Monitoring of marine pollution and stress responses: Radionuclides concentration and antioxidant molecules in macroalgae and seagrass

The biological effects of marine radionuclides on the macroalgae Cystoseira crinita and Halopteris scoparia, as well as the seