Microplastics are increasingly seen as an environmental problem of global proportions. While the focus to date has been on microplastics in the ocean and their effects on marine life, microplastics in soils have largely been overlooked. Researchers are concerned about the lack of knowledge regarding potential consequences of microplastics in agricultural landscapes from application of sewage sludge.
Microplastics are tiny plastic particles (1?m – 5 mm) which originates from degeneration of car tires, domestic goods, industrial processes and from degeneration of surfaces composed of, or coated with, plastics, i.e. artificial grass. Most of these particles originate in urban areas. In most developed regions, urban run-off water ends up in sewage treatment plants.
Sewage sludge is in principle waste, but it can also represent a resource in agriculture and horticulture. Fertilizer based on sludge contains valuable nutrients, but sustainable use requires that the levels of undesirable substances in the sludge is kept under control. Waste water treatment plants receive large amounts of microplastics emitted from households, industry and surface run-off in urban areas. Most of these microplastics accumulate in the sewage sludge.
Today, sludge from municipal sewage treatment plants is applied to agricultural areas as a supplement to traditional fertilizers. These applications are generally well regulated as sludge might contain hazardous substances of different sorts. Microplastics are however not currently on the regulatory agenda for the use of sludge in agriculture. The potential consequences for sustainability and food security have not been adequately analyzed.
These concerns have been expressed in an article recently published in the journal Environmental Science & Technology. The researchers behind the article are Luca Nizzetto and Sindre Langaas from the Norwegian Institute for Water Research (NIVA) and Martyn Futter from the Swedish University of Agricultural Sciences (SLU) in Uppsala.
– We have found figures from the Nordic countries suggesting that a large fraction of all the microplastics generated in Western societies tend to end up in the sludge in wastewater treatment plants, says Nizzetto. Via the sludge the particles are transferred to agricultural soils.
The amount of sewage sludge used as fertilizer varies greatly from country to country. In Europe and North America approximately 50 % of this sludge is reused as fertilizer on average. According to Statistics Norway, about two thirds of the sludge is reused in this manner.
– Our estimates suggest that between 110.000 and 730.000 tons of microplastics are transferred every year to agricultural soils in Europe and North America, comprehensively. This is more than the estimated total burden of microplastics currently present in ocean water.
These figures are of concern since the effects of microplastics accumulating in agricultural soils are unknown.
– We have very little knowledge on the effect of microplastics on soil organisms, and their impact on farm productivity and food safety is unknown.
Microplastics are tiny plastic particles which originates from household articles, industrial processes and degeneration of plastic products. (Photo: Oregon State University)
The first simulation of microplastic fate on land and rivers
In an earlier study from the same authors, and researchers of Oxford University, the first mathematical model describing the dynamics of microplastics’ fate in terrestrial environments and rivers was presented. Due to a lack of empirical data on microplastics emissions and concentrations in soils and the stream system, this study was conceived to provide a purely theoretical, nevertheless rigorous, assessment of microplastics circulation.
The model is called INCA Microplastics, and simulations have showed a strong influence of meteorological conditions and river characteristics and flows in controlling the export of microplastics from agricultural soils and their transport to the ocean. Application of sewage sludge to soils likely represent a considerable source of microplastics to the coastal and ocean environments. Similar predictions for the transport of microplastics in rivers were independently confirmed by a follow-up study by Besseling et al.
INCA Microplastics is an important tool for risk assessment and evaluating sludge management scenarios. It is the first model able to simulate microplastic applications to land, and the consequent fate of these materials in soils and surface waters.
Surprising knowledge gap
The consequences of transfers of microplastics from urban waste water to agricultural soil barely have been considered by researchers and authorities, particularly in lieu of the extended attention directed at microplastics in the ocean.
– Clearly further research is needed to get an overview of the problem – and to find solutions – so that the growing need in the community for recycling and so-called circular economy can be safeguarded, Luca Nizzetto says.
Scientists have found evidence of microfibers ingested by deep sea animals, revealing for the first time the environmental fallout of microplastic pollution.
The UK government recently announced that it is to ban plastic microbeads, commonly found in cosmetics and cleaning materials, by the end of 2017. This followed reports by the House of Commons Environmental Audit Committee about the environmental damage caused microbeads. The Committee found that a single shower can result in 100,000 plastic particles entering the ocean.
Researchers from the universities of Bristol and Oxford, working on the Royal Research Ship (RRS) James Cook in the mid-Atlantic and south-west Indian Ocean , have now found evidence of microbeads inside hermit crabs, squat lobsters and sea cucumbers, at depths of between 300m and 1800m. This is the first time microplastics – which can enter the sea via the washing of clothes made from synthetic fabrics or from fishing line nets – have been shown to have been ingested by animals at such depth.
The results are published in the journal Scientific Reports.
