Valery Forbes

Few in vivo studies have been conducted to assess how nanoparticle (NP) characteristics such as particle form and shape affect their toxicity and bioaccumulation. In the present study, the deposit feeder, Capitella teleta, was used to investigate the influence of copper form (CuO NPs, micron-sized CuO particles, and aqueous Cu) and CuO NP shape (spheres, rods and platelets) on toxicity and bioaccumulation through sediment exposures of approximately 250 μg Cu/g dw sed. There were no effects of nanoparticle form or shape on mortality or growth rate during the exposure period. However, mortality increased to approximately 26.3% on average in all Cu treatments after the depuration period indicating a delayed effect of Cu exposure, despite more than 90% depuration of Cu during this period. A significant effect of nanoparticle shape was detected on body burden, the gross uptake rate constant and the depuration rate constant, suggesting preferential accumulation of rods by the worms. We recommend that additional sublethal endpoints and longer exposure durations should be examined to fully understand the environmental risks of CuO nanoparticles compared to other forms of Cu entering marine sediment systems.

Copper oxide (CuO) nanoparticles (NPs) are among the most widely used engineered NPs and are thus likely to end up in the environment, predominantly in sediments. Copper oxide NPs have been found to be toxic to a variety of (mainly pelagic) organisms, but to differing degrees. In the present study, the influence of CuO NP shape on bioavailability and toxicity in the sediment-dwelling freshwater gastropod Potamopyrgus antipodarum was examined. In 2 separate studies, snails were exposed to either clean sediment or sediment spiked with either aqueous Cu or CuO NPs of different shapes (rods, spheres, or platelets) at 240 µg Cu/g dry weight of sediment (nominal). In neither of the studies was survival found to be related to Cu form (i.e., free ion vs particle) or shape, whereas snail growth was severely influenced by both form and shape. Reproduction was affected (by CuO NP spheres and aqueous Cu) only when estimated as the total number (live plus dead) of juveniles produced per snail per week. Both the aqueous and particulate forms of Cu were available for uptake by snails when mixed into sediment. However, Cu body burden was not directly related to observed effects. The present study stresses the need for both a better understanding of uptake mechanisms and internal distribution pathways of NPs and an assessment of long-term consequences of NP exposure.

ABSTRACT Background/Question/Methods Populations in frequently disturbed landscapes, such as agroecosystems, may often experience significant losses. In such systems, many species carry important roles as providing units of ecosystem services, those ecosystem functions that are essential for sustaining human populations. To ensure the provision of such services, we need to therefore ensure the population persistence of key species in ecosystems. Recolonization of stressed habitats is one of the major and initial mechanisms of population recovery. The stressed and adjacent, non-stressed areas, can be compared to sinks and sources in classical metapopulation theory which predicts that movement between sinks and sources will not adversely affect the sources, as, by definition, the sinks are suboptimal habitats to which organisms are not generally adapted. When the sink habitats are those that are in essence the same as source habitats, only frequently disturbed species will not be adapted to avoiding them and significant losses from source areas may be assumed. This has been shown in theoretical and some field studies. Furthermore, this phenomenon may be enhanced in riverine networks where habitats are fully connected with a directional movement of organisms (through current velocities and drift). In our study, we tested such a riverine system and looked for consequences of colonization for the source habitats and the population in the total landscape. We simulated the dynamics of two species often found in European freshwater networks, Asellus aquaticus and Gammarus pulex, both significant contributors to the process of leaf litter decomposition. Our simulated landscapes span from simple linear water bodies to more complex ditch systems found in agricultural landscapes. We looked into how the severity and frequency of stress affected the population sizes in the sink and source habitats. Furthermore, we explored the consequences of recolonization on survival in sink habitats, as a possible compensatory mechanism for the population in the whole landscape. Results/Conclusions Our results show that the adverse effects of colonization in source areas depend on the complexity of the specific water network, and are in general spatially constrained. Expectedly, they increase with the frequency and severity of stress and are also dependent on the organism mobility. We discuss these findings in relation to real systems, with a special emphasis on the level of spatial scale at which such effects may be both measured and relevant.

ABSTRACT Background/Question/Methods Compared to marine hard-bottom communities, the exact mechanisms of density dependence in marine soft-bottom communities are less well understood. Deposit feeders are key components of soft-bottom communities. Though it is widely accepted that populations of deposit-feeders are food limited, other factors than exploitation competition, such as competition for space and inter-individual interference, may also affect population density. We explored the mechanisms of density dependence in the widespread deposit feeder, Capitella teleta (formerly Capitella sp. I), which dominates in polluted sediments and which shows highly variable population dynamics. There are at least two mechanisms by which worms may compete: through competition for ingestible particles and through direct physical interference among individuals. We designed our study to distinguish between these two mechanisms of density dependence by independently manipulating the amount and quality of sediment available to worm populations. The experiment was set up with 5 treatments: a control treatment (100% natural sediment; low worm density), two treatments with reduced organic content (75 % natural sediment and 50 % natural sediment) and two treatments with increased initial worm densities (manipulated by reducing the amount of natural sediment per worm to achieve a medium density and a high density compared to the control treatment). Results/Conclusions For all treatments there was an initial increase in population size measured both as worm biomass and abundance. Population size peaked after a number of weeks, and thereafter declined as the sediment was depleted of food. Populations in the 100 % natural sediment (low density) seemed to grow to a higher total biomass and abundance compared to both populations with less space (i.e., higher initial density) and populations that lived in sediment of a lower food quality. Whereas time to reach peak population size did not differ among treatments, peak size (i.e., total biomass) did differ. In addition, there was a clear trend of decreasing peak size with increasing initial population density or decreasing sediment quality (sediment organic content). These results provide insights into the relative importance of food limitation and inter-individual interactions in limiting worm population dynamics.