282 - The Unexpected Pathway Mercury from Artisanal Mining Takes to Contaminate Fish in Tropical Gabon

In January 2019, we alongside the Agence Nationale des Parcs Nationaux and CENAREST a conducted a mercury survey in Gabon, Africa. We focused on assessing mercury levels in fish, but analyzed leaves, water, soils, sediment, and air. We found high fish-mercury concentrations throughout Gabon, more than double the continental average, and no obvious trophic-driven biomagnification patterns. While the severity of fish contamination cannot be understated, other medias were not alarming. Liquid mercury is illegally used in small-scale artisanal gold mining in Gabon but unlike many tropical nations, Gabon’s history of mercury use is comparatively unremarkable. We measured mercury isotope ratios on these medias, both far-from and proximate-to mining activities and discovered most of the mercury in fish is linked to gaseous elemental mercury deposition to the surrounding watersheds rather than from direct aquatic releases. We hypothesize mining activities enhancing gaseous mercury emissions, have increased the importance of this depositional pathway as intact rainforests are excellent repositories for dry deposition. Yet, no obvious correlation between mercury levels and mining locations was observed and low levels of mercury were recorded in the air due to frequent rain events. With mercury concentrations in fish and all other medias conflicting and the nationwide consistency in mercury isotope values we ask whether our assumptions regarding mercury cycling in the tropics need re-evaluation. We hypothesize that fish in Gabon’s aquatic ecosystems are broadly, consistently, and highly contaminated with mercury firstly because these ecosystems are very sensitive to inputs of mercury and secondly because resource utilization by fish is maximized. Therefore, we predict that Gabon, with its diverse mosaic of forested ecotypes and grasslands and strong formalization in government-sponsored environmental protection, represents the ideal experimental laboratory to test fundamental processes of mercury cycling in the tropics both now and as shifts in economic activities persist.

Authors: Ryan Lepak, Peter McIntyre, Jean Hervé Mve Beh, Casey Dillman, Sarah Janssen, Jacob Ogorek, Mike Tate ,Clotaire Moukegni Sika ,Jean Noel Bibang Bi Nguema, Marie-Claire Paiz, Lee White