Could soil microplastic pollution exacerbate climate change? A meta-analysis of greenhouse gas emissions and global warming potential

Shahid Iqbal; Jianchu Xu; Muhammad Saleem Arif; Awais Shakoor; Fiona R Worthy; Heng Gui; Sehroon Khan; Dengpan Bu; Sadia Nader; Sailesh Ranjitkar

doi:10.1016/j.envres.2024.118945

Could soil microplastic pollution exacerbate climate change? A meta-analysis of greenhouse gas emissions and global warming potential

Environ Res. 2024 Apr 16;252(Pt 2):118945. doi: 10.1016/j.envres.2024.118945. Online ahead of print.

Authors

Shahid Iqbal¹, Jianchu Xu², Muhammad Saleem Arif³, Awais Shakoor⁴, Fiona R Worthy⁵, Heng Gui⁶, Sehroon Khan⁷, Dengpan Bu⁸, Sadia Nader⁷, Sailesh Ranjitkar⁹

Affiliations

¹ Department of Economic Plants and Biotechnology, Yunnan Key Laboratory for Wild Plant Resources, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China; Honghe Centre for Mountain Futures, Kunming Institute of Botany, Chinese Academy of Science, Honghe, 654400, Yunnan, China. Electronic address: shahiduaf85@gmail.com.
² Department of Economic Plants and Biotechnology, Yunnan Key Laboratory for Wild Plant Resources, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China; Honghe Centre for Mountain Futures, Kunming Institute of Botany, Chinese Academy of Science, Honghe, 654400, Yunnan, China; East and Central Asia Regional Office, World Agroforestry Centre (ICRAF), Kunming, Yunnan, China.
³ Department of Environmental Sciences, Government College University Faisalabad, Allama Iqbal Road, Faisalabad, 38000, Pakistan.
⁴ Soils West, Centre for Sustainable Farming Systems, Food Futures Institute, Murdoch University, Murdoch, WA, 6105, Australia; Teagasc, Environment, Soils and Land Use Department, Johnstown Castle, Co, Wexford, Y35 Y521, Ireland; Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, 2751, Australia.
⁵ CAS Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan, 650201, China.
⁶ Department of Economic Plants and Biotechnology, Yunnan Key Laboratory for Wild Plant Resources, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China; Honghe Centre for Mountain Futures, Kunming Institute of Botany, Chinese Academy of Science, Honghe, 654400, Yunnan, China.
⁷ Department of Biotechnology, Faculty of Natural Sciences, University of Science and Technology Bannu, Bannu Township, 28100, Bannu, Khyber Pakhtunhuwa, Pakistan.
⁸ State Key Laboratory of Animal Nutrition, Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China; Joint Laboratory on Integrated Crop-Tree-Livestock Systems, Chinese Academy of Agricultural Sciences (CAAS), Ethiopian Institute of Agricultural Research (EIAR), And World Agroforestry Center (ICRAF), Beijing, 100193, China.
⁹ N. Gene Solution of Natural Innovation, Kathmandu, Nepal; School of Development Studies, Lumbini Buddhist University, Devdaha, Nepal; MICD, Faculty of Humanities and Social Science, Mid-West University, Lalitpur, Nepal.

PMID: 38631466
DOI: 10.1016/j.envres.2024.118945

Abstract

Microplastics pollution and climate change are primarily investigated in isolation, despite their joint threat to the environment. Greenhouse gases (GHGs) are emitted during: the production of plastic and rubber, the use and degradation of plastic, and after contamination of environment. This is the first meta-analysis to assess underlying causal relationships and the influence of likely mediators. We included 60 peer-reviewed empirical studies; estimating GHGs emissions effect size and global warming potential (GWP), according to key microplastics properties and soil conditions. We investigated interrelationships with microbe functional gene expression. Overall, microplastics contamination was associated with increased GHGs emissions, with the strongest effect (60%) on CH₄ emissions. Polylactic-acid caused 32% higher CO₂ emissions, but only 1% of total GWP. Phenol-formaldehyde had the greatest (175%) GWP via 182% increased N₂O emissions. Only polystyrene resulted in reduced GWP by 50%, due to N₂O mitigation. Polyethylene caused the maximum (60%) CH₄ emissions. Shapes of microplastics differed in GWP: fiber had the greatest GWP (66%) whereas beads reduced GWP by 53%. Films substantially increased emissions of all GHGs: 14% CO₂, 10% N₂O and 60% CH₄. Larger-sized microplastics had higher GWP (125%) due to their 9% CO₂ and 63% N₂O emissions. GWP rose sharply if soil microplastics content exceeded 0.5%. Higher CO₂ emissions, ranging from 4% to 20%, arose from soil which was either fine, saturated or had high-carbon content. Higher N₂O emissions, ranging from 10% to 95%, arose from soils that had either medium texture, saturated water content or low-carbon content. Both CO₂ and N₂O emissions were 43%-56% higher from soils with neutral pH. We conclude that microplastics contamination can cause raised GHGs emissions, posing a risk of exacerbating climate-change. We show clear links between GHGs emissions, microplastics properties, soil characteristics and soil microbe functional gene expression. Further research is needed regarding underlying mechanisms and processes.

Keywords: Carbon dioxide; Climate warming; Methane; Nitrous oxide; Plastic residues; Soil pollution.