RESUMO
Artisanal and small-scale gold mining (ASGM) has been performed in the southern Ecuadorian Amazon since the colonial period. However, its effects on fluvial systems have been poorly investigated. Thus, in order to calculate the normalized enrichment factors (NEF) of several heavy metals in fluvial sediments of the Zamora River basin (Ecuadorian Amazon), we analyzed bottom sediments along ASGM-affected and unaffected river sections. The results indicated that sediments of the Congüime River have NEF between 2.2 and 2.3 for Cu (moderate contamination) and higher than 3 for Mn, Zn, Pb, and Hg (severe contamination). Similarly, a severe contamination is also observed in the lower Nangaritza River, due to sediments of this sector have NEF > 3 for Zn, Pb, and Hg. Bottom sediments from the Nambija and Zamora rivers showed a severe contamination with Hg (NEF > 3), suggesting the existence of ASGM activities in the upper Zamora River basin.