Martin Ogonowski

The Effects of Natural and Anthropogenic Microparticles on Individual Fitness in Daphnia magna.

Concerns are being raised that microplastic pollution can have detrimental effects on the feeding of aquatic invertebrates, including zooplankton. Both small plastic fragments (microplastics, MPs) produced by degradation of larger plastic waste (secondary MPs; SMPs) and microscopic plastic spheres used in cosmetic products and industry (primary MPs; PMPs) are ubiquitously present in the environment. However, despite the fact that most environmental MPs consist of weathered plastic debris with irregular shape and broad size distribution, experimental studies of organism responses to MP exposure have largely used uniformly sized spherical PMPs. Therefore, effects observed for PMPs in such experiments may not be representative for MP-effects in situ. Moreover, invertebrate filter-feeders are generally well adapted to the presence of refractory material in seston, which questions the potential of MPs at environmentally relevant concentrations to measurably affect digestion in these organisms. Here, we compared responses to MPs (PMPs and SMPs) and naturally occurring particles (kaolin clay) using the cladoceran Daphnia magna as a model organism. We manipulated food levels (0.4 and 9 μg C mL-1) and MP or kaolin contribution to the feeding suspension (<1 to 74%) and evaluated effects of MPs and kaolin on food uptake, growth, reproductive capacity of the daphnids, and maternal effects on offspring survival and feeding. Exposure to SMPs caused elevated mortality, increased inter-brood period and decreased reproduction albeit only at high MP levels in the feeding suspension (74% by particle count). No such effects were observed in either PMP or kaolin treatments. In daphnids exposed to any particle type at the low algal concentration, individual growth decreased by ~15%. By contrast, positive growth response to all particle types was observed at the high algal concentration with 17%, 54% and 40% increase for kaolin, PMP and SMP, respectively. When test particles comprised 22% in the feeding suspension, both MP types decreased food intake by 30%, while kaolin had no effect. Moreover, SMPs were found to homoaggregate in a concentration-dependent manner, which resulted in a 77% decrease of the ingested SMPs compared to PMPs. To better understand MP-processing in the gut, gut passage time (GPT) and evacuation rate of MPs were also assayed. SMPs and PMPs differed in their effects on daphnids; moreover, the particle effects were dependent on the MP: algae ratio in the suspension. When the MP contribution to the particle abundance in the medium changed from 1 to 4%, GPT for daphnids exposed to SMPs increased 2-fold. Our results suggest that MPs and, in particular, SMPs, have a greater capacity to negatively affect feeding in D. magna compared to naturally occurring mineral particles of similar size. Moreover, grazer responses observed in experiments with PMPs cannot be extrapolated to the field where SMPs dominate, because of the greater effects caused by the latter.

Too short to spawn? Implications of small body size and swimming distance on successful migration and maturation of the European eel Anguilla anguilla

Individual net fat reserves after migration and reproductive investments were calculated for migrating female silver eels Anguilla anguilla (n = 387) collected in the outlet region of the Baltic Sea during the autumn run. It is estimated that 20·4% of the A. anguilla had completely exhausted all initial fat reserves and that 45·0% of A. anguilla were within 90% of complete energy depletion after migration and reproduction. This study concludes that a combination of body size and distance (6900 km) to the spawning area in the Sargasso Sea explains the results. An increase in the costs of migration due to heavy infection with Anguillicoloides crassus was also evaluated in an additional scenario with results showing that 26·4% of the A. anguilla had completely depleted all fat reserves. It is hypothesized that a large proportion of female silver A. anguilla from the Baltic Sea catchment area will have inadequate or suboptimal reserves for successful migration and reproduction.

Abundance and composition of near surface microplastics and plastic debris in the Stockholm Archipelago, Baltic Sea

We collected plastic debris in the Stockholm Archipelago using a manta trawl, and additionally along a transect in the Baltic Sea from the island of Gotland to Stockholm in a citizen science study. The samples were concentrated by filtration and organic material was digested using hydrogen peroxide. Suspected plastic material was isolated by visual sorting and 59 of these were selected to be characterized with Fourier transform infrared spectroscopy. Polypropylene and polyethylene were the most abundant plastics identified among the samples (53% and 24% respectively). We found nearly ten times higher abundance of plastics near central Stockholm than in offshore areas (4.2×105plastics km-2 compared to 4.7×104plastics km-2). The abundance of plastic debris near Stockholm was similar to urban areas in California, USA, and the overall abundance in the Stockholm Archipelago was similar to plastic abundance reported in the northwestern Mediterranean Sea.

Microplastic-mediated transport of PCBs? A depuration study with Daphnia magna

The role of microplastic (MP) as a carrier of persistent organic pollutants (POPs) to aquatic organisms has been a topic of debate. However, theoretically, the reverse POP transport can occur at higher relative contaminant concentrations in the organism than in the microplastic. The effect of microplastic on the PCB removal in planktonic animals was evaluated using the cladoceran Daphnia magna with a high body burden of polychlorinated biphenyls (PCB 18, 40, 128 and 209) exposed to a mixture of microplastic and algae (with 77% MP by mass); daphnids exposed to only algae served as the control. As the endpoints, we used PCB body burden, growth, fecundity and elemental composition (%C and %N) of the daphnids. We found that PCB 209 was removed more efficiently in the daphnids fed with microplastic, while there was no difference for the ΣPCBs between the microplastic-exposed and control animals. Effects of the microplastic exposure on fecundity were of low biological significance, even though both the starting PCB body burden and the microplastic exposure concentrations were high and greatly exceeding environmentally relevant concentrations.

