Selection and optimization of a protocol for extraction of microplastics from Mactra veneriformis

Microplastics (MPs) in marine food chains: Is it a food safety issue?

The enormous usage of plastic over the last seven decades has resulted in a massive quantity of plastic waste, much of it eventually breaking down into microplastic (MP) and nano plastic (NP). The MPs and NPs are regarded as emerging pollutants of serious concern. Both MPs and NPs can have a primary or secondary origin. Their ubiquitous presence and ability to sorb, desorb, and leach chemicals have raised concern over their presence in the aquatic environment and, particularly, the marine food chain. MPs and NPs are also considered vectors for pollutant transfer along with the marine food chain, and people who consume seafood have began significant concerns about the toxicity of seafood. The exact consequences and risk of MP exposure to marine foods are largely unknown and should be a priority research area. Although several studies have documented an effective clearance mechanism by defecation, significant aspect has been less emphasized for MPs and NPs and their capability to translocate in organs and clearance is not well established. The technological limitations to study these ultra-fine MPs are another challenge to be addressed. Therefore, this chapter discusses the recent findings of MPs in different marine food chains, their translocation and accumulations potential, MPs as a critical vector for pollutant transfer, toxicology impact, cycling in the marine environment and seafood safety. Besides, the concerns and challenges that are overshadowed by findings for the significance of MPs were covered.

Extraction of biodegradable microplastics from tissues of aquatic organisms

Biodegradable plastics (BPs) have been given high hopes to substitute conventional plastics, but their biodegradation requires strict conditions. BPs can accumulate for a long time in the environment and even derive biodegradable microplastics (BMPs), thus threatening wildlife and ecosystems. However, no efficient method is available for extracting BMPs from organisms' tissues. This study used multi-criteria decision-making (MCDM) methods to comprehensively evaluate and optimize extraction protocols of five BMPs from economic aquatic species. Digestion time, digestion efficiency, mass loss, cost, polymer integrity and size change were selected as evaluating indictors. According to the screening results of MCDM methods, Pepsin+H₂O₂ was selected as the optimal digestion method of BMPs because of its highest comprehensive score, which has high digestion efficiency (99.56%) and minimum plastic damage. Compared with olive oil, NaI is more suitable for separating BMPs from the digested residues. Furthermore, the combination of Pepsin+H₂O₂ digestion and NaI density separation was used to extract all five kinds of BMPs from the bivalve, crab, squid, and crayfish tissues, and all the recovery rates exceeded 80%. These results suggest that the optimal protocol is practicable to extract various BMPs from various aquatic organisms.

An assessment workflow to recover microplastics from complex biological matrices

A criteria-guided workflow was applied to assess the effectiveness of microplastic separation methods on complex marine biological matrices. Efficacy of four methods (nitric acid, HNO₃, and potassium hydroxide, KOH, digestions, and sodium chloride, NaCl, and potassium iodide, KI, density flotations) was evaluated on four taxa (hard coral, sponge, sea squirt, sea cucumber) using five microplastics (polyethylene, polystyrene, polyethylene terephthalate, PET, polyvinylchloride, rayon). Matrix clarification was only unacceptably low for KOH. PET discoloured regardless of reagent. Rayon threads unravelled into monofilaments after exposure to all reagents, with discolouration also occurring with HNO₃. Recovery rates were overall high, except for dense microplastics treated with NaCl and only KI yielded high rayon recovery efficiency. All polymers were accurately assigned, with subtle spectral changes observed. These results demonstrate specific limitations to separation methods applied to different biological matrices and microplastics and highlight the need to assess their suitability to provide estimates of microplastic contamination.

