American oyster (Crassostrea virginica) as a biosentinel for radium: influence of age on radium-226 levels in shell and soft tissues

Radium-226 ( 226 Ra) concentrations and their distribution were investigated in 1,650 American oysters ( Crassostrea virginica ) collected from five oyster farms in New Brunswick, Canada. The objective of this study was to quantify age-related variations in 226 Ra concentrations and to assess the potential of the 226 Ra/Ba ratio for improving spatial discrimination among sites. Oysters aged 1 to 4 years were pooled by site and age into composite samples of shells and soft tissues. Mean 226 Ra concentrations ranged from 3.4 ± 2.3 fg g -1 (124 ± 84 μBq g -1 ) in dried soft tissues to 23.9 ± 10.9 fg g -1 (874 ± 399 μBq g -1 ) in shells, indicating relatively low environmental exposure in the studied ecosystems. Concentrations of twenty additional elements (Li, Na, Mg, Al, P, K, Ca, V, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Cd, Ba, and U) were also measured. Principal component analysis (PCA) and analysis of variance (ANOVA) were used to evaluate the respective influences of oyster age and site of origin. In shells, 226 Ra concentrations increased significantly with age, whereas the opposite trend was observed in soft tissues. Normalization of 226 Ra concentrations using barium (Ba), a chemically analogous alkaline earth element, markedly reduced age-related variability and improved spatial discrimination among sites. However, site rankings differed slightly depending on the biological matrix and the parameter considered (absolute 226 Ra concentrations versus 226 Ra/Ba ratios). These results highlight the importance of considering biological factors, particularly age, when interpreting 226 Ra concentrations in oysters, and support the potential use of elemental normalization approaches for improving spatial comparisons in biomonitoring studies.