Microplastic Analysis and the Future Detection Landscape
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They’re in the bottled water and seafood we consume, the health and beauty products we use and now even in the placentas of unborn babies – we’re talking about microplastics. These tiny plastic fragments may end up small, but many start out life as macroplastics, broken down over time by the actions of the sea, UV light or in the case of the humble tire, just general wear and tear. The vast quantities of single-use plastic personal protective equipment (PPE) being used in the current pandemic is yet another source of potential microplastics. The full impact that microplastics have on health and the environment is still not well understood, however, mounting evidence regarding their negative effects has made microplastics a topic of interest for scientists, governments and regulatory bodies.
As scientists work to try and get a handle on the presence and effects of microplastics and as discussions around potential regulations circulate, there are several testing and analysis trends and pressures making their way to the fore. These include a need for standardized testing and identification methods to help scientists get accurate and repeatable insights more quickly and easily. Combining techniques is one very promising area in solving this problem that is bringing more power to the bench.
In part two of this two-part series on the state of microplastics testing and analysis, we’re speaking again with Kathleen A. Young, environmental market leader, PerkinElmer Inc., about microplastics detection techniques and technologies, the importance of standards and how regulations may come to fruition in the years to come.
Karen Steward (KS): Not all labs around the world have access to the equipment, technology and skills required to perform all potential microplastic detection techniques. How much of a barrier do you think this will be to improving the reliability and consistency of microplastic detection?
Kathleen A. Young (KY): Focusing first on technology accessibility, there are a range of techniques for detection with an equally wide range of cost and capabilities, from low-end optical microscopes, starting at USD300, to comprehensive, hyphenated technologies well-over USD250K, so it depends mostly on what a scientist or lab is trying to achieve.
There can also be a gap between where the greatest plastic pollution challenges exist today and accessibility to the technology and expertise that can effectively measure the impact of plastic pollution, and ultimately microplastics, on the environment and human health. For example, a study from 2017 examined sources of marine plastic debris, finding that a substantive amount comes from land-based sources and rivers, derived from mis-managed plastic waste. The study also indicated that just 10 rivers, located on the continents of Asia and Africa, transport approximately 90% of the global plastics load into the seas coming from their own plastics use and importing the waste of other regions of the world. These concentrated areas of plastic and microplastic pollution, however, are not always fully aligned with an abundance of labs, instruments and trained scientists. There are, however, several organizations such as eXXpedition, and One Earth-One Ocean, focused on protecting the environment and eradicating microplastics from waters of the world. They invest their time, resources and expertise in regions highly impacted by plastic pollution. PerkinElmer’s portable Spectrum™ Two Fourier transform infrared (FTIR) spectrometers have been key to the research these teams are conducting. Another group, PAN-microplast Network, was developed to promote knowledge exchange and scientific collaborations across Africa. With 5 African countries listed among the top 20 countries that are the largest contributors to marine plastic pollution and with most of the related research being dominated by entities outside of Africa, access to scientific expertise and technology is of paramount importance.
As discussed in part one of our discussion, continued development and adoption of standard methods in concert with experienced researchers from collaborations and organizations referenced above are critical to helping remove technology barriers and establish a path to reliable and consistent microplastics analysis. These efforts will help close the analytical and technology gap that has existed in certain regions plagued with tremendous plastic pollution.
As the analysis of microplastics continues to shift from purely academic, non-governmental organizations (NGO) and governmental research to inclusion as a service offered by environmental testing laboratories, the demand for and adoption of standardized methods will become critical.
Environmental testing labs are extremely skilled and familiar with following analytical methods, even new methods. Additionally, most environmental labs have expertise in and a broad portfolio of analytical instruments in order to offer their clients a wide range of testing services. Whether methods are established by the US Environmental Protection Agency, (EN)-ISO standards for the European Union or GB (Guobiao) standards issued in China, environmental labs have to demonstrate proficiency in contaminate testing methods to achieve accreditation or authorization for those methods. It is this emphasis on core competencies in method certification and utilization that will ensure standard methods become mainstream and integral to standard operating procedure for microplastics analysis in environmental matrices.
KS: How might combining multiple analytical methodologies improve microplastic detection and identification?
KY: A range of analytical techniques have been adopted for the detection, identification, and quantification of microplastics in environmental, food, animal and plant matrices, which can help create richer data that can look at the problem and potential solutions from various angles.
Technique(s) selection is dependent upon the objective for the analysis, with each technique having advantages and some drawbacks. Factors such as cost, accessibility, portability, accuracy, sensitivity, level of effort and automation truly drive what technology or technologies are selected. As discussed earlier, optical microscopes are at the lower end of analytical instrument price range and simple to use, where scientists can determine the presence, color and morphology of particles; however, the method is labor intensive, prone to human error and cannot identify the chemical or polymer composition, mass or reliable quantification of the microplastics present in an environmental matrix.
Combining microscopy with FTIR or Raman spectroscopy eliminates false positives, expands the detection range to much smaller particles and offers the additional benefits of identifying chemical composition and structure while preserving the sample. These additional data parameters provide valuable information on the type (and sometimes source) of the plastics found in the various matrices analyzed. Sample preparation can be time-consuming, especially based on the type of environmental matrix the microplastics residue is in; samples must be free of organic and inorganic materials to remove analytical interferences and to ensure reliable and accurate microplastics detection and identification. Instrumentation vendors like PerkinElmer, Inc. offer automated data evaluation, such as particle detection algorithms, within the software. The software can analyze the visible images gathered by the infrared (IR) microscope and automatically scan the spectra of all particles. Imaging offers the advantage of being able to scan complete filters in an automated process from a single click and to determine the spatial distribution of particles. Portable or handheld FTIR and Raman instruments make it possible to take the measurement in-situ, useful for larger microplastics and plastic fragments, enabling high uptime for analysis. We have also seen some researchers include scanning electron microscopy to gain information on particle shape which can yield insights on sources and effects on the environment.
