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Abstract Title: Gold mining impacts: Acute ecotoxicological effects of Hg(CN)2 in Danio rerio (zebrafish)
Presenter Name: Henrique Da Silva
Session: Special Session - Mercury in the Southern Hemisphere
Co-Authors: Henrique Da Silva

Abstract Information :

Artisanal and small-scale gold mining (ASGM) is the largest source of anthropogenic Hg emissions on the planet. In addition, Hg-contaminated tailings are often reprocessed with sodium cyanide (NaCN) to extract the residual gold remaining in the material. This leads to the formation of mercury cyanide (Hg(CN)2) complexes, which are often discharged in untreated form into local drainages, leading to large amounts of free cyanide being released. However, data on mercury-cyanide interactions are scarce. In this study, we investigated the impact of cyanide and Hg bioavailability in zebrafish when added as Hg(CN)2. Different concentrations of Hg(CN)2 and NaCN were used, leading to an EC50 of 0.53 mg.L-1 for NaCN and 0.16 mg.L-1 for Hg(CN)2. Analyzing free cyanide concentrations in aquarium water, > 40 % dissociation was observed for NaCN and about 5% for Hg(CN)2. The accumulation of total Hg (THg) in the brain, muscle and kidney was quantified. All fish exposed to Hg(CN)2 had higher THg levels than their controls and kidney was the tissue with higher Hg(CN)2 accumulation. Histological effects of both cyanides on zebrafish kidney and gill tissues were investigated. The results alert to the risks of the presence of these complexes in aquatic environments.

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