Microplastics have become ubiquitous in the marine environment. Microplastics have been detected in many coastal environments and species, including commercial seafood. This triggers concern about potential economic impacts and the risks of dietary exposure, especially for coastal communities. However, data regarding the levels of microplastics in coastal seafood and their toxicological effects are still limited. Accordingly, the dietary risk is still poorly explored. This review summarizes and discusses recent scientific findings on (i) the presence of microplastics in coastal waters, (ii) the occurrence of microplastics in coastal seafood and the likelihood of trophic transfer, and (iii) the effects of microplastics on coastal fish and shellfish species. Human toxicity data are also reviewed, but the risks for human health are difficult to determine due to limited data. Based on available worldwide data, the estimation of microplastics intake through seafood consumption shows a huge variation. Additionally, a lack of standardized analytical methods complicates the comparison of results between studies and therefore seriously affects the reliability of risk assessments. It is concluded that more exposure and toxicity data are needed properly to assess human health risks of microplastics in coastal seafood, and the lack of data currently impede the derivation of a risk-based food safety standard. The pros and cons of an interim solution, i.e. setting a provisional action level, are being discussed.

Several studies have suggested Indonesia to be among the top plastic polluting countries globally. Data on the presence and amounts of plastic pollution are required to help design effective plastic reduction and mitigation strategies. Research quantifying plastic pollution in Indonesia has picked up in recent years. However, a lack of central coordination in this research has led to research output with different goals, methods, and data formats. In this study we present a meta-analysis of studies published on plastic pollution in Indonesia to uncover gaps and biases in current research, and to use these insights to suggest ways to improve future research to fill these gaps. Research gaps and biases identified include a clear preference for marine research, and a bias toward certain environmental compartments within the marine, riverine, and terrestrial systems that have easy to apply methods. Units of measurement used to express results vary greatly between studies, making it difficult to compare data effectively. Nevertheless, we identify polypropylene (PP) and polyethylene variants (PE, HDPE, LDPE) to be among the most frequently found polymers in both macro- and microplastic pollution in Indonesia, though polymer identification is lacking in a large part of the studies. Plastic research is mostly done on Java (59% of the studies). We recommend research methods used to quantify plastic pollution to be harmonized. Moreover, we recommend a shift in focus of research toward the riverine and terrestrial environments and a shift of focus of environmental compartments analyzed within these systems, an increase in spatial coverage of research across Indonesia, and lastly, a larger focus on polymer characterization. With these changes we envision future research which can aid with the design of more effective and targeted reduction and mitigation strategies.

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Currently, we lack crucial knowledge on how the physicochemical properties of particles affect cellular health, resulting in an important gap in our understanding of the human toxicity of microplastics (MPs). Our aim was to evaluate the impact of the size and the shape of MPs on uptake and the intracellular effects in a human epithelial colorectal adenocarcinoma (Caco-2) cell line. Spherical (200 nm and 2 µm) and fibre-/fragment-shaped (8.9 ± 10.1 µm by 1.14 ± 0.97 µm) polystyrene microplastics (PS-MPs) were used to study their uptake and the potential to induce redox and mitochondrial stress responses after 24 h of exposure. We demonstrated the cellular uptake of both spherical and fibre-/fragment-shaped MPs in a size-dependent manner. In response to 2 µm spheres, we observed differential expressions of redox-related genes, including HMOX1, CAT, and GPX1. All PS-MPs decreased the intracellular H2O2 levels, which can be attributed to mitochondrial stress responses, such as increased mitochondrial DNA content, footprint, and morphology. Altogether, we demonstrated uptakes and changes in redox and mitochondrial parameters for all PS-MPs, with the 200 nm spheres showing the most profound effects. This suggests that the induction of defensive responses in Caco-2 cells mainly correlates with the number of particles taken up.