Alexei Volkov
The presence of plastic in water, especially drinking water, is a growing concern for people worldwide. Microplastics have been detected in over 90% of the world's most popular bottled water brands, with concentrations as high as 10,000 plastic pieces per litre of water. Various methods are used to sample and detect microplastics in water, including suction-based filtration, surface and subsurface water sampling, and spectroscopic techniques such as FTIR and Raman spectroscopy. The standard method involves digestion, density separation, and filtration with glass fiber filter paper. While the health effects of consuming microplastics are still under review by organisations like the WHO, the contamination of water by plastic is an emerging area of concern that requires further investigation and mitigation.
| Characteristics | Values |
|---|---|
| Detection Methods | Infrared spectroscopy (micro-FTIR), Raman spectroscopy, and Nile Red dye |
| Sampling Methods | Suction-based filtration, surface and subsurface water sampling |
| Plastic Sources | Primary: cosmetics, cleaners, ship-breaking industry, synthetic "sandblasting" media; Secondary: mechanical, photochemical, or thermal breakdown of larger plastics |
| Health Concerns | Microplastics can enter the human food chain through marine animals and contaminated freshwater sources |
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What You'll Learn
Sampling methods for microplastics in water
The detection of microplastics in water is a growing area of concern. There is no single standardised method for sampling and preparing microplastic samples, and knowledge of sources, fate and environmental concentration over time and space is limited. However, several sampling methods have been identified and are currently in use.
Selective Sampling
Selective sampling involves the direct collection of items from the environment that are recognisable by the naked eye. This method is usually used on the surface of shore sediments and is more practical for larger microplastics (1-5mm).
Volume-Reduced Sampling
This method involves taking a portion of the sample, usually from water, and reducing the volume during the process.
Bulk Sampling
Bulk sampling refers to the collection of the whole volume of the sample without reducing it during the process.
Manta Trawls
Manta trawls are the primary tool for microplastic separation from surface water.
Shovel, Trowel, Spade, Scoop and Spatula
These tools are the most frequently used devices in microplastic studies of sediments.
Van Veen Grab
This tool is used for deep sediment sampling.
Suction-Based Filtration
A new design of the sampling system uses suction-based filtration onto cylindrical filters. The design has been used to sample down to a theoretical size of 10 microns (mesh size).
Organic Digestion and Density Separation
Organic digestion and density separation are used to improve the identification of microplastics.
Visual Identification
Visual inspection can be improved through the use of staining dyes.
Chemical Characterization
Chemical identification is essential for validating the results and can be improved through the generalized use of chemical characterization.
Membrane Bioreactors
Sorption and filtration processes coupled with membrane bioreactors lead to higher microplastics removal compared to other methods.
Photocatalysts
ZnO nanorod photocatalysts excited by visible light were used to degrade low-density polyethylene film in water.
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Infrared spectroscopy for detection
Infrared spectroscopy is a widely used technique for detecting and identifying plastics in water. This method is based on the interaction of infrared radiation with the chemical bonds within a plastic molecule, which causes the molecule to absorb or transmit energy at specific wavelengths. By analysing the absorption or transmission spectrum, it is possible to identify the functional groups and chemical structure of the plastic.
One common type of infrared spectroscopy used for plastic detection is Fourier Transform Infrared (FT-IR) spectroscopy. This technique has been shown to detect a significantly higher number of microplastics within environmental samples compared to visual sorting using a microscope. It is also cost-effective, reliable, and easy to use. Additionally, FT-IR spectroscopy is nondestructive, allowing for the analysis of small samples without causing damage or altering the sample.
To enhance the detection of plastics in water, FT-IR spectroscopy can be combined with other techniques such as optical microscopy and chemical mapping. For example, micro-FT-IR spectroscopy uses smaller infrared wavelengths to improve spatial resolution and facilitate the identification of microplastics directly on membrane filters. This method has been successfully applied to the detection of microplastics in both water and sediment samples, demonstrating its versatility and effectiveness in environmental analysis.
Another variation of FT-IR spectroscopy is focal plane array-based reflectance micro-FT-IR imaging, which enables rapid analysis of thick and opaque samples. This technique is particularly useful for detecting microplastics in environmental samples, as it can distinguish between microplastics and naturally occurring particles. By selecting specific regions of absorbance for each plastic type, positive identification can be achieved even in complex organic backgrounds.
In addition to FT-IR spectroscopy, other types of infrared spectroscopy have been explored for plastic detection. Near-infrared (NIR) spectroscopy, for example, is effective for quantifying organic compounds, including polymers, elastomers, and plastics. NIR spectroscopy can be used to directly analyse solid particles or aqueous suspensions, making it a valuable tool for quantifying microplastics in environmental samples based on their concentration. Furthermore, laser-induced plasma spectroscopy (LIPS) has been investigated for the identification of major elemental ratios in organic compounds such as polymers, providing another approach to plastic detection using infrared absorption.
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Visual inspection and chemical identification
Detecting plastic in water is a complex process that requires careful sampling and analysis. While standard methods exist for collecting and preparing microplastic samples, the identification of microplastics within these samples is challenging. Visual inspection and chemical identification are crucial aspects of this process.
