In this post, Mirco Weil presents his recent paper “The oxidized state of the nanocomposite Carbo-Iron® causes no adverse effects on growth, survival and differential gene expression in zebrafish”.

Currently, colleagues at the Helmholtz Centre for Environmental Research (UFZ) are developing the nanocomposite Carbo-Iron for remediation of aquifers polluted with halogenated chemicals. Carbo-Iron consists of active carbon and nanoscaled zero-valent iron, the primary particle size of the composite is approximately 200 nm. To observe potential risks in the environment that may arise after application of Carbo-Iron in an aquifer, we investigated its effects on selected organisms of different trophic levels. Since the zero-valent iron in Carbo-Iron readily oxidizes under test conditions, we decided to use oxidized Carbo-Iron in our ecotoxicological experiments. Besides the determination of effect levels, we wanted the data obtained to be useful for a risk assessment of Carbo-Iron. For this reason, we selected OECD and EPA guideline tests. In our present manuscript, we describe the tests and results from three test systems with the zebrafish Danio rerio.

Test systems with the zebrafish used to investigate potential effects of the nanocomposite Carbo-Iron (image by M. Weil)

We modified the existing OECD test guidelines for the fish embryo toxicity test (OECD 236, 2013), fish acute toxicity test (OECD 203, 1992) and the fish early life stage test (OECD 210, 2013) to suit the nanoparticle-like characteristics and behaviour of Carbo-Iron. Additionally to the endpoints described in the respective guidelines, we investigated potential particle uptake with microscopic methods. Further, we performed a gene expression analysis in D. rerio embryos after exposure to Carbo-Iron with microarrays.

Though Carbo-Iron was visibly adhering to the eggs and fish in test concentration above 10 mg/L, we observed no acute lethal effects of Carbo-Iron in the fish embryos or adult fish up to 100 mg/L. Further, we did not see a significant influence of Carbo-Iron on survival or growth of the early life stages of the zebrafish in the investigated concentrations between 0.25 and 25 mg/L. Carbo-Iron was detected in the gut of fish, but was excreted in less than 5 days when transferred from exposure to control conditions. Microscope images suggested that Carbo-Iron could not pass the chorion around the zebrafish embryos. This finding was supported by the fact that we did not find any significant difference in gene expression in embryos exposed to Carbo-Iron compared to control conditions.

The results in our manuscript suggest that the environmental risk of Carbo-Iron to fish is low. Nevertheless, for a more complete risk assessment, data for other organisms are necessary and currently we are preparing a manuscript describing the effects observed in the amphipod Hyalella azteca after exposure to oxidized Carbo-Iron. We will post it here as soon as it is available.

The present manuscript was authored by Mirco Weil, Tobias Meißner, Wibke Busch, Armin Springer, Dana Kühnel, Ralf Schulz and Karen Duis and published in Science of The Total Environment.