Fish eyes and brain as primary targets for mercury accumulation — A new insight on environmental risk assessment

Abstract

Fish eyes and brain are highly susceptible to environmental Hg exposure but this issue is still scarcely investigated, mainly regarding methylmercury (MeHg) accumulation. Yet, Hg levels in fish lens have not been previously examined under field conditions. Total Hg (tHg), MeHg and inorganic Hg (iHg) levels were assessed in the brain, eye wall and lens of the golden grey mullet (Liza aurata) from an Hg contaminated area, both in winter and summer, together with water and sediment levels. Sampling was performed at Aveiro lagoon (Portugal) where a confined area (LAR) is severely contaminated by Hg. Fish brain, eye wall and lens accumulated higher levels of tHg, MeHg and iHg at LAR than the reference site, reflecting faithfully environmental spatial differences. The brain and eye wall responded also to the winter-summer changes found in water and sediment, accumulating higher levels of MeHg (and tHg) in winter. Contrarily, lens was unable to reflect seasonal changes, probably due to its composition and structural stability over time. The three neurosensory structures accumulated preferentially MeHg than iHg (MeHg was higher than 77% of tHg). Lens exhibited a higher retention capacity of MeHg (mean around 1 μg g(-1) at LAR), accumulating higher levels than the other two tissues. Interestingly, MeHg and iHg levels were significantly correlated for the brain and eye wall but poorly associated within the two analysed eye components. The high levels of MeHg found in the brain, eye wall and lens could compromise their functions and this needs further research.

The sub-cellular fate of mercury in the liver of wild mullets (Liza aurata) – Contribution to the understanding of metal-induced cellular toxicity

“…Inter-site differences of Hg were mostly found in the sediment, suggesting that this compartment is the main source of Hg to mullets. Results obtained in this study are in line with other studies performed at Ria de Aveiro revealing a higher accumulation of Hg in L. aurata liver from LAR in comparison to individuals caught at R (Guilherme et al, 2008;Mieiro et al, 2009;Pereira et al, 2014). The partitioning of tHg among the four sub-cellular fractions varied between individuals from R and LAR.…”

Unravelling the mechanisms of mercury hepatotoxicity in wild fish (Liza aurata) through a triad approach: bioaccumulation, metabolomic profiles and oxidative stress

“…It has an inner basin, the Laranjo Basin, located near Estarreja, Portugal (Fig. [2][3][4] As a result of the absence of other important sources of contaminants, Laranjo Basin is considered to be a field laboratory offering a unique opportunity to assess Hg toxicity under realistic conditions. The high levels of contamination resulted from five decades of continuous discharges from a chlor-alkali plant, which generated a contamination gradient for Hg.…”

“…Both sites were selected based on previous ecotoxicological studies [2][3][4]18 (Fig. Both sites were selected based on previous ecotoxicological studies [2][3][4]18 (Fig.…”

Insights into neurosensory toxicity of mercury in fish eyes stemming from tissue burdens, oxidative stress and synaptic transmission profiles

“…High levels of Hg are still stored in sediments [Coelho et al, 2005] and could be found in the biota [Guilherme et al, 2008a;Mieiro et al, 2010;Pereira et al, 2013]. Due to the absence of other important sources of contaminants, Largo do Laranjo is considered a ''field laboratory", offering a unique opportunity to assess Hg toxicity under realistic conditions [Guilherme et al, 2008a;Mieiro et al, 2010;Pereira et al, 2014]. São Jacinto is located near the lagoon entrance, about 10 km from Largo do Laranjo.…”

“…It was demonstrated that Hg may target the eyes under environmental exposures [Pereira et al, 2013[Pereira et al, , 2014 and that MeHg is preferentially accumulated in the eyes in comparison with other key organs such as liver [Korbas et al, 2012[Korbas et al, , 2013. A recent innovative study showed that MeHg accumulates in the secondary lens fibers immediately underlying the lens epithelial cells [Korbas et al, 2013].…”