Picarro | Effects of microplastics on greenhouse gas emissions and microbial communities

Microplastics (particles< 5 mm) have been found in the atmosphere, terrestrial, ocean and lake environments. Different microplastics have different densities, from 20 to 1400 kg/m³. A considerable part of manufactured plastics is heavier than water when they enter water environment, and they can enter sediments system. Some studies have showed that the presence of microfibers in sediment could change the composition of marine sediment microbial communities and significantly affect the nitrogen cycling, and affect the biogeochemical process of marine sediment in the coastal zone. Under the background of global climate warming, the material exchange of the lake ecosystem at the sediment-water-atmosphere interface is more frequent. Furthermore, freshwater lakes, reservoirs and their sediments are important sources of greenhouse gas emissions. Therefore, attention should be paid to that whether microplastics will affect its ecological environment, greenhouse gas emissions and microbial community when microplastics enter freshwater sediment. Recently, the research focus on microplastics gradually shifted from marine water environment to freshwater and sedimentary environment. However, few studies are focused on the influence and ecological effect of microplastics in freshwater sediment.

Based on this, in this article, a group of Chinese scientists from Nankai University selected microplastics ranging from 5 μm to 2 mm for the experiment, which is considered to be environmentally relevant. Through long-term exposure of PET with six different particle sizes to freshwater sediment, and detection its effect on greenhouse gas emissions (CO₂, CH₄ and N₂O, by Picarro G2508 N₂O, CH₄, CO₂, NH₃, H₂O analyzer), nutrients cycle and microbial communities. The following hypothesis are set: (1) PET with different particle sizes can promote greenhouse gas emissions of the freshwater sediment system to varying degrees; (2) PET can affect the biochemical environment of the microcosm and the microbial community in freshwater sediment; (3) microplastics with different particle sizes play a role in different culture periods. nutrient concentration.

[Results]:

Greenhouse gas emission rate.

 Principal component analysis biplot of biochemical variables. (a) variables measured after culturing 3 days, (b) variables measured after culturing 90 days

[Conclusion]:

The authors concluded that CO₂ emissions were promoted by PET with particle size of 5 μm, from 7 to 30 days after microplastics directly entering into freshwater sediment. After 3 days of exposure, microplastics range from 50 μm to 800 μm have particle size effect on CO₂ emissions. In the 5 μm experimental group, N₂O emissions were significantly promoted in the 7 days after cultivation. Under the action of microorganism, microplastics gradually decompose, and microplastics also affect the richness of microorganisms and the structure of microbial community. During microplastics exposure, the released organic matters affect the ecosystem’s carbon and nitrogen cycle. More attention should be paid to the potential impact of resuspension of microplastics containing sediments on the circulation of carbon and nitrogen elements in the global ecosystem. Which organic matter will be affected by microplastics exposure and which organic matter will play a decisive role in the change of microbial community structure need further study.