The mercury found at very low concentrations in water is concentrated along the entire food chain, from algae via zooplankton to small fish and on to the largest fish—the ones we eat. Mercury causes severe and irreversible neurological disorders in people who have consumed highly contaminated fish. Whereas we know about the element’s extreme toxicity, what happens further down the food chain, all the way down to those microalgae that are the first level and the gateway for mercury? By employing molecular biology tools, a team of researchers from the University of Geneva (UNIGE), Switzerland, has addressed this question for the first time. The scientists measured the way mercury affects the gene expression of algae, even when its concentration in water is very low, comparable to European environmental protection standards. The research is published in Scientific Reports.