title: Regulation of body metal concentrations: Toxicokinetics of cadmium and zinc in crickets.
abstract: Previous studies indicated that essential and xenobiotic metals differ substantially in terms of their toxicokinetics. Whether these differences are due to different assimilation rates, different elimination rates, or both, and whether all metals are regulated in a similar manner but with different efficiency remains unclear. To compare the mechanisms responsible for the regulation of different metals, parameters for toxicokinetic models have to be tested under exposures to the identical molar concentration of those metals. In this study, the cricket Gryllus assimilis was exposed to Zn or Cd at 2.5, 10, and 40mMkg(-1) dry food. The body concentrations of the metals were not perfectly regulated by the crickets. For Zn, a clear increase in the body concentration was found only at the highest treatment; whereas at the lowest treatment, the internal concentration remained unchanged throughout the experiment. At the lowest Zn concentration, the assimilation (kA) [day(-1)] and elimination (kE) [day(-1)] rate constants were balanced (kA=0.024, kE=0.024). When increasing the Zn exposure, kA decreased to 0.018 at 10mMkg(-1) and 0.01 at 40mMkg(-1), and kE increased to 0.05 and 0.07, respectively. Therefore, the body concentration of Zn was regulated by simultaneously changing the assimilation and elimination rate. By contrast, even at the lowest treatment, a significant increase in Cd concentration was observed in the crickets. The equilibrium Cd concentration resulted almost exclusively from increasing kE from 0.17, through 0.28 to 0.61 at 2.5, 10 and 40mMkg(-1). The kA for Cd did not reveal any clear trend. Zn was more efficiently regulated by crickets than was Cd: a 16-fold increase in exposure concentration (from 2.5 to 40mM Znkg(-1)) resulted only in a twofold increase of internal concentration, whereas the identical increase in Cd exposure concentration resulted in almost a sevenfold increase in internal concentration of this metal.
authors.affiliation: Institute of Nature Conservation, Polish Academy of Sciences, Al. Mickiewicza 33, 31-120 Kraków, Poland. Electronic address: bednarska@iop.krakow.pl.
authors.forename: Agnieszka J
authors.initials: AJ
authors.lastname: Bednarska
authors.affiliation: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Opyd
authors.affiliation: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
authors.forename: Ewelina
authors.initials: E
authors.lastname: Żurawicz
authors.affiliation: Institute of Environmental Sciences, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland.
authors.forename: Ryszard
authors.initials: R
authors.lastname: Laskowski
mesh_terms: D000818:Animals; D002104:Cadmium / Q000493:pharmacokinetics* / Q000633:toxicity; D004781:Environmental Exposure; D006135:Gryllidae / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000493:pharmacokinetics*; D015032:Zinc / Q000493:pharmacokinetics* / Q000633:toxicity
chemical_list: D014874:Water Pollutants, Chemical; D002104:Cadmium; D015032:Zinc
keywords: Assimilation; Elimination; Gryllus assimilis; Metal; One-compartment model