Selenium in brown bears (Ursus arctos) from Croatia: Relation to cadmium and mercury

Abstract

Muscle (n = 111), liver (n = 111), and kidney cortex (n = 101) samples from brown bears (Ursus arctos) were collected in the 2009 and 2010 hunting seasons in Croatia and analysed for selenium (Se), cadmium (Cd), and total mercury (Hg). The aim was to assess the levels of these elements according to age, sex, and season of collection, and to investigate possible Se/Cd and Se/Hg interactions. Median Se concentrations were 0.139 μg/g in muscle, 0.409 μg/g in liver and 1.75 μg/g wet mass in kidney cortex. Median Cd and Hg were 0.0078 and 0.0018 μg/g in muscle, 1.09 and 0.031 μg/g in liver, and 16.5 and 0.206 μg/g wet mass in the renal cortex, respectively. Se/Cd molar ratios were less than 1 in the kidney cortex, and close to or above 1 in liver and muscle, respectively. Toxic Cd and Hg correlated with Se in all of the studied tissues. Sex differences were found for all three elements (except Se in liver), with females having higher tissue concentration than males. Only Cd showed age-dependence. Bear samples collected in fall had higher Se in muscles, and Hg in muscles and liver compared to samples collected in spring. Element concentrations in brown bear tissues were within the range of previously reported studies. Bear meat is considered a rich source of Se, safe for consumption with regard to its Cd and Hg content. According to the molar ratio and correlation results, we assume that Se binding is not the primary detoxification pathway for Cd and Hg in brown bears.

Lead and Other Trace Element Levels in Brains of Croatian Large Terrestrial Carnivores: Influence of Biological and Ecological Factors

“…Molar ratios of unity or lower imply that the available Se levels are not enough to detoxify Hg presently, binding it to an inert complex that precipitates [ 91 ]. The median liver Se/Hg molar ratio in our bears was similar to the ratios reported previously for Croatian bears (26 vs. 34, respectively [ 47 ]), but five times lower than in the livers of Croatian wolves. Such results reflect lower Hg levels in wolf livers and higher Se levels compared to bears, meaning that wolves are at lower risk of Hg-related toxicity.…”

“…The most studied interaction of Hg with an essential element is that with Se and Se-containing compounds resulting in Hg sequestration, especially in the liver, but also in the kidney and brain [ 11 , 34 ]. Previous wildlife studies reported concurrent accumulations of Hg and Se in the liver and kidney [ 47 , 87 , 88 , 89 , 90 ], but brain samples did not follow this trend due to the limited Hg levels which were greatly surpassed by Se levels in polar bears [ 29 ], as well as in our brown bears and wolves. The Se/Hg molar ratios in Croatian bear and wolf brains were similar (128 and 161, respectively) and more than 20 times higher than in polar bears’ brain stems (5.6 [ 29 ]).…”

“…Except for the already mentioned age of carnivores, sex, season and body condition as determinants of an animal’s health are important confounding factors that have to be taken into consideration while interpreting tissue element levels [ 40 , 41 , 44 , 45 , 46 ]. It should be stressed that Croatian bears and other predators are concomitantly exposed to trace elements and organic pollutants with toxic potential [ 40 , 47 , 48 ]. The health of those protected species (brown bear, grey wolf ( Canis lupus ) and Eurasian lynx ( Lynx lynx ); EU Habitats Directive, Bern Convention) is of both national and European interest [ 49 ], Croatia being one of the rare European countries with all three large carnivore species [ 50 ].…”

Cadmium, Lead, and Mercury Exposure Assessment Among Croatian Consumers of Free-Living Game

“…However, the vast majority of game is not controlled for residues because non-marketed food is not subject to these tests. Data about toxic metal levels in free-living game from Croatia are mainly limited to scientific research (29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). In 2012, the Croatian Food Agency published a heavy metal exposure assessment (40) based on data for wild boar meat, liver, and kidney.…”