The performance of solution nebulization (SN), electrothermal vaporization (ETV) and laser ablation (LA) of dried micro-droplets as sample introduction systems for ICP-MS are compared for the determination of several radionuclides in digested biological tissue, nearshore sea-water and river water. Samples were subjected to a Ca3(PO4)2 co-precipitation preconcentration prior to analysis. Each introduction system possesses unique advantages and disadvantages. ETV accommodates samples having higher dissolved solids content; consequently, for SN and LA, sample concentrates require additional dilution by 50- and 10-fold, respectively. ETV and LA achieved similar sensitivities and limits of detection, the latter ranging from 0.017 to 0.029 pg ml−1. Although SN provides the best precision (2% RSD versus 7 and 8% for ETV and LA, respectively), formation of uranium hydride can be reduced at least 100-fold using LA of dried micro-droplets of samples. The accuracy of the method was validated by determination of U and Th in NIST SRM 1566b Oyster Tissue, NRC CRM CASS-4 Nearshore Seawater and SLRS-4 Riverine Water and via spike recoveries for Pu.