Assessment of microplastic bioconcentration, bioaccumulation and biomagnification in a simple coral reef food web.

Plastics, and more specifically, microplastics (MPs, <5 mm) are considered a marine contaminant of emerging concern. To accurately assess the ecological risk of MPs, it is critical to first understand the relationship between MP contamination in organisms with that in their surrounding environment. The goal of this study was to examine the ecological risk of MPs in coral reef ecosystems by assessing the MP contamination found within a simple food web against contamination in the surrounding environment. Taxa representing three trophic levels (zooplankton, benthic crustaceans, and reef fish), as well as the distinct environmental matrices which they inhabit (i.e., mid-column water and sediment) were collected from two mid-shelf reefs in the central Great Barrier Reef, Australia. Microplastics were isolated using validated clarification techniques, visually characterised (i.e., shape, colour, size) by microscopy, chemically confirmed by Fourier transform infrared spectroscopy and recorded in all three trophic levels and all abiotic samples. MPs were found to bioconcentrate, with similar concentrations, polymer types, sizes, shapes, and colours at each trophic level compared to their surrounding environment. However, MP contamination varied across the three trophic levels, with no evidence of bioaccumulation. Further, MP concentrations did not increase up the food web, discounting MP biomagnification. Regardless, given the heterogeneity of MPs found in the marine environment, and the complexity of marine food webs, trophic transfer represents a prominent pathway of exposure from lower to higher trophic levels.

Temporal patterns of plastic contamination in surface waters at the SS Yongala shipwreck, Great Barrier Reef, Australia.

Plastic pollution is ubiquitous within the marine environment, including surface waters, water column and benthic sediments. Marine plastic contamination is expected to increase if future projections of increased plastic production eventuate. Conversely, national and international efforts are aiming to reduce marine plastic contamination. In this context, scientists, managers and the general public are increasingly interested in understanding the status and temporal trends of plastic contamination in the marine environment. Presented here is the first temporal assessment of plastic contamination in surface waters of the Great Barrier Reef (GBR), Australia. Specifically, duplicate surface seawater samples (n = 66) were collected at the SS Yongala shipwreck (Central GBR) monthly from September 2016 to September 2019 and analysed for plastic presence and abundance. The processing workflow involved density separation, followed by filtration, visual identification and sizing of putative plastics using stereomicroscopy, and chemical characterisation using Fourier transform infrared spectroscopy. A total of 533 plastic items were identified across all tows, consisting of macro-, meso- and microplastic fragments and fibres, with polypropylene and polyethylene being the most common polymers. Plastic contamination was detected in every replicate tow, bar one. Plastic concentrations fluctuated and spiked every three months, although contamination did not significantly alter across the three-year period. Wind speed, salinity and river discharge volume, but not surface current speed nor sea surface temperature, had a significant influence on the levels of plastic contamination. This study reveals, for the first time, the chronic presence of plastic debris in the surface waters of the GBR highlighting the need for long-term and on-going monitoring of the marine environment for plastic contamination.

Efficacy of Microplastic Separation Techniques on Seawater Samples: Testing Accuracy Using High-Density Polyethylene.

AbstractMicroplastic contamination of the marine environment has been reported globally. Its pervasiveness has highlighted the importance of accurate quantification to enable comparability within and between different environmental matrices. The potential efficacy of different methods to separate microplastics from their environmental sample matrix, however, is rarely validated. In this study, we examine the effects of four commonly used separation methods for seawater samples, namely, visual separation, density flotation, acidic digestion, and enzymatic digestion, using high-density polyethylene as our model microplastic. For each separation method, clarification efficiencies of the sample matrix, spiked recovery of high-density polyethylene microparticles, and potential changes in the chemical and physical characteristics of high-density polyethylene were assessed. High, albeit variable, recovery rates (>83%) of high-density polyethylene microparticles were achieved across all methods. Concentrated nitric acid was most effective at eliminating biological material from seawater samples. No apparent physical (i.e., length or color) or chemical changes due to separation treatments were observed in recovered high-density polyethylene microparticles, with the one exception that enzymatic digestion obscured polymer identification of high-density polyethylene. Our findings highlight the need to determine and report on the accuracy of separation methods for different polymer types and specific environmental sample matrices to ensure accurate quantification of marine microplastic contamination.

Relevance and reliability of evidence for microplastic contamination in seafood: A critical review using Australian consumption patterns as a case study.

