Sources, distribution, and environmental effects of microplastics: a systematic review.

Microplastics (MPs) are receiving increasing attention from researchers. They are environmental pollutants that do not degrade easily, are retained for prolonged periods in environmental media such as water and sediments, and are known to accumulate in aquatic organisms. The aim of this review is to show and discuss the transport and effects of microplastics in the environment. We systematically and critically review 91 articles in the field of sources, distribution, and environmental behavior of microplastics. We conclude that the spread of plastic pollution is related to a myriad of processes and that both primary and secondary MPs are prevalent in the environment. Rivers have been indicated as major pathways for the transport of MPs from terrestrial areas into the ocean, and atmospheric circulation may be an important avenue for transporting MPs between environmental compartments. Additionally, the vector effect of MPs can change the original environmental behavior of other pollutants, leading to severe compound toxicity. Further in-depth studies on the distribution and chemical and biological interactions of MPs are highly suggested to improve our understanding of how MPs behave in the environment.

Microplaastics as potential bisphenol carriers: role of adsorbents, adsorbates, and environmental factors.

Microplastics (MPs) are widely found in the environment and can act as carriers for various toxic substances, promoting their diffusion and bioenrichment. Accordingly, it is necessary to investigate the transfer of MPs between the environment and organisms. This study investigated the adsorption potential of four types of MPs, namely polystyrene (PS), polypropylene (PP), polyamide (PA), and polyvinyl chloride (PVC), for bisphenol (BP) A, B, F, and S (BPA, BPB, BPF, and BPS, respectively). The results showed that all four types of MP could act as environmental carriers of BP. PA had the highest BPA adsorption capability, with a value of 109.0 ± 39.93 µg·g-1, followed by PS (89.24 ± 26.12 µg·g-1), PVC (53.08 ± 15.32 µg·g-1), and PP (41.83 ± 11.51 µg·g-1).Thepolymer type, SSA, and surface functional groups were the main factors affecting the BP adsorption capacity of MPs. The concentration, hydrophobicity, and dissociation ability of BPs also substantially affected their adsorption behavior. The adsorption efficiency of different BPs on the same MPs ranged from 37.4 ± 3.7% to 59.1 ± 2.8%. The adsorption capacity of BPs on MPs decreased with increasing temperature. Salt ions in the solution significantly enhanced BP partitioning in the solid phase owing to the salting-out effect. Additionally, the adsorption of BPs on MPs was pH dependent. Higher pH values increased electrostatic repulsion, which decreased the adsorption capacity. These results demonstrate that MPs can serve as BP carriers in the environment and their potential BP loads might be considerably greater than that of BP additives used during plastic production.

Ingestion of microplastics by silver carp (Hypophthalmichthys molitrix) larvae: Quantification of ingestion and assessment of microbiota dysbiosis.

The adverse effects of microplastics ingested by aquatic organisms have been reported previously. However, most studies are primarily qualitative; therefore, it is challenging to determine the direct interactions between microplastics and organisms. In this study, for the first time, the microplastic intake behavior of silver carp (Hypophthalmichthys molitrix) larvae, a popular fish in China, as well as intestine accumulation and excretion of the microplastics were quantitatively investigated. The results showed that the intake of microplastics by silver carp larvae was negatively correlated with the particle size of microplastics but positively correlated with the exposure concentration. After intaking microplastics of different sizes, small-sized microplastics (≤ 150 µm) were rapidly excreted from the intestine of silver carp, whereas some large-sized microplastics (≥ 300 µm) remained in the intestine for a long time. The presence of food significantly increased the intake of large-sized microplastics, while small-sized microplastics intake was unaffected by the food. More importantly, the ingested microplastics caused specific changes in the diversity of intestinal microflora, potentially leading to abnormal immune and metabolic functions. The results of this study provide a new understanding on the potential impacts of microplastics on aquatic organisms.

Development and validation predictive models of sperm retrieval for azoospermic men undergoing testicular sperm aspiration: a multicentre, retrospective, cohort study.

PURPOSE: Testicular sperm aspiration (TESA) is widely used to retrieve sperm from testis. Diagnostic testicular biopsy should not be routinely performed for azoospermia. Therefore, a good predictive model is needed before TESA. METHODS: A total of 1972 azoospermia patients constituted the modelling set, and 260 azoospermia patients from two other centres constituted the validation set. An integrated predictive model was built using logistic regression. Receiver operating characteristic (ROC), calibration and decision curve analyses were performed to evaluate the performance of follicle-stimulating hormone (FSH), semen volume, testicular volume and the integrated model. RESULTS: The FSH level was the best univariate predictor for successful sperm retrieval (SSR) and was better than semen volume and testicular volume alone (p<0.001, threshold 6.17 IU/L, modelling set area under receiver operating characteristic curve (AUC) 0.80, accuracy 0.79; validation set AUC 0.87, accuracy 0.78). The integrated predictive model had excellent accuracy for predicting SSR (modelling set: AUC 0.93, accuracy 0.89; validation set: AUC 0.96, accuracy: 0.89). Calibration curve analysis indicated that the integrated model calibration was good and better than that of FSH, semen volume and testicular volume alone. Decision curve analysis indicated with a threshold probability between 0.05 and 0.98, the integrated model added more benefit than treating either all or no patients. CONCLUSIONS: The integrated model has excellent discrimination and good calibration. It can help azoospermic men make better decisions before TESA. It should be noted that TESA is not the first-line treatment for non-obstructive azoospermia because of a low sperm retrieval rate.

Migration behaviors of microplastics in sediment-bearing turbulence: Aggregation, settlement, and resuspension.

The interaction between microplastics (MPs) and suspended sediment (SS) is important for the environmental fate of MPs. This study explored the interaction of MPs with SS and the vertical migration behavior of MPs in sediment-bearing turbulence. The turbulent shear flow caused MPs to aggregate. This aggregation resulted in a rapid increase in particle size, which peaked when the shear rate was 19.94 s-1, and then declined with a further increase in the shear rate. Compared to large MPs, small MPs were more prone to aggregation, which formed heterogeneous aggregate MPs-SS in sediment-bearing turbulence. Owing to the formation of heterogeneous aggregates, small MPs had a much higher settlement rate in sediment-bearing turbulence than in sediment-free turbulence. MPs in bottom sediments may resuspend owing to turbulent shear flow acting on sediments, causing secondary pollution. These results provide new insights into the aggregation, settlement, and resuspension behaviors of MPs in natural waters.

Nanoplastic adsorption characteristics of bisphenol A: The roles of pH, metal ions, and suspended sediments.

Nanoplastics (NPs) are widely found in the environment and can act as a vector for various toxic substances and promote their diffusion and bioenrichment, but the underlying mechanisms are largely unknown. Here, the adsorption characteristics of bisphenol A (BPA) onto NPs were explored. The results show that the adsorption of BPA on NPs was dominated by saturated single-layer adsorption and affected by both intra-particle diffusion and liquid film diffusion. Electrostatic interaction, π-π interaction, and hydrophobic effects played key roles in adsorption. In addition, the introduction of electrolytes inhibited the adsorption of BPA onto NPs. Interestingly, the introduction of suspended sediment promoted the formation of heterogeneous aggregates of NPs-SS, thereby reducing the adsorption capacity, indicating that aggregation may play an important role in the adsorption behavior of NPs. Overall, our results provide new insights into the adsorption behavior of BPA on NPs and the underlying mechanisms under different environmental conditions.

Differences in Immune Responses between Children and Adults with COVID-19.

Over 85 590 000 individuals have been infected with severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2). Although there have been an increasing number of reports on coronavirus disease 2019 (COVID-19), it is unclear why infected children show milder symptoms than adults. A retrospective case study was performed at two designated hospitals for COVID-19. Patients (56 children and 63 adults) with confirmed SARS-CoV-2 infection and mild pneumonia were randomly enrolled in this study. The median age of the children was 7.0 years, and 51.79% of them were boys. The median age of the adults was 57 years, and 47.62% were men. The most common symptoms were fever, cough, sputum and diarrhoea. There were no significant differences in symptoms between children and adult patients. In terms of immunological indices on admission, adult patients displayed typical leukopenia and markedly higher levels of IL-2, IL-4, and IL-6 than child patients. The elevation of IL-2, IL-4 and IL-6 in adults induced more extensive lung injury. The effective and non-aggressive immune response successfully resisted SARS-CoV-2 invasion and maintained mild symptoms in child patients. The correlation of higher IL-2, IL-4, and IL-6 with the lung injury might be evidence that preventing excessive cytokine production can avoid further lung damage in these patients.

[Application of modified anterolateral supra-fibular-head approach in treatment of tibial plateau fractures involving posterolateral column].

