Nickel tissue residue as a biomarker of sub-toxic exposure and susceptibility in amphibian embryos

Abstract

Although low level exposure to physicochemical agents is the most common environmental scenario, their effects on living organisms are very controversial. However, there is an increasing need to integrate low level exposures from risk assessment to remediation purposes. This study focus on the possibility to employ Ni tissue residue values as biomarkers of sub-toxic exposure and susceptibility to this metal in a range of almost pristine to sub-toxic concentrations for Rhinella arenarum embryos. For that purpose, three batches of amphibian embryos were pretreated during 10 days with three increasing concentrations of Ni starting in 2, 8 and 20 ìg Ni2+ L-1 and ending in 16, 64 and 160 ìg Ni2+ L-1 (in natural fresh waters this value ranges from 2 to 10 ìg L-1; the LC50-24 hr for R. arenarum is 26.2 mg Ni2+ L-1). For the experimental conditions, the Ni tissue residue values at 360 hr post exposure were 0.5, 2.1 and 3.6 ìg Ni g-1 embryo w/w respectively, corresponding to BCFs of 31, 33 and 23. The susceptibility to Ni in those experimental embryos was evaluated by means of challenge exposures to three lethal concentrations of this metal (10, 20 and 30 mg Ni2+ L-1), registering survival during the following 10 days of treatment. As a general pattern, the lower, intermediate and higher pretreatments with Ni resulted in enhanced, neutral and adverse effects on embryonic survival respectively. Thus, sub-toxic exposure to Ni could modify the resistance of the amphibian embryo to this metal and Ni tissue residue values could be considered as biomarkers of both, exposure and susceptibility.