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Artificial humic acid reshapes microbial C-N metabolism and nitrogen partition in microplastic-contaminated soils
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Microplastics from common plastics like polypropylene are building up in farm soils and disrupting the nitrogen cycle that crops depend on. This study found that adding a compost-derived soil additive called artificial humic acid helped rebalance soil nitrogen and boosted helpful soil bacteria, even when microplastics were present. While this research focused on soil health rather than direct human health effects, healthier soil nitrogen cycling matters because it supports safer, more sustainable food production as plastic pollution keeps rising in farmland.
Microplastics pose a serious threat to soil ecosystems, particularly nitrogen cycling. Among the diverse types of microplastics, polypropylene (PP) and polylactic acid (PLA) are frequently detected in agricultural soils. Artificial humic acid (A-HA), a humic-like substance derived from lignocellulosic waste, may regulate soil carbon and nitrogen dynamics, but its effects on nitrogen partitioning and microbial C-N metabolic potential under different microplastic stresses remain unclear. Here, a 90-day microcosm experiment integrating soil physicochemical analyses, dissolved organic matter characterization, bacterial community profiling, and metagenomics was conducted in PLA- and PP-contaminated soils. At day 15, 600 mg kg A-HA decreased nitrate (NO⁻-N) by 11.36% and 6.46% in PLA- and PP-contaminated soils, respectively, while increasing soluble organic nitrogen (SON) by 17.32% and 23.89%. A-HA also enriched Nitrospira and Steroidobacter and altered the abundance of genes associated with nitrogen transformation, assimilation, and carbon metabolism, including nrfA, GLU, gltB, and icd. Increased abundance of nrfA suggested greater dissimilatory nitrate reduction to ammonium (DNRA) potential, while enrichment of NADP-dependent icd indicated altered potential for 2-Oxoglutarate generation in the TCA cycle. Overall, A-HA modified nitrogen partitioning toward soluble and microbial organic pools and was associated with coordinated changes in microbial C-N metabolic potential under microplastic exposure.
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Tiny plastic particles from everyday waste are building up in farm soils, potentially messing with the nitrogen cycle that helps crops grow. This study found that adding biochar (a charcoal-like soil additive made from burned plant material) helped boost nitrogen levels in plastic-contaminated soil, though it also shifted the balance of soil bacteria in ways scientists don't fully understand yet. While this doesn't directly test food safety or human health, it's an early step toward finding ways to protect soil health, and the food grown in it, from the growing problem of plastic pollution.
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This study tested how polyethylene microplastics, their base resin, and plastic additives each affect nitrogen cycling in soil -- a process essential for plant growth. All three altered the soil's nitrogen balance and microbial communities in different ways, with microplastics increasing certain nitrogen transformation rates the most. These findings matter because disrupted nitrogen cycling in farmland could affect crop nutrition and ultimately the quality of food humans eat.
The addition of humic acid into soil contaminated with microplastics enhanced the growth of black gram (Vigna mungo L. Hepper) and modified the rhizosphere microbial community
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A pot experiment found that microplastic-contaminated soil reduced germination, chlorophyll production, and beneficial root bacteria in black gram (a legume), but that adding humic acid to the contaminated soil largely reversed these negative effects. The finding suggests that humic acid soil amendments could serve as a practical and affordable tool to protect crop productivity in agricultural soils that are already contaminated with microplastics.
Polyethylene and polyvinyl chloride microplastics promote soil nitrification and alter the composition of key nitrogen functional bacterial groups
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Researchers found that polyethylene and PVC microplastics in soil increased nitrification (a key step in the nitrogen cycle) and changed the composition of nitrogen-processing bacteria. These changes could affect soil fertility and the availability of nutrients for crops. The study highlights how microplastic contamination in agricultural soil may have hidden effects on food production by altering fundamental soil processes.
Role of polyamide microplastic in altering microbial consortium and carbon and nitrogen cycles in a simulated agricultural soil microcosm
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Researchers added polyamide microplastics to simulated agricultural soil and tracked their effects on microbial communities and nutrient cycling over time. They found that microplastics altered the composition of soil bacteria and disrupted both carbon and nitrogen cycling processes. The study highlights how microplastic contamination in farmland can affect the invisible but essential microbial processes that maintain soil health and fertility.
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