OBJECTIVE: To explore effectiveness of reduction and internal fixation via modified anterolateral supra-fibular-head approach in treatment of tibial plateau fractures involving posterolateral column. METHODS: Between January 2016 and September 2018, 19 patients diagnosed as tibial plateau fractures involving posterolateral column were treated with reduction and internal fixation via modified anterolateral supra-fibular-head approach. There were 11 males and 8 females with an average age of 43.2 years (range, 28-65 years). The causes of tibial fracture were traffic accident (12 patients), falling injury (5 patients), and falling from height (2 patients). According to the Schatzker typing, the tibial fractures were rated as type Ⅱ in 9 cases, type Ⅲ in 4 cases, type Ⅴ in 4 cases, and type Ⅵ in 2 cases. The time from injury to operation was 5-13 days (mean, 8.5 days). There were 2 patients with osteoporosis. The operation time, intraoperative blood loss, and postoperative complications were recorded. The knee X-ray film was reviewed regularly to observe the fracture healing. At last follow-up, the fracture reductions were evaluated by Rasmussen radiological score. The knee joint function was evaluated by Hospital for Special Surgery (HSS) score system. RESULTS: The average operation time was 95 minutes (range, 65-130 minutes). The average intraoperative blood loss was 220 mL (range, 150-350 mL). All incisions healed by first intention. No complications such as infection or deep venous thrombosis occurred. All patients were followed up 12-20 months (mean, 15.4 months). X-ray films showed that the fractures healed with the healing time of 12-20 weeks (mean, 14.5 weeks). No complications such as loosening or breakage of internal fixation occurred. At last follow-up, according to the Rasmussen radiological score, the fracture reductions were evaluated as excellent in 13 cases, good in 4 cases, fair in 1 case, and poor in 1 case. HSS scores of knee joint function were excellent in 14 cases, good in 3 cases, fair in 1 case, and poor in 1 case. The knee joint range of motion was 90°-135°, with an average of 113.4°. CONCLUSION: Application of modified anterolateral supra-fibular-head approach in reduction and internal fixation for tibial plateau fractures involving posterolateral column has the advantages of full exposure, less trauma, safety, and reliable reduction and fixation.

[Research progress in molecular pharmacognosy of Pogostemon cablin].

Molecular pharmacognosy( MP) is a new interdisciplinary science,which integrates the pharmacognosy and molecular biology,and focuses on the crude drugs' classification and identification,cultivation and protection,and production of active ingredients at the molecular level. Pogostemon cablin is one of the ten major southern medicines in China,MP research on this famous herb has developed on the basis of traditional research methods,and achieved certain results. This article summarized the MP research achievements of P. cablin in recent years,the prospect of this field is also discussed to provide references for the protection,development and utilization of P. cablin resources.

[Inhibition and Remediation of Methylmercury Contaminated Soil by Use of Modified Montmorillonite].

Montmorillonite was modified by 3-mercaptopyl trimethoxysilane and chitosan. The modified montmorillonite was characterized by XRD technology. The effects of thiol montmorillonite and chitosan montmorillonite on the inhibition and remediation of methylmercury contaminated soil under different water conditions were studied using laboratory simulation. XRD results showed that both thiol and chitosan were successfully loaded on the montmorillonite. The results of simulation tests showed that the addition of the remediation material to soil contaminated with methylmercury produced a better remediation effect. Compared with the blank control, the content of methylmercury in the soil was reduced by 82.10% (thiol montmorillonite) and 45.20% (chitosan montmorillonite), respectively, in the flooded condition. Under dry/wet alternation, the content of methyl mercury in soil decreased by 66.70% (thiol montmorillonite) and 49.79% (chitosan montmorillonite), respectively. Under drought conditions, the content of methylmercury in soil decreased by 44.66% (thiol montmorillonite), and the concentration of methylmercury in soil decreased by 54.37% after adding chitosan montmorillonite for 4 weeks. Compared with single modified montmorillonite, the repair effect of combined modified montmorillonite and lime treatment was not improved significantly.

[Effects of Organic Substrates on ANAMMOX-MFC Denitrification Electrogenesis Performance].

