Understanding hazards of nanoplastics using Daphnia magna

This thesis presents the results of studies focused on effects caused by nano-sized particles using freshwater filter feeder Daphnia magna. I showed that both positively and negatively surface charged PS NPs induced significant mortality in D. magna after a life-time (103 days) of exposure at low concentrations. Previously, it was shown that negatively surface charged PS NPs are acutely not toxic toward D. magna.Secondly, I analyzed metabolic responses in D. magna after 37 days of exposure to low concentrations of PS NPs. The observed results revealed that levels of free amino acids were affected at PS NPs concentrations as low as 3.2 μg/L, which is lower than various NPs concentrations quantified in nature. Nanomaterials, including PS NPs, adsorb biomolecules on their surfaces and form corona. Therefore, I identified proteins that bind to differently surface charged PS NPs. The results showed that the profiles of bound proteins are different depending on the particle size and charge, which can partly explain differences in acute toxicity.PLA is recognized as an alternative to synthetic plastics, therefore recently has received a lot of attention. I evaluated the effects of PLA breakdown nanoplastics and PLA NPs on D. magna after acute exposure. The observed results showed that neither PLA NPs nor PLA nanoplastics induced adverse effects on D. magna. Contrarily, PLA plastic cup nanoplastics significantly extended the survival of D. magna compared to a control group

Metabolomics-based analysis in Daphnia magna after exposure to low environmental concentrations of polystyrene nanoparticles

Larger plastic pieces break down into micro- and eventually nano-sized plastics. This makes nanoplastics ubiquitous in the environment, giving rise to great concern for its effect on biota. Many studies use polystyrene nanoparticles (PS-NPs) as a model for nanoplastics, showing a negative impact on various organisms, but the molecular effects are yet not fully explored. Here we applied 1H nuclear magnetic resonance (NMR) metabolomics to characterize the metabolic changes in Daphnia magna during long-term (37 days) exposure to low concentrations of positively and negatively charged (aminated and carboxylated) PS-NPs. We show that exposure to PS-NPs at concentrations down to 3.2 μg L−1 affected amino acid metabolism and the bacterial metabolite isopropanol in D. magna. These effects were largely independent of particle concentration and surface charge. The results highlight the importance of (1) performing chronic exposures under low concentrations and (2) further investigation of particles with different surface charges

Integrating multiple dimensions of ecological stability into a vulnerability framework

Ecological stability encompasses multiple dimensions of functional and compositional responses to environmental change. Though no single stability dimension used in isolation can fully reflect the overall response to environmental change, a common vulnerability assessment that integrates simultaneously across multiple stability components is highly desirable for ecological risk assessment. We develop both functional and compositional counterparts of a novel, integrative metric of overall ecological vulnerability (OEV). We test the framework with data from a modularized experiment replicated in five lakes over two seasons, examining functional and compositional responses to both pulse and press disturbances across three trophic groups. OEV is measured as the area under the curve integrated over the entire observation period, with the curve delimiting the difference between the disturbance treatment and undisturbed parallel controls, expressed either as the log response ratio of biomass (functional OEV) or community dissimilarity index (compositional OEV). Both, functional and compositional OEV correlated negatively with functional and compositional 'resistance', 'temporal stability' and 'final/extent of recovery' following both pulse and press disturbances, though less so with 'resilience' following a pulse disturbance. We also found a positive correlation between functional and compositional OEV, which reveals the potential to also evaluate the intricate linkage between biodiversity and functional change. Our findings demonstrate that OEV comprises a robust framework to: (a) capture simultaneously multiple functional and compositional stability components, and (b) quantify the functional consequences of biodiversity change. Our results provide the basis for an overarching framework for quantifying the overall vulnerability of ecosystems to environmental change, opening new possibilities for ecological risk assessment and management. Synthesis. Ecological stability comprises multiple dimensions that together encapsulate how ecosystems respond to environmental change. Considering these multiple aspects of stability simultaneously often poses a problem in environmental assessments, which frequently require overarching indicators of risk or vulnerability. While an analysis of multiple dimensions allows for deeper exploration of mechanisms, here we develop and test a new univariate indicator that integrates stability aspects under a broad range of disturbance regimes. Using a modularized experiment in Swedish lakes, we show that this integrative measure captures multiple stability dimensions reflecting compositional and functional vulnerability and their relationships between them

Prolonged survival time of Daphnia magna exposed to polylactic acid breakdown nanoplastics

