Caddisfly Larvae are a Driver of Plastic Litter Breakdown and Microplastic Formation in Freshwater Environments

Plastic Litter Emits the Foraging Infochemical Dimethyl Sulfide after Submersion in Freshwater Rivers

Plastic pollution is widespread throughout aquatic environments globally, with many organisms known to interact with and ingest plastic. In marine environments, microbial biofilms that form on plastic surfaces can produce the odorous compound dimethyl sulfide (DMS), which is a known foraging cue. This has been shown to increase the ingestion of plastic by some invertebrates and therefore act as a biological factor which influences the risks of plastic to marine ecosystems. In freshwater however, the production of DMS has been largely overlooked, despite the known sensitivity of some freshwater species to this compound. To address this gap, the present study analyzed the production of DMS by biofilms which formed on low-density polyethylene and polylactic acid films after 3 and 6 weeks of submersion in either a rural or an urban United Kingdom river. Using gas chromatography-mass spectrometry, the production of DMS by these biofilms was consistently identified. The amount of DMS produced varied significantly across river locations and materials, with surfaces in the urban river generally producing a stronger signal and plastics producing up to seven times more DMS than glass control surfaces. Analysis of biofilm weight and photosynthetic pigment content indicated differences in biofilm composition across conditions and suggested that DMS production was largely driven by nonphotosynthetic taxa. For the first time this work has documented the production of DMS by plastic litter after submersion in freshwater rivers. Further work is now needed to determine if, as seen in marine systems, this production of DMS can encourage the interaction of freshwater organisms with plastic litter and therefore operate as a biological risk factor in the impacts of plastic on freshwater environments. Environ Toxicol Chem 2024;43:1485-1496. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Beneath the surface: Decoding the impact of Chironomus riparius bioturbation on microplastic dispersion in sedimentary matrix

A detailed understanding of microplastics (MPs) behaviour in freshwater ecosystems is crucial for a proper ecological assessment. This includes the identification of significant transport pathways and net accumulation zones, considering their inherent, and already proven influence on aquatic ecosystems. Bioavailability of toxic agents is significantly influenced by macroinvertebrates' behaviour, such as bioturbation and burrowing, and their prior exposure history. This study investigates the effect of bioturbation activity of Chironomus riparius Meigen, 1804 on the vertical transfer of polyethylene MPs ex-situ. The experimental setup exposes larvae to a scenario of 10× the environmentally relevant high concentration of MPs (80 g m-2). Bioturbation activity was estimated using sediment profile imaging with luminophore tracers. This study demonstrated that spherical MPs are vertically transferred in the sediment due to the bioturbation activity of C. riparius larvae and that their presence influences the intensity of the bioturbation activity over time. The present findings provide a noteworthy contribution to the understanding of the relationship between ecosystem engineers and the dispersion and accumulation of MPs within freshwater ecosystems.

Macroplastic litter colonization by stream macroinvertebrates relative to that of plant litter: A meta-analysis

Environmental pollution by anthropogenic litter is a global concern, but studies specifically addressing the interaction between macroplastics and macroinvertebrates in streams are scarce. However, several studies on plant litter decomposition in streams have also used plastic strips as a methodological approach to assess if macroinvertebrates colonize plant litter mostly as a substrate or a food resource. Looking at these studies from the plastic strips perspective may provide useful information on the interaction between macroplastics and macroinvertebrates in streams. I carried out a meta-analysis of 18 studies that have compared macroinvertebrate colonization of macroplastic litter and plant litter in streams to estimate the overall macroinvertebrate colonization of macroplastic litter relative to plant litter, and identify moderators of this difference. Macroinvertebrate colonization of macroplastic litter was overall lower (by ∼ 40%) compared with plant litter. However, differences in macroinvertebrate colonization between macroplastic litter and plant litter were observed when considering leaf litter but not wood litter, which may be a poorer substrate and food resource for macroinvertebrates. Also, differences in macroinvertebrate colonization between macroplastic litter and leaf litter were observed for shredders, collectors and predators, but not for grazers that may feed on the biofilm developed on macroplastics. Macroplastic litter supported lower macroinvertebrate density, biomass, abundance, and richness, but higher macroinvertebrate diversity than leaf litter. Higher macroinvertebrate diversity on macroplastic litter may have occurred when macroplastics represented more heterogeneous substrates (e.g., mixture of plastic types) than leaf litter (e.g., needles). Differences in macroinvertebrate abundance between macroplastic litter and leaf litter were not significantly affected by plastic type, mesh opening size, plant functional group or plant identity. By testing previously untested hypotheses, this meta-analysis guides future empirical studies. Future studies should also consider the geographical areas most affected by macroplastic pollution and the plastic types most often found in the streams.

The Microplastics Iceberg: Filling Gaps in Our Understanding

Plastic is an indispensable material in modern society; however, high production rates combined with inadequate waste management and disposal have resulted in enormous stress on ecosystems. In addition, plastics can become smaller particles known as microplastics (MPs) due to physical, chemical, and biological drivers. MP pollution has become a significant environmental problem affecting terrestrial and aquatic ecosystems worldwide. Although the topic is not entirely new, it is of great importance to the field of polymers, drawing attention to specific gaps in the existing literature, identifying future areas of research, and improving the understanding of MP pollution and its environmental impacts. Despite progress in this field, problems remain. The lack of standardized methods for MP sampling, separation, extraction, and detection makes it difficult to collect information and establish links between studies. In addition, the distribution and pathways of MPs in ecosystems remain unknown because of their heterogeneous nature and the complex matrices in which they occur. Second, toxicological tests showed that MPs can be ingested by a wide range of organisms, such as Danio rerio and Eisenia fetida, resulting in gut obstruction, physical damage, histological changes, and oxidative stress. The uptake of MP and their toxicological effects depend on their shape, size, concentration, and polymer composition. Furthermore, MPs can enter the food chain, raising concerns regarding potential contaminations for human and environmental health. This review paper sheds light on the pressing issue of MP pollution and highlights the need for interdisciplinary collaboration between scientists, policymakers, and industry leaders.