Abstract
To predict internal metal concentrations in animals under specific environmental exposures, the relationship between the exposure concentrations and values of toxicokinetic parameters must be known. At high exposure levels, the availability of carriers transporting metal ions through cellular membranes may become limited, thereby decreasing the assimilation rates (kA). Furthermore, increased metal concentrations in food may result in greater damage to the gut and reduce the assimilation efficiency and/or increase the elimination rate (kE). Therefore, kA should decrease and kE should increase with increasing metal concentrations. In fact, our study on Tribolium castaneum exposed to Cu at 500, 1000, 2000 and 4000 mg kg−1 of dry flour showed that with increasing Cu concentrations, kA decreased from 0.0042 day−1 at 500 mg kg−1 to 0.0026 day−1 at 4000 mg kg−1 in females and from 0.0029 to 0.001 day−1 in males and kE increased from 0.027 to 0.064 day−1 and from 0.018 to 0.04 day−1 in females and males, respectively. Significant differences in kA between the sexes were observed at 2000 and 4000 mg kg−1, whereas significant differences between treatments were found for kA in males. Copper was efficiently regulated by T. castaneum: an eightfold increase in exposure concentrations resulted in only a ca. twofold increase in the internal concentration. No Cu effect on the respiratory metabolism of T. castaneum was found.
Highlights
Nutritional trace metals, such as Zn or Cu, are generally assumed to be efficiently regulated, whereas xenobiotics, such as Pb or Cd, are not (Spurgeon and Hopkin 1999)
Our study on Tribolium castaneum exposed to Cu at 500, 1000, 2000 and 4000 mg kg-1 of dry flour showed that with increasing Cu concentrations, kA decreased from 0.0042 day-1 at 500 mg kg-1 to 0.0026 day-1 at 4000 mg kg-1 in females and from 0.0029 to 0.001 day-1 in males and kE increased from 0.027 to 0.064 day-1 and from 0.018 to 0.04 day-1 in females and males, respectively
Copper was efficiently regulated by T. castaneum: an eightfold increase in exposure concentrations resulted in only a ca. twofold increase in the internal concentration
Summary
Nutritional trace metals, such as Zn or Cu, are generally assumed to be efficiently regulated, whereas xenobiotics, such as Pb or Cd, are not (Spurgeon and Hopkin 1999) This difference should be reflected in distinct changes in the assimilation rate (kA) and/or the elimination rate (kE). Our recent study indicated that crickets, Gryllus assimilis, exposed to metals in food regulated their internal body concentrations of Zn by simultaneously changing their kA and kE, whereas Cd was regulated almost exclusively through an increasing kE (Bednarska et al 2015). It is unknown whether other nutritional and xenobiotic metals are regulated in a similar manner. The availability of carriers by which metal ions are transported through membranes may become limited, and assimilation rates may decrease (Li et al 2009)
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