In recent years, researchers have incorporated gas chromatography-mass spectrometry (GC-MS) with a thermal technique, such as pyrolysis or thermogravimetric analysis (TGA), to heat and decompose the microplastic sample, thus identifying the native polymer type. These techniques offer better limits of detection, less data analysis and modest time per sample. The thermal decomposition provides insights (thermal stability correlated to weight and temperature) as to the type of polymer and when coupled to a GC-MS, scientists can obtain chemical identification as well. However, mass information is gathered at the per sample level and no information on morphology or numbers of plastic particles present in the sample is obtained.
There are certainly several other techniques available including an example that truly demonstrates the power of combining multiple techniques. Coupling two or more techniques is commonly referred to as hyphenated or multi-hyphenated techniques. TGA-FTIR-GC-MS is one that a few of our customers, including the University of Birmingham are leveraging. This approach synergizes the benefits of each individual technique to drive further insights on microplastics analysis. Depending on research and analytical objectives, technology workflows can vary such that FTIR may be utilized first for detection, particle count and identification of microplastics and then TGA-FTIR-GC-MS utilized to gather information on physical and chemical properties, detect additives such as plasticizers and increase the efficacy of polymer identification.
Much innovation over the past few years have advanced the ability to detect, characterize and quantify microplastics -- including the utilization of hyphenated techniques. Further iterations on hyphenated variations will continue to emerge and advance the measurement of microplastics, both qualitatively and quantitatively.
KS: How do you think regulatory changes could be used to improve microplastic analyses, remediation and prevention efforts?
KY: Standardization of methods and their wide adoption, as discussed, will provide regulatory agencies and governing bodies with the consistent and accurate framework for data comparability and determination of the negative impact microplastics may have to humans and environmental ecosystems. This in turn will help to develop regulations that may help to impact the issue.
Regulations will then help raise general, political and scientific awareness and could help with remediation and hopefully ultimately prevention. Microplastics are on the agenda of most environmental regulatory agencies and bodies globally. The process of rulemaking, public review and comment and promulgation of regulations is measured and sometimes lengthy.
In the US, one could look at the Senate Bill 1422 “Safe Drinking Water Act: Microplastics” passed in California in 2018 to understand key elements and timelines to microplastics legislation. It lays a framework similar to other regulatory bodies regarding the legislation for new or “emerging” contaminants:
· Establishing a scientific and precise definition for the targeted contaminant – microplastics, by July 2020.
· Develop and adopt a standard method for the testing of the contaminant (microplastics) in drinking water by July 2021. Note: method development and standardization efforts by ASTM, ISO, CEN and other organizations lay the foundation for state- or country-specified methods, such as ASTM D8333.
· Establish a monitoring program by required regulated entities for a period of four years (2022 – 2026).
· Create a public reporting and communication process to share testing results of the monitoring program and if appropriate, issue a notification level or other guidance to aid consumers in interpretation of testing results - microplastics - in public drinking water.
· Develop an accreditation program for laboratories to analyze microplastics.
From this multi-year legislative framework will come a multitude of monitoring results, public health, environmental and human toxicological data through extensive collaboration networks to determine how microplastics will be regulated. This could take form in a variety of regulations focused on health risk-based levels, for example, maximum contaminant levels in drinking water, treatment of drinking water, effluent discharge requirements for wastewaters and more rigorous monitoring requirements for waste management operations, including related emissions for plastics recycling, could all come into play.
This is truly an extrapolation of how the regulatory agenda could look in a few years from now. Most of our commentary, though, has been centered around water – drinking, surface, ground and wastewaters; however airborne microplastic particles and fibers have been measured in several studies over the past couple of years. This may open the door for measuring microplastic particulate in legislatively mandated air pollution monitoring programs as well. Tires are a significant source to microplastic pollution so it is not a stretch to consider the particulate matter being measured for air quality may include microplastic fibers from this source.
Considering remediation initiatives to date, much of the activities have focused on the macroplastic pollution (plastic particles well above 5mm in size) to remove sources that ultimately contribute to microplastics pollution. Having regulatory standards that dictate microplastic clean up levels in our waterways then is probably further out than drinking water quality standards.
Ultimately, preventing harmful contaminants in our environment requires regulators to look at sources of pollution and eliminate them from the ecosystem altogether. Like phasing out polychlorinated biphenyls (PCBs), perfluorochemicals (PFCs), specific per- and polyfluoroalkyl substances (PFAS) and trichloroethylene, this means manufacturing of these chemicals and contaminants are eliminated and thus, never enter the environmental ecosystem to start with.
This is probably the most challenging obstacle to a microplastics-free environment. Plastics are integral to so many products and processes that we use every day. Bans on single-use plastics, requirements for incorporation of recycled plastics in the manufacturing of plastics and zero waste initiatives will contribute to turning off the plastic waste spigot, but more studies, based on widely adopted standardized analytical methods, will need to be conducted to reinforce evidence that microplastics in our environment have a detrimental effect.
Kathleen A. Young was speaking to Dr Karen Steward, Senior Science Writer for Technology Networks.
Read part one here.