Visual inspection involves the physical examination of water samples to detect the presence of plastic particles. This method can be improved by using specialised equipment such as microscopes or magnifying lenses to enhance the visibility of microplastics, which can range from larger pieces to microscopic particles. Visual inspection can also involve the use of netting or filtration systems to collect and concentrate plastic particles, making them easier to identify. However, it is important to use microplastic-free equipment, such as plastic-free nets or filters, to avoid contaminating the sample.
Chemical identification is essential for confirming the presence of plastic polymers and differentiating them from other substances. One commonly used technique is Fourier Transform Infrared (FTIR) spectroscopy, which identifies the chemical composition of a sample by measuring how it interacts with infrared light. This method can detect the unique chemical "fingerprint" of plastic polymers, allowing for accurate identification. Another powerful technique is Raman spectroscopy, which examines how light scatters off a sample and can provide complementary data to FTIR analysis. By using these techniques in conjunction, scientists can more effectively identify microplastics and gather information on their size and shape.
In addition to these lab-based techniques, advancements are being made in the development of field-portable systems for detecting microplastics. These systems employ chemical, mechanical, and electrical operations to assess microplastic volume in a sample. The goal is to create sturdy, portable equipment that minimises contamination risks and enables researchers to identify microplastics more efficiently while working in the field.
Overall, visual inspection and chemical identification play critical roles in detecting plastic in water. By employing a range of techniques and technologies, scientists can improve the accuracy and efficiency of microplastic identification, leading to a better understanding of plastic pollution and its potential impacts on human health and the environment.
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Microplastics in drinking water
Microplastics are bits of plastic smaller than 5mm, including microbeads and microfibers. They are found in every ecosystem on Earth and have been detected in air samples, food, and drinking water. Microplastics in drinking water can come from various sources, such as river water, lake water, groundwater, tap water, and bottled drinking water.
The presence of microplastics in drinking water has raised concerns among the public and scientists alike. While there is limited data on the human health effects of ingesting or inhaling microplastics, animal studies suggest that they may accumulate and cause particle toxicity by inducing an immune response. There are also potential chemical, particle, and microbial hazards associated with microplastics. For example, biofilms growing on microplastics may be a source of microbial pathogens.
Detecting microplastics in water typically involves sampling and separation techniques, followed by identification and analysis. Standard methods include digestion, density separation, and filtration with glass fiber filter paper. However, there are challenges in extracting microplastic particles that get stuck on the filter paper, and there is a need for improved standardisation and quality assurance in sampling and analysis.
To address the issue of microplastics in drinking water, the World Health Organisation (WHO) has launched a health review. This review aims to assess the potential risks associated with plastic in drinking water, filling gaps in the scarce available evidence and establishing a research agenda for a thorough risk assessment. Additionally, efforts are being made to reduce plastic pollution and improve wastewater treatment processes to minimise the presence of microplastics in our water systems.
Overall, the detection and understanding of microplastics in drinking water is an ongoing area of research, with a focus on improving sampling and analysis techniques to better inform human health risk assessments.
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Microplastics in bottled water
Microplastics are widespread contaminants, virtually present in all environmental compartments. A US study found plastic in over 90% of the world's most popular bottled water brands. The World Health Organization (WHO) has since launched a health review to assess the potential risks of plastic in drinking water.
The amount of microplastics in bottled water samples varies, ranging from 8 to 22 particles per litre, with an average of 11.7 ± 4.6 particles per litre. However, a bottle of Nestlé Pure Life was found to contain 10,000 plastic pieces per litre of water. The most common type of plastic fragment found was polypropylene, the same plastic used to make bottle caps. Other common plastic types found in bottled water include polyethylene terephthalate (PET) and nylon, which are used in the bottled drinks industry.
The presence of microplastics in bottled water is concerning due to the potential health risks to humans. While the specific impacts on human health are unknown, there is a growing need to determine the occurrence of microplastics in bottled water and its potential risks. Nanoplastics, in particular, may pose an even greater risk to human health than microplastics as they can be more easily misidentified as natural components in our bodies and are small enough to enter the body's cells and tissues.
To avoid microplastics in bottled water, it is recommended to use glass or steel water bottles instead of plastic ones. Home filtration systems such as reverse osmosis, distillation, and ultrafiltration can also help reduce microplastic consumption.
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Frequently asked questions
Researchers have used Nile Red dye to detect plastic particles in bottled water. This method can identify plastic particles larger than the width of a human hair. Other methods include infrared spectroscopy (micro-FTIR) and Raman spectroscopy, which can be used to analyse microscopic-sized samples.
Microplastics can come from primary sources, such as cosmetic products, the ship-breaking industry, and industrial abrasives. They can also be derived as secondary products from the mechanical, photochemical, or thermal breakdown of larger plastic products. Another primary source is plastic pellets, sometimes called nurdles, that are lost during plastic production.
The impact of microplastics on human health is an area of growing concern. While there is no evidence of the impacts on human health, the World Health Organization (WHO) has acknowledged it as an emerging area of concern and has initiated a review to assess the risks.