Laura Robinson, Professor of Geochemistry in Bristol’s School of Earth Sciences, said: “This result astonished me and is a real reminder that plastic pollution has truly reached the furthest ends of the Earth.”
Microplastics are generally defined as particles under 5mm in length and include the microfibres analysed in this study and the microbeads used in cosmetics that will be the subject of the forthcoming Government ban.
Among the plastics found inside deep-sea animals in this research were polyester, nylon and acrylic. Microplastics are roughly the same size as ‘marine snow’ – the shower of organic material that falls from upper waters to the deep ocean and which many deep-sea creatures feed on.
Dr Michelle Taylor of Oxford University’s Department of Zoology, and lead author of the study, said: “The main purpose of this research expedition was to collect microplastics from sediments in the deep ocean – and we found lots of them. Given that animals interact with this sediment, such as living on it or eating it, we decided to look inside them to see if there was any evidence of ingestion. What’s particularly alarming is that these microplastics weren’t found in coastal areas but in the deep ocean, thousands of miles away from land-based sources of pollution.”
The animals were collected using a remotely operated underwater vehicle. The study, funded by the European Research Council (ERC) and the Natural Environment Research Council (NERC), was a collaboration between The University of Oxford, the University of Bristol, the Natural History Museum in London, and Staffordshire University’s Department of Forensic and Crime Science, which made sure the results were robust and the study was free from potential contamination.
Dr Claire Gwinnett, Associate Professor in Forensic and Crime Science at Staffordshire University, said: “Existing forensic approaches for the examination of fibres are tried and tested for their robustness and must stand up to the scrutiny of the courts of law. These techniques were employed in this research in order to effectively reduce and monitor contamination and therefore provide confidence in the fact that the microplastics found were ingested, and not from the laboratory or other external contaminant.
“Using forensic laboratory techniques, we have identified that microplastics are present in ingested material from deep sea creatures. Forensic science is still a fairly new science, but we are delighted that our work and techniques are starting to inform other sciences and important environmental research such as this.”
Plastics became widespread after the second World War, and as a material, plastic is still relatively young. Microscopic plastic particles, or microplastics, have caught the eye of researchers only quite recently. Microplastics come with plenty of questions, but for the time being, only few answers are available.
“Microplastics are a Pandora’s Box of a kind, or at least an infinite source of research questions. However, research evidence relating to microplastics and their effects remains scarce,” says Researcher Samuel Hartikainen from the University of Eastern Finland. His research focuses on the chemical properties of microplastics.
Whirlpools of plastics and microplastics in oceans have received plenty of attention in the media. However, microplastic concentrations in lakes and other closed bodies of water may be higher than in oceans, where the water flows freely.
“Microplastics are present in practically all bodies of water, although the remotest ones haven’t been scientifically studies, of course. We can nevertheless assume that airborne microplastics have found their way also in these waters,” says Research Manager Arto Koistinen, who also studies microplastics chemistry.
Microscopic particles of plastic have also been found in the intestines of fish and other seafood. Microplastics aren’t poisonous as such, but they are known to absorb hormone disruptors and heavy metals. So, can microplastics find their way on our plates, and can hazardous materials absorbed by microplastics make our food poisonous?
Microplastics – tiny particles of plastic less than five millimeters in size – are polluting rivers and ponds along with chemical contaminants. The particles come from cosmetics such as exfoliating body scrubs or are washed out of synthetic fabrics. Until now, scientists have primarily investigated the concentrations and effects of microplastics in seawater.
Professor Christiane Zarfl of the Center for Applied Geosciences (ZAG) of the University of Tübingen has cooperated with Saskia Rehse and Werner Kloas from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) in Berlin in testing how high concentrations of standardized plastic particles affect water fleas. Their experiments showed that the ubiquitous residents of bodies of freshwater ingest tiny particles of a micrometer, or one thousandth of a millimeter in size. This clearly limited the water fleas’ mobility, and as a result, their intake of nutrients. Larger particles had no measurable effect. The results of the study have been published in the scientific journal, Chemosphere. The scientists see this as the first of further, necessary research into the effects of microplastic pollution of freshwater. One of their further research directions will focus on the interactions of plastics with various chemicals that also end up in the environment. They say the experiments must also be extended to include entire ecosystems.
Research into the presence of microplastics in seawater has shown that they are found almost everywhere – on ocean surfaces, near the mouths of rivers, on coasts and even in deep sea sediments. Only recently have scientists turned their attention to lakes and rivers. Says Christiane Zarfl, “Measurements taken in Europe, South and North America, Africa and Asia show that up to several hundred-thousand particles of microplastic can be found per square kilometer of water.” In addition, concentrations were higher in areas that are densely populated, intensively farmed and where industry is nearby. Sewage treatment plants are not yet filtering out microplastics. Zarfl explains, “Depending on the type of plastic, the particles remain in the water or they are deposited in lake or riverbed sediment.”