Concentrations and isotope ratios of mercury in sediments from shelf and continental slope at Campos Basin near Rio de Janeiro, Brazil

Abstract

Mercury (Hg) may originate from both anthropogenic and natural sources. The measurement of spatial and temporal variations of Hg isotope ratios in sediments may enable source identification and tracking of environmental processes. In this study we establish the distribution of mercury concentrations and mercury isotope ratios in surface sediments of three transects along the continental shelf and slope in Campos Basin-RJ-Brazil. The shelf showed on average lower total Hg concentrations (9.2 ± 5.3 ng g) than the slope (24.6 ± 8.8 ng g). MMHg average concentrations of shelf 0.15 ± 0.12 ng g and slope 0.13 ± 0.06 ng g were not significantly different. Distinct differences in Hg isotope ratio signatures were observed, suggesting that the two regions were impacted by different sources of Hg. The shelf showed more negative δHg and ΔHg values ranging from -0.59 to -2.19‰ and from -0.76 to 0.08‰, respectively. In contrast, the slope exhibited δHg values from -0.29 to -1.82‰ and ΔHg values from -0.23 to 0.09‰. Mercury found on the shelf, especially along the "D" and "I" transects, is depleted in heavy isotopes resulting in more negative δHg compared to the slope. Isotope ratios observed in the "D" and "I" shelf region are similar to Hg ratios commonly associated with plants and vegetation and very comparable to those detected in the estuary and adjoining mangrove forest, which suggests that Hg exported from rivers may be the dominating source of Hg in near coastal regions along the northern part of the shelf.

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

“…The finding that litterfall is the dominant terrestrial Hg 0 source fundamentally reshapes our understanding of Hg deposition to terrestrial landscapes and Hg mobility, demonstrating the need for monitoring strategies to measure net ecosystem Hg 0 deposition, including direct exchange/deposition measurements. The dominant role of foliar Hg 0 uptake also results in a specific “terrestrial” Hg isotope signature that can be used to trace terrestrial contributions and transfer to aquatic ecosystems (Tsui et al 2012 ; Kwon et al 2015 ; Jiskra et al 2017 ), aquatic biota (Li et al 2016 ), and lake and ocean sediments (Grasby et al 2015 ; Lepak et al 2015 ; Enrico et al 2016 ; Araujo et al 2017 ; Gleason et al 2017 ). Finally, whole-ecosystem flux measurements using micrometeorological techniques can further confirm the dominant Hg 0 deposition source to terrestrial ecosystems.…”

Branched GDGTs as Proxies in Surface Sediments From the South-Eastern Brazilian Continental Margin

“…As a consequence of the upwelling events, predominance of autochthonous OM in the basin's sediments on a regional scale is observed (Yoshinaga et al, 2008;Carreira et al, 2010;Cordeiro et al, 2018), a scenario also favored by a relatively low input of allochthonous OM (Carreira et al, 2015). The major contributor to continentally-derived materials to the Campos Basin is the Paraíba do Sul river, located to the north of the basin (Figure 2), as evidenced by isotopic and molecular markers (Souza et al, 2010;Albuquerque et al, 2014;Carreira et al, 2015), dissolved black carbon (Dittmar et al, 2012) and metals (Lacerda et al, 1993;Araujo et al, 2017). Even though the Paraíba do Sul River plays a minor role as source of material to the global oceans when compared to other rivers, the influence of Paraíba do Sul River is relevant on a regional scale .…”

The trophic ecology of marine catfishes in south-eastern Brazil

“…Previous studies developed along this area support the Hg assimilation related to predator–prey interactions (Carvalho et al ., 2008; Kehrig et al ., 2009; Di Beneditto et al ., 2012), suggesting that the past practices of gold-mining and the use of mercurial fungicides on sugarcane plantations in the PSR drainage basin are the main input sources of Hg in this fluvial ecosystem, which is largely exported to the adjacent marine areas, coupled with Hg atmospheric deposition (Lacerda et al ., 1993; Lacerda, 1996; Araujo et al ., 2017; Azevedo et al ., 2018). Reinfelder et al .…”

“…(2015), at times of higher PSR discharge, G. genidens and A. luniscutis were more abundant, thus contributing to higher mean THg values for both species compared with B. bagre . At times of lower PSR discharge, B. bagre is more abundant; thus as suggested by authors worldwide and for the PSR estuary, during low river discharge the main source of Hg is the direct deposition of the contaminant from the atmosphere to surface waters, resulting in higher concentrations of THg in fish due to the rapid methylation and absorption by biota, thus becoming more bioavailable (Harris et al ., 2007; Mason et al ., 2012; Araujo et al ., 2017; Azevedo et al ., 2018).…”