6 research outputs found
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The ecotoxicological impact of microplastics on freshwater invertebrates
Microplastics (MPs) are small plastic particles released directly from the use of cosmetic products, or indirectly through the degradation of large plastic items under environmental conditions. Microplastics have been found in marine and freshwater environments around the world, raising concerns about the long term impact on animals and ecosystems in addition to recent discoveries of MPs entering the human food chain. The impacts of MP pollution on ecosystems and their functioning remain poorly quantified and there is a paucity of information on the impacts of MPs in freshwater ecosystems, despite the broad range of pathways through which MPs can proliferate and the extensive range of species which actively ingest MPs in these systems. This thesis aims to obtain key data on the uptake, fate and ecotoxicological impact of MPs on freshwater invertebrates. Initially, MP uptake and chronic toxicity tests were gathered by exposing the crustacean water flea Daphnia magna Straus 1820 (Cladocera) to polystyrene MPs of sizes 2 and 15 µm. The endpoints were mortality, growth and number of offspring. The results indicate that D. magna selectively uptake food particles over MPs, and that the toxicity was mainly linked to the availability of food. Moreover, a significant size dependent increase of toxicity was observed, with exposures to 2 µm sized particles being more toxic than 15 µm sized particles. Uptake, fate and toxicity of MPs were also studied in a holometabolous insect by exposing the common house mosquito Cu/ex pipiens Linnaeus 1758 (Diptera) to polystyrene MPs of sizes 2 and 15 µm. Results showed both particle sizes were readily taken up by larval mosquitoes then transferred to the adults via pupae. There were more transfer of MPs size 2 µm compare it to 15 µm without any effecting on mortality and weight of adults. This work is the first to demonstrate that MPs can be transferred ontogenically through organisms with complex life histories, presenting a potential pathway for dispersal of MPs into terrestrial environments. Laboratory studies were followed up with a field study exposing a small freshwater pond community to 15 µm polystyrene MPs. The results show that a high proportion of MPs accumulated in the sediment while only a small amount remained in the water column, with a significant correlation between the number of MPs in the water and the freshwater invertebrate. The presence of MPs had no real impact on the freshwater community, with season being a more important variable. Finally, the predatory ability of non-biting midge larvae, Chaoborus flavicans, towards larvae of C. pipiens mosquitoes loaded with 2 µm was quantitatively examined by linking MP trophic transfer with predation rates in a functional response framework. Results demonstrated a lack of effect of MPs on predation rates and correlation number of MPs transferred through predation
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Examining the effects of ontogenic microplastic transference on Culex mosquito mortality and adult weight
Microplastics (MPs) continue to proliferate and pollute aquatic and terrestrial environments globally. The impacts of MP pollution on ecosystems and their functioning remain poorly quantified, with most research hitherto focusing on marine ecosystems. There is a paucity of information on the impacts of MPs in freshwater ecosystems, despite the broad range of pathways through which MPs can proliferate and the extensive range of species which actively ingest MPs in these systems. Of particular interest are organisms that bridge aquatic and terrestrial habitats. The present study thus examines the uptake, ontogenic transference and effect of different concentrations (0, 50, 100 and 200 MPs mL-1) and sizes (2 and 15 µm) concentrations and sizes of polystyrene MPs between aquatic and terrestrial life stages of Culex pipiens complex mosquitoes. Both 2 and 15 µm MPs transferred from the aquatic larval to terrestrial adult stage of Culex mosquitoes, and uptake correlated tightly with initial exposure concentration. However, neither concentration nor size of MPs significantly influenced mortality rates between the aquatic larval and terrestrial adult stage. There was also no impact of MPs on the weight of emerging mosquito adults. We thus demonstrate that MPs can be transferred ontogenically through organisms with complex life histories, presenting a potential pathway for dispersal of MPs into terrestrial environments. We also show that MPs exposure does not affect mortality rates between life stages of freshwater Culex populations. This suggests that MPs do not impact nutritional uptakes, with unhampered development to adulthood facilitating subsequent dispersal of MPs aerially and between freshwater and terrestrial habitats
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Up and away: ontogenic transference as a pathway for aerial dispersal of microplastics
