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Widespread Microplastic Pollution Observed in Soils

Extensive amount of microplastics have been detected in soils of both artificial and natural ecosystems in tropical areas, highlighting the emerging global plastic problem.

From 1950 to 2015, the global manufacture of plastics has increased from 2 million tons to 380 million tons. As of 2017, humans have already produced 8.3 billion tons of plastics, of which 79 per cent have been discarded into the environment or landfills. Most plastic wastes persist in the environment for a long time and microplastics (plastic particles < 5 mm in size) have been detected in many terrestrial ecosystems like farmlands, lakes, and even the summit of Mount Everest.

Environmental risks caused by microplastics are increasing. Microplastics particles can become smaller, where they may bioaccumulate in the food web, affecting the safety of the ecosystem. Due to their wide distribution, environmental persistence, and extensive interaction with animals, microplastic pollution has become an emerging concern. Yet, the distribution characteristics of microplastics across different land uses remain largely unexplored, threatening the development of more ambitious and realistic research on toxicology, ecology, and management.

Published in Chemosphere, scientists from the Xishuangbanna Tropical Botanical Garden of the Chinese Academy of Sciences reported the extensive presence of soil microplastics in tropical areas, from artificial ecosystems to natural ecosystems, in both the top and deep soil layers.

Based on the intensity (from weak to strong) of human activities, the team chose two natural ecosystems (primary and secondary forests) and two artificial ecosystems (rubber and banana plantations) in the Xishuangbanna tropical region as their study areas.

To assess the overall characteristics and possible sources of soil microplastics in Xishuangbanna tropical region, the team measured the abundance, size, type, shape, and colour of the microplastics in both the upper and lower layers of soil.

The results obtained revealed that the dominant size of soil particles was < 1mm and the major shapes were fragments and fibres that were mostly blue, yellow, or green-blue in colour. The microplastics were also mostly polyethylene, rayon, and polypropylene. Microplastics that were found in the top soil were observed to be smaller than that in deep soil layers. This observation was attributed to the top soil’s exposure to ultraviolet (UV) radiation and weathering that will fragment large plastics into microplastics.

With regards to its abundance, there were more microplastics in the top soil layer than the deep soil layers in artificial ecosystems while there were more microplastics in the deep soil layer than top soil in natural ecosystems. The team pointed out that this observation could be due to the continuous input of plastics by farmers in these artificial ecosystems, while fewer plastics are introduced by human activities in natural ecosystems in the Xishuangbanna National Nature Reserve.

This study highlights the emerging plastic problem across all major land uses in tropical areas, especially in artificial ecosystems, which was observed to have a significantly higher amount of microplastics than natural ecosystems. In providing important background data for further research on the various ecosystem risks of microplastics, we are better poised to develop effective measures and policies to control microplastic pollution in tropical areas. [APBN]

Source: Xu et al. Soil microplastic pollution under different land uses in tropics, southwestern China. Chemosphere, 289, 133176.