Polylactic acid nanoparticles (PLA NPs) according to food and drug administration are biodegradable and biocompatible polymers that have received a lot of attention due to their natural degradation mechanism. Although there is already available information concerning the effects of PLA microplastic to aquatic organisms, the knowledge about PLA NPs is still vague. In the present study, we analyzed the chemical composition of engineered PLA NPs, daily used PLA items and their breakdown products. We show that PLA breakdown products are oxidized and may contain aldehydes and/or ketones. The breakdown produces nanosized particles, nanoplastics, and possibly other small molecules as lactide or cyclic oligomers. Further, we show that all PLA breakdown nanoplastics extended the survival rate in Daphnia magna in an acute toxicity assay, however, only PLA plastic cup breakdown nanoplastics showed a significant difference compared to a control group

Environmental impact of nanoplastics from fragmentized consumer plastics : Final project reportMikael

Misplaced plastics is an ongoing environmental problem. The breakdown of plasticsinto smaller pieces, microplastics, likely cause additional environmental burdensas they affect animals and plants at the beginning of the food chain. This may beeven more true for the smallest of microplastics: the nanoplastics as they will behavedifferentlyin nature and interact in new ways with organisms and potentially be takenup by the organisms and affect internal organs. The small size of nanoplasticsandtheir chemical resemblance with the surrounding environment makes them difficultto find, isolate and study. Most of what is known about nanoplastics behaviourinnature and their effect on nature derives from studies using commercially availablepolystyrene nanoparticles. These are probably different in many ways, such as structure,surface chemistry, and size distribution, compared to nanoplastics brokendownin nature from plastic debris. Despite this, we have used polystyrene nanoparticlestostudy knowledge gaps. The toxicity to zooplankton Daphnia magna (D. magna) of smallpositively charged amine-modified polystyrene nanoparticles is not affected byprotein-induced aggregation. All tested polystyrene nanoparticles were toxic toD. magna regardless of their toxicity in acute tests. Proteins bound to polystyrenenanoparticles after filtrationby D. magna were different on acutely and non-acutelytoxic particles which may imply different mechanisms behind the toxicity. In orderto study the effect of nanoplastics that resemble what can be expected in nature wehave mechanically broken down 8 different plastics and rubbers from 14 differentconsumer products and isolated the nanoplastics. Careful characterization shows thatthe nanoplastics are irregular in shape, have a slightly negative surface charge, andoften have a strongly oxidized surface compared to the starting material. The nanosizedfractions are not toxic to D. magna in the used concentrations. In contrary, forat least two plastics High Density Polyethylene (HDPE) and Polylactic acid (PLA) thenanoplastics increase the lifetime of the D. magna probably because the nanoplasticscan be utilized by bacteria which in turn serve as additional food for the zooplankton.However, leached additives and/or smaller polymers from HDPE are toxic to D. magna.We have also seen that UV irradiation further degrade polystyrenenanoparticles.The bacterial growth and the UV breakdown may imply that the nanoplastics breakdown faster than believed in nature and that they with time may disappear

Environmental impact of nanoplastics from fragmentized consumer plastics : Final project reportMikael

Misplaced plastics is an ongoing environmental problem. The breakdown of plasticsinto smaller pieces, microplastics, likely cause additional environmental burdensas they affect animals and plants at the beginning of the food chain. This may beeven more true for the smallest of microplastics: the nanoplastics as they will behavedifferentlyin nature and interact in new ways with organisms and potentially be takenup by the organisms and affect internal organs. The small size of nanoplasticsandtheir chemical resemblance with the surrounding environment makes them difficultto find, isolate and study. Most of what is known about nanoplastics behaviourinnature and their effect on nature derives from studies using commercially availablepolystyrene nanoparticles. These are probably different in many ways, such as structure,surface chemistry, and size distribution, compared to nanoplastics brokendownin nature from plastic debris. Despite this, we have used polystyrene nanoparticlestostudy knowledge gaps. The toxicity to zooplankton Daphnia magna (D. magna) of smallpositively charged amine-modified polystyrene nanoparticles is not affected byprotein-induced aggregation. All tested polystyrene nanoparticles were toxic toD. magna regardless of their toxicity in acute tests. Proteins bound to polystyrenenanoparticles after filtrationby D. magna were different on acutely and non-acutelytoxic particles which may imply different mechanisms behind the toxicity. In orderto study the effect of nanoplastics that resemble what can be expected in nature wehave mechanically broken down 8 different plastics and rubbers from 14 differentconsumer products and isolated the nanoplastics. Careful characterization shows thatthe nanoplastics are irregular in shape, have a slightly negative surface charge, andoften have a strongly oxidized surface compared to the starting material. The nanosizedfractions are not toxic to D. magna in the used concentrations. In contrary, forat least two plastics High Density Polyethylene (HDPE) and Polylactic acid (PLA) thenanoplastics increase the lifetime of the D. magna probably because the nanoplasticscan be utilized by bacteria which in turn serve as additional food for the zooplankton.However, leached additives and/or smaller polymers from HDPE are toxic to D. magna.We have also seen that UV irradiation further degrade polystyrenenanoparticles.The bacterial growth and the UV breakdown may imply that the nanoplastics breakdown faster than believed in nature and that they with time may disappear

