Toxicokinetics of selenium in Chelonians: trophic exposure in Trachemys scripta scripta

Background. Se is primordial for all development stages in oviparous species but can induce cellular damages (e.g. oxidative stress, histopathotoxicity) , embryo- and immunotoxicity (Usdi 1998; Hoffman 2002) , even at low concentration. Unlike birds and fishes, little is currently known on Se toxicology in reptiles, such as turtles. Most studies reported tissue burdens from field-captured or death animals but rarely provided an understanding of the dose, duration or pathway of exposure. Our present study aims to investigate toxicokinetic of Se through an in vivo and per os exposure of the yellow-bellied slider turtle Trachemys scripta scripta. Furthermore relationship between Se concentration in internal tissues (liver, kidney, muscle ) and external tissues (carapace, skin, blood) will evaluate usefulness of these last in the framework of non-invasive sampling in protected turtle species.
Methodology. 160 yellow-bellied slider turtles, around four weeks old, were acquired in September 2010 and placed by pair in individual tank for a six-month acclimatization period. Lengths, as straight carapace length SCL, ranged from 1.7 to 6.4 cm. Three groups of 42 individuals each were designed. The feeding trial consisted in an eight-week supplementation period followed by a four-week depuration period. At some intervals during that time scale, six individuals per group were sacrificed and tissues were collected (carapace, scutes, skin, blood, liver, kidney, muscle) for selenium analysis. During the supplementation period, turtles were fed with diet containing 0 (control) , 23 or 47 µg.g-1 of selenium as seleno-L-methionine. During the depuration period, the remaining individuals were fed with non-supplemented control diet. Total selenium was investigated by ICPMS.
Results and discussion. The Se-concentration in all collected tissues increased in a dose-dependent way over the course of the supplementation period. Se accumulation had no effect on survival, diet behavior or growth. Higher Se levels were observed in kidney, followed by muscle and blood. During the recovery period, Se levels decreased in tissues in a significantway except in blood, muscle and carapace. Blood, skin and carapace Se levels were positively correlated to those in kidney and muscle. Such relationships were also observed between liver and carapace, and blood. Results suggested a Se transfer through the food intake and the potential use of carapace and skin as relevant tools in non-invasive biomonitoring studies.