Historical Hg accumulation (∼65 cal kyr BP) in upland lakes of the Southeastern Brazilian Amazonia: New evidence of the extent of geogenic and diagenetic control

Prafulla Kumar Sahoo; José Tasso Felix Guimarães; Gabriel Negreiros Salomão; Luiza Santos Reis; Edilson Freitas da Silva; Mariana Maha Jana Costa de Figueiredo; Karen Lopes da Silva; Roberto Dall'Agnol

doi:10.1016/j.scitotenv.2023.168930

Historical Hg accumulation (∼65 cal kyr BP) in upland lakes of the Southeastern Brazilian Amazonia: New evidence of the extent of geogenic and diagenetic control

Sci Total Environ. 2024 Feb 20:912:168930. doi: 10.1016/j.scitotenv.2023.168930. Epub 2023 Dec 1.

Authors

Prafulla Kumar Sahoo¹, José Tasso Felix Guimarães², Gabriel Negreiros Salomão², Luiza Santos Reis³, Edilson Freitas da Silva², Mariana Maha Jana Costa de Figueiredo², Karen Lopes da Silva², Roberto Dall'Agnol²

Affiliations

¹ Department of Environmental Science and Technology, Central University of Punjab, VPO-Ghudda 151401 Bathinda, India. Electronic address: prafulla.iitkgp@gmail.com.
² Instituto Tecnológico Vale, Rua Boaventura da Silva 955, Nazaré, Belém 66055-090, PA, Brazil.
³ Instituto Tecnológico Vale, Rua Boaventura da Silva 955, Nazaré, Belém 66055-090, PA, Brazil; Micropaleontology Laboratory, University of São Paulo, Rua do Lago, 562-Cidade Universitária, São Paulo 05508-080, SP, Brazil.

PMID: 38042179
DOI: 10.1016/j.scitotenv.2023.168930

Abstract

The historical upland lake sediments in the Brazilian Amazon witnessed significant enrichment of total mercury (Hg). However, its spatio-temporal relationships between lakes and the main factors responsible for this enrichment are still poorly constrained. Given this, we geochemically investigated 12 radiometrically dated (extending back to ∼65 cal kyr BP) sediment cores from the Carajás plateau, Brazil. The Hg level in historical sediments presented a large temporal variability (from 1 to 3200 μg/kg), with maximum accumulation peaks observed between 30 and 45 cal kyr BP in core R2, LB3, and R1. However, the lack of the Hg peak in other cores (LV2 and LTI3) during the same period despite being proximity and non-correlation of these Hg peaks with the onset of major volcanic events indicates that this source has little bearing. Hg enrichment is highly dependent on the type of sedimentary facies, with higher values were associated with detritic facies (MI) and detritic+organic facies (P/M). Principal component analysis shows that aluminosilicate minerals and organic matter are essential hosts of Hg in sediments. The positive correlation between Al, Ti, and Hg in detritic facies and their strong coherence with Hg/TOC in R1, R5, LSL, ST02, and LB3 cores indicate that Hg is primarily of lithogenic origin. This can be substantiated by the higher background threshold value of Hg (574 μg/kg) in historical lake sediments compared to those in recent lake sediments (340 μg/kg). However, the most pronounced Hg peak (3200 μg/kg) in R2 around 45 cal kyr BP, which correlates positively with TOC, S, Se, As, and Mo indicates their diagenetic enrichment in organic-rich sediments under anoxic conditions. Thus, in addition to the lithogenic effect, it can be argued that diagenesis can play a significant role in prompting Hg enrichment in the Carajás lake sediments in Amazonia.

Keywords: Brazilian Amazon; Diagenetic control; Geogenic enrichment; Mercury; Quarternary sediments; Upland lakes.