Sublethal effects of repeated intraperitoneal cadmium injections on rainbow trout (Oncorhynchus mykiss)

Acute and chronic effects of cadmium have been widely described for different aquatic organisms and exposure routes. However, there is clearly a lack of information on the potential of cadmium to cause genotoxic effects. This work presents genotoxic and nongenotoxic parameters analyzed in cadmium-exposed rainbow trout. The assessment was performed for sublethal levels after long-term exposure using six intraperitoneal injections of 0.5 mg/kg (Day 1), 1 mg/kg (Days 3, 7 and 11), and 2 mg/kg (Days 15 and 19) to allow precise estimation of the dose. Cadmium accumulation in target tissues, essential metal mobilization by cadmium at the subcellular and tissue levels, and induction of metallothioneins were selected as exposure and effect parameters. Induction of micronuclei and variation in DNA content (expressed as variation coefficient in the G1 phase of the cell cycle) in blood cells, determined by flow cytometry, were selected as biomarkers for genotoxic effects. Cadmium accumulation, induction of metallothioneins, and mobilization of essential metals at the subcellular level were observed in different organs in response to cadmium exposure. The highest metallothionein induction was observed in liver, reaching 270+/-90 nmol/g wet tissue in treated fish versus 2.68+/-1.1 nmol/g wet tissue in controls. The highest cadmium accumulation was also observed in the liver (27.8+/-9.5 microgram Cd/g wet wt in treated animals versus 1.0+/-1.7 in the control group). However, no genotoxic effects were observed in blood cells. The frequency of micronuclei was 0.012+/-0.008 for the control group and 0.013+/-0.021 for treated animals. The variation coefficient of G1-phase nuclei was 3.61+/-0.66 and 3.22+/-0.29 for control and cadmium-exposed groups, respectively. Thus, it is concluded that under the experimental conditions employed here, treatment of rainbow trout with cadmium chloride at doses that produce significant toxicological alterations at the tissue and subcellular levels does not provoke observable alterations in the genotoxic parameters considered in this study.