Microplastics (MPs) are ubiquitous pollutants found in marine, freshwater and terrestrial ecosystems. With so many MPs in aquatic systems it is inevitable that they will be ingested by aquatic organisms, and be transferred up through the food chain. However, to date, no study has considered whether MPs can be transmitted by means of ontogenic transference i.e. between life stages that utilise different habitats. Here, we determine whether fluorescent polystyrene beads could transfer between Culex mosquito life stages and, particularly, could move into the flying adult stage. We show for the first time that MPs can be transferred ontogenically from a feeding (larva) into a non-feeding (pupa) life stage and subsequently into the adult terrestrial life stage. However, transference is dependent on particle size, with smaller 2 µm MPs transferring readily into pupae and adult stages, whilst 15 µm MPs transferred at a significantly reduced rate. Microplastics appear to accumulate in the Malpighian tubule renal excretion system. The transfer of MPs to the adults represents a potential aerial pathway to contamination of new environments. Thus, any organism that feeds on terrestrial life phases of freshwater insects could be impacted by MPs found in aquatic ecosystems
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Impacts of polystyrene microplastics on Daphnia magna: a laboratory and a mesocosm study
Most research into microplastics (MPs) in freshwaters has concentrated on measurements under controlled conditions without any link to the natural environment. Here we studied the effects of a 15 μm polystyrene MP on Daphnia magna survival, growth, and reproduction in the laboratory. We also exposed fifteen 25 L freshwater mesocosms to a high concentration of the same MPs. Five were controls seeded with five species found in all ponds (mosquito, water flea, midge, spire shell and water mite), five identical but treated with 15 μm polystyrene MPs and five seeded with only mosquitoes and water fleas. The laboratory chronic toxicity test for both adults and neonate Daphnia magna revealed that effects were more related to the availability of food rather than the toxicity of MPs. In the mesocosms most of the MPs settled in the sediment after the first week of exposure. After four weeks the D. magna population decreased significantly in the MP mesocosms compared to the control mesocosms, although it subsequently recovered. There was no impact on other organisms added to the mesocosms, other than a difference in timing of lesser water boatman (Corixa punctata) colonisation, which colonised the control mesocosms in week 4 and the treated 4 weeks later. The detrivorous, sediment sifting, mayfly Leptophlebia marginata appeared in mesocosms in the fourth week of sampling and with significantly higher numbers in the MP treated mesocosm. Their activity had no significant impact on MPs in the water column, although numbers did increase above zero. The significant decline of D. magna suggests that their effect in a natural situation is unpredictable where environmental conditions and invertebrate communities may add additional stresses
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The influence of microplastics on trophic interaction strengths and oviposition preferences of dipterans
Microplastic (MP) pollution continues to proliferate in freshwater, marine and terrestrial environments, but with their biotic implications remaining poorly understood. Biotic interactions such as predation can profoundly influence ecosystem structuring, stability and functioning. However, we currently lack quantitative understandings of how trophic interaction strengths and associated behaviours are influenced by MP pollution, and how transference of MPs between trophic levels relates to consumptive traits. We also lack understanding of key life-history effects of MPs, for example, reproductive strategies such as oviposition. The present study examines the predatory ability of non-biting midge larvae, Chaoborus flavicans, towards larvae of Culex pipiens mosquitoes when the latter are exposed to MPs, using a functional response (FR) approach. Transfer of MPs occurred from larval mosquitoes to larval midges via predation. Microplastics transfer was significantly positively related to predation rates. Predation by C. flavicans followed a Type II FR, with average maximum feeding rates of 6.2 mosquito larvae per hour. These and other FR parameters (attack rates and handling times) were not significantly influenced by the presence of MPs. Further, C. pipiens adults did not avoid ovipositing in habitats with high concentrations of MPs. We thus demonstrate that MPs can move readily through freshwater food webs via biotic processes such as predation, and that uptake correlates strongly with consumption rates. Further, as MPs do not deter adult mosquitoes from ovipositing, our experiments reveal high potential for MP exposure and transference through ecosystems
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Microplastics in freshwater ecosystems with special reference to tropical systems: detection, impact, and management
Microplastics (MPs) are defined as diverse plastic fragments smaller than 5 mm in size. They are ingested by aquatic organisms at various trophic levels and stages of development, including freshwater invertebrates and fish. Microplastics are highly abundant in freshwater environments worldwide and yet we know little about their impact on biodiversity, movement through the food chain, ability to change community composition and alter predator-prey interactions. Many of these questions remain unanswered, with studies tending to focus on toxic effects in laboratory settings. Although there are studies to investigate the occurrence and abundance of MPs in freshwater environments including rivers and lakes, relatively few have looked at the impact in tropical ecosystems or with organisms found therein. This chapter will review research on MPs in freshwater systems, highlighting tropical waters where research has been undertaken. The chapter will include a review and comparison of detection and quantification methodology with some practical suggestions and recommendations for future work