Microplastics in Australian crustaceans: occurrence, trophic transfer and a vector for metals

On a global scale, plastic pollution has become a major environmental concern due to its widespread occurrence in the marine ecosystem. The first reports of plastic debris in the oceans date back to the early 1970s and received minimal attention from the scientific community. In the following decades, with increasing data on the ecological consequences of such debris, plastics became a topical issue of sustained research interest. Growth in the production of plastics, coupled with illegal disposal and poor waste management has resulted in the transport and existence of plastic in the marine environment. From there, plastics are fragmented into microplastics, where they may be consumed by marine species, including crustaceans, and other seafood species that are consumed by humans. In my first research chapter (Chapter 2), I investigated the extent and occurrence of microplastics in decapod crustaceans, prawns and crabs, in Australia. Specifically, I determined spatial and species differences of microplastic ingestion, suggested possible sources of contamination, and compared my results globally using a systematic review extracting publications that used a similar methodology. Approximately half (48%) of the crustaceans from Australian waters had microplastics in their muscle tissues and digestive tracts, with lower abundance compared to global studies. This section of my thesis provides an important baseline for my subsequent research chapters. As the Australian population continues to grow, the demand for seafood continues to increase. Aquaculture practices were developed to provide a solution to the shortfall in wild-caught seafood products, and support consumer demand. The lack of information comparing the presence of microplastics in farmed and wild prawns globally prompted me to investigate and compare microplastic contamination from these two sources in Australia, and internationally, in my second data chapter (Chapter 3). Overall, microplastics were detected in 15.8% of all prawn species examined, with no significant difference between wild and farmed prawns. The ingestion of microplastics from water and sediment in lower trophic organisms could transfer and biomagnify in higher trophic organisms of marine food webs, causing added concern for human beings consuming seafood. Because there is little information from Australia on the trophic transfer and biomagnification of microplastics, in Chapter 4, I investigated microplastics in environmental matrices, water, sediment and biota, collected from a coastal region of South Australia. There was variation in the frequency of occurrence of microplastics in water (35%), sediment (45%) and marine biota (39%). Overall, there was no significant difference in microplastic contamination in biota species, suggesting a similar level of exposure, with no biomagnification identified. I recommend further research on sites with different contamination loads, broader food webs, and investigating the potential effects of microplastics at population and ecosystem levels. Lastly, the ability of microplastics to sorb metals when suspended in the marine environment is understudied globally and could pose synergistic hazardous effects on marine biota when ingested. In Chapter 5, I compared how two polymer types, low-density polyethylene and polypropylene, could sorb and accumulate 12 metals, (Iron, Fe, Aluminium, Al, Manganese, Mn, Zinc, Zn, Copper, Cu, Chromium, Cr, Cobalt, Co, Tin, Sn, Lead, Pb, Arsenic, As, Silver, Ag and Cadmium, Cd) within a 12 month period. These two polymer types were chosen and examined because they are commonly ingested and found in marine biota. Accumulation of metals on plastic pellets differed significantly by polymer type and also by temporal scale with higher occurrence in LDPE than PP with some metals showing increasing (Fe, Al, Mn, Zn, Cu, Pb, As and Cd) or decreasing (Cr, Co, Ag and Sn) trends over time. Future research efforts should be conducted with a larger suite of polymers, and investigate how location (land use) and abiotic factors (environmental variables) may impact the type of heavy metals that sorb onto plastics. Ultimately, this research provides tangible and reliable datasets that create local and global awareness of microplastic pollution that can support the development of regulatory measures.Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 202