Mercury in the Amazon basin: Human influence or natural geological pattern?

One of the main scientific discussions on Hg levels in the Amazon region concerns the possible sources of this element. This research was conducted between 1999 and 2015 in the region between the coastal zone and the Amazonian Continental Shelf (ACS). The total Hg concentration values found in the sediments in ACS ranged from 14 to 160 ng g−1. The main contribution of metallic elements to ACS comes from the sedimentary load transported by the Amazon River basin. Among the main tributaries of the Amazon River, the Negro River, which for decades has had mining activity, and the Madeira River, which is still present today, although currently in decline. The analysis of the total Hg results associated with the suspended solids load, both in the Continental Amazon and ACS, suggest that the anthropogenic influence, although evident in sites sources of pollution, is not the main source of total Hg for ACS, and in this case the participation of the natural contributions should be attributed from the natural geological activity in the regional soil, which is considered as naturally enriched in Hg.