Metal pollution behind world's largest extinction events?

Heavy metal pollution might have contributed to some of the world's largest extinction events, according to the study of 415-million-year old malformed fossil plankton.
Several Palaeozoic mass extinction events during the Ordovician and Silurian periods (485 to 420 million years ago) shaped the evolution of life on our planet.
Although some of these short-lived, periodic events were responsible for eradication of up to 85 per cent of marine species, the exact kill-mechanism responsible for these crises remains poorly understood.
An international team led by Thijs Vandenbroucke, researcher at the French CNRS and invited professor at Ghent University (UGent) in Belgium and Poul Emsbo from the US Geological Survey investigated a little known association between 'teratological' or 'malformed' fossil plankton assemblages coincident with the initial stages of these extinction events.

They present evidence that malformed fossil remains of marine plankton from the late Silurian (415 million years ago) contain highly elevated concentrations of heavy metals, such as iron, lead, and arsenic.
These are well-known toxins that cause morphologic abnormalities in modern aquatic organisms; which led the authors to conclude that metal poisoning caused the malformation observed in these ancient organisms and may have contributed to their extinction and that of many other species.

Documented chemical behaviour of these metals, which correlates with previously observed disturbances in oceanic carbon, oxygen and sulphur signatures, strongly suggests that these metal increases resulted from reductions of ocean oxygenation.

Thus, metal toxicity, and its expressions in fossilised malformations, could provide the 'missing link' that relates organism extinctions to widespread ocean anoxia.
As part of a series of complex systemic interactions accompanying oceanic geochemical variation, the mobilisation of metals in spreading anoxic waters may identify the early phase of the kill-mechanism that culminated in these catastrophic events.
The recurring correlation between fossil malformations and Ordovician-Silurian extinction events raises the provocative prospect that toxic metal contamination may be a previously unrecognised contributing agent to many, if not all, extinction events in the ancient oceans.
The study was published in the journal Nature Communications.