Uptake and Transfer of Polyamide Microplastics in a Freshwater Mesocosm Study

Microplastic infiltration into mobile sediments

This study investigates the dynamics of microplastic infiltration into non-stationary sandy sediments, a pressing environmental concern due to the rising prevalence of microplastics in aquatic ecosystems. An annular flume was used to simulate riverine bedform motion, examining the suspension and infiltration of denser-than-water microplastic particles, including polyvinyl chloride (PVC), polyamide (PA), and polylactide (PLA). The experiments focused on various particle sizes (ranging from 0.2 to 5 mm in diameter) and bedform migration speeds, known as celerities. The findings indicate that particle size is a significant factor influencing the depth of infiltration and distribution within sediment layers, whereas the impact of bedform celerities and particle densities appears less significant. This research provides novel insights into the behavior of microplastics in dynamic sedimentary environments, highlighting the intricate interaction between microplastic characteristics and sedimentary processes. The results contribute to an enhanced understanding of microplastic distribution and accumulation in riverine systems, offering crucial data for developing predictive models and formulating potential remediation strategies for microplastic pollution.

Life in plastic, it's not fantastic: Sublethal effects of polyethylene microplastics ingestion throughout amphibian metamorphosis

Microplastics (MP) are an abundant, long-lasting, and widespread type of environmental pollution that is of increasing concern as it might pose a serious threat to ecosystems and species. However, these threats are still largely unknown for amphibians. Here, we used the African clawed frog (Xenopus laevis) as a model species to investigate whether polyethylene MP ingestion affects amphibian growth and development and leads to metabolic changes across two consecutive life stages (larvae and juveniles). Furthermore, we examined whether MP effects were more pronounced at higher rearing temperatures. Larval growth, development, and body condition were recorded, and standard metabolic rate (SMR) and levels of stress hormone (corticosterone, CORT) were measured. We determined variation in size, morphology, and hepatosomatic index in juveniles to identify any potential consequences of MP ingestion across metamorphosis. In both life stages, MP accumulation in the body was assessed. MP ingestion was found to result in sublethal effects on larval growth, development, and metabolism, to lead to allometric carry-over effects on juvenile morphology, and to accumulate in the specimens at both life stages. In larvae, SMR and developmental rate increased in response to MP ingestion; there additionally was a significant interaction of MP ingestion and temperature on development. CORT levels were higher in larvae that ingested MP, except at higher temperature. In juveniles, body was wider, and extremities were longer in animals exposed to MP during the larval stage; a high rearing temperature in combination with MP ingestion counteracted this effect. Our results provide first insights into the effects of MP on amphibians throughout metamorphosis and demonstrate that juvenile amphibians may act as a pathway for MP from freshwater to terrestrial environments. To allow for generalizations across amphibian species, future experiments need to consider the field prevalence and abundance of different MP in amphibians at various life stages.

Subtle ecosystem effects of microplastic exposure in marine mesocosms including fish

For two months, communities in 5.8 m³ outdoor marine mesocosms were exposed to 700 μm sphere-shaped polystyrene (PS) beads in dosages between 0.08 and 80 g/m². Barnacle (Semibalanus balanoides) densities were reduced at dosages of 0.8 g/m² onwards without following a standard dose response curve. Lugworms and fish (Solea solea) ingested PS-beads without accumulating them. Lugworms (Arenicola marina) ingested the beads nonselective with the sediment without negative effects. The fish seemed to ingest the plastics only occasionally and at the final sampling day even in the highest dosed mesocosms (>30 beads/cm²) only 20% contained plastic. The condition index of the fish was slightly reduced in mesocosms with dosages of 0.8 g/m² onwards. No difference in condition was found between fish with and without ingested plastic across mesocosms, illustrating the difficulty to relate plastic ingestion with condition from field data. The fish also ingested mollusks with shells exceeding the size of the PS-beads. Bivalves rejected the PS-beads as pseudofeces, without obvious impact on their condition. Mussel's (Mytilus edulis) pseudofeces present an effective matrix to monitor microplastic presence in the water column. Species richness and diversity of the pelagic and benthic community were not affected although, a trend was found that the lower microplastic dosages had a positive effect on the total abundance of benthic invertebrates. In general, the observed effects at even the highest exposure concentrations were that subtle that they will be obscured by natural variation in the field. This underlines the importance of experiments under semi-field conditions for meaningful assessment of the ecological impact of microplastics. This study was performed with the real life, non-toxic, sphere-shaped polystyrene beads as were lost during an actual spill near the Dutch Wadden sea in January 2019. We recommend future mesocosm studies with other types of microplastics, including microfibers, weathered microplastics from sea, and smaller sized particles down to nanoplastics.