An increasing number of organisations are undertaking research, monitoring, and data collection on the presence of plastic contamination in the environment. This information is essential for establishing baseline data to support the establishment of indicators and targets for decision-making to mitigate plastic contamination.
Recognising the imperative need for improved data harmonisation, there is a requirement to develop standardised approaches to allow reliable data comparison. This includes developing sets of reproducible practices and guidelines, covering all steps from sample collection, processing, laboratory procedures, and plastic characterisation. It also includes ensuring consistent terminology and data reporting parameters.
This manual is part of a suite of marine sampling field manuals that aim to facilitate reliable data comparisons across regions, and national and international collections, by implementing reproducible and comprehensive guidelines, covering all steps from sample collection, processing, laboratory procedures, and plastic characterisation. The approaches in these manuals provide methods for collecting data that are endorsed by researchers, managers, and technicians from multiple agencies with a variety of experience and subject-matter expertise. The manuals follow the FAIR Guiding Principles for scientific data (Wilkinson et al., 2016), aiming to be findable, accessible, interoperable and reusable. See Chapter 1 and Przeslawski et al. (2023) for a description of the process undertaken to develop these manuals.
This manual focuses on microplastics in water, sediment, biota and air matrices, and spans everything from sampling design, sample collection, processing and laboratory procedures, and plastics characterisation (i.e., size, shape, polymer composition). It establishes recommended terminology and makes a distinction between essential and desirable data reporting parameters needed to guarantee accurate, efficient and standardised approaches to microplastic analysis in the environment. It also includes a checklist to facilitate reporting. Aligned with international guidelines, such as those set by the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) (GESAMP, 2019) the manual is divided into four sections, each dedicated to a specific environmental matrix (Sediment, Water, Air, and Biota). Such information is critical for establishing consistent guidelines in the collection and processing of microplastic data from different environments, enabling scientifically robust comparisons between studies, sites, projects, and organisations at a national level.
What are microplastics?
Microplastics are defined as “any synthetic solid particle or polymeric matrix, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water” (Frias and Nash, 2019).
Scope, format and purpose
The manual focuses on the identification and quantification of microplastics between 1 μm and 5 mm, with the caveat that smaller pieces, namely between 1 μm and 20 μm, require added specialised approaches. Though many researchers find it useful to delineate groupings of plastic size (i.e., nano, micro, meso, and macro plastics), it is important to note that plastic size exists on a continuum. The chosen size categories are based on widely available methodologies to sample, characterise and identify microplastics. While the methods presented here are also appropriate for larger plastic debris (>5 mm), the described processes are designed for microplastics (<5 mm). Analysis of nanoplastics below the set threshold of 1 µm requires increasingly specialised approaches and quality controls that would warrant independent and targeted field manuals in their own right, and are thus not included here.
Due to the differences in methods required to sample microplastics across the defined size range between 1 μm and 5 mm, this manual is divided into sampling, identifying, and reporting microplastics in two main size tiers. These include those that are visible to the naked eye (1 mm – 5 mm; visible microplastics) and those that are microscopic (1 μm – 1 mm; microscopic microplastics).
This tiered approach allows research groups and organisations to accurately identify microplastics depending on the research question, level of experience, available facilities, and budget. It is an inclusive strategy to ensure microplastic sampling can occur accurately and comparably between NGOs, consultants, research and government institutions.
These manuals are designed to deliver improved data collection across surveys and collectors with different levels of background expertise and knowledge. Several sections refer to essential methodological steps and reporting parameters needed that allow data integration across different approaches (e.g., from citizen science to scientific research to government monitoring). To identify microplastics in the smaller size category (1 μm – 1 mm), there is a higher level of analysis that must be followed, and subsections throughout the manual highlight how and where this further detail is required.
A checklist is also provided as a quick reference guide to enhance reproducibility, promote consistency, and facilitate uptake and reporting.