Accelerometer-measured sedentary volume and bouts during the segmented school day among Chinese school students.

Background: This study examined sedentary volume and bouts of Chinese primary and middle school students during different segments of a school day and determined whether gender and school level are associated with their sedentary volume and bouts. Methods: A total of 472 students participated in this study. Accelerometers were used to measure the sedentary volume and sedentary bouts of different durations (i.e., 1-4 min, 5-9 min and ≥10 min) during all segments. Results: The participants spent the majority of their time in sitting (61.7%) and sitting bouts of ≥10 min (37.3%). They spent higher percentages of time in sitting during regular classes (76.7%) and out-of-school time (54.5%), and lower during physical education (PE) classes (32.2%), lunch break (35.4%) and recess (38.0%). The highest proportions of time were in sedentary bouts of ≥10 min during regular classes (50.2%), out-of-school time (28.0%) and lunch break (18.8%), while the greatest percentages occurred in sitting bouts of 1-4 min during PE class (16.4%) and recess (18.6%). Girls and middle school students had higher percentages of sedentary volume than boys and primary school students during most segments. They spent greater proportions of time in sitting bouts of ≥10 min during regular classes, lunch break, and out-of-school time, and higher proportions in sedentary bouts of 1-4 min than boys and primary students during PE classes. Conclusion: Regular class and out-of-school time were identified as key segments for reducing sedentary volume and breaking up prolonged sitting. Interventions on interrupting prolonged sitting during lunch break should also be explored. Girls and middle school students should receive more attention in future interventions.

[Spatial Variation and Potential Sources of Microplastics in Rivers in Tongzhou District, Beijing].

Microplastics are emerging contaminants, which can also absorb other contaminants, threatening the health of river ecosystems. However, research on the pollution of microplastics in rivers in northern China is still lacking. In this study, based on the sampling and analysis of water samples in 19 sites in six rivers in Tongzhou district, Beijing, the composition, spatial variation, and potential sources of microplastics were explored. The results showed that all sites were contaminated by microplastics, and the abundance of microplastics in the Xiaozhong River was the highest among all sites (3.50×104 n·m-3), which was 4.04 times that in the Yunchaojian River. The proportion of microplastics with particle sizes smaller than 2000 µm was 90.49%, and microplastics with particle sizes larger than 4000 µm were only found in two out of 19 sampling sites. The microplastics were fiber, film, fragment, and granule shaped. The proportion of fiber microplastics was the highest (90.23%) among all shapes. Most (84.29%) of the microplastics were transparent and blue. Rayon was the most common microplastic in each site, and its proportion in each site was over 66.67%. The proportions of other types of microplastics differed largely among different sites. Spatially, the abundance and types of microplastics in the upper reaches were higher than those in the lower reaches. According to spatial variations in shapes, types, colors, and abundance of microplastics, the potential sources of microplastics were identified. The potential sources of fiber microplastics were washing clothing and using fishing gear and dust-proof nets.

[Composition and Distribution of Microplastics in the Water and Sediments of Urban Rivers in Beijing].

It has been confirmed that microplastics widely exist in the natural environment, causing potential harm to organisms and humans. An investigation into the occurrence of microplastics is helpful to understand the level of pollution of microplastics in urban rivers and sediments. In this study, eight sampling points of water samples and three of sediments samples were placed along the North Canal and Huaihe River in Beijing, to compare the composition and distribution characteristics of the abundance, particle size, color, shape, and species of microplastics. The results showed that the abundance of microplastics in the water and sediments of the North Canal were(1941±201)-(8155±1781) n·m-3(n refers to the number of microplastics) and (120±11)-(268±31) n·kg-1, respectively. The average abundance of microplastics in the water of the North Canal was 4160 n·m-3. Compared with the North Canal, the pollution degree of microplastics in the Huaihe River was lower with an average abundance of 2357 n·m-3. Furthermore, the abundance of microplastics in the water and sediments in the upper reaches of the North Canal was higher than that in the lower reaches. No significant difference of microplastics distribution was observed in the water of the Huaihe River on the whole; however, there was a marked difference in abundance between the two distant locations. The main particle size range of microplastics at all site points was<300 µm, and mostly white/transparent(50.75%-83.91%); the main shape were fragments(50.00%-95.08%) and fibers(3.86%-30.00%). Polyurethane(PU) and ethylene vinyl acetate(EVA) were two main plastic species found at all sites. Microplastics in the water and sediments of the North Canal might have originated from urban construction and development, while the surrounding villages might have only affected the abundance of microplastics in the Huaihe River.