Distribution and availability of mercury and methylmercury in different waters from the Rio Madeira Basin, Amazon

Abstract

Waters from the Amazon Basin have distinct physicochemical characteristics that can be optically classified as "black", "clear" and "white". We studied the distribution of total-Hg (THg) and methyl-Hg (MeHg) in these waters and respective suspended solids, sediment, phytoplankton, zooplankton, and benthic macroinvertebrates (BM) in the Madeira River Basin. Compared with the other types of water, the more acidic "black" kind had the highest THg and MeHg concentrations. The trend (black > clear > white) occurred for the concentrations of THg and MeHg in sediments and in the biotic compartment (plankton, macroinvertebrates). Organic Hg accounted for a small percentage (0.6-0.4%) of the THg in sediments but was highest in water (17-15%). For plankton and BM, the biota sediment accumulation factor (BSAFs) of MeHg (53-125) were greater than those of THg (4.5-15); however, the BSAF trend according to water type (black > clear > white) was only significant for MeHg. Sediment THg is correlated with all forms of Hg in biotic and abiotic matrices. The results indicate that water acidity in the Amazon is an important chemical characteristic in assessing Hg contamination of sediments and bioaccumulation in the aquatic food web. The differences in the BSAFs between THg and MeHg support the use of this factor for evaluating the bioaccumulation potential of sediment-bound Hg. The results add information critical to assessing environmental and health risks related to Hg methylation and potential fish-MeHg contamination, especially in tropical aquatic environments.

Evaluation of Total Mercury in Sediments of the Descoberto River Environmental Protection Area—Brazil

“…In general, the highest values of the variables were found in the lentic environment, except for DO, Turbidity (Tur), HCO The pH values in the sampled sites showed no significant difference (p = 0.983) between the lentic (6.81) and lotic (6.83) systems, being within the average of the rivers of the Federal District (5.6 to 6.85) [25]. The pH is an important variable to evaluate Hg behavior in the aquatic environment, because, among other factors, it can favor mobilization and methylation processes in acidic waters, or hinder it in alkaline environments [10].…”

“…Direct analysis of Hg in sediments is a reliable indicator of its distribution, since sediments represent the main environmental compartment for methylation of inorganic Hg. However, mobilization of sediment-bonded Hg depends on environmental conditions [10], making it important to evaluate the correlations of the physicochemical parameters of water with THg in order to verify possible processes of accumulation, transport, and transformation of this metal in the aquatic environment. Areas that house lotic and lentic ecosystems are governed by several factors, among them anthropogenic activities, hydrogeochemical processes, and local climatic conditions, these being the main influences of water quality conditions [26].…”

“…In the Amazon rainforest, for example, which is a complex aquatic environment, the biological and physicochemical properties of its water bodies are linked to its biogeochemical origin and the drainage of watersheds. Moreover, these properties have a detectable influence on the distribution and availability of Hg species [10].…”

Mercúrio nos sedimentos aquáticos e sua distribuição espacial em solos superficiais no bioma Cerrado: estudo de caso no Distrito Federal, Brasil

“…Uma vez depositados em ecossistemas aquáticos, materiais particulados ricos em Hg 2+ são agregados aos sedimentos e/ou dissolvidos na coluna d'água, disponibilizando-o para o processo de metilação (DÍEZ et al, 2016;HSU-KIM et al, 2018); um processo realizado principalmente por bactérias sulfato-redutoras, convertendo o Hg na sua forma mais biodisponível, sendo assim, a principal força que controla a bioacumulação e biomagnificação de mercúrio nas cadeias alimentares aquáticas (BIGHAM et al, 2016;VIEIRA et al, 2018;FERRIZ et al, 2021). Desse modo, a análise direta do Hg nos sedimentos é um indicador confiável de poluição por mercúrio em ambientes aquáticos continentais (PORTELA et al, 2020).…”

Mapping the Evolution of Mercury (Hg) Research in the Amazon (1991–2017): A Scientometric Analysis

“…In fact, due to regional and worldwide interest, mercury in the Amazon region has been studied with several different foci, such as environmental sciences [17], ecotoxicology [18], occupational health, and public health [19]. Therefore, the aim of this study was to make a scientometric analysis of mercury research in the Amazon in order to identify and integrate published Hg research related to the fragile and threatened Amazonian ecosystem.…”