Around the world, some 1.5 billion tires are produced each year, and tire-wear particles are increasingly recognized as one of the largest sources of microplastic pollution.
As these particles accumulate in agricultural landscapes through the atmosphere, road runoff, wastewater irrigation, and biosolids, understanding their environmental and food-safety implications has become increasingly urgent.
Every trip in a vehicle leaves behind more than exhaust emissions. Additives such as accelerators, vulcanization agents, and antioxidants are added to the main rubber polymer during the manufacturing process and can make up to 15% of the tire’s weight. As they wear down against the road surface, they continuously release tire particles that accumulate in soils and waterways surrounding both roads and major highways.
Now, a new Israeli study has uncovered a previously overlooked pathway linking road-traffic pollution and cultivated crops. While plant uptake of tire-wear-derived contaminants was already known, their study is among the first to show under environmentally realistic conditions that tire-wear particles themselves act as short- and long-term sources of contamination, gradually released into soil.
By replicating real-world agricultural exposure pathways, the research provides an important missing link among road traffic emissions, soil contamination, and food production.
Rubber particles released when tires rub against asphalt don’t simply accumulate in the environment as microplastics; they also serve as reservoirs of toxic additives that may be released into the agricultural systems and potentially enter the food chain.
The findings, just published in the journal Environmental Research under the title “Tire-wear particles as a source of organic contaminants in the agro-environment: Release of tire wear-derived compounds and their plant uptake,” provide new insight into how everyday road traffic can contribute to contaminant exposure through food production.
The research was led by Chinese post-doctoral student Chao Gao, soil and water sciences Prof. Benny Chefetz, and the study’s corresponding author, Dr. Evyatar Ben Mordechay of the Hebrew University of Jerusalem’s Faculty of Agriculture, Food and Environment in Rehovot and the Volcani Institute in Rishon LeZion.
Scientists in the past have detected tire-derived chemicals in vegetables and demonstrated plant uptake under lab conditions. But they introduced the chemicals directly into water or soil. What remained unclear was to what extent the tire particles themselves could function as an ongoing source of contamination under realistic agricultural conditions. The new study answers that worrisome question.
“Our research shows that tire-wear particles are not simply passive microplastics accumulating in the environment,” Ben Mordechay told The Jerusalem Post in an interview. “They behave as short- and long-term reservoirs of chemicals, gradually releasing contaminants into soil where they become available for plant uptake.”
The international research team grew alfalfa, which is also fed to cows and other farm animals, and lettuce in agricultural soil that contained environmentally relevant levels of tire-wear particles similar to those reported in roadside and agricultural environments of 0.1-1%. The researchers then monitored how six common tire-derived compounds were transferred from the particles into the soil and ultimately into plant tissues.
Where contaminants from tires can be found
The results revealed a two-stage release process: Some chemicals were quickly released from the particle surface, while others slowly diffused from within the rubber matrix over time. This means tire-wear particles can continue supplying contaminants to soils long after they are deposited, creating an ongoing source of exposure for plants.
“Until now,” said Ben Mordechay, “there have been studies on materials in tires and how they enter land, but not how they affect the real conditions and how much harmful material is released into the environment. Many contaminants are released quickly. The speed depends on rain, wind, heat, and other factors. The closer agricultural fields are to busy highways, the more contaminants reach the crops. It also depends on where in the tires the contaminants are located, at the surface or more deeply. Larger tires apparently produce more than smaller ones.”
Ben Mordechay, who completed all his degrees in environmental chemistry at the Hebrew University campus in Rehovot, added that all tires sold in Israel are imported, mostly from China, which are cheaper and wear down faster than US-made products and thus probably spread more contaminants than American-made tires.
Among the compounds studied – 1,3-diphenylguanidine (DPG) – emerged as a particular concern. The chemical was released continuously from tire particles at relatively high levels, persisted in soil, and accumulated in both alfalfa and lettuce.
In lettuce, DPG concentrations reached levels significantly higher than those observed for other tire-derived compounds, suggesting that tire particles may represent an important and previously underestimated source of dietary exposure.
In addition, 6PPD-quinone, a highly toxic tire-derived compound, was detected in both soils and plants, raising concerns about the potential environmental impacts of tire particles reaching the environment.
Since 6PPD-quinone has already been linked to toxicity in fish species, they can also affect humans, but the concentrations may be low, he stated. “We didn’t test this on mice. Toxicologists should be involved in future research, as there is concern about such crops, especially leafy ones. Fruit on trees, grains, and seeds are less affected. Crops in organic farms can also be affected. Exposure can’t be prevented completely, but the risks can be reduced,” he continued.
One should always wash fruits and vegetables, but contaminants from tires are mostly inside the leaves and not on the outside. If the foods are cooked, it could break down the contaminants, Ben Mordechay said.
Small children eat more fruits and root vegetables but fewer leafy greens, so they are probably less exposed than adults. As for produce brought or smuggled in from the Palestinian Authority, where there is a lot of wastewater irrigation, we are all one ecosystem and not separate, said Ben Mordechay. “As electric cars are heavier than gas-powered vehicles, they likely cause more tire particles to be released. Climate change, with higher temperatures, heavier rainfall, droughts, and flooding, could change the way tire pollutants spread.”
Asked whether workers in garages that change tires should be better protected, he responded that they should definitely all wear gloves. “We didn’t study tire dust in such places, but face masks could help protect them. Research on this is needed. There are good regulations on tire chemistry, but they have to be strictly enforced.”
Chefetz, the senior author, said the study changes the way we think about tire-wear pollution. “Tire particles are often discussed primarily as a microplastic issue. Our findings show that they should also be viewed as long-term carriers of chemical contaminants capable of moving through soils and into crops.”
The authors stress that additional research is needed to determine the long-term implications of tire-derived contaminants in agricultural systems and to better understand how these compounds behave in soils, crops, and food webs.
Source:
www.jpost.com
