Bioaccumulation of pollutants in the green-lipped mussel Perna viridis: Assessing pollution abatement in Victoria Harbour and its adjacent aquaculture area, Hong Kong, and the minimal human health risks from mussel consumption.

The green-lipped mussel Perna viridis was utilised for pollution biomonitoring in Victoria Harbour and its adjacent aquaculture area in Hong Kong. P. viridis was collected from a reference site and redeployed at five study sites for five weeks during the dry and wet seasons of 2019. Our study found various polycyclic aromatic hydrocarbons (PAHs) and heavy metals in the mussel tissue, while polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were not detected. P. viridis at the reference site generally displayed lower levels of pollutants. Comparing with previous research in the 1980s and 2000s, we observed substantial reduction in the tissue levels of PAHs, PCBs, OCPs and heavy metals in P. viridis. The human health risks associated with consuming these mussels were determined to be insignificant. Our findings imply that the Harbour Area Treatment Scheme has been effective in improving the water quality in Victoria Harbour and its adjacent aquaculture area.

Adverse impacts of high-density microplastics on juvenile growth and behaviour of the endangered tri-spine horseshoe crab Tachypleus tridentatus.

The impacts of high-density microplastics, namely polyamine 6,6 (nylon), polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET), on growth and behaviour of the endangered tri-spine horseshoe crab Tachypleus tridentatus were investigated for 100 days. Negative changes in wet weight and prosomal width of the juveniles were observed in all treatments of microplastics, but significant difference was only detected in prosomal width between control and PMMA. T. tridentatus became significantly less active upon exposure to nylon and PET. The extent of burrowing by T. tridentatus did not significantly differ among the treatments but was overall significantly reduced towards day 100. T. tridentatus exposed to PET significantly showed the lowest survival probability (30 %), compared to the other treatments (70-90 %). In conclusion, high-density microplastics compromised growth and behaviour of juvenile horseshoe crabs. Among the polymers that were tested, PET was considered more harmful and associated with higher mortality.

A short review on the recent method development for extraction and identification of microplastics in mussels and fish, two major groups of seafood.

The prevalence of microplastics in the marine environment poses potential health risks to humans through seafood consumption. Relevant data are available but the diverse analytical approaches adopted to characterise microplastics have hampered data comparison among studies. Here, the techniques for extraction and identification of microplastics are summarised among studies of marine mussels and fish, two major groups of seafood. Among the reviewed papers published in 2018-2021, the most common practice to extract microplastics was through tissue digestion in alkaline chemicals (46 % for mussels, 56 % for fish) and oxidative chemicals (28 % for mussels, 12 % for fish). High-density solutions such as sodium chloride could be used to isolate microplastics from other undigested residues by flotation. Polymer analysis of microplastics was mainly carried out with Fourier-transform infrared (FTIR) spectroscopy (58 % for both mussels and fish) and Raman spectroscopy (14 % for mussels, 8 % for fish). Among these methods, we recommend alkaline digestion for microplastic extraction, and the automated mapping approach of FTIR or Raman spectroscopy for microplastic identification. Overall, this study highlights the need for a standard protocol for characterising microplastics in seafood samples.

Determination of microplastics in the edible green-lipped mussel Perna viridis using an automated mapping technique of Raman microspectroscopy.

Microplastics are prevalent in marine environments and seafood and thus can easily end up in human diets. This has raised serious concerns worldwide, particularly in Hong Kong where the seafood consumption per capita can be three times higher than the global average. This study focused on the green-lipped mussel Perna viridis, a popular seafood species which is subject to a high risk of contamination by microplastics due to its filter-feeding nature. P. viridis was collected from five mariculture sites in Hong Kong and assessed for its body load of microplastics using an automated Raman mapping approach. Microplastics were found in all sites, with an average of 1.60-14.7 particles per mussel per site, or 0.21-1.83 particles per g wet weight. Polypropylene, polyethylene, polystyrene and polyethylene terephthalate were detected among the microplastics, mainly as fragments or fibres in the size range of 40-1000 µm. It was estimated that through consumption of P. viridis, the population in Hong Kong could ingest up to 10,380 pieces of microplastics per person per year. These estimated rates were high compared to the values reported worldwide, suggesting the potential human health risk of microplastics in Hong Kong and adjacent areas.

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.

Microplastics from effluents of sewage treatment works and stormwater discharging into the Victoria Harbor, Hong Kong.

Sewage treatment works and stormwater outfalls were identified as sources of microplastics in the Victoria Harbor, Hong Kong. Local treated sewage and stormwater effluents contained up to 10,816 pieces per m3 of microplastics, mainly polyethylene (PE) and polypropylene (PP), being discharged at an average rate of 3.5 mg per capita daily. Bioaccumulation of microplastics in marine fish collected from the vicinity of the effluent discharge outfalls was also studied. The temporal variations of microplastics in terms of abundance, shape and polymer type in fish were found consistent with those in the effluents and surface water. The abundance of microplastics was significantly higher in March 2017 (dry season). Microplastics in fish were predominantly in fiber form and identified as PE and PP. The observed temporal variations suggest uptake of microplastics by fish from the treated sewage and stormwater effluents.