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Long term crumb rubber leachate reduces symbiotic nitrogen fixation and nitrogen metabolism in Medicago sativa L.
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Chemicals leaching from tire crumb rubber, like those used in playgrounds and turf, can seep into soil and harm plants, this study found that alfalfa exposed to tire leachate grew weaker roots and struggled to convert nitrogen into nutrients. Since alfalfa is a key livestock feed crop, this raises concerns about how tire pollution might affect soil health, food crops, and ultimately the food supply.
Tire wear particles (TWPs) generated by vehicle tire abrasion mainly enter soil ecosystems via deposition and runoff pathways. However, the toxicity of TWPs to terrestrial plants, particularly legumes, remain largely unexplored. Long-term leachate was obtained by immersing crumb rubber (CR) with varying particle sizes (0.5–1 mm, 1–2 mm, and 2–4 mm) in water from 2004 to 2022. Alfalfa ( Medicago sativa L.), a typically leguminous forage, was used as a model plant, and the effects of long-term CR leachates on symbiotic nitrogen fixation in an alfalfa–rhizobium system and the underlying mechanisms were investigated through transcriptome analysis. The results demonstrate that long-term CR leachate significantly decreased root growth, inhibited photosynthesis, and induced oxidative stress. Especially, root biomass, root length, root vitality, and total chlorophyll content decreased by 24.5%, 28.7%, 37.0%, and 64.3%, respectively, under 0.5–1 mm CR leachate ( p < 0.05). Furthermore, qualitative live/dead staining revealed that cell death in root tips increased with decreasing CR size. Compared with the control plants, the alfalfa stressed with the CR leachates had fewer root nodules, and decreased nitrogen fixation parameters such as the leghemoglobin (Lb) content, nitrate reductase activity, and ammonia content. Transcriptomic analysis revealed that leachate stress triggered downregulation of key nitrogen assimilation genes (e.g., nitrate/nitrite transporter, nitrate/nitrite reductase, formamidase, and glutamine synthase). The integrated data suggest that CR leachate impairs nodulation, induces oxidative stress, and disrupts the transcriptional regulation of nitrogen assimilation, ultimately suppressing symbiotic nitrogen fixation. However, the specific chemical characterization of the leachate and qRT-PCR validation of nitrogen metabolism genes were not performed, which represents limitations of the study for mechanistic attribution.
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Co-exposure to tire wear particles and nickel inhibits mung bean yield by reducing nutrient uptake
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Researchers grew mung bean plants for a full lifecycle in soil contaminated with tire wear particles and nickel, finding that tire particles alone reduced crop yields by up to 52%. When combined with high levels of nickel, a heavy metal, yields dropped by as much as 88%. This study shows that tire-derived microplastics in agricultural soil can significantly reduce food production and, when mixed with other pollutants, the damage is far worse than either contaminant alone.
Crumb Rubber Microplastics Alter Soil Water Dynamics and Plant Biomass Allocation in Soybeans
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Recycled tire crumbs (used in artificial turf and sometimes mixed into soil) don't stunt soybean plants on the surface, but they change what's happening underground: plants grew more roots, held onto soil moisture differently, and absorbed noticeably more zinc into their leaves — enough to exceed normal healthy levels. Since soybeans and other crops can take up these metals from contaminated soil, this raises questions about whether recycled tire materials near farmland or gardens could quietly work their way into the food we eat, even when plants look perfectly normal above ground.
Impact of tire particles and tire leachate contaminants on plant physiology and soil health: Case study in mung bean and tomato
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Researchers compared how tire particles and tire leachate affect two crop species, finding that tomatoes mount a successful antioxidant defense and maintain growth while mung beans suffer severe oxidative damage and chlorophyll loss, and that the water-soluble leachate fraction poses the greatest acute risk — underscoring the need for species-specific risk assessment of tire-derived pollution near agricultural land.
A common contaminant shifts impacts of climate change on a plant-microbe mutualism: effects of temperature, CO 2 and leachate from tire wear particles
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Researchers investigated how leachate from tire wear particles interacts with climate change stressors to affect a plant-microbe symbiosis. The study found that tire-particle chemicals can modify how temperature and CO2 interact with plant-rhizobium mutualism, demonstrating complex interactions between pollution and climate stressors.
Tire abrasion particles negatively affect plant growth even at low concentrations and alter soil biogeochemical cycling
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Researchers found that tire abrasion particles—a major source of microplastic pollution on land—negatively affected plant growth and disrupted soil nutrient cycling even at low concentrations. This is concerning because tire particles are shed in enormous quantities on roads and accumulate in roadside soils where plants grow.
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