Toxicokinetics of selenium in the slider turtle, Trachemys scripta

Abstract

Selenium (Se) is an essential element that can be harmful for wildlife. However, its toxicity in poikilothermic amniotes, including turtles, remains poorly investigated. The present study aims at identifying selenium toxicokinetics and toxicity in juvenile slider turtles (age: 7 months), Trachemys scripta, dietary exposed to selenium, as selenomethionine SeMet, for eight weeks. Nondestructive tissues (i.e. carapace, scutes, skin and blood) were further tested for their suitability to predict selenium levels in target tissues (i.e. kidney, liver and muscle) for conservation perspective. 130 juvenile yellow-bellied slider turtles were assigned in three groups of 42 individuals each (i.e. control, SeMet 1 and SeMet 2 ). These groups were subjected to a feeding trial including an eight-week supplementation period SP 8 and a following 4-week elimination period EP 4 . During the SP 8 , turtles fed on diet containing 1.1 ± 0.04, 22.1 ± 1.0 and 45.0 ± 2.0 lg g -1 of selenium (control, SeMet 1 and SeMet 2 , respectively). During the EP 4 , turtles fed on non-supplemented diet. At different time during the trial, six individuals per group were sacrificed and tissues collected (i.e. carapace, scutes, skin, blood, liver, kidney, muscle) for analyses. During the SP 8 (Fig. 1), both SeMet 1 and SeMet 2 turtles efficiently accumulated selenium from a SeMet dietary source. The more selenium was concentrated in the food, the more it was in the turtle body but the less it was removed from their tissues. Moreover, SeMet was found to be the more abundant selenium species in turtles' tissues. Body condition (i.e. growth in mass and size, feeding behaviour and activity) and survival of the SeMet 1 and SeMet 2 turtles seemed to be unaffected by the selenium exposure. There were clear evidences that reptilian species are differently affected by and sensitive to selenium exposure but the lack of any adverse effects was quite unexpected.

Incidence of 49 elements in the blood and scute tissues of nesting hawksbill turtles (Eretmochelys imbricata) in Holbox Island

“…Some authors like Ley-Quiñonez et al (2011) mention the difficulty in establishing whether the high concentrations of Se in sea turtles can be considered a toxic factor; however, selenomethionine is considered to be the primary form of organic selenium relevant for bio-accumulation and toxicity in wildlife (Dyc et al, 2015(Dyc et al, , 2016. It has been suggested that the presence of Se in sea turtle eggs could be toxic for the embryo (Lam et al, 2006), and a mother-embryo metal transfer has been demonstrated in sea turtles (Paez-Osuna et al, 2010a,b, 2011; Dyc et al, 2015).…”

Trace element reference intervals in the blood of healthy green sea turtles to evaluate exposure of coastal populations

“…Moreover, species-specific toxicokinetic processes (absorption, distribution, metabolism, and elimination), which are poorly understood for reptiles in general, govern the trace element differences among various tissues. Only a few descriptions of these processes exist for freshwater turtle species, and even then only for Cd, Se, and Hg (Blanvillain et al, 2007;Dyc et al, 2016;Guirlet and Das, 2012;Schwenter, 2007). Since internal tissue concentrations reflect the integration of all trace element exposure pathways, they are more informative as biomonitoring matrices than external ones (i.e.…”

Toxic elements and associations with hematology, plasma biochemistry, and protein electrophoresis in nesting loggerhead sea turtles (Caretta caretta) from Casey Key, Florida

“…The keratinized scutes surround and protect the carapace in chelonids. It has been suggested that keratin is more indicative of long-term toxic element exposure and represents a non-lethal sampling method for determining total body toxic element burden (Sakai et al, 2000;Day et al, 2005;van de Merwe, 2008;Komoroske et al, 2011;Dyc et al, 2016). In turtles from this study, we found that arsenic and selenium were higher in blood compared to keratin, suggesting a more recent exposure to these elements, while mercury was lower in the blood compared to keratin, indicative of a more historal exposure to this element.…”

“…Leatherbacks have been shown to have the highest selenium concentrations in blood for reasons that remain unknown, but this has been attributed to their diet (Innis et al, 2010) and high daily food intake (Heaslip et al, 2012;Perrault, 2014). It is likely that blood selenium concentrations are accurate predictors of diet, as turtle toxicokinetic studies have observed increasing blood selenium concentrations with an increase in selenium dosage (Dyc et al, 2016). This suggests that loggerheads are less exposed to dietary selenium than leatherbacks, but have a greater intake than green turtles due to diet and volume of food intake.…”

“…Additionally, four publications have reported risk assessments of toxic elements in freshwater and marine turtles. Those studies found that arsenic, cadmium, mercury, and selenium may impose risks to marine turtle embryos and hatchlings (Lam et al, 2006;van de Merwe et al, 2009;Perrault et al, 2013;Dyc et al, 2016). Interestingly, due to these risk assessment studies, it is thought that metals may present a higher risk to marine turtle eggs/embryos than organic contaminants (Finlayson et al, 2016).…”