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Microplastics promote methane emission in estuarine and coastal wetlands
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This study found that microplastics in coastal and estuarine wetlands increase methane emissions by boosting the activity of methane-producing microorganisms while reducing methane-consuming ones. Both conventional and biodegradable plastics had this effect, meaning microplastic pollution is not just a direct health concern but also contributes to climate change by amplifying greenhouse gas release from natural ecosystems.
Increasing microplastic (MP) pollution poses significant threats to estuarine and coastal ecosystems. However, the effects of MPs on the emission of methane (CH), a potent greenhouse gas, within these ecosystems and the underlying regulatory mechanisms have not been elucidated. Here, a combination of C stable isotope-based method and molecular techniques was applied to investigate how conventional petroleum-based MPs [polyethylene (PE) and polyvinyl chloride (PVC)] and biodegradable MPs [polylactic acid (PLA) and polyadipate/butylene terephthalate (PBAT)] regulate CH production and consumption and thus affect CH emission dynamics in estuarine and coastal wetlands. Results indicated that both conventional and biodegradable MPs enhanced the emission of CH (P < 0.05), with the promoting effect being more significant for biodegradable MPs. However, the mechanisms by which conventional and biodegradable MPs promote CH emissions were different. Specifically, conventional MPs stimulated the emission of CH by inhibiting the processes of CH consumption, but had no significant effect on CH production rate. Nevertheless, biodegradable MPs promoted CH emissions via accelerating the activities the methanogens while inhibiting the oxidation of CH, thus resulting in a higher degree of promoting effect on CH emissions than conventional MPs. Consistently, quantitative PCR further revealed a significant increase in the abundance of methyl-coenzyme M reductase gene (mcrA) of methanogens under the exposure of biodegradable MPs (P < 0.05), but not conventional MPs. Furthermore, the relative abundance of most genes involved in CH oxidation exhibited varying degrees of reduction after exposure to all types of MPs, based on metagenomics data. This study reveals the effects of MPs on CH emissions in estuarine and coastal ecosystems and their underlying mechanisms, highlighting that the emerging biodegradable MPs exhibited a greater impact than conventional MPs on promoting CH emissions in these globally important ecosystems, thereby accelerating global climate change.
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