Microplastics (plastic particles smaller than <5 mm) are an ever-increasing problem around which discoveries of important and unpredicted consequences to society and nature are occurring at an accelerated pace . Studies of microplastics pollution have flourished, helped by efficient science communication  until the issue reached policy/decision makers. Techniques to sample and characterize these pollutants in all environmental compartments have been also developed rapidly [6-9]. However, it is still difficult to establish a unique and standardized operation protocol .
Microplastics are present in soils, forest litter, sewage sludge, effluents, and all environmental compartments on the continents [15,16], which mainly, through the aquatic systems, become sources to the sea [17,18]. Plastic litter in the sea is a demographical, societal, and economic problem, and microplastics are part of it. We will not end the excess of plastics unless consistent evidence of its harm to the aquatic biota [20,21], especially food resources , emerges in a scientifically-proven and consistent way.
Always on my mind
In science, practical observations and measurements take place after questions arise under their simplest and clearest forms. Sampling strategies are crucial when answering scientific questions if they are to become relevant to society [1,2]. Considerable time must be invested in gathering previous information and tracing strategies for scientific knowledge, evolving into virtuous cycles towards pollution source control and mitigation of environmental passives . Microplastics science is no different, and although it has evolved differently at many places around the globe, it will eventually need to be “checked” by peers in order to be validated and accepted as a real advance.
In the field
The marine environment functions according to processes that often follow cycles and/or gradients. Both must be accounted for when planning to study microplastics sources, distribution and fate at sea, thus becoming nearly impossible to answer all the pressing questions at once, or during a single-study effort. A project involves a series of pre-set steps, planning and sampling being the first two of them. Sampling means collecting representative portions of the environment (air, water, sediments, animals, and plants) and then isolating our analyte of interest (microplastics) from the “matrix.” Only then can microplastics be analyzed for confirmation of their composition and associated pollutants.
Each coastal or marine habitat will need a different and particular approach for sampling. Beaches, for example, can be approached from numerous points of view. Do you wish to know how many microplastics arrived with the last tide? Or whether there are microplastics burrowed in the sand? Or whether microplastics tend to accumulate at the backshore? Each of these questions will need a different strategy. In addition, if tidal cycles, seasons, and periods of time are to be considered, replication will also be necessary. Last, but not least, there is interest in investigating interactions between microplastics and the fauna and flora of beaches. Therefore, ecology knowledge and strategies will need to come into play simultaneously. The marine atmosphere, water column, and submerged marine sediments are also special and will need to be studied following techniques that follow the best possible consensus and strictest scientific protocols.
In the lab…
Microplastics quantification and characterization are subject to contamination from the environment and from the operator due to the ubiquity of synthetic polymers , and extreme care must be taken, especially as we intend to work with decreasing sizes of particles. Other steps, such as storage and sample cleaning, are also challenging as it always involves risks of contamination and microplastics alterations. The laboratory procedure is also a key feature in microplastics science, as laboratories have widely different working conditions. Therefore, each lab will have different capabilities and needs. To focus on a particular talent (fieldwork, chemical analysis, post-analysis data treatments, etc) is a possibility that encourages interactions with other groups with diverse cultures in order to collaborate when conducing microplastics research!
And finally, on our plates!
When microplastics interact with marine fauna and flora, resulting in detectable and quantifiable harm, their importance for marine conservation and society increase. Toxicological experiments demonstrated that interactions, as ingestion and desorption of pollutants, pose real dangers, especially for animals . The present challenge is the demonstration of such harm in field studies, especially in more complex ecological contexts, as food webs [29-32]. Contaminated seafood (from both aquaculture and fisheries)  recently became one of the most important lines of microplastics studies . Bivalves and fish contamination represent a threat to humans and will start to be mandatorily monitored after suitable sentinel organisms are judiciously elected . Therefore, sound sampling, preserving, and examining methodologies must be developed to guarantee the accuracy of this crucial information.
Lessons for young scientists to take home
Microplastics quantification might have a wide reported variation, but the accuracy of sample design and choice of animal models must be highly valued [29,35,36], make ecological sense, and be coupled to environmental changes across time and space. Bearing in mind what microplastics are and how they behave may help in understanding their sources and sinks in the marine environment. Hence, a more ecologically-minded sample design and the addition of other variables will support data in describing habitats and processes involving microplastics are involved, including ecotoxicological effects.
These findings are described in the article entitled, “Sampling of micro(nano)plastics in environmental compartments: How to define standard procedures?” recently published in the journal Current Opinion in Environmental Science & Health. This study was conducted by Monica F. Costa from the Universidade Federal de Pernambuco, and João Pinto de Costa and Armando C. Duarte from the University of Aveiro.
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