A serial dilution method for assessment of microplastic toxicity in suspension

The occurrence of microplastic (MP) in the environment is of global concern. MP risk assessment, however, is currently hampered by lacking ecotoxicological methods due to conceptual and practical problems with particle exposure. Natural particles of similar size as MP, e.g., clay and cellulose, occur abundantly in the environment. For MP risk assessment and regulation it must be established whether the addition of MP to these particles represents an additional hazard. We present a novel approach employing a serial dilution of MP and reference particles, in mixtures, which allows the differentiation of MP effects from other particulates. We demonstrate the applicability of the method using an immobilisation test with Daphnia magna exposed to polyethylene terephthalate (MP) and kaolin clay (reference material). In the concentration range of 0.1 to 10000 mg L-1 of total suspended solids (TSS), with MP contributing 0-100 %, the LC50 values for MP-kaolin mixtures were significantly lower compared to the pure kaolin suspension. MP particles were thus more harmful to daphnids than the reference material. The estimated threshold for %MP contribution above which higher mortality was observed was 1 % MP at 36 mg TSS L-1. This approach has a potential for standardisation of MP ecotoxicological testing as well as other particulate material of anthropogenic origin.

Hydrophobic organic contaminants are not linked to microplastic uptake in Baltic Sea herring

It is commonly accepted that microplastic (MP) ingestion can lead to lower food intake and bioaccumulation of hydrophobic organic contaminants (HOCs) in aquatic organisms. However, causal links between MP and contaminant levels in biota are poorly understood and in situ data are virtually non-existent. Here, we investigated whether HOC concentrations in herring muscle tissue (Clupea harengus membras) are related to MP ingestion using fish caught along the West coast of the Baltic Sea. The MP occurrence exhibited a large geographic variability, with MP found in 28% of the fish examined. The population average was 2.4 MP ind-1; however, when only individuals containing MP were considered, the average MP burden was 8.4 MP ind-1. We also found that MP burden decreased with reproductive stage of the fish but increased with its body size. To predict MP abundance in fish guts, we constructed a mass-balance model using literature data on MP in the water column and physiological rates on ingestion and gut evacuation for clupeids of a similar size. The model output was in agreement with the observed values, thus supporting the validity of the results. Contaminant concentrations in the muscle tissue were unrelated to the MP levels in fish, suggesting a lack of direct links between the levels of HOCs and MP ingestion. Thus, despite their ubiquity, MP are unlikely to have a measurable impact on food intake or the total body burden of hydrophobic contaminants in Baltic herring.

Alterations in swimming behavior of Daphnia exposed to polymer and mineral particles: towards understanding effects of microplastics on planktonic filtrators

Concerns have been raised that microplastics (MP) can impact aquatic organisms by compromising their nutrition. However, little is understood about the mechanisms of the adverse effects of MP in suspension-feeders that routinely ingest particles of low nutritional value, such as mineral particles. We compared effects of non-edible particles (MP and kaolin) mixed with microalgae on the swimming and filtering behavior of a planktonic filtrator Daphnia magna; incubations with only algae served as controls. The following questions were addressed: (1) Are there differences in swimming movements between the daphnids exposed to MP and those exposed to kaolin? and (2) Whether occurrence of biofilm on the particle surface affects daphnid swimming and how these effects differ between the kaolin- and MP-exposed animals? We found that both kaolin and MP altered swimming, yet in opposite way, with a decrease of filtration-related movements in kaolin and their increase in MP. The difference was amplified in biofilm coated particles, indicating that daphnids spend more energy when swimming in suspension with MP, and even more when the MP have biofilm. The increased swimming activity of filtrators exposed to plastic litter decaying to microparticles may translate into changes in energy balance and growth.

Multi-level toxicity assessment of engineered cellulose nanofibrils in Daphnia magna

Abstract Cellulose nanofibril (CNF)-based materials are increasingly used in industrial and commercial applications. However, the impacts of CNF on aquatic life are poorly understood, and there are concerns regarding their potential toxicity. Using a combination of standard ecotoxicological tests and feeding experiments, we assessed the effects of CNF exposure (0.206–20.6 mg/L) on the feeding (food uptake and gut residence time) and life-history traits (growth and reproduction) in the cladoceran Daphnia magna. No mortality was observed in a 48 h acute exposure at 2060 mg/L. Moreover, a 21-day exposure at low food and moderate CNF levels induced a stimulatory effect on growth, likely driven by increased filtration efficiency, and, possibly, partial assimilation of the CNF by the animals. However, at low food levels and the highest CNF concentrations, growth and reproduction were negatively affected. These responses were linked to caloric restriction caused by dilution of the food source, but not an obstruction of the alimentary canal. Finally, no apparent translocation of CNF past the alimentary canal was detected. We conclude that CNF displays a low toxic potential to filter-feeding organisms and the expected environmental risks are low.

Evidence for selective bacterial community structuring on microplastics: Selective bacterial community structuring

In aquatic ecosystems, microplastics are a relatively new anthropogenic substrate that can readily be colonized by biofilm-forming organisms. To examine the effects of substrate type on microbial community assembly, we exposed ambient Baltic bacterioplankton to plastic substrates commonly found in marine environments (polyethylene, polypropylene and polystyrene) as well as native (cellulose) and inert (glass beads) particles for 2 weeks under controlled conditions. The source microbial communities and those of the biofilms were analyzed by Illumina sequencing of the 16S rRNA gene libraries. All biofilm communities displayed lower diversity and evenness compared with the source community, suggesting substrate-driven selection. Moreover, the plastics-associated communities were distinctly different from those on the non-plastic substrates. Whereas plastics hosted greater than twofold higher abundance of Burkholderiales, the non-plastic substrates had a significantly higher proportion of Actinobacteria and Cytophagia. Variation in the community structure, but not the cell abundance, across the treatments was strongly linked to the substrate hydrophobicity. Thus, microplastics host distinct bacterial communities, at least during early successional stages.