A new study has found that microplastic pollution can lead to significant reduction of communities of soil-dwelling insects, which can have potential consequences on soil carbon and nutrient cycling, thereby affecting soil fertility.
Published in Proceedings of the Royal Society on Wednesday, this is the first ever field study that explores how the presence of microplastics in soil can affect soil fauna like microarthropods and nematodes, and microbial communities like bacteria and fungi. The study cites reports stating that humanity has generated 6,300 million metric tonnes of plastic waste between 1950 and 2015 — 79% of which has accumulated in landfills, dumps or the natural environment. However, over the years, several studies on the ecological impacts of microplastics have focused on the aquatic ecosystems, leading to a limited understanding of its effect on terrestrial ecosystems, which prompted the researchers to take it up.
To conduct the study, the researchers divided a plot of land, in the sub-tropical region of Chongqing in China, into six blocks of four test areas each, and contaminated them with four different densities of microplastics, ranging across: zero, five, 10 and 15 grams per square metre. Then, after 287 days, they collected samples from the test areas, and examined the species in the soil. At the highest level of contamination, of 15 grams per square metre, the researchers noted a significant reduction of 62% in ants, 41% in arthropods like the larvae of flies, moths and butterflies, 20% in roundworms, and 15% in moss, or beetle, mites. However, no significant effect of microplastic pollution was noted in the microbial communities of bacteria and fungi.
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According to the UNEP, terrestrial microplastic pollution is estimated to be between four to 23 times higher than marine microplastic pollution, depending on the environment. Studies also warn these microplastics could transfer from terrestrial agriculture, to the human food chain, thus posing a future threat to food safety and sustainable agriculture. We have begun to acknowledge its accumulation in our food, with studies suggesting that we’re eating one credit card of plastic, or 5 grams — each day. Even so, their impact on soil ecosystems, which are integral to food security, continue to remain relatively less-studied, and the present research provides interesting insights into how microplastics affect the food webs within the soil.
Noting that “the effects of microplastics strongly cascade through the soil food webs, leading to the modification of microbial functioning with further potential consequences on soil carbon and nutrient cycling,” the study called for “a reduction in the use of plastics and to avoid burying plastic wastes in soils, as this may bring adverse ecological consequences on soil communities and biogeochemical cycling in terrestrial ecosystems.”
