conducted, using archived sewage sludge samples collected from 68 wastewater treatment plants in the United States (U.S.). The sum concentrations of four target compounds in sludge ranged from 34 to 1800 ng/g dry weight (dw), with a mean concentration of 240 ng/g dw; melamine (46%) and cyanuric acid (40%) collectively accounted for 86% of the total mass of analytes. No significant geographical variation in the concentrations of melamine and its derivatives in sewage sludge was found. The estimated emission of melamine and its derivatives via land-application of sludge was approximately 1600 kg/yr in the U.S. The hazard quotient values for melamine in sludge-amended soils ranged from 2.2 × 10^-5 to 4.4 × 10^-3, indicating that the current levels of melamine in sludge pose a minimal risk to the soil environment.

Inter-day and inter-individual variability in urinary concentrations of melamine and cyanuric acid

Melamine is used extensively in household products, such as furniture, dinnerware, and food utensils. Several studies have shown that melamine adversely affects kidney function. Nevertheless, little is known about urinary melamine concentrations, and its temporal variability. In this study, 213 first-morning-void urine samples were collected from 19 volunteers for over a month to assess longitudinal variability in concentrations of melamine and its three structural analogues, i.e., cyanuric acid, ammeline, and ammelide. Target analytes were found in all urine samples at mean concentrations of 3.3, 16, 0.99, and 0.62 ng/mL, for melamine, cyanuric acid, ammelide, and ammeline, respectively. Cyanuric acid was the major compound found in all urine samples, accounting for 74-80% of the total concentrations, followed by melamine (12-20%), ammelide (4-6%), and ammeline (2-4%). Gender- and age-related differences in melamine concentrations were observed, although no such pattern was found for cyanuric acid. After adjusting for creatinine, melamine and cyanuric acid concentrations were moderately predictable with inter-day intraclass correlation coefficients (ICCs) in the range of 0.541-0.763. Nevertheless, substantial inter-individual variation in melamine levels existed even after creatinine adjustment, as evidenced by low ICCs (0.008-0.108). Cumulative daily intake of melamine and cyanuric acid was calculated on the basis of urinary concentrations and the mean values were found to be at least 10-fold below the current tolerable daily intake.

Melamine and its derivatives in dog and cat urine: An exposure assessment study

Melamine is a nitrogen-containing organic compound that is used in a wide range of products, including paints, plastics, and paper, as a flame retardant. A few studies have reported the occurrence of melamine and its derivatives in pet food, following a number of deaths of cats and dogs from kidney failure in 2007, which was attributed to melamine contamination in ingredients used in pet food. Nevertheless, studies that report the occurrence of melamine and its derivatives in pet urine are scarce. In this study, we measured melamine and its derivatives (i.e., ammeline, ammelide, and cyanuric acid) in dog (n = 30) and cat (n = 30) urine collected from Albany, New York, USA, during March through July 2017. The mean (±SD) concentrations of melamine, ammeline, ammelide, and cyanuric acid in dog urine were 21.1 ± 51.2, 2.3 ± 3.8, 9.9 ± 1 0.4, and 79.0 ± 105 ng/mL, respectively; the corresponding concentrations in cats were 21.4 ± 26.1, 1.2 ± 2.5, 6.1 ± 3.9, and 105 ± 94.6 ng/mL, respectively. No significant difference was observed in urinary concentrations of melamine derivatives between cats and dogs. Age and gender were important determinants of the concentrations of the target chemicals in cats and dogs. Cumulative daily intake of melamine and its derivatives was calculated on the basis of urinary concentrations and was found to be 10-500-fold below the tolerable daily intake.

Synergistic effects between hydroxyl radicals and hydrated electrons on strengthening decomposition of an s-triazine compound: A combined experimental and theoretical study

The decomposition of an environmentally recalcitrant s-triazine compound, prometry (PMT), was carried out by experimental and theoretical approaches to study the combined effects of hydroxyl radicals (OH) and hydrated electrons (e_aq^-). With the participation of strongly oxidative radicals OH and reductive radicals e_aq^- induced by electron beam (EB), PMT obtained a good decomposition performance, which was obviously better than those methods simply using OH as the single active species. The evolution of cyanuric acid (CA) during the EB and UV irradiation processes elucidate that former method could efficiently decompose such chemically stable intermediate. The experiments of radical scavengers further suggest that OH was the predominant radical during PMT degradation, while e_aq^- was beneficial to further decomposition and mineralization. Combined with the results of density functional theory (DFT) calculations, the strengthened synergistic effects between OH and e_aq^- were proven. The calculations illustrated OH could attack the carbon-branch-chains of s-trazine ring and form OH-adducts rather than nitrogen oxides. Moreover, the presence of e_aq^- could not only greatly change the geometry of the s-triazine ring, but also help cleaving alkyl chain on ring, thus facilitate the complete mineralization.

