Assimilation of cadmium in a European lacertid lizard: Is trophic transfer important?

Abstract

Apart from analyses for elemental contaminants in field-collected specimens, very little is known about the assimilation and accumulation of inorganic contaminants in reptiles. Recent dietary studies with reptiles (and some other vertebrates and invertebrates) have taken care to incorporate the principles of trophic transfer by pre-exposing prey items to the elemental contaminant of interest. However, there are conflicting data in the literature as to whether biologically incorporated metals are more bioavailable to consumers in a food chain than simple salts added to the diet, and this study examines this issue in a lacertid lizard. Adult individuals of Podarcis carbonelli were exposed to cadmium (Cd) in a 21-week dietary study to determine whether the form in which the Cd is provided influences assimilation efficiency for this metal. Lizards were provided with Cd that had either been biologically incorporated into crickets or as Cd(NO3)2 added superficially to crickets just prior to feeding. Radiospectrometric analysis for 109Cd in animal tissues and fecal material was used to follow Cd accumulation over the duration of exposure. The highest levels of accumulation were found within the gut. This, combined with the observation of higher rates of assimilation over the first five weeks, strongly suggests a rapid accumulation of Cd within the gut tissue followed by a slower redistribution to other tissues. No statistically different levels of Cd assimilation efficiency were detected between the two treatment groups, nor were there any statistically significant differences between the two treatment groups in relation to the proportional distribution to the gut, liver, or kidneys.

Cadmium toxicokinetics and bioaccumulation in turtles: trophic exposure of Trachemys scripta elegans

“…Our results on levels of gastrointestinal absorption are consistent with levels reported in various vertebrate experiments ranging from 0.5 to 16% (Neathery and Miller 1975;Xu andWang 2002, Hispard et al 2008;Mann et al 2006;Zalups and Ahmad 2003) according to the Cd-concentration in diet that individuals were fed. In our study, the proportional accumulation in liver and kidney depended on the amount of Cd ingested with decreasing assimilation efficiency when ingestion increased, suggesting that as the dose of Cd increases, assimilation decreases.…”

“…Cd concentration in feces suggest that gastrointestinal uptake of Cd was highest during the first weeks of exposure, after which assimilation decreased significantly, reflecting reduced binding of Cd in the membranes of gastro-intestinal tracts. Higher levels of Cd assimilation in the first weeks have already been reported in lizards and have been related to accumulation and therefore saturation of the binding sites for Cd transport (Mann et al 2006). Intestinal absorption of Cd is characterized by a high accumulation of Cd within the intestinal mucosa and a low rate of subsequent transport of Cd into the blood.…”

“…However, most ecotoxicological research on reptiles relies on the assessment of tissue concentrations from field-captured individuals (Hopkins 2006) and few studies have focused on the fate and the effects of contaminants (Ganser et al 2003;Hopkins et al 2002;Mann et al 2006Mann et al , 2007. Nevertheless, assessing the fundamental processes of distribution and accumulation and kinetics such as the uptake and depuration rates of contaminants is necessary in order to understand the mechanisms of bioavailability, trophic transfer, the path taken by contaminants in the body and the biological effects on reptiles.…”

Concentração de elementos traços em serpentes do litoral e da região serrana do Espírito Santo

“…No presente estudo, não foram encontradas concentrações elevadas deste elemento no rim das serpentes analisadas, o que sugere que este único tecido não pode ser um biomarcador deste metal do organismo. Burger et al (2005) afirmam que níveis sanguíneos de Cd podem ser indicadores de exposição recente, mas o metal pode se acumular em tecidos moles e, alguns estudos afirmam que os principais órgãos-alvo para a acumulação de Cd em mamíferos e outros vertebrados, incluindo rép-teis, são o fígado, rim e da mucosa intestinal (Gutleb & Gutleb 1991, Cooke & Johnson 1996, Linder & Grillitsch 2000, Mann et al 2006. Campbell et al (2005) sugerem que as concentrações de Cd acima de 0,44 μg/g no rim podem indicar uma grande exposição ambiental a esse metal e, grande parte das espécies de serpentes estudas na presente pesquisa, apresentaram concentrações bem abaixo do que a sugerida pelo referido autor.…”

Addressing current knowledge gaps on radionuclide transfer to reptiles

“…However, excretion of sequestered contaminants via the skin may not be as prevalent in other reptile groups. For example, laboratory-based research ICRER 2011 S523 on Cd uptake in Podarcis carbonelli (Carbonell's wall lizard) demonstrated minimal loss of the Cd body-burden via skin shedding [21]. Skin samples may thus show promise as a non-lethal technique but relationships between skin and internal tissue concentrations for different elements and reptile groups would need to be well-defined.…”