Toxicity of radium (226-Ra) to early life stages of fishes

This study generated chronic early life stage (ELS) toxicity data for regulatory guideline derivation using three freshwater fish species: rainbow trout (Oncorhynchus mykiss), white sucker (Catostomus commersonii), and fathead minnow (Pimephales promelas). Embryos were exposed at fertilization (O. mykiss, C. commersonii) or 4 hours post‑fertilization (P. promelas) to environmentally relevant activities of radium-226 (i.e., 0, 0.1, 0.5, 2.5, 12.5, and 62.5 Bq/L, nominal). Exposures were conducted in reconstituted very soft water (10–13 mg/L CaCO₃) for O. mykiss and C. commersonii, and in hard water (160–180 mg/L CaCO₃) for P. promelas. Sensitive toxicity thresholds were estimated at swim‑up for multiple endpoints, including ELS mortality, condition (as the scaled mass index), developmental timing (eyed stage, hatch, swim‑up), morphometric indicators (length and mass), and structural deformities. These results strengthen and support: (1) the data gap for radiological risk assessment with radium-226, (2) species sensitivity distribution (SSD) modeling, and (3) the development of a protective regulatory water quality guidelines for radium-226 in aquatic environments.

Note:
FHM = fathead minnow
RBT = rainbow trout
WS = white sucker