Microplastics – their occurrence in marine and soil ecosystems

 By Noor Fazreen Dzulkafli,

Department of Science and Biotechnology,

FELS

Plastics are widely used because they are lightweight, durable, and inexpensive. Low recovery rates and improper disposal of plastic waste have resulted in the accumulation of plastics in the environment After entering the environment, plastics may degrade into microplastics through various processes, such as hydrolysis, oxidation, photodegradation, mechanical corrosion, and biological degradation.

Microplastics, commonly defined as plastic particles smaller than 5 mm are widely distributed in many types of habitats from land to the ocean. Microplastics are ubiquitous and interact with the biotic and abiotic environment, potentially threatening the biota and ecological functioning of biogenic habitats in aquatic ecosystems. The common microplastics can be found in the form of fibres, fragments, pellets, microbeads, and foam (Figure 1).

Figure 1 Example of common microplastics that can be found in our environment

Microplastic in the marine ecosystem

The distribution and transportation of microplastics into marine environments are influenced by anthropogenic activities, wind, tides, and water current conditions. Microplastics are distributed in the oceans globally where accumulation takes place. Due to the relatively small size, microplastics are easily ingested by marine organisms and have been found to accumulate in tissues, the circulatory system, and the brain. More importantly, microplastics can enter food webs (Figure 2), and therefore, they pose negative consequences for human health.

 Furthermore, microplastics in the environment can serve as vectors for organic and metallic contaminants owing to their remarkable binding capacity. It was also reported that the density of microplastics and their interaction with the surrounding biological life affect their distribution in the marine water column.

Figure 2 Pathway of microplastic in marine ecosystem

Occurrence of microplastics in soils

As industrial development has accelerated and the manufacture and disposal of plastics have increased, concerns about plastic pollution on soil are growing. Compared with the aquatic ecosystem, microplastics in soils are poorly understood. However, soils are considered the major storage for microplastics, and they may enter the soils through agricultural film breaking, sewage sludge utilization, organic manure application, water irrigation, atmospheric deposition, surface runoff, mulch films, and landfilling activities (Figure 3).

The development of modern agriculture results in the extensive use of agricultural membranes and sludge, as well as the changes in irrigation methods, leaving plenty of microplastics on the soil surface. Moreover, due to the disturbance of farming, harvesting, and other agronomic practices on the soil, the plastic on the surface may migrate downward or spread around. Additionally, the infiltration process of water flow such as rainfall or irrigation from top to bottom in the soil renders microplastics to transfer downward along the soil voids, and eventually possibly enter the groundwater. Adsorption of potentially toxic elements onto microplastic can be toxic to soil organisms (microorganisms and microorganisms), reducing soil fertility and having an impact on crop quality and quantity.

Figure 3 Sources and impacts of microplastics in soil