Simultaneous determination of ⁹⁰Sr and Pu isotopes in marine biological samples

^239,240Pu and ⁹⁰Sr are highly important radionuclides in the environment, which can accumulate in the human body through the food chain and cause radiation exposure. With the continuous discharge of treated nuclear contamination water from the Fukushima Daiichi nuclear power plant, it is crucial to investigate and monitor the levels of ^239,240Pu and ⁹⁰Sr in seafood. However, it is still a challenge to determine ^239,240Pu and ⁹⁰Sr in seafood at environmental levels, owing to their extremely low concentrations, labor-intensive and time-consuming pre-treatment for large-sized samples. In this study, a method for simultaneously determining ⁹⁰Sr and ^239,240Pu in various marine biological samples was developed. The distinct behaviors of Sr during Fe(OH)₃ co-precipitation among different marine biota were observed, causing a low yield of strontium in its separation, which is related to the phosphorus content. Using a sequential separation of plutonium and strontium, the sample size required can be reduced to half of the conventional one. Meanwhile, the labor costs and total analysis duration were significantly reduced compared to traditional methods for analyzing ⁹⁰Sr and ^239,240Pu individually. The chemical recoveries of Pu and Sr of more than 75% were obtained, and the detection limits for ^239,240Pu and ⁹⁰Sr were 1-2 orders of magnitude lower than their concentration in environmental marine samples. The accuracy and robustness of this method were validated using standard reference material and spiked samples. The developed method has been successfully applied for simultaneously determining ^239,240Pu and ⁹⁰Sr in fish, shrimp, and seaweed samples from the China Seas.