The fate of cyanuric acid in biological wastewater treatment system and its impact on biological nutrient removal

Cyanuric acid (CA) is widely used in living and production. It is a kind of environmental priority pollutants which exists chronically in soil and water, but is difficult to be chemically hydrolyzed or oxidized. The behavior of CA at different levels of 0, 0.01, 0.10 and 1.00 mg L^-1 in biological wastewater treatment process was investigated in this paper. Experimental results showed that CA (0.01 and 0.10 mg L^-1) was removed in biological wastewater treatment process, which was mainly achieved by biodegradation of particular species (Acidovorax and Pseudomonas) in the anaerobic condition. However, 1.00 mg L^-1 CA was reluctant to be degraded in biological wastewater treatment system. With the CA level increase from 0 to 1.00 mg L^-1, total nitrogen removal efficiency decreased from 97.23 to 74.72%. The presence of CA promoted both the synthesis and decomposition metabolisms of poly-hydroxyalkanoates and glycogen, thereby providing the advantage for phosphorus removal. CA could inhibit nitrification process because of inhibition to nitrite oxidizing bacteria (NOB). Moreover, the microbial community of activated sludge was changed by the exposure of CA. Polyphosphate accumulating organisms, such as Bacteroidetes, Chloroflexi and Saccharibacteria increased, but the abundance of Nitrospirae was decreased.

A step into the RNA world: Conditional analysis of hydrogel formation of adenosine 5'-monophosphate induced by cyanuric acid

Nucleotide polymerization occurs by the nucleophilic attack of 3'-oxygen of the 3'-terminal nucleotide on the α-phosphorus of the incoming nucleotide 5'-triphosphate. The π-stacking of mononucleotides is an important factor for prebiotic RNA polymerization in terms of attaining the proximity of two reacting moieties. Adenosine and adenosine 5'-monophosphate (AMP) are known to form hydrogel in the presence of cyanuric acid at neutral pH. However, we observed that other canonical ribonucleotides did not gel under the same condition. The π-stacking-induced hydrogel formation of AMP was destroyed at pH 2.0, suggesting that the protonation of N at position 1 of adenine abolished hydrogen bonding with the NH of cyanuric acid and resulted in the deformation of the hexad of adenine and cyanuric acid. A liquid-like gel was formed in the case of adenosine with cyanuric acid and boric acid, whereas AMP caused the formation of a solid gel, implying that the negative charge inherent to AMP prevented the formation of esters of boric acid with the cis-diols of ribose. Cyanuric acid-driven oligomerizations of AMP might have been the first crucial event in the foundation of the RNA world.

Integrated preservation and sample clean up procedures for studying water ingestion by recreational swimmers via urinary biomarker determination

The use of cyanuric acid as a biomarker for ingestion of swimming pool water may lead to quantitative knowledge of the volume of water ingested during swimming, contributing to a better understanding of disease resulting from ingestion of environmental contaminants. When swimming pool water containing chlorinated cyanurates is inadvertently ingested, cyanuric acid is excreted quantitatively within 24 h as a urinary biomarker of ingestion. Because the volume of water ingested can be quantitatively estimated by calculation from the concentration of cyanuric acid in 24 h urine samples, a procedure for preservation, cleanup, and analysis of cyanuric acid was developed to meet the logistical demands of large scale studies. From a practical stand point, urine collected from swimmers cannot be analyzed immediately, given requirements of sample collection, shipping, handling, etc. Thus, to maintain quality control to allow confidence in the results, it is necessary to preserve the samples in a manner that ensures as quantitative analysis as possible. The preservation and clean-up of cyanuric acid in urine is complicated because typical approaches often are incompatible with the keto-enol tautomerization of cyanuric acid, interfering with cyanuric acid sample preparation, chromatography, and detection. Therefore, this paper presents a novel integration of sample preservation, clean-up, chromatography, and detection to determine cyanuric acid in 24 h urine samples. Fortification of urine with cyanuric acid (0.3-3.0 mg/L) demonstrated accuracy (86-93% recovery) and high reproducibility (RSD < 7%). Holding time studies in unpreserved urine suggested sufficient cyanuric acid stability for sample collection procedures, while longer holding times suggested instability of the unpreserved urine. Preserved urine exhibited a loss of around 0.5% after 22 days at refrigerated storage conditions of 4 °C.

