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Impact of aging of primary and secondary polystyrene nanoplastics on the transmission of antibiotic resistance genes in anaerobic digestion
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Researchers studied how aged and non-aged nanoplastics from both manufactured and environmentally degraded polystyrene affect the spread of antibiotic resistance genes during sewage sludge treatment. They found that higher concentrations of nanoplastics inhibited the treatment process and increased the abundance of antibiotic resistance genes, with environmentally degraded particles having a stronger effect due to their altered surface properties. The study raises concerns that nanoplastic pollution in sewage systems may be contributing to the spread of antibiotic resistance.
Sewage sludge is a significant reservoir of nano/microplastics (NPs/MPs) and antibiotic resistance genes (ARGs). Research has revealed that NPs/MPs may exert an inhibitory effect on anaerobic digestion (AD) of sludge. Moreover, NPs/MPs can influence microbial community diversity and composition, potentially increasing ARGs dissemination. The morphological changes to NPs/MPs surface due to aging contribute to modifying hydrophobic properties. To date, there is limited comprehension regarding how various surface properties of NPs influence ARGs dissemination during AD. This study investigated the impact of primary aged/non-aged and secondary aged/non-aged polystyrene nanoplastics (PSNPs) on ARGs and mobile genetic elements (MGEs) propagation during AD. The findings indicated that the UV-aging process resulted in surface oxidation and distinct morphological characteristics in both primary and secondary PSNPs, while the surface oxidation effect was more pronounced in the secondary aged PSNPs. High concentrations (150 μg/L) of primary and secondary PSNPs inhibited methane production, with secondary PSNPs causing greater inhibition by 16 to 20 % compared to control. In contrast, low concentration (25 μg/L) had negligible or slightly positive effects on methane production. PSNPs at 150 μg/L reduced total VFA concentration, indicating an inhibitory effect on the fermentation step in the AD process. Primary and secondary PSNPs exhibited changes in EPS characteristics. ARGs abundance was enriched in reactors amended with PSNPs, with the highest abundance of 8.54 × 10 copies/g sludge observed in the secondary aged PSNPs (150 μg/L) reactor. Reactors exposed to aged PSNPs exhibited a relatively higher abundance of ARGs compared to reactors exposed to non-aged PSNPs. Exposure to PSNPs increased the microbial community diversity within the digesters and triggered the enrichment of Comamonadaceae and Syntrophaceae, belonging to Proteobacteria phylum. On the other hand, archaeal communities tended to shift towards hydrogenotrophic methanogens in PSNPs reactors. The correlation analysis showed that Comamonadaceae were positively correlated with the majority of ARGs and intl1. A positive correlation was observed between MGEs and most ARGs, suggesting that the increased proliferation of ARGs under PSNPs exposure may be linked to the abundance of MGEs, which in turn promotes the growth of hosts carrying ARGs. These findings suggest that aged and non-aged NPs could substantially impact the spread of ARGs and MGEs, which also led to notable alterations in the composition of the microbial community. Overall, this study provides valuable insights into the multifaceted impacts of PSNPs with various characteristics on AD processes, microbial communities, and ARGs proliferation, highlighting the urgent need for comprehensive assessments of NPs pollutants in the environment.
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This study found that aged (weathered) microplastics and nanoplastics promoted the spread of antibiotic resistance genes during sewage sludge treatment more than fresh plastics did. The weathering process changed the surface properties of the plastics, making them better carriers for drug-resistant bacteria and their genes. This is concerning because sludge from treatment plants is often applied to farmland, potentially spreading antibiotic resistance through soil and into the food supply.
Impact of polystyrene nanoplastics on primary sludge fermentation under acidic and alkaline conditions: Significance of antibiotic resistance genes
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Researchers studied how polystyrene nanoplastics affect the fermentation of sewage sludge at different pH levels. They found that low doses stimulated hydrogen gas production while higher concentrations suppressed it, and that nanoplastic exposure promoted the spread of antibiotic resistance genes in the microbial community. The findings raise concerns about nanoplastics in wastewater systems potentially contributing to the broader problem of antibiotic resistance.
Metagenomic insight into the enrichment of antibiotic resistance genes in activated sludge upon exposure to nanoplastics
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Researchers used metagenomic analysis to show that polystyrene nanoplastics at environmentally relevant concentrations increased antibiotic resistance genes in activated sludge by up to 59%, primarily by promoting horizontal gene transfer and enriching Proteobacteria host populations — raising concerns about nanoplastic-driven spread of antibiotic resistance in wastewater treatment.
Photoaged nanoplastics with multienzyme-like activities significantly shape the horizontal transfer of antibiotic resistance genes
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Researchers found that UV-aged polystyrene nanoplastics develop enzyme-like activity that generates reactive oxygen species, enabling them to suppress horizontal gene transfer of antibiotic resistance genes at higher concentrations by degrading plasmid DNA and damaging bacterial membranes — a paradoxical finding where pollution aging may inhibit antibiotic resistance spread under some conditions.
Aging attenuates threat: how moderate aging of microplastics suppresses antibiotic resistance gene proliferation during sludge anaerobic digestion
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Researchers examined how the degree of weathering of polyethylene and polypropylene microplastics affects their tendency to promote antibiotic resistance gene spread during sewage sludge digestion, and found a counterintuitive U-shaped relationship: moderately aged plastics actually suppressed resistance gene proliferation by up to 50% compared to fresh plastics, while more heavily aged plastics saw the effect bounce back. The mechanism involves weathering altering how microplastics affect microbial stress responses and gene transfer pathways. The findings highlight that the environmental history of microplastics matters when assessing their biological risks.
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