Benjamin Daniels

Accumulation and Distribution of Multiwalled Carbon Nanotubes in Zebrafish (Danio rerio)

No data on the bioaccumulation and distribution of multiwalled carbon nanotubes (MWCNTs) in aquatic vertebrates is available until now. We quantified uptake and elimination of dispersed radiolabeled MWCNTs ((14)C-MWCNT; 1 mg/L) by zebrafish (Danio rerio) over time. The influences of the feeding regime and presence of dissolved organic carbon (DOC) on accumulation of the nanomaterial were determined. The partitioning of radioactivity to different organs and tissues was measured in all experiments. A bioaccumulation factor of 16 L/kg fish wet weight was derived. MWCNTs quickly associated with the fish, and steady state was reached within 1 day. After transfer to clear medium, MWCNTs were quickly released to the water phase, but on average 5 mg of MWCNTs/kg fish dry weight remained associated with the fish. The nanomaterial mainly accumulated in the gut of all fish. Feeding led to lower internal concentrations due to facilitated elimination via the digestive tract. In the presence of DOC, 10-fold less was taken up by the fish after 48 h of exposure compared to without DOC. Quick adhesion to and detachment from superficial tissues were observed. Remarkably, little fractions of the internalized radioactivity were detected in the blood and muscle tissue of exposed fish. The part accumulated in these fish compartments remained constant during the elimination phase. Hence, biomagnification of MWCNTs in the food chain is possible and should be a subject of further research.

Life-stage-dependent sensitivity of the cyclopoid copepod Mesocyclops leuckarti to triphenyltin

The effects of triphenyltin (TPT) on non-target aquatic groups like copepods have not yet been studied in detail. Recently, Mesocyclops leuckarti was suggested as a representative species for freshwater cyclopoid copepods to study the effects of plant protection products. We conducted 96h acute toxicity tests in the laboratory to study the effects of TPT on the different life stages of M. leuckarti. We used the recently proposed General Unified Threshold model of Survival (GUTS) to mechanistically describe the underlying toxicokinetic and toxicodynamic process for the nauplii, copepodites and adults (males and females) of M. leuckarti. Experimental results showed that nauplii were significantly more sensitive to TPT compared to the other stages. Also, the 96h LC50 values were much lower than the 48h LC50 values, suggesting that standard acute toxicity test durations for aquatic invertebrates may underestimate toxic effects with respect to compounds like TPT which have a slow mechanism of action. The GUTS analysis, which mechanistically described the toxicity of TPT to the different life stages of M. leuckarti, suggested that the differences in sensitivity were a consequence of a lower threshold of effects in the nauplii compared to a higher threshold in the later stages. This study shows the potential of using the GUTS to understand how toxic compounds interact with different life-stages. Further experiments to provide a more detailed understanding of toxicokinetics of TPT in copepods could be useful.

Assessment of urban green space structures and their quality from a multidimensional perspective

Facing the growing amount of people living in cities and, at the same time, the need for a compact and sustainable urban development to mitigate urban sprawl, it becomes increasingly important that green spaces in compact cities are designed to meet the various needs within an urban environment. Urban green spaces have a multitude of functions: Maintaining ecological processes and resulting services, e.g. providing habitat for animals and plants, providing a beneficial city microclimate as well as recreational space for citizens. Regarding these requirements, currently existing assessment procedures for green spaces have some major shortcomings, which are discussed in this paper. It is argued why a more detailed spatial level as well as a distinction between natural and artificial varieties of structural elements is justified and needed and how the assessment of urban green spaces benefits from the multidimensional perspective that is applied. By analyzing a selection of structural elements from an ecological, microclimatic and social perspective, indicator values are derived and a new, holistic metrics1 is proposed. The results of the integrated analysis led to two major findings: first, that for some elements, the evaluation differs to a great extent between the different perspectives (disciplines) and second, that natural and artificial varieties are, in most cases, evaluated considerably different from each other. The differences between the perspectives call for an integrative planning policy which acknowledges the varying contribution of a structural element to different purposes (ecological, microclimatic, social) as well as a discussion about the prioritization of those purposes. The differences in the evaluation of natural vs. artificial elements verify the assumption that indicators which consider only generic elements fail to account for those refinements and are thus less suitable for planning and assessment purposes. Implications, challenges and scenarios for the application of such a metrics are finally discussed.