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Published on: July 27, 2022
Bioavailable concentration of aged polystyrene microplastics governs the phytotoxicity and metabolic reprogramming in
Xueer Ma1, Yuze Xu2, Xuejiao Zhang3
1School of Resources, Environment and Materials, Guangxi University, Nanning, 530004, China; National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou, 510650, China.
Abstract:
Microplastic (MP) contamination in soils poses a growing risk, yet the effects of environmentally aged MPs on crops remain unclear. Here, we investigated polystyrene (PS) MPs (average size 4.65 ± 3.01 μm) prepared via sequential dry-wet milling and thermal annealing (95 °C) to mimic natural aging. Characterization confirmed aged-like properties, including high surface roughness, crystallinity (0.397), and carbonyl index (0.63). In pot experiments, PS MPs accumulated exclusively in soybean roots (444-688 μg/g; PS1.0 > PS1.5 > PS0.5) but not in leaves. Phytotoxic effects correlated with the internalized (bioavailable) concentration of MPs: PS0.5 showed negligible impact, whereas PS1.0 severely reduced biomass and triggered the strongest oxidative stress (ROS +204 %, MDA +118 %). Sucrose content declined sharply under PS1.0 (-77.9 %) and PS1.5 (-55.1 %), linking oxidative stress to impaired carbon allocation. Metabolomic profiling revealed broad reprogramming of carbohydrate and defense pathways, with sucrose and galactose metabolism disrupted at PS1.0, and lipid-related defenses enriched at PS1.5. These findings establish a standardized protocol for producing environmentally relevant aged MPs and demonstrate that their phytotoxicity is governed by oxidative stress-driven carbon reallocation in a bioavailable concentration-dependent manner.
Insights
Environmentally aged microplastics (MPs) accumulate in soybean roots, causing oxidative stress and impaired carbon allocation. Their phytotoxicity depends on bioavailable concentration, impacting crop health.
Area of Science:
- Environmental Science
- Plant Science
- Materials Science
Background:
- Microplastic (MP) contamination in soils presents a significant environmental risk.
- The impact of aged MPs on crop physiology is not well understood.
Purpose of the Study:
- To investigate the effects of environmentally aged polystyrene (PS) MPs on soybean plants.
- To establish a method for producing aged MPs that mimic natural environmental conditions.
Main Methods:
- Polystyrene MPs were aged using dry-wet milling and thermal annealing.
- Aged MPs were characterized for surface roughness, crystallinity, and carbonyl index.
- Soybean plants were exposed to aged MPs in pot experiments, with analysis of MP accumulation, phytotoxicity, oxidative stress markers, and metabolic profiles.
Main Results:
- Aged PS MPs accumulated in soybean roots but not leaves.
- Phytotoxicity and oxidative stress (ROS, MDA) increased with MP concentration.
- Sucrose and galactose metabolism were disrupted, indicating impaired carbon allocation.
Conclusions:
- A standardized method for producing environmentally relevant aged MPs was developed.
- The phytotoxicity of aged MPs is concentration-dependent and linked to oxidative stress and carbon reallocation.
- Understanding aged MP effects is crucial for assessing soil contamination risks to agriculture.
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