Oil extraction following digestion to separate microplastics from mussels

Mussels are often used as biological indicators for monitoring marine microplastic pollution. The crucial procedure during monitoring is the separation of microplastics from mussel samples. We investigated the separation efficiencies of six combinations of two digestion solutions (10% KOH and 30% H₂O₂) and three extraction solutions (NaCl, oil in H₂O, and oil in NaCl) for mussels with low- and high-density microplastics. After KOH digestion, no polyethylene terephthalate (PET) could be extracted using the three extraction solutions, which might be due to the degradation of PET. After H₂O₂ digestion, the total extraction recovery rates of polypropylene, polyvinyl chloride, and PET for oil in H₂O and oil in NaCl solution ranged from 95.6% ± 5.09%-100%, which were higher than those of the saturated NaCl solution (51.1% ± 17.1%-67.8% ± 13.9%). The first extraction recovery rates of oil in NaCl solution for PP, PET, and PVC were higher than those of oil in H₂O. In this study, extraction by oil in NaCl solution after 30% H₂O₂ digestion was suggested to separate microplastics from mussels. This method is conducive to promoting the standardization of microplastic monitoring in mussels and might be suitable for large-scale monitoring of marine microplastic pollution.

Optimization of a new multi-reagent procedure for quantitative mussel digestion in microplastic analysis

Over the last few years, different digestion protocols have been proposed to extract microplastics from mussels, an important product from aquaculture and a relevant economic resource, always scrutinized as a potential pollutant concentrator. In this study, a full factorial experimental design technique has been employed to achieve efficiency in removing biological materials while maximizing the recoveries of five common microplastics (polyethylene, polystyrene, polyethylene terephthalate, polypropylene and polyamide). A robust setpoint was calculated, 2.5% potassium hydroxide at 60 °C for 3 h with 5% hydrogen peroxide and 2.7% of methanol, permitting the quantitative digestion of mussel tissues and recovery of microplastics. These experimental conditions were successfully used to digest whole mussels bought from a local market, which possess high levels of microplastic contamination (41 items/g dry weight). The results highlight the importance of optimizing protocols to develop robust, easy to use and cheap quantitative approaches for analysing microplastic accumulation in edible organisms.

Improved Raman spectroscopy-based approach to assess microplastics in seafood

Microplastics represent an emerging environmental issue and have been found almost everywhere including seafood, raising a great concern about the ecological and human health risks they pose. This study addressed the common technical challenges in the assessment of microplastics in seafood by developing an improved protocol based on Raman spectroscopy and using the green-lipped mussel Perna viridis and the Japanese jack mackerel Trachurus japonicus as the test models. Our findings identified a type of stainless-steel filter membranes with minimal Raman interference, and a combination of chemicals that achieved 99-100% digestion efficiency for both organic and inorganic biomass. This combined chemical treatment reached 90-100% recovery rates for seven types of microplastics, on which the surface modification was considered negligible and did not affect the accuracy of polymer identification based on Raman spectra, which showed 94-99% similarity to corresponding untreated microplastics. The developed extraction method for microplastics was further combined with an automated Raman mapping approach, from which our results confirmed the presence of microplastics in P. viridis and T. japonicus collected from Hong Kong waters. Identified microplastics included polypropylene, polyethylene, polystyrene and poly(ethylene terephthalate), mainly in the form of fragments and fibres. Our protocol is applicable to other biological samples, and provides an improved alternative to streamline the workflow of microplastic analysis for routine monitoring purposes.

Are microplastics destabilizing the global network of terrestrial and aquatic ecosystem services?

Plastic has created a new man-made ecosystem called plastisphere. The plastic pieces including microplastics (MPs) and nanoplastics (NPs) have emerged as a global concern due to their omnipresence in ecosystems and their ability to interact with the biological systems. Nevertheless, the long-term impacts of MPs on biotic and abiotic resources are not completely understood, and existing evidence suggests that MPs are hazardous to various keystones species of the global biomes. MP-contaminated ecosystems show reduced floral and faunal biomass, productivity, nitrogen cycling, oxygen-generation and carbon sequestration, suggesting that MPs have already started affecting ecological biomes. However, not much is known about the influence of MPs towards the ecosystem services (ESs) cascade and its correlation with the biodiversity loss. MPs are perceived as a menace to the global ecosystems, but their possible impacts on the provisional, regulatory, and socio-economic ESs have not been extensively studied. This review investigates not only the potentiality of MPs to perturb the functioning of terrestrial and aquatic biomes, but also the associated social, ecological and economic repercussions. The possible long-term fluxes in the ES network of terrestrial and aquatic niches are also discussed.