Plants can absorb tiny pieces of plastic through their roots that stunt their growth and simultaneously reduce their nutritional value, a study has found.
The findings from experts from the US and China are the first to provide direct evidence that nanoscale plastic particles can accumulate within land plants.
Widespread use of plastic products and the material’s ability to persist in the environment has resulted in an ‘enormous’ amount of pollution, the team said.
Existing research into the impacts of micro- and nanoplastics have mainly focused on their impact on marine ecosystems and, from their, on seafood.
Additional studies will be needed, the researchers said, to assess the extent of the impact these pollutants are having on both the yield of food crops and their safety.
Plants can absorb tiny pieces of plastic through their roots that stunt their growth and simultaneously reduce their nutritional value, a study has found. Pictured, imaging revealed how two different types of nanoplastic (in red and green) accumulated in the roots (left, and root tips, right) of the model plant Arabidopsis thaliana after seven weeks of exposure
‘Our experiments have given us evidence of nanoplastic uptake and accumulation in plants in the laboratory at the tissue and molecular level,’ said environmental scientist Baoshan Xing of the University of Massachusetts Amherst.
‘We have demonstrated this from root to shoot,’ he added.
In their study, Professor Xing and colleagues grew Arabidopsis thaliana — a commonly-used model plant — in soil into which charged, fluorescence-labelled nanoplastics had been mixed and assessed the impact on plant development.
Nanoplastic particles — which can be as small as a protein or a virus — are changed by degradation and weathering, making them distinct from the pristine polystyrene nanoplastics typically used in laboratory tests, Professor Xing explained.
‘This is why we synthesised polystyrene nanoplastics with either positive or negative surface charges for use in our experiments,’ he added.
After seven weeks, the team reported that plants exposed to nanoplastics had taken up both positively and negatively charged particles of the pollutants — and were both smaller overall and shorter than plants allowed to grow in unpolluted soil.
‘Nanoplastics reduced the total biomass of model plants. They were smaller and the roots were much shorter,’ Professor Xing explained.
‘If you reduce the biomass, it’s not good for the plant — yield is down and the nutritional value of crops may be compromised.’
‘We found that the positively charged particles were not taken up so much, but they are more harmful to the plant.’
‘We don’t know exactly why, but it’s likely that the positively charged nanoplastics interact more with water, nutrients and roots, and triggered different sets of gene expressions.’
‘That needs to be explored further in crop plants in the environment. Until then, we don’t know how it may affect crop yield and food crop safety.’
After seven weeks, the team reported that plants exposed to nanoplastics had taken up both positively and negatively charged particles of the pollutants — and were both smaller overall and shorter than plants allowed to grow in unpolluted soil. Pictured, an illustration of how both positively and negatively charged nanoplastic particles are taken in by plant roots
‘Our findings provide direct evidence that nanoplastics can accumulate in plants,’ the researchers wrote in their paper.
‘Regardless of the surface charge, Arabidopsis can take up and transport nanoplastics with sizes of less than 200 nanometres.’
‘In this study, we mainly demonstrate that the pathway of uptake and transport of nanoplastics in root tissues differed between differentially charged nanoplastics.’
‘Plant accumulation of nanoplastics can have both direct ecological effects and implications for agricultural sustainability and food safety.’
The full findings of the study were published in the journal Nature Nanotechnology.
WHAT FURTHER RESEARCH IS NEEDED TO ASSESS THE SPREAD AND IMPACT OF MICROPLASTICS?
The World Health Organisation’s 2019 report ‘Microplastics in Drinking Water’ outlined numerous areas for future research that could shed light on how far spread the problem of microplastic pollution is, how it may impact human health and what can be done to stop these particles from entering our water supplies.
How widespread are microplastics?
The following research would clarify the occurrence of microplastics in drinking-water and freshwater sources:
- More data are needed on the occurrence of microplastics in drinking-water to assess human exposure from drinking-water adequately.
- Studies on occurrence of microplastics must use quality-assured methods to determine numbers, shapes, sizes, and composition of the particles found. They should identify whether the microplastics are coming from the freshwater environment or from the abstraction, treatment, distribution or bottling of drinking-water. Initially, this research should focus on drinking-water thought to be most at risk of particulate contamination.
- Drinking-water studies would be usefully supplemented by better data on fresh water that enable the freshwater inputs to be quantified and the major sources identified. This may require the development of reliable methods to track origins and identify sources.
- A set of standard methods is needed for sampling and analysing microplastics in drinking-water and fresh water.
- There is a significant knowledge gap in the understanding of nanoplastics in the aquatic environment. A first step to address this gap is to develop standard methods for sampling and analysing nanoplastics.
What are the health implications of microplastics?
Although water treatment can be effective in removing particles, there is limited data specific to microplastics. To support human health risk assessment and management options, the following data gaps related to water treatment need to be addressed:
- More research is needed to understand the fate of microplastics across different wastewater and drinking-water treatment processes (such as clarification processes and oxidation) under different operational circumstances, including optimal and sub-optimal operation and the influence of particle size, shape and chemical composition on removal efficacy.
- There is a need to better understand particle composition pre- and post-water treatment, including in distribution systems. The role of microplastic breakdown and abrasion in water treatment systems, as well as the microplastic contribution from the processes themselves should be considered.
- More knowledge is needed to understand the presence and removal of nanoplastic particles in water and wastewater treatment processes once standard methods for nanoplastics are available.
- There is a need to better understand the relationships between turbidity (and particle counts) and microplastic concentrations throughout the treatment processes.
- Research is needed to understand the significance of the potential return of microplastics to the environment from sludge and other treatment waste streams.
To better understand microplastic-associated biofilms and their significance, the following research could be carried out:
- Further studies could be conducted on the factors that influence the composition and potential specificity of microplastic-associated biofilms.
- Studies could also consider the factors influencing biofilm formation on plastic surfaces, including microplastics, and how these factors vary for different plastic materials, and what organisms more commonly bind to plastic surfaces in freshwater systems.
- Research could be carried out to better understand the capacity of microplastics to transport pathogenic bacteria longer distances downstream, the rate of degradation in freshwater systems and the relative abundance and transport capacity of microplastics compared with other particles.
- Research could consider the risk of horizontal transfer of antimicrobial resistance genes in plastisphere microorganisms compared to other biofilms, such as those found in WWTPs.
Can water treatment stop microplastics entering our water supplies?
Although water treatment can be effective in removing particles, there is limited data specific to microplastics. To support human health risk assessment and management options, the following data gaps related to water treatment need to be addressed:
- More research is needed to understand the fate of microplastics across different wastewater and drinking-water treatment processes (such as clarification processes and oxidation) under different operational circumstances, including optimal and sub-optimal operation and the influence of particle size, shape and chemical composition on removal efficacy.
- There is a need to better understand particle composition pre- and post-water treatment, including in distribution systems. The role of microplastic breakdown and abrasion in water treatment systems, as well as the microplastic contribution from the processes themselves should be considered.
- More knowledge is needed to understand the presence and removal of nanoplastic particles in water and wastewater treatment processes once standard methods for nanoplastics are available.
- There is a need to better understand the relationships between turbidity (and particle counts) and microplastic concentrations throughout the treatment processes.
- Research is needed to understand the significance of the potential return of microplastics to the environment from sludge and other treatment waste streams.
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