Mercury concentrations in different tissues of turtle and caiman species from the Rio Purus, Amazonas, Brazil

Abstract

Total mercury (Hg) concentrations of muscle, liver, blood, and epidermal keratin were measured in typically consumed, economically and culturally important species of turtle (Podocnemis unifilis and Podocnemis expansa) and caiman (Melanosuchus niger and Caiman crocodilus) from the Rio Purus in the Amazon basin, Brazil. Methylmercury (MeHg) concentrations were also measured in muscle tissue, representing the first analysis of MeHg concentrations in Amazonian reptile species. In muscle tissues Hg was mostly MeHg (79-96%) for all species. No correlations existed between animal size and total Hg or MeHg concentrations for any species other than M. niger, possibly as a result of growth dilution or the evolution of efficient Hg elimination mechanisms. Significant linear correlations were found between total Hg concentrations in all pairs of nonlethally sampled tissues (keratin and blood) and internal tissues (muscle and liver) for M. niger and between keratin and internal tissues for P. expansa, indicating that nonlethally sampled tissues can be analyzed to achieve more widespread and representative monitoring of Hg bioaccumulation in Amazonian reptiles. Although mean Hg concentrations in muscle for all species were below the World Health Organization guideline for safe consumption (500 µg kg(-1)), mean concentrations in caiman liver were above the safe limit for pregnant women and children (200 µg kg(-1)). No significant differences were found between total Hg and MeHg concentrations in tissues from wild-caught and farm-raised P. expansa, suggesting that farming may not reduce Hg exposure to humans.

Impacts of dams on freshwater turtles: a global review to identify conservation solutions

“…Few ecotoxicological studies focused on freshwater turtles exist [(Thompson et al, 2018) but see (Lu et al, 2019; Tada et al, 2007)], with most focusing on fish due to their economic importance and use as a food resource (Duponchelle et al, 2021; Moran et al, 2018). Despite this, the presence of mercury has been documented in turtles from temperate (Burger and Gibbons, 1998; Meyer et al, 2014; Slimani et al, 2018) and tropical regions (Eggins et al, 2015; Schneider et al, 2009; Schneider et al, 2010). As freshwater turtles are often consumed by riverside populations there is a strong potential for freshwater turtles to represent a source of dietary methylmercury (Green et al, 2010).…”

Assessment of Mercury Concentration in Turtles (Podocnemis unifilis) in the Xingu River Basin, Brazil

“…Several studies have reported positive correlations between body size and Hg concentration in aquatic turtles, including Chelydra serpentina [ 24 ], Chelodina parkeri , Heosemys spinosa , Leucocephalon yuwonoi , Malaclemys terrapin [ 41 ], Podocnemis erythrocephala [ 20 ], and Podocnemis unifilis [ 43 ]. Among Chelydra serpentina , Sternotherus odoratus , Chrysemys picta , and Pseudemys rubriventris , the older and larger individuals tend to have proportionally higher Hg concentrations than the younger and smaller individuals [ 27 ].…”

Freshwater aquatic reptiles (Testudines and Crocodylia) as biomonitor models in assessing environmental contamination by inorganic elements and the main analytical techniques used: a review

“…However, in another study, with the turtle species Podocnemis unifilis, Podocnemis expansa, Podocnemis erythrocephala, Podocnemis sextuberculata, Peltocephalus dumerilianus and Chelus fimbriatus, the same authors observed that muscle was considered to be a good predictor of Hg (Schneider et al, 2010), demonstrating interspecific differences in mercury concentrations likely due to different feeding habits and foraging behaviour. In the same year, Eggins et al (2015) demonstrated that blood was a better predictor of Hg compared to scales for M. niger and was able to predict 72% of variation in muscle tissues and 61% of variation in liver tissues. Keratin, in contrast, showed low predictability (47% of variation in muscle tissues and 32% of variation in liver tissues) and was unreliable.…”