The effects of melamine with or without cyanuric acid on immune function in ovalbumin-sensitized mice

Melamine is commonly used in the chemical industry, and it has been found to exist on food processing equipment and utensils. Previous investigations suggested that melamine alone or its combination with cyanuric acid appears to be toxic to immune system in animals. The objective of this study is to investigate the potential effects of melamine with or without cyanuric acid on immune function in ovalbumin- sensitized mice. Our data indicated that melamine-related administration caused a significant decreasing in the content of IL-4 in mice in comparison to negative control group. Significant increasing in the content of histamine (HIS) was recorded in almost all treated groups. The co-administration of melamine and cyanuric acid with high dose (each at 16mgkg^-12d^-1) led to a significantly lower contents of IL-10, IL-16 and monocyte chemoattractant protein-1 (MCP-1) in mouse serum in comparison to negative control group. Moreover, our data indicated that the number of Th1 and Th2 cells, and the ratio of Th1/Th2 spleen lymphocytes were significantly changed after treatment. Also, our results demonstrated that the profiles of both CD40 and CD40L were significantly altered in spleen lymphocytes after treatment.

Melamine-associated urinary stone

The devastating contamination of milk formula with Melamine, which caused havoc in China, happened almost eight years ago. Although most patients with melamine-associated urinary stone were given conservative medical treatment, the impact was not completely eliminated. Extensive studies are needed to assess chronic effects in the affected population. In this review, we describe the pathogenesis, pathology, clinical manifestations, management and epidemiology; and the need for longer term follow-up of melamine-associated urinary stones.

Effects of a 28-day dietary co-exposure to melamine and cyanuric acid on the levels of serum microRNAs in male and female Fisher 344 rats

We showed previously that a 28-day combined dietary exposure to melamine and cyanuric acid (MEL&CYA) induced kidney lesions in NCTR Fisher 344 (F344) rats. Histopathological changes were significant in females dosed with ≥240 ppm MEL&CYA and in males dosed with ≥180 ppm MEL&CYA; however, the nephrotoxicity biomarkers blood urea nitrogen (BUN) and serum creatinine (SCr) were increased only by ≥240 ppm MEL&CYA. The serum miRNome has been reported to reflect toxicity of several organs, including the kidney. Here, we compared the dose-response of alterations in serum miRNAs to those of BUN, SCr, and kidney histopathology in rats co-exposed to MEL&CYA. The serum miRNome of male F344 rats dosed with 0, 180, or 240 ppm MEL&CYA was screened using quantitative real-time RT-PCR (qRT-PCR) and the levels of selected serum miRNAs were analyzed further in both sexes over the full dose range. The levels of several miRNAs were significantly reduced in rats treated with 240 ppm MEL&CYA versus control. In addition, miR-128-3p and miR-210-3p were decreased in males treated with 180pm MEL&CYA, a dose at which the levels of BUN and SCr were not yet affected by treatment. These data suggest that the serum miRNome is affected by nephrotoxic doses of MEL&CYA in male and female rats.

Measuring water ingestion from spray exposures

Characterisation of exposure levels is an essential requirement of health risk assessment; however for water exposures other than drinking, few quantitative exposure data exist. Thus, regulatory agencies must use estimates to formulate policy on treatment requirements for non-potable recycled water. We adapted the use of the swimming pool chemical cyanuric acid as a tracer of recreational water ingestion to permit detection of small water volumes inadvertently ingested from spray exposures. By using solutions of 700-1000 mg/L cyanuric acid in an experimental spray exposure scenario, we were able to quantify inadvertent water ingestion in almost 70% of participants undertaking a 10 min car wash activity using a high pressure spray device. Skin absorption was demonstrated to be negligible under the experimental conditions, and the measured ingestion volumes ranged from 0.06 to 3.79 mL. This method could be applied to a range of non-potable water use activities to generate exposure data for risk assessment processes. The availability of such empirical measurements will provide greater assurance to regulatory agencies and industry that potential health risks from exposure to non-potable water supplies are well understood and adequately managed to protect public health.