Controlled protein mediated aggregation of polystyrene nanoplastics does not reduce toxicity towards Daphnia magna

Microplastics have recently become a growing environmental issue, whereas the smaller fractions, nanoplastics, have received less attention. Due to their small size, nanoplastics may affect organisms differently and potentially more severely than larger microplastics. In natural environments nanoplastics also interact with organic material and form larger aggregates, which may, potentially, reduce their toxicity as they grow in size. We tested the change in toxicity towards Daphnia magna by controlling the size of the aggregates of positively charged 50 nm polystyrene nanoplastics, which are highly toxic as single particles. We show that although 200 to 500 nm nanoplastics are not toxic, aggregates of 50 nm nanoplastics in the same size range are at least as toxic as the free, 50 nm, nanoplastics. Hence, an increase in size through aggregation, a process likely to occur as nanoparticles enter natural ecosystems, does not reduce toxicity. In a broader context this finding provides a firm basis for societal decision making regarding the potency of nanoparticles as they enter natural ecosystems

Size fractionation of high-density polyethylene breakdown nanoplastics reveals different toxic response in Daphnia magna

Plastic litter is a growing environmental problem. Recently, microplastics and nanoplastics, produced during breakdown processes in nature, have been in focus. Although there is a growing knowledge concerning microplastic, little is still known about the effect of nanoplastics. We have showed that mechanical breakdown of high-density polyethylene (HDPE), followed by filtration through 0.8 µm filters, produces material toxic to the freshwater zooplankton Daphnia magna and affected the reproduction in life-time tests. However, further size fractionation and purification reveals that the nanoplastics fraction is non-toxic at these concentrations, whereas the fraction with smaller sizes, below ~ 3 nm, is toxic. The HDPE nanoplastics are highly oxidized and with an average diameter of 110 nm. We conclude that mechanical breakdown of HDPE may cause environmental problems, but that the fraction of leached additives and short chain HDPE are more problematic than HDPE nanoplastics

Label-free detection of polystyrene nanoparticles in Daphnia magna using Raman confocal mapping

Micro- and nanoplastic pollution has emerged as a global environmental problem. Moreover, plastic particles are of increasing concern for human health. However, the detection of so-called nanoplastics in relevant biological compartments remains a challenge. Here we show that Raman confocal spectroscopy-microscopy can be deployed for the non-invasive detection of amine-functionalized and carboxy-functionalized polystyrene (PS) nanoparticles (NPs) in Daphnia magna. The presence of PS NPs in the gastrointestinal (GI) tract of D. magna was confirmed by using transmission electron microscopy. Furthermore, we investigated the ability of NH2-PS NPs and COOH-PS NPs to disrupt the epithelial barrier of the GI tract using the human colon adenocarcinoma cell line HT-29. To this end, the cells were differentiated for 21 days and then exposed to PS NPs followed by cytotoxicity assessment and transepithelial electrical resistance measurements. A minor disruption of barrier integrity was noted for COOH-PS NPs, but not for the NH2-PS NPs, while no overt cytotoxicity was observed for both NPs. This study provides evidence of the feasibility of applying label-free approaches, i.e., confocal Raman mapping, to study PS NPs in a biological system

Review of ecotoxicological studies of widely used polystyrene nanoparticles

With polystyrene nanoparticles being widely used in various applications, there is a great need for deeper knowledge on the safety, fate and biological effects of these particles on both individual living organisms and the whole ecosystems. Due to this, there is a growing interest in performing ecotoxicological studies using model plastic nanoparticles, and consequently it generates an increasing number of published papers describing the negative impact on wildlife caused by such nanoparticles. Polystyrene is the most studied nanosized plastic, therefore this review focuses on research conducted with manufactured polystyrene nanoparticles. The aim of the present article is to provide a critical methodological outline of the existing ecotoxicological studies on the effects of polystyrene nanoparticles on aquatic organisms. Going through the published articles, we noted that particle characterization especially in the test medium, can be improved. The analysis also highlights the importance of purifying the polystyrene nanoparticles before studying its toxicity. Furthermore, the size characterization of such nanoparticles is underemphasized, and in future studies, authors should consider including more techniques to achieve this goal. Finally, short-term or direct exposure scenarios do not add the most environmentally relevant knowledge in terms of the toxicity caused by polystyrene nanoparticles