Based on a literature review and an overview of toxic effects of engineered nanoparticles in aquatic invertebrates, this paper proposes a number of recommendations for the developing field of nanoecotoxicology by highlighting the importance of invertebrates as sensitive and relevant test organisms. Results show that there is a pronounced lack of data in this field (less than 20 peer-reviewed papers are published so far), and the most frequently tested engineered nanoparticles in invertebrate tests are C(60), carbon nanotubes, and titanium dioxide. In addition, the majority of the studies have used Daphnia magna as the test organism. To date, the limited number of studies has indicated acute toxicity in the low mg l(-1) range and higher of engineered nanoparticles to aquatic invertebrates, although some indications of chronic toxicity and behavioral changes have also been described at concentrations in the high microg l(-1) range. Nanoparticles have also been found to act as contaminant carriers of co-existing contaminants and this interaction has altered the toxicity of specific chemicals towards D. magna. We recommend that invertebrate testing is used to advance the level of knowledge in nanoecotoxicology through standardized short-term (lethality) tests with invertebrates as a basis for investigating behaviour and bioavailability of engineered nanoparticles in the aquatic environment. Based on this literature review, we further recommend that research is directed towards invertebrate tests employing long-term low exposure with chronic endpoints along with more research in bioaccumulation of engineered nanoparticles in aquatic invertebrates.

Ecotoxicity of engineered nanoparticles to aquatic invertebrates: a brief review and recommendations for future toxicity testing.

The tremendous increases in production of plastic materials has led to an accumulation of plastic pollution worldwide. Many studies have addressed the physical effects of large-sized plastics on organisms, whereas few have focused on plastic nanoparticles, despite their distinct chemical, physical and mechanical properties. Hence our understanding of their effects on ecosystem function, behaviour and metabolism of organisms remains elusive. Here we demonstrate that plastic nanoparticles reduce survival of aquatic zooplankton and penetrate the blood-to-brain barrier in fish and cause behavioural disorders. Hence, for the first time, we uncover direct interactions between plastic nanoparticles and brain tissue, which is the likely mechanism behind the observed behavioural disorders in the top consumer. In a broader perspective, our findings demonstrate that plastic nanoparticles are transferred up through a food chain, enter the brain of the top consumer and affect its behaviour, thereby severely disrupting the function of natural ecosystems.

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Brain damage and behavioural disorders in fish induced by plastic nanoparticles delivered through the food chain

At times, freshwater zooplankton consume phytoplankton populations at rates similar to or faster than that at which they are growing (Hargrave and Geen, 1970; Gulati, 1975; Horn, 1981; Persson, 1985; Borsheim and Anderson, 1987). Such high losses certainly must help direct seasonal succession as they force a subset of algal species to suffer high mortality rates. Some studies have concluded that losses in general (Kalff and Knoechel, 1978; Reynolds, et al., 1982) and grazing losses in particular (Porter, 1973, 1976, 1977; Lynch and Shapiro, 1981; Crumpton and Wetzel, 1982; Kerfoot, 1987) are important in seasonal succession. In addition, the influence of zooplankton on algal succession is not limited to their selective effect on algal numbers. Zooplankton also interact indirectly with phytoplankton by making some nutrients more available to them (Gliwicz, 1975; Lehman, 1980a, b; Redfield, 1980; Lehman and Scavia, 1982; Sterner, 1986a). Zooplankton thus act not only as predators in the classic sense, but they also have an effect on the competition among algae (Elser et al., 1988).

The Role of Grazers in Phytoplankton Succession

Short-term exposure with high concentrations of pristine microplastic particles leads to immobilisation of Daphnia magna.

https://backend.orbit.dtu.dk/ws/files/132391698/Rist_et_al_Postprint.pdf

Ingestion of micro- and nanoplastics in Daphnia magna - Quantification of body burdens and assessment of feeding rates and reproduction.

Food size selection of four Daphnia, species (D. magna, D. hyalina, D. galeata, D. pulicaria) was investigated using spherical plastic beads as artificial food and with small bacteria. The size of the particles ranged from 0.1 to 35 μm with special emphasis to the particle diameters between 0.1 and 1 μm. In one set of experiments a mixture of differently sized particles was offered as food suspension and the selectivity of filtering was determined by comparing the size spectrum of the particles found in the gut contents with the spectrum in the food suspension. In a second series of experiments suspensions of uniformly sized particles were offered to single animals and their feeding activity was observed directly. In both types of experiments the mesh sizes of the filtering apparatus of the respective animals studied were measured after the experiments by, scanning electron microscopy. The mean sizes of the filter meshes were about 0.4–0.7 μm. In all experiments the size of the particles found in the gut or those which caused high feeding activities were larger than the smallest mesh sizes of the filters. As a consequence simple mechanical sieving provides a sufficient explanation for the mechanism of particle retention of the filtering process in Daphnia. D. magna was found to feed with high efficiency on suspended freshwater bacteria, the residual species investigated showed low filtering efficiencies when bacteria were offered as food.

Filter mesh size and food particle uptake by Daphnia

The appearance of Mesocyclops leuckarti (Claus) in Lake Kinneret was found to be as a population with mixed age structure present throughout the year, when average epilimnic temperatures varied between 14 to 28°C. Some Physiological features were studied, at three temperatures (15, 22, and 27°C), in order to give an insight into such an occurrence: the development time of instars, egg production, longevity, ammonia excretion, food intake and oxygen consumption of adult females. It is suggested that the high rate of metabolism and respiration and smaller body size at 22–27°C is compensated for by the higher rate of development of the offspring and egg production of the adult females.

Moshe Gophen

Papers

Filter mesh size and food particle uptake by Daphnia

Temperature effect on lifespan, metabolism, and development time of Mesocyclops leuckarti (Claus).