The phrase "mercury concentrations" refers to the amount or level of mercury that is present in a certain substance or environment. It is a way to measure how much mercury is contained within a specific sample. Full definition
They then used their observed values to calculate the total amount of mercury stored in permafrost in the northern hemisphere and create a map of mercury concentrations in the region. (sciencedaily.com)
The finding suggests that reductions in mercury emissions could rapidly lead to reduced mercury concentrations in some marine fish, the researchers say. (sciencedaily.com)
So, the bottom - feeding fish have both lower mercury concentrations and diluted growth. (sciencedaily.com)