Microplastic pollution is an emerging environmental problem, and little research has focused on its impact on the human body. Based on retrospective case series, the study required participants to fill out a questionnaire and provide sputum samples in order to investigate the presence of microplastics in human sputum and determine whether humans involuntarily inhale them. A total of 22 patients suffering from different respiratory diseases were recruited. We used an Agilent 8700 laser infrared imaging spectrometer and Fourier-transform infrared microscope to analyze sputum samples and evaluate microplastics in the respiratory tract. Remarkably, the size range of the method for detecting microplastics in our study is 20–500 μm. The results showed that 21 types of microplastics were identified, and polyurethane was dominant, followed by polyester, chlorinated polyethylene, and alkyd varnish, accounting for 78.36% of the total microplastics. Most of the aspirated microplastics detected are smaller than 500 μm in size (median: 75.43 μm; interquartile range: 44.67–210.64 μm). Microplastics are ubiquitous in all sputum, indicating that inhalation is a potential way for plastics to enter the human body. Additionally, the quantities of microplastic types in the respiratory tract are related to smoking, invasive examination, etc. (P < 0.05). This study sheds new light on microplastic exposure, which provides basic data for the risk assessment of microplastics to human health.

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Eutrophication is one of the greatest threats to global freshwater ecosystems. The phytoplankton responses to nutrient inputs vary in different water bodies, so it is particularly important to determine the nutrient thresholds and synergistic interactions between nutrients in different freshwater ecosystems. Field sampling and bioassay experiments were conducted to determine the thresholds of soluble reactive phosphorus (SRP), nitrate-nitrogen (NO 3 -N), and ammonium-nitrogen (NH 4 -N) in Miyun Reservoir. A separate nutrient addition bioassay was designed to assess the synergistic interactions between these nutrients. Chlorophyll a (Chl a) concentrations were used to estimate phytoplankton biomass. The results showed the following: (1) nutrient threshold bioassay indicated that eutrophication thresholds of SRP, NO 3 -N, and NH 4 -N should be targeted at below 0.04 mg P L −1 , 0.5 mg N L −1 , and 0.3 mg N L −1 , respectively, to limit the growth of phytoplankton. (2) The stimulatory effect of BNH 4 -N plus P^on phytoplankton biomass was greater than (4) Ammonium was an important factor for the growth of phytoplankton and inputs of both NH 4 -N and NO 3 -N should be reduced to control bloom formation. Our findings imply that although P load reduction is important, appropriate reductions of all forms of N in watershed is recommended in the nutrient management strategy for Miyun Reservoir.