An anaerobic ammonium oxidation microbial fuel cell (ANAMMOX-MFC) was successfully started by inoculating anaerobic ammonium oxide sludge into the anode of a microbial fuel cell and then used to study the effect of glucose and phenol on ANAMMOX-MFC denitrification electrogenesis performance. The results showed that the ANAMMOX bacteria promoted ANAMMOX-MFC denitrification when the concentration of glucose was low (100-200 mg·L-1). At that time, the chemical oxygen demand (COD) concentration of the reactor was not significant. The electrogenesis production performance and NH4+-N removal rate gradually decreased when the glucose concentration was higher than 300 mg·L-1, but the NO2--N removal rate generally remained unchanged. The COD concentration was also reduced, indicating that the activity of the ANAMMOX bacteria was inhibited and the activity of denitrification bacteria began to increase. The polarization curve fitting degree was low, and the change in COD concentration had little effect on the battery internal resistance. When the concentration of phenol was low (50-100 mg·L-1), there was little effect on ANAMMOX-MFC denitrification electrogenesis performance. When the concentration of phenol exceeded 200 mg·L-1, ANAMMOX-MFC denitrification performance was gradually inhibited. Overall, in the process, the COD concentrations of the water influent and effluent changed little, the polarization curve fitting degree was low, and the apparent internal resistance increased slowly.

Serum Levels of the Inflammatory Cytokines in Patients with Lumbar Radicular Pain Due to Disc Herniation.

STUDY DESIGN: Cohort study. PURPOSE: This study primarily aimed to evaluate the serum levels of tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-4 in patients with lumbar radiculopathy 1 and 12 months after microdiscectomy. OVERVIEW OF LITERATURE: Lumbar radiculopathy is possibly caused by inflammatory changes in the nerve root. The intraneural application of pro-inflammatory cytokines induces behavioral signs associated with pain. Anti-inflammatory cytokine treatment effectively reduces hyperalgesia. METHODS: The role of TNF-α and IL-4 in long-lasting lumbar radiculopathy was addressed. A total of 262 patients were recruited from Anqing Hospital, Anhui Medical University. During inclusion at 1 and 12 months, serum concentrations of TNF-α and IL-4 were analyzed by enzyme-linked immunosorbent assay, and pain intensity was reported on a 0-10 cm visual analog scale (VAS). RESULTS: Sixty six patients had VAS <3 and 196 patients had VAS ≥3. Serum concentrations of pro-inflammatory TNF-α and anti-inflammatory IL-4 in patients with lumbar radiculopathy related to disc herniation were measured at 1- and 12-month follow-up. TNF-α decreased in both VAS groups with time. In contrast, IL-4 increased in both groups at 1 month and then decreased gradually until month 12. The changes in serum levels of TNF-α and IL-4 over time between the VAS ≥3 and VAS <3 groups were significantly different. CONCLUSIONS: Chronic lumbar radiculopathy may be associated with high level of pro-inflammatory substances, such as TNF-α, in serum after disc herniation, and elevated anti-inflammatory cytokine in patients with lumbar radiculopathy may indicate a favorable outcome.

Role of (pro)rennin receptor in cardiomyocytes of heart failure rat model.

The role of (pro)rennin receptor (PRR) in cardiomyocytes of a heart failure (HF) rat model was studied. Spontaneously hypertensive rats (SHR) with HF (SHR-HF) or not were identified by two-dimensional (2-D) ultrasound. Age-matched Wistar Kyoto normotensive (WKY) rats were used as controls. PRR short hair RNA (sh-RNA) was injected into the heart of SHR-HF. Simultaneously SHR and controls received the same shRNA injection into the heart. Scramble shRNA was injected into the heart as controls. The expression of PRR mRNA and protein in cardiomyocytes was detected by using real-time PCR and Western blotting respectively. The heart function was evaluated by 2-D ultrasound, including eject fraction (EF%), fractional shortening (FS%), left ventricle thickness (LV), and inter-ventricular septal thickness (IVS). The number of apoptotic cardiomyocytes was counted by using flow cytometry. The results showed that the mRNA and protein expression levels of PRR were significantly higher in cardiomyocytes of SHR-HF group than in those of SHR group or control group. The apoptosis of myocytes in SHR-HF group was increased as compared with SHR group or control group. After knock-down of PRR with shRNA in SHR-HF group, the apoptosis of myocytes was reduced, resulting in the improved heart function. It was suggested that down-regulation of PRR might protect the heart from development of HF in SHR-HF by inhibiting the apoptosis of cardiomyocytes.

[Effect of Panax notoginseng saponins on APP gene transcription in the brain tissue of SAMP8].

