Maya Ellison
Plastic pollution in soil is a growing environmental concern, with microplastics in soils reaching >40,000 particles kg–1. These microplastics can be primary, manufactured for industrial applications, or secondary, resulting from the degradation of larger plastics. They affect soil structure and water dynamics, with consequences for soil microbial activity and plant growth. Plastic pollution in agricultural soils is a particular area of focus, as plastic products like mulching films and fertilizers are commonly used in farming. The slow deterioration of these products can leach plastic into the soil, reducing its quality and entering the food chain. While the impact of plastic pollution in soils is not yet fully understood, it is clear that it has the potential to cause significant environmental harm.
| Characteristics | Values |
|---|---|
| Microplastics in soil | >40,000 particles kg–1 |
| Microplastics as a percentage of soil weight in Swiss natural reserves | ~0.002% |
| Microplastics as a percentage of soil weight in roadside soils near industrial areas | ~7% |
| Microplastics in agricultural soils | Transferred horizontally and vertically across and within soil profiles |
| Soil parameters affected by microplastics | Bulk density, density, water dynamics, microbial activity, water stable aggregates, soil structure, water evaporation, water availability |
| Soil properties affected by plastic | Soil water content, soil texture, soil porosity, soil pH, soil stability, soil ammonium-N, nitrate–N |
| Soil fauna affected by microplastics | Earthworms, mites, larvae, other tiny creatures that maintain the fertility of the land |
| Plastic contaminants in agricultural soils | Sewage sludge, coated fertilizers, irrigation water, agrochemicals, mulching, greenhouse films |
| Plastic in soil can leach | Potentially toxic substances, harmful chemicals |
| Plastic waste in soils or freshwater | 133 million tons of plastic waste in soils or freshwater out of 400 million tons of plastic produced globally each year |
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What You'll Learn
Microplastics can change soil properties
Plastic pollution is a pressing issue, and microplastics are a significant contributor to this problem. They are tiny plastic particles that can come from the breakdown of larger plastics or be manufactured as such for industrial applications. These microplastics are infiltrating our soils, with studies finding them in agricultural lands, farmlands, and even natural reserves. The presence of microplastics in soil can lead to changes in soil properties and subsequent impacts on plant performance and the broader ecosystem.
Soil is a complex mixture of minerals, organic matter, gases, and organisms. It has various physical, chemical, and biological properties that are essential for plant growth and ecosystem functioning. However, the introduction of microplastics can alter these properties, leading to potential consequences for water dynamics, microbial activity, and plant health. For example, studies have shown that microplastics can decrease soil bulk density, increase soil density in the rhizosphere, and affect water stable aggregates, leading to changes in water evaporation and availability.
The PES microplastic fibres, which are commonly found in sewage sludge used as agricultural amendments, have been found to have the most significant impact on soil structure and water interactions. Their linear shape, size, and flexibility differ from natural soil components, thus driving changes in soil biophysical properties. These changes can then influence root structure and biomass allocation, as seen in experiments with spring onions.
The presence of microplastics in soil can also affect soil fauna, such as earthworms, which are crucial for soil fertility and health. A study published in the Proceedings of the Royal Society in 2020 found that microplastics led to a decrease in species living below the surface, such as mites, larvae, and other tiny organisms that contribute to land fertility. Additionally, chlorinated plastic can release harmful chemicals into the soil, which can then contaminate groundwater and surrounding water sources.
The impact of microplastics on soil properties and the broader ecosystem is a growing area of research. While studies have provided valuable insights, there are still gaps in our understanding of the full extent and long-term consequences of microplastic pollution in soils. The complexity of soil systems and the varying properties of microplastics themselves present challenges in fully comprehending their interactions and impacts.
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Microplastics can affect plant performance
Plastic pollution in the soil is a growing environmental concern. The presence of microplastics in the soil can affect plant performance in various ways.
Microplastics can alter the physical properties of the soil, such as bulk density and aggregation, which in turn impacts water dynamics and microbial activity. For instance, studies have shown that the addition of microplastics like PEHD, PES, PET, PP, and PS decreased soil bulk density, while increasing soil density in the rhizosphere. These changes in soil structure can significantly affect water evaporation, water availability, and soil microbial activity, ultimately influencing plant growth and performance.
The shape, size, and flexibility of microplastic particles differ significantly from natural soil components. PES microplastic fibers, for example, have been found to have strong effects on soil structure and interactions with water. This can lead to changes in root structure and biomass allocation, as observed in experiments with spring onions.
Microplastics can also act as vectors for contaminants and toxic substances. They can attract and bind to contaminants, resulting in toxic accumulation. These toxins can then be absorbed by plants, potentially impacting their growth and performance. While microplastics themselves may not be absorbed by plant cells, they can accumulate on the tips of roots, which could have implications for root crops.
The presence of microplastics in the soil can also affect soil fauna, such as earthworms, mites, and larvae. Earthworms, for example, exhibit altered burrow-building behavior in the presence of microplastics, which can impact their fitness and soil condition.
Additionally, microplastics can interact with soil texture to influence water availability, particularly under drought conditions. Plastic fragments can introduce fracture points within soil aggregates, affecting soil water content and potentially exacerbating the effects of water scarcity on plant performance.
While the impact of microplastics on plant performance is a growing area of research, the existing evidence suggests that microplastics can indeed affect plant growth and health through various mechanisms. More studies are needed to fully understand the extent and complexity of these effects.
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Plastic can affect soil water content
Plastic pollution in the soil is a growing environmental concern. Plastic waste in the soil can take the form of macroplastics, mesoplastics, microplastics, and nanoparticles. Microplastics are the most common type of plastic waste found in the soil, and they can have a significant impact on soil properties and plant growth.
Microplastics in the soil can affect soil water content, which is a crucial factor in plant growth and performance. Studies have shown that plastic fragments introduce fracture points within soil aggregates, which can affect the stability of soil aggregates and alter the soil's water-holding capacity. The effect of plastic fragments on soil water content is influenced by the soil texture, particularly the clay versus sand content. Clay-rich soils have a higher water-holding capacity under optimal watering conditions due to the presence of aggregates, while sand-rich soils have faster water percolation through loose soil grains. However, during droughts, clay-rich soils form larger aggregates, resulting in wider soil pores and faster water loss compared to sand-rich soils. Therefore, the presence of plastic fragments in clay-rich soils may have a more pronounced effect on soil water content during droughts.
The shape, size, and flexibility of microplastic particles also play a role in their interaction with water in the soil. PES microplastic fibers have been found to have strong effects on soil structure and water dynamics. The linear shape and flexibility of these particles are distinct from most natural components of soils, making them likely drivers of changes in soil biophysical properties.
The impact of plastic on soil water content can have both positive and negative effects on plant growth. On the one hand, plastic-mediated shifts in soil water content can either mitigate or amplify the effects of drought on plants. For example, in a study on the plant Arabidopsis thaliana, it was observed that increasing concentrations of plastic had positive effects on plant growth. On the other hand, plastic fragments can negatively affect plant performance by altering water dynamics and availability. Evapotranspiration, for example, was increased by PA and PES microplastics, leading to higher water loss in the soil.
The presence of plastic in the soil can also affect soil fauna, such as earthworms, and the health of the soil. Earthworms create their burrows differently when microplastics are present, impacting their fitness and the soil condition. Additionally, plastic pollution in the soil can release harmful chemicals, which can seep into groundwater and other water sources, further impacting the ecosystem.
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Chlorinated plastic can release harmful chemicals into the soil
Plastic pollution in the soil is a pressing issue that requires further research. The presence of microplastics in the soil has been shown to affect soil properties and plant performance.
Chlorinated plastic, in particular, poses a significant risk as it can release harmful chemicals into the soil. These chemicals can then seep into groundwater, nearby water sources, and the surrounding ecosystem. This type of plastic contains organic contaminants, including polychlorinated biphenyls (PCBs), which can be released into the environment. The impact of these contaminants is evident in studies that show their accumulation in soil-dwelling organisms. For example, research has demonstrated that lugworms can take up contaminants from plastic in their environment, with higher concentrations measured in their tissues over time.
The use of plastic in agriculture contributes to the presence of chlorinated plastics in the soil. Primary sources of plastic contaminants in agricultural soils include sewage sludge, coated fertilizers, irrigation water, and agrochemicals. The application of agrochemicals containing sulfur, halogen, iron, and chlorine has been found to cause early aging of plastic films, leading to increased degradation and the potential release of harmful chemicals.
Furthermore, secondary sources of plastic contamination in agricultural soils include the gradual breakdown of larger plastic materials, such as mulching and greenhouse films. The extensive use of plastics in agriculture increases the generation and disposal of plastic waste, leading to increased contamination of farmland.
The impact of chlorinated plastic on the soil ecosystem is a serious concern, and further research is needed to fully understand the long-term effects of microplastic pollution on land.
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Plastic can affect soil fauna
Plastic can have detrimental effects on soil fauna in several ways. Firstly, microplastics can interact with soil fauna, negatively impacting their health and behaviour. For example, earthworms, a vital part of soil fauna, exhibit altered burrow-building behaviour when microplastics are present in the soil. This change in behaviour can affect the earthworms' fitness and the overall soil condition.
Moreover, the presence of microplastics in the soil has been linked to a decline in the population of soil fauna that live below the surface, such as mites, larvae, and other small organisms that play a crucial role in maintaining soil fertility. This decrease in biodiversity can have far-reaching consequences for the health and functionality of ecosystems that depend on these organisms.
The surfaces of plastic fragments may also serve as vectors for disease-causing organisms, further endangering the health of soil fauna and the wider ecosystem. Additionally, certain types of plastics, such as chlorinated plastic, can release toxic chemicals into the soil, which can then contaminate groundwater and other water sources, posing a threat to aquatic organisms and any fauna that depend on those water sources.
Furthermore, microplastics can alter soil properties, including bulk density and aggregation, which can impact the water dynamics and root structure of plants. These changes in soil structure can have cascading effects on soil-dwelling organisms, affecting their distribution, activity, physiology, and growth. The effects of microplastics on soil fauna are not yet fully understood, and more research is needed to comprehend the full scope of their impact on these vital organisms.
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Frequently asked questions
Microplastics are plastic particles smaller than 5mm in size. They can be further broken down into nanoparticles, which are less than 0.1 micrometres in size.
Plastic enters the soil through single-use plastic products, such as plastic mulch films, plastic-encapsulated fertilisers, and plastic films used in greenhouses. These products can break down into microplastics and nanoparticles, which can spread through wind and water.
Plastic contamination can alter soil structure, including soil bulk density, soil aggregation, and water dynamics. It can also affect soil microbial activity and soil pH. These changes can impact plant growth and performance.
Plastic pollution in soil can have negative consequences for the environment. It can reduce soil quality, affect the health of soil fauna, and release harmful chemicals into the surrounding soil and groundwater.
Addressing plastic pollution in soil requires a multi-faceted approach. Farmers need training on plastic management and sustainable alternatives. Clear guidelines on the use and disposal of agricultural plastics are necessary. Additionally, standardised methods for detecting microplastics in soil and removing microplastics from soil need to be developed to better understand their long-term impacts.
