| Aim:PM2.5 is a major by-product released during moxibustion. Its physicochemical characteristics and toxicology are closely associated with the safety of moxibustion in clinical usage. Studies on PM2.5 have emerged to be one of the more important and difficult areas of moxibustion research. Safey concerns surrounding moxa smoke PM2.5 has impeded the clini-cal usage and industry development of moxibustion, as well as issues regarding the clinical safety and effectiveness of moxibustion. The main aim of this study was to evaluate the safety of moxa smoke PM2.5 and assess the health risks associated with moxa smoke exposure in moxibustion clinics.Materials and methods:This study focused on investigating moxa smoke PM2.5 from four aspects, namely PM2.5 mass concentration, chemical composition, health risk assessment of moxa smoke exposure and toxicology studies. PM2.5mass concentration was monitored and compared against international air quality standards, the characteristics of the trace elemenrs were analysed, the health risks of exposure in moxibustion clinics were estimated and in vivo and in vitro toxicological studies were performed to evaluate the safety of moxa smoke PM2.5.1. PM2.5 mass concentrations in moxibustion clinic:International standard detection method for environmental sciences was used (gravimetric method) to measure ambient par-ticulate concentration;2. Conversion coefficient K value of microcomputer laser dust monitor LD-5C (B): Three samples of moxa floss, specifically 3 years 3:1 ratio,3 years 15:1 ratio and 10 years 10:1 ratio, were burned separately in a sealed combustion chamber. The concentrations of the particles were measured by the gravimetric method and monitored using the dust monitor at random times to form a concentration gradient. The correlation between the results from the gravimetric weighing method and the dust monitor was analysed to find the best method for monitoring particles concentration in moxibustion clinics;3. PM2.5 trace elements:Inductively Coupled Plasma-Mass Spectrometry was used to determine 27 trace elements in whole sample and water-soluble fraction of PM2.5 in moxibus-tion clinic, classroom and outdoor environment;4. Health risk assessment in moxibustion clinic:The inhalation risk assessment model for occupational exposure recommended by the US Environmental Protection Agency was used to estimate PM2.5 carcinogenic and non-carcinogenic health risks for acute and chronic exposure in moxibustion clinic;5. PM2.5 in vitro toxicology research:Plasmid DNA assay was used to compare the oxidative damage caused by particles collected in moxibustion clinic, classroom and outdoor environment to analyze the health impact of particles from moxa smoke;6. In vivo toxicology study for moxa smoke:Animal studies using Wistar rats were performed to study the effects of moxa smoke on Wistar rats’ lung and skeletal muscles and changes in the levels of serum leptin, TNF-α and IL-8 of the diaphragm and extensor digito-rum longus tendon after 12 weeks of exposure to different concentrations of moxa smoke.Results:1. PM2.5 mass concentration:1) Average PM2.5 mass concentration in moxibustion clinic, classroom and outdoor environment was 224.28 μg/m3,106.78 μg/m3 and 90.45 μg/m3, respectively. All three results exceeded the limit of 35 μg/m3 recommended in the China national daily PM2.5 quality standard and the Environmental Protection Agency Air Quality Guidelines, and also the limit of 25μg/m3 stated by the World Health Organization;2) Average PM2.5 mass concentration in moxibustion clinic from burning 3 years 3:1 moxa floss was 224.28 μg/m3,3 years 15:1 moxa floss was 226.39 μg/m3 and 10 years 3:1 moxa floss was 210.56μg/m3. The mass concentrations for all three samples exceeded international standards and there was no significant difference in the mass concentrations among the three samples of different storage years and ratios.2. Conversion coefficient K value of microcomputer laser dust monitor LD-5C (B):1) Conversion coefficient K values were 0.000792,0.000672 and 0.000784 for samples 3 years and 3:1,3 years 15:1 and 10 years 3:1, respectively. Samples that were of the same storage year but different ratios had significantly different K values (P<0.05), implying that the processing of moxa floss into different ra- tios has a greater impact on the physicochemical properties of particulate matter produced during combustion.2) When the reading on the LD-5C (B) PM2.5 dust monitor showed a value exceed-ing 8 mg/m3, K value had a larger standard deviation and weaker correlation. Therefore, greater attention had to be paid between the change in the conversion coefficient K value with the reading on the dust monitor when the dust monitor showed a value greater than 8 mg/m3.3. PM2.5 trace elements:1) The concentration of most trace elements for individual PM2.5 in moxa smoke was lower than that in classroom and outdoor environments;2) The concentrations of Hg, Ag, U, Li and Be in the PM2.5 of moxibustion clinic were higher, however the remaining 22 trace elements were lower than class-room and outdoor environments. Concentrations of heavy metal elements Pb, Cd, Hg and As were also lower than the national air quality standard concentration limits in moxibustion clinic;3) Trace elements such as Na, Mg, Ca, Cr52, Cr53, Co, Ga, Sr, Cs, Ba, Hg, Cd, Ag, Li, Be and U in the PM2.5 of moxibustion clinic may be derived from the burning of moxa floss.4. Health risk assessment in moxibustion clinic:1) The annual cancer risk for doctors in moxibustion clinics through the respiratory route due to 5 types of carcinogenic metals Be, Cr52, Cr53, Cd and As elements ranged between 1.79xlO-9～6.23xlO-8, with an average of 1.31×10-7. The annual cancer risk for all carcinogenic metal elements was lower than the risk limit (1x10-6), indicating that there was no carcinogenic risk for a year for doctors in moxibustion clinics due to exposure. If the doctor was exposed for a prolonged period to a certain concentration of moxa smoke, it will take 7.62 years for the limit to reach carcinogenic risk, suggesting that a doctor’s exposure to moxa smoke in moxibustion clinics for 7 years may likely lead to carcinogenic risks.2) Carcinogenic health risk assessment for patients in moxibustion clinics showed that the annual cancer risk through the respiratory route ranged from 4.48x10-13～ 1.56x10-11. The order of risk for the carcinogenic metal elementsis was Cr52> Cr53> As> Cd> Be. The average annual cancer risk for patients in moxibustion clinics was 3.28x10-11, which was much lower than the total cancer risk limit (1 x10-6). This suggests that patients who are exposed to moxa smoke daily for 30 minutes in moxibustion clinics for one year will not lead to carcinogenic risk. There would be no cancer risk in the lifetime even if patients were exposed daily to a certain concentration of smoke in moxibustion clinics for 30 minutes (longer than one year), indicating that there was no carcinogenic risk for patients ex-posed in a moxibustion environment;3) The acute non-carcinogenic risk assessment for doctors for Hg and Mn was 0.007361 and 0.00744, respectively, with a total hazard index of 0.015. This in-dex was lower than the threshold acceptance limit for risk by the population;4) The acute non-carcinogenic risk assessment for patients for Hg and Mn was 0.032 and 0.033, respectively, with a total hazard index of 0.065, which was lower than the risk limit. Thus, the health risks for non-carcinogenic substances Mn and Hg in moxibustion clinic population were lower than the threshold ac-ceptance range and would not lead to significant health effects for a moxibustion clinic population;5) The average exposure concentration for a moxibustion clinic population in clini-cal practice is not constant. Therefore, epidemiological studies have to be per-formed to verify if the limits derived from the health risk assessment model is truly reflective of the risk exposure level.5. Plasmid DN A assay:1) TD25 for moxibustion clinic PM2.5was significantly higher than classroom and outdoor environment (P<0.05). This was due to a weak correlation between oxidative damage and trace elements for moxibustion clinic, resulting in lower oxidative damage of individual particulate matter than other environments;2) The oxidative damage caused by PM2.5 in moxibustion clinic was 3.65 and 2.19 times lower than that of the classroom and outdoor environments respectively. When the PM2.5 sample concentrations of the three environments were 224 μg/mL,107 μg/mL and 90 μg/mL, there was no significant difference in the plasmid DNA oxidative damage between moxibustion clinic and the other two environments. This suggested that it did not have significant health effects on the body although PM2.5 mass concentration in moxibustion clinic was significantly higher than the other two environments.3) The D500 oxidative damage between moxa floss samples of 3 years 3:1,3 years 15:1 and 10 years3:1 and its corresponding moxa ash had no significant differ-ence, suggesting that the heavy metal content and transition metal content may not have significant differences. T he heavy metal content and transition metal content may not be the best evaluating indicators for moxa floss quality.6. In vivo toxicological evaluation for moxa smoke:1) Wistar rats exposed to different concentrations of moxa smoke for 12 weeks did not show any obvious signs of poisoning and there was no significant difference in body weight;2) The levels of serum leptin, TNF-a and IL-8 content in the diaphragm and exten-sor digitorum longus tendon in rats exposed to low, middle and high concentra-tions of moxa smoke did not show any significant difference as compared with the control group. The lungs, diaphragm and extensor digitorum longus tendon did no show significant pathological change.Results:This is the first known study conducted to analyze the PM2.5 from moxa smoke and to construct a health risk assessment model to estimate the health risks in exposed popu-lation. This study also systematically investigated the toxicological effects of particulate mat-ter from moxa smoke. The results obtained from this study can help to provide reference for future studies in the establishment of a quality monitoring system in moxibustion environment for the evaluation of the safety of moxa smoke.
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