Seafood contamination with, and human consumption of, microplastics (MPs) have recently been highlighted as an emerging concern for global food security. While there is evidence that commercial marine species are contaminated with MPs, it is still unknown if seafood can act as a vector for MP transfer to human consumers. Microplastics have been reported in the digestive tract, gills and in select internal organs of marine animals. However, many of these tissues are not typically eaten by human consumers but discarded. In this critical review, we examined the peer-reviewed literature for evidence of MP contamination in seafood, and the potential transfer to human consumers. Based on known seafood consumption patterns in a typical Australian diet, we assessed the relevance and reliability of the current body of literature to examine the prospect and risk of MP transfer. The relevance of data was considered based on the organism studied, origin of the samples, and the tissues analysed, while reliability was assessed based on procedural methodologies used to derive the data. A review of 132 studies found limited evidence of MP contamination in edible tissues from fresh fish or crustaceans. MP presence was confirmed in packaged fish, as well as in fresh and packaged bivalve molluscs. The limited number of studies satisfying the relevance and reliability criteria (n = 24) precluded a quantitative assessment of the potential risk associated with MP transfer. While consumption of packaged fish and bivalve molluscs may result in the consumption of MPs by humans, it is currently unknown whether this presents a health risk.

Bioaccumulation and biomagnification of microplastics in marine organisms: A review and meta-analysis of current data.

Microplastic (MP) contamination has been well documented across a range of habitats and for a large number of organisms in the marine environment. Consequently, bioaccumulation, and in particular biomagnification of MPs and associated chemical additives, are often inferred to occur in marine food webs. Presented here are the results of a systematic literature review to examine whether current, published findings support the premise that MPs and associated chemical additives bioaccumulate and biomagnify across a general marine food web. First, field and laboratory-derived contamination data on marine species were standardised by sample size from a total of 116 publications. Second, following assignment of each species to one of five main trophic levels, the average uptake of MPs and of associated chemical additives was estimated across all species within each level. These uptake data within and across the five trophic levels were then critically examined for any evidence of bioaccumulation and biomagnification. Findings corroborate previous studies that MP bioaccumulation occurs within each trophic level, while current evidence around bioaccumulation of associated chemical additives is much more ambiguous. In contrast, MP biomagnification across a general marine food web is not supported by current field observations, while results from the few laboratory studies supporting trophic transfer are hampered by using unrealistic exposure conditions. Further, a lack of both field and laboratory data precludes an examination of potential trophic transfer and biomagnification of chemical additives associated with MPs. Combined, these findings indicate that, although bioaccumulation of MPs occurs within trophic levels, no clear sign of MP biomagnification in situ was observed at the higher trophic levels. Recommendations for future studies to focus on investigating ingestion, retention and depuration rates for MPs and chemical additives under environmentally realistic conditions, and on examining the potential of multi-level trophic transfer for MPs and chemical additives have been made.

Boat noise in an estuarine soundscape - A potential risk on the acoustic communication and reproduction of soniferous fish in the May River, South Carolina.

The impact of boat related noise on marine life is a subject of concern, particularly for fish species that utilize acoustic communication for spawning purposes. The goal of this study was to quantify and examine the risk of boat noise on fish acoustic communication by performing acoustic monitoring of the May River, South Carolina (USA) from February to November 2013 using DSG-Ocean recorders. The number of boats detected increased from the source to the mouth with the highest detections near the Intracoastal Waterway (ICW). Boat noise frequency ranges overlapped with courtship sounds of silver perch (Bairdiella chrysoura), black drum (Pogonias cromis), oyster toadfish (Opsanus tau), spotted seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellatus). In the May River estuary, red drum may experience the greatest risk of auditory masking because of late afternoon choruses (21% time overlap with boat noise) and only one spawning location near the noisy ICW.

Recovering microplastics from marine samples: A review of current practices.

An important component of microplastic research is development of reproducible methods for microplastic recovery and characterization. Presented is a review of the literature comparing microplastic separation and identification methodologies from seawater, sediment and marine organisms. The efficiency of methods was examined, including processing time, recovery rates, and potential destruction of microplastics. Visual examination and acid digestion were the most common separation methods for seawater samples and organisms, while density flotation was the primary method for sediment. Few studies reported recovery rates, or investigated the physical or chemical impact on plastics. This knowledge gap may lead to misidentification of plastic or unreliable pollution estimates. Further investigation of the impact chemical treatments have on plastic is warranted. Factors, i.e. biomass loading, recovery rates, and chemical compatibility, must be considered to allow for appropriate methodology. Standardizing this will contribute to efficient sample processing, and allow for direct comparison of microplastic contamination across environments.