OBJECTIVE: To study the effect of Panax notoginseng saponins (PNS) on learning and memory ability and APP gene transcription in the brain tissue in senescence accelerated mouse prone 8 (SAMP8). METHODS: SAMP8 were randomly divided into high-does PNS group, low-does PNS group, huperzin A group and model group,the treatment groups were treated with the designed drugs respectively by intragastric administration for 4 consecutive weeks. The same volume of double distilled water was given to model group. After treatment, the abilities of learning and memory of the mice were tested with morris water maze, the mRNA content of APP was assayed by reverse transcription (RT) and real-time polymerase chain reaction (RT-PCR). RESULTS: PNS could improve the abilities of learning and memory, high-does PNS could reduce the mRNA content of APP in the brain tissue of SAMP8. CONCLUSION: PNS can improve the abilities of learning and memory of SAMP8, the mechanism may be relevant to down-regulating the expression of APP gene at transcriptional level.

The influence of trace NO(2) on the kinetics of ammonia oxidation and the characteristics of nitrogen removal from wastewater.

Ammonia oxidizing bacteria-enriched sludge was obtained in a sequencing batch reactor with synthetic wastewater. Batch tests of ammonia oxidation were carried out with the sludge, in the presence of only trace NO(2) and in the presence of O(2) and trace NO(2), respectively. The Andrews model is used to describe NO(2)-dependent ammonia oxidation. The maximum ammonia oxidation rate of 139.11 mg N.(g sludge COD h)(-1), occurred in the presence of 21% O(2) and 100 ppm NO(2), which was 3 times higher than the aerobic ammonia oxidation rate without NO(2). The kinetic model of ammonia oxidation in the presence of O(2) and trace NO(2) is developed, and the function of NO(2) apparently enhancing ammonia oxidation is suggested. The maximal nitrogen removel of 34.19% occurred at the 21% O(2) and 100 ppm NO(2) in the mixed gases. Nitrogen removal principally depended on the denitrification activity and NO(2)-dependent ammonia oxidation activity of ammonia-oxidizing bacteria (AOB).

Repair effect of Wnt3a protein on the contused adult rat spinal cord.

OBJECTIVE: To explore the repair effect of Wnt3a on injured spinal cord in rats. METHODS: Moderate spinal cord contusion injury was made in 40 adult Sprague-Dawley rats at T10. Fifteen rats served as contusion controls (Group 1). Fifteen rats were treated with Wnt3a 3 days after injury (Group 2). Ten additional rats received only T10 laminectomies to serve as non-injured controls (Group 0). The functional recovery of the rats was observed through Basso-Beattie-Bresnahan (BBB) open field locomotor score. Rats were killed at 14 or 28 days after injury, then spinal cords were removed for histopathologic examinations, and the expression of the bromodeoxyuridine (BrdU) plus neural cell markers was stained with immunohistochemical method. RESULTS: After an initial complete hindlimb paralysis, rats of all groups receiving a contusive injury recovered substantial function within 1 week. By 28 days, the BBB score for rats in Group 2 is better than that for rats in Group 1 by 7 points (Group 2 = 16.94, after 28 days versus Group 1 = 9.89 points; p < 0.05). Light and electron microscopic works showed that the Wnt3a-treated group had moderate repair effect of myelin and axons. Immunohistochemical analysis showed a significant increase in the number of the inducing differentiated neurons in Wnt3a-treated rats compared with control rats 2 weeks after injury. CONCLUSIONS: Exogenous Wnt3a administration can improve axonal conduction and spinal cord function in the injured spinal cord, and the administration of Wnt3a result in the increase in the populations of neurons, suggesting that these cells may be derived from neural precursors and stem cells.

On evolution under symmetric and asymmetric competitions.

This paper considers the coevolution of phenotypic traits in a community comprising two competitive species subject to strong Allee effects. Firstly, we investigate the ecological and evolutionary conditions that allow for continuously stable strategy under symmetric competition. Secondly, we find that evolutionary suicide is impossible when the two species undergo symmetric competition, however, evolutionary suicide can occur in an asymmetric competition model with strong Allee effects. Thirdly, it is found that evolutionary bistability is a likely outcome of the process under both symmetric and asymmetric competitions, which depends on the properties of symmetric and asymmetric competitions. Fourthly, under asymmetric competition, we find that evolutionary cycle is a likely outcome of the process, which depends on the properties of both intraspecific and interspecific competition. When interspecific and intraspecific asymmetries vary continuously, we also find that the evolutionary dynamics may admit a stable equilibrium and two limit cycles or two stable equilibria separated by an unstable limit cycle or a stable equilibrium and a stable limit cycle.

