Dredging Activities Carried Out in a Brazilian Estuary Affect Mercury Levels in Swimming Crabs

Abstract

(1) Although suffers from intense pollution inputs, Guanabara Bay, the most socioeconomically and environmentally important estuary in Rio de Janeiro, Brazil, is still home to a diverse fauna, including several fish and crab species consumed by humans. The bay presents high sedimentation rates and sediment contamination, further aggravated by dredging processes carried out in recent years. In this context, this study aimed to verify the effect of the dredging process on total mercury (THg) concentrations at Guanabara Bay through swimming crab assessments sampled before (2016), during (2017), and after (2018) the dredging process, and mainly, if the detected concentrations can be harmful to consumer health; (2) Methods: Swimming crab samplings were carried out at the same time and sampling points in 2016, 2017 and 2018 and the total Hg was determined using a Direct Mercury Analyzer (DMA-80, Milestone, Bergamo, Italy); (3) Results: Increased Hg concentrations were observed during the dredging process, decreasing to lower values, close to the initial concentrations, at the end of the process. Some of the investigated abiotic factors favor Hg dynamics in the aquatic environment, while others were positively altered at some of the assessed sampling areas at the end of the dredging process; (4) Conclusions: Although crab Hg levels were below maximum permissible limits for human consumption, it is important to note that these animals are significantly consumed around Guanabara Bay, which may lead to public health issues in the long term.

Mercurial Contamination: A Consumer Health Risk Assessment Concerning Seafood From a Eutrophic Estuary in Southeastern Brazil

“…Still, on the aspects that can influence the concentration of the contaminant, in addition to the biotic part, there are also abiotic factors, such as water temperature, salinity, oxygenation and pH. These factors were not evaluated in this study; however, based on other previously published studies, it is possible to indicate that such factors are responsible for influencing the bioavailability, speciation, and toxicity of Hg in the Guanabara Bay region (Rodrigues et al, 2019b;Rodrigues et al, 2020;Rodrigues et al, 2021b). The salinity of BG varies between 31 and 35 g.L -1 , being closer to the salinity of the marine environment, while the pH is around 8, indicating an alkaline environment (Rodrigues et al, 2021b).…”

“…Mercury (Hg) contamination in aquatic environments is a serious concern, especially due to the deleterious effects of this metal on the health of seafood consumers, because of its accumulation and toxic effects (Sadhu et al, 2015;Dias et al, 2016;Harayashiki et al, 2018;Rodrigues et al, 2019a;Rodrigues et al, 2019b;Rodrigues et al, 2020). Mercury is a non-essential metal found both naturally in the environment due to volcanic emanations and atmospheric degassing, and anthropogenically, due to pollution especially caused by mining, sewage activity by industrial sectors like chlor-alkalis and metallurgy plants, fossil fuel burning, and domestic sewage (Baptista Neto et al, 2016;Soares-Gomes et al, 2016;Condini et al, 2017;Harayashiki et al, 2018).…”

“…In Brazil, the Guanabara Bay estuary, located in the state of Rio de Janeiro, is considered an important Hg contamination area, mainly due to the discharges of industrial and domestic sewage. Despite this, it is a prominent artisanal fishing area in the state, due to a very high diversity of species displaying economic value, found even in polluted waters (Baptista Neto et al, 2016;Rodrigues et al, 2019b;Rodrigues et al, 2020).…”