Microplastic pollution in neotropical rainforest, savanna, pine plantations, and pasture soils in lowland areas of Oaxaca, Mexico: Preliminary results

Microplastic (<5 mm plastic pieces) pollution is a worldwide serious problem, particularly in terrestrial ecosystems. The presence and abundance of such contaminants in tropical areas are unknown, despite their potentially harmful effects on human health and biodiversity. Tropical lowland areas often are densely populated by humans. However, the level of microplastic contamination in human-modified tropical ecosystems remains unknown. In the tropical lowland coastal plain of the Gulf of Mexico, we compared the concentration and particle size distribution of soil microplastics in five contiguous ecosystems: a neotmpical rainforest, a native savanna, two pine plantations, one with the understory removed and the other with the understory left intact, and a human-induced grassland used for cattle grazing. Micmplastic extraction was performed using the density separation and filtration method. Microplastics (only fibers and fragments) were present in the soils of all the studied ecosystems. We do not detect the presence of films and pellets. We found between 1.53 and 1.49 (g(-1)dry soil) particles of fibers and fragments. Microplastics from 150 to 500 tan were the most common, whereas those from 40 to 60 mu m were the rarest. The concentration of fibers and fragments was significantly different among the studied ecosystems, being higher in the pasture than in the tropical rainforest, the pine plantations, and the savanna, which displayed similar concentrations. Micmplastics (fibers and fragments) appear to increase as the levels of clay and sand increased. The observed high abundance of micmplastic in tropical lowland areas warrants further studies on their abundance and ecosystem impact.

Automated summary

The study found that microplastics, mainly fibers and fragments, were present in the soils of various ecosystems in tropical lowland areas, with films and pellets not detected. Fibers and fragments ranged mainly from 150 to 500 micrometers, with sizes from 40 to 60 micrometers being the rarest. The concentration of fibers and fragments varied significantly among different ecosystems, and appeared to increase with higher levels of clay and sand.