[Determination of 16S rRNA gene sequence for a new ANAMMOX bacterial species].

The anaerobic ammonium oxidation (ANAMMOX) activity of the sludge was about 9.84 x 10(-4) mg x (mg x h)(-1) by measuring the simultaneous consumption of ammonium and nitrite under anoxic conditions in the batch tests. The consumption of NO2(-) -N and NH4+ -N was 1.311 for ANAMMOX bacteria. The partial 16S rDNA sequence was obtained by using molecule biology methods. Crude DNA of the total bacteria in granular sludge from EGSB reactor was extracted and purified. Then, PCR amplification by using specific primer, clone and sequence determination was performed. ANAMMOX bacterial species(anaerobic ammonium-oxidizing Planctomycete cquenviron-1) which was enrichment cultivated from EGSB reactor were the same genera with Candidatus "Anammoxoglobus propionicus" and Candidatus "Jettenia asiatica" by analyzing phylogenetic tree. The maximum identities of anaerobic ammonium-oxidizing Planctomycete cquenviron-1 with other ANAMMOX bacterial species was about 93%. The results showed that a new ANAMMOX bacterial species which was enrichment cultivated from EGSB reactor was found and anaerobic ammonium-oxidizing Planctomycete cquenviron-1 was denominated.

[Effect of trace NO2 and kinetic characteristics for anaerobic ammonium oxidation of granular sludge].

The effect of trace NO2 and kinetic characteristics for anaerobic ammonium oxidation of granular sludge was investigated by batch experiment. The sludge anammox rates could be described by the Haldane model. The kinetic parameters were determined, where the maximum anammox rate was 6.65 x 10(-3) mg (mg h)(-1). The half saturate coefficient and inhibition coefficient for ammonium nitrogen were 87.1 mg L(-1) and 1,123 mg L(-1) respectively, and the half saturate coefficient and inhibition coefficient for nitrite nitrogen were 15.39 mg L(-1) and 159.5 mg L(-1) respectively. Trace NO2 apparently enhanced anammox under trace NO2 atmosphere conditions. The function for NO2 to enhance anammox was suggested by the Haldane based model. The parameters in the function were estimated, where the maximum enhancing anammox coefficient was 48.79, and the half saturate coefficient and inhibition coefficient for NO2 were 2480 mg m(-3) and 4.22 mg m(-3) respectively, and the basic rate coefficient was 0.0182. The most of NOx in the experiment was lost.

[Ammonia oxidation kinetics of ammonia oxidizer mixed culture under the conditions of O2 and trace NO2 mixed gasses].

The kinetics of the NO2-dependent ammonia oxidation was developed for ammonia oxidizer mixed culture when there was no molecular oxygen in the batch tests. The kinetics parameters were determined, where the half saturate coefficient of NO2 was 0.821 micromol x L(-1), inhibition coefficient of NO2 concentration was 1.721 micromol x L(-1), and the maximum ammonia oxidation rate were 0.144 mg x (mg x h)(-1). After adding the volume fraction of O2 was 2% to trace NO2, the ammonia oxidation rates increased obviously. The maximum ammonia oxidation rate, 0.198 mg x (mg x h)(-1) occurred under the condition of the mixed gasses containing the volume fraction of O2 was 2% and 50 x 10(-6) NO2. Under the condition of mixed gasses containing the volume fraction of O2 was 21% to trace NO2, the ammonia oxidation rates further increased greatly. The maximum ammonia oxidation rate, 0.477 mg x (mg x h)(-1) occurred when the volume fraction of O2 was 21% and 100 x 10(-6) NO2 in the mixed gas, which is 3 times higher than the general aerobic ammonia oxidation rate. The function for NO2 apparently to enhance ammonia oxidation was suggested. The kinetics model of ammonia oxidation under the conditions of O2 and trace NO2 mixed gasses was developed. The model was validated by the results of ammonia oxidation experiments under the conditions of the mixed gasses containing 2% O2 and trace NO2. The mechanism for NO2 to enhance ammonia oxidation under the conditions of O2 and trace NO2 mixed gasses was discussed.