This is a boring headline about zebrafish embryos exposed to heavy metals

Today I report on a study that was published already a while ago, but tells a nice story about the challenge and necessity to design meaningful experiments. Also, this one deals with heavy metals, which is not common in our research; we mainly focus on organic contaminants.

In this particular study we investgated whether heavy metals spiked into sediments are bioavailable to unhatched zebrafish embryos, and whether it makes a difference if the sediment was a natural one - just taken from, e.g., a riverbed out there - or a formulated, meaning components that typically make up a sediment mixed together. Besides the single heavy metals we also spiked mixtures.

We investigated mortality, several heavy metal-specific proteins and the regulation of a couple of genes that are known to react to heavy metal exposure. What we found was actually not very surprising: the heavy metals in the formulated sediment were better bioavailable than those in the natural one. An artificial mixture of sediment components can never resemble a real "grown" sediment. The matrix in the natural sediment is just much more complex and provides a multitude of possibilities for heavy metals to be trapped, bound, blocked, and thus not able to enter the test organism. Nevertheless, this had to be proven first. Science does not rely on hypotheses. We  have to challenge them to be sure.

However, formulated sediments are widely used in research. And our study shows that using such matrices could largely overestimate bioavailability and thus risk of heavy metal contaminations in sediments. Furthermore, the study revealed that the accumulation of the individual heavy metals from a mixture is relatively lower compared to that in the single metal exposure experiments. Since not all metals show the same toxicity for the embryos this has to be taken into account when doing risk assessment of heavy metal burden.

Last not least we identified some promising biomarkers for low-dose detection of heavy metal exposure. Read the full story on "Bioaccumulation and molecular effects of sediment-bound metals in zebrafish embryos". (fulltext only with a subscription to the journal, sorry...)