Cytotoxicity, organ distribution and morphological effects of melamine and cyanuric acid in rats

Melamine (Mel) is used widely as a basic organic chemical intermediate in several products. Within the last 10 years there have been two high-profile Mel exposures that caused toxicological concern, especially regarding food adulteration.

OBJECTIVE

This study aimed to determine the toxicity of Mel and one of its homologs, cyanuric acid (Cya), in vitro and in vivo.

MATERIALS AND METHODS

The IC₅₀ of Mel and Cya was determined by the MTT assay in NRK-52E and 293T cell lines. Organ-specific toxicity was assessed using the following dosing paradigm of Wistar rats: group 1: normal saline; group 2: Mel (180 mg/kg); group 3: Cya (150 mg/kg); and group 4: Mel (180 mg/kg) + Cya (150 mg/kg).

RESULTS

The NRK cell toxicity studies on Mel and Cya revealed IC₅₀ values of 1.89 mg/mL and 4.20 mg/mL, respectively. Similarly, Mel and Cya IC₅₀ values in 293T cells were 2.07 mg/mL and 3.71 mg/mL, respectively. Histopathologic studies revealed crystals in the renal medulla-cortex and loss of chief cells in the lining of the stomach in the group receiving Mel plus Cya. HPLC-MS analysis of organ homogenates showed that the concentration of Mel was greatest in the animals receiving a combination of both Mel and Cya.

DISCUSSION AND CONCLUSION

Mel is more toxic than its homolog Cya. The kidney is the most affected organ. Mel was present at high concentration not only in the kidneys, but also in the uterus and liver, informing the scope of future studies on the mechanism of Mel and Cya toxicity.

The contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using diamond anodes

In this work, the contribution of mediated oxidation mechanisms in the electrolytic degradation of cyanuric acid using boron-doped diamond (BDD) anodes was investigated in different electrolytes. A complete mineralization of cyanuric acid was obtained in NaCl; however lower degrees of mineralization of 70% and 40% were obtained in Na2SO4 and NaClO4, respectively. This can be explained by the nature of the oxidants electrogenerated in each electrolyte. It is clear that the contribution of active chlorine (Cl2, HClO, ClO(-)) electrogenerated from oxidation of chlorides on BDD is much more important in the electrolytic degradation of cyanuric acid than the persulfate and hydroxyl radicals produced by electro-oxidation of sulfate and water on BDD anodes. This could be explained by the high affinity of active chlorine towards nitrogen compounds. No organic intermediates were detected during the electrolytic degradation of cyanuric acid in any the electrolytes, which can be explained by their immediate depletion by hydroxyl radicals produced on the BDD surface. Nitrates and ammonium were the final products of electrolytic degradation of cyanuric acid on BDD anodes in all electrolytes. In addition, small amounts of chloramines were formed in the chloride medium. Low current density (≤10mA/cm(2)) and neutral medium (pH in the range 6-9) should be used for high efficiency electrolytic degradation and negligible formation of hazardous chlorate and perchlorate.

Comment on "Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid"

In a recently published paper [Spectrochim. Acta A: Mol. Biomol. Spect. 138 (2015) 711-722], Prabhaharan, Prabakaran, Srinivasan, and Gunasekaran presented a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid, and explain their findings using the tri-hydroxy tautomeric form of the compound. In reality, the compound adopts the tri-oxo tautomeric form, which is by over 100kJmol(-1) more stable comparatively to the tri-hydroxy tautomer discussed and characterized by Prabhaharan et al.

The toxic effect of a mixture of melamine and cyanuric acid on the gastrointestinal tract and liver in mice

The aim of this study was to investigate the effects of a mixture of melamine (MA) and cyanuric acid (CA) on the gastrointestinal tract and liver in mice. Kunming mice were given 0, 10, 100, or 200mg/kg.bw/day MA and CA mixture (MC, each compound) in corn oil by gavage for 7 consecutive days. Autopsy showed severe renal injury in all MC-treated mice and histopathological examination revealed dose-related lesions in the gastrointestinal tract and liver other than the kidneys. Subsequently, Kunming mice were given 0, 0.3, 1.5, or 7.5mg/kg · bw/day MC (each compound) in corn oil by gavage for 28 consecutive days. The results showed that higher doses of MC caused mortality and alteration on the body weights, relative liver weights, and blood chemistry parameters related to treatment. Histopathologically, the liver revealed scattered hepatic necrosis and apoptosis. Villous height and villus-to-crypt depth ratios were decreased in the duodenum and jejunum, with marked expression of proliferating cell nuclear antigen in the epithelium compared with controls. In conclusion, MC mixture could cause toxic effects in the gastrointestinal tract and liver in mice during acute and sub-acute toxicity study.

Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid

The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000cm(-1)) and FT-Raman spectra (400-4000cm(-1)) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ and Δα) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000K.

Tissue deposition and residue depletion in rainbow trout following continuous voluntary feeding with various levels of melamine or a blend of melamine and cyanuric acid

This study determined the deposition and depletion in rainbow trout after continuous administration of melamine (MEL) alone or a blend of MEL and cyanuric acid (CYA). The plasma, muscles, kidneys, liver and gills were sampled at 0, 3, 7, 13, 21, 28 and 42d. After the final sampling at 42d, fish from the MEL0.05, MEL20 and MCA groups were fed the control diet (MEL0) for the depletion test. Co-administration with cyanuric acid accelerated the deposition time to the Css for melamine; during the withdrawal phrase, the melamine and CYA concentrations in the tissues decreased exponentially. Compared to the t(½) for single oral administration, the t(½) for melamine and cyanuric acid after 42d continuous feeding was prolonged. The presence of trace CYA in the plasma and kidneys of trout was detected in the MEL20 group, indicating that MEL can convert into CYA in rainbow trout.

Evaluation of renal toxicity by combination exposure to melamine and cyanuric Acid in male sprague-dawley rats

Melamine-induced nephrotoxicity is closely associated with crystal formation in the kidney caused by combined exposure to melamine (Mel) and cyanuric acid (CA). However, there are few dosage-finding studies for toxicological evaluation of chronic co-exposure to Mel and CA. The objective of this study was to investigate the possible mechanism by which a Mel and CA mixture lead to renal toxicity in rats. Mel and CA were co-administered to rats via oral gavage for 50 days. Nephrotoxicity was determined by measuring blood urea nitrogen (BUN) and serum creatinine (sCr) levels. Relative kidney weights were significantly increased in rats after co-exposure to Mel+CA (63/6.3 or 630/6.3 mg/kg) mixtures. BUN and sCr levels were significantly increased after Mel and CA co-exposure. Taken together, significant increase in KIM-1, NGAL, and calbindin levels were observed in the urine of rats exposed to Mel+CA (63/6.3 or 630/6.3 mg/kg) compared with the corresponding control group. Histological analysis revealed epithelial degeneration and necrotic cell death in the proximal tubules of the kidney after co-exposure to Mel+CA (63/6.3 or 630/6.3 mg/kg). Our data suggest that Mel-mediated renal toxicity may be influenced by CA concentrations in Mel-contaminated milk or foods.

Acute testicular toxicity induced by melamine alone or a mixture of melamine and cyanuric acid in mice

Eight-week-old male Kunming mice were administered either melamine (MA, 30, 140, or 700 mg/kg/day), a melamine and cyanuric acid mixture (MC, each at 15, 70, or 350 mg/kg/day), or vehicle (control) for 3 consecutive days. Testicular toxicity was evaluated on days 1 and 5 after the final exposure. The testicular and epididymal weights and serum testosterone level were significantly decreased in the highest MC group (350 mg/kg/day). Histopathologically, both MA and MC caused obvious lesions in the testis and epididymis, with significant increases in sperm abnormalities. By TEM, the blood-testis barrier was damaged dose dependently. TUNEL staining showed that both MA and MC induced increases in germ cell apoptosis. The Sertoli cell vimentin was collapsed in the treated animals as detected by immunohistochemical staining and Western blotting. This study demonstrated that both MA and MC treatments could disrupt the blood-testis barrier and cause a clear testicular toxicity.

Urinary melamine: proposed parameter of melamine adulteration of food

Melamine is widely being reported as a food adulterant. Although its toxicity is currently recognized, melamine adulterations of food items are ongoing for falsely inflating the protein content of the food. Melamine alone or in combination with cyanuric acid or uric acid causes nephrotoxicity, and melamine-induced nephrotoxicity is now a global concern. It has been proven that when consumed, melamine is metabolized at a slower rate and excreted unchanged in urine. There is every possibility that when individuals consume melamine-adulterated food items, the melamine may be excreted unchanged in the urine. Therefore, melamine estimation in urine may be a yardstick to check for melamine adulteration of food items. In the present review, recent literature on this subject is analyzed justifying.