Keywords: 
• cyclic volatile methylsiloxanes /
• environmental distribution /
• environmental behavior /
• environmental effect

Abstract: In recent years, the cyclic volatile methyl siloxanes (cVMS) are widely used in the process of production and people's daily life because of their excellent performance, meanwhile leading to increasing environmental and human exposure risks and receiving dramatic concerns because of their persistence, potential biological accumulation and toxicity. At present, researchers have a certain understanding about the occurrence, behavior and effects of cVMS in various environmental media all over the world. Most cVMS were discharged into the atmosphere, and some cVMS were found in water, sediment, soil and organism. Many studies have shown that the highest median of the total cyclic siloxane of indoor air dust was from Greek (1 380 ng·g^-1), and followed by China (362 ng·g^-1). The total siloxane flux per capita for sewage treatment plant in China (10 g·y^-1) was much lower than that of UK (48.3 g·y^-1 for D4-D6) and the United States (93.5 g·y^-1for D4-D6). The total cVMS concentration (1.05 μg·L^-1) from a sewage treatment plant with CWSBR in Dalian was generally lower than that of Greece (5.14 μg·L^-1), Spain (9.2 μg·L^-1), Canada (44 μg·L^-1) and some of the Nordic countries (17 μg·L^-1). In the aspect of the methyl siloxane of sewage sludge from wastewater treatment plant, China (0.1-l μg·g^-1 dw) was also much lower than some of the Nordic countries (26 μg·g^-1 dw), Greece (20 μg·g^-1 dw) and Canada (64 μg·g^-1 dw). The PEL (pseudo-exposure level) median (173 ng·d^-1) of D4-D6 by inhaling and feeding for ordinary residents was much lower than the average median (18.5 μg·d^-1) by skin exposure in China, and much lower than the exposure level (1.875 mg·d^-1) for adult in the UK and for women (307 mg·d^-1) exposed to the total siloxane in the United States. Generally, the behavior and the effect of cVMS discharged into environment depend on the physical and chemical properties and the specific environmental condition. The cVMS into the air will react with·NO₃, O₃,·OH, and demethylating reaction with·OH to form silanol is its main end mechanism. Most of the cVMS was fixed by the sewage sludge during the sewage treatment process, and their adsorption capacity for D6 was the strongest, followed by D4 and D5. Volatilization, adsorption and biodegradation were the major environmental behaviors for cVMS in the soil. The biological amplification effect for D4 and D5 was possible. The TMF (trophic magnification factor) results of cVMS were inconsistent with each other, and were even contrary to those by BCF (bioconcentration factor), BMF (biomagnification factor) and BSAF (biota-sediment accumulation factor). Conclusively, most of the research of cVMS was on its occurrence, migration, transformation, and behavior in the process of wastewater treatment at home and abroad; furthermore, the research priority was given to the influent, effluent and remaining sludge, while the specific change in the whole process, the characteristics of its biological accumulation, degradation mechanism and degradation products were scarcely studied. Therefore, it needs effort to complement the cVMS distribution in other kinds of environmental media in the future, particularly in living and working environment. Besides, exploring degradation process in real environment, including the environmental behavior of degradation products and intermediate products, and further evaluating eco-environment effect and human health risks are the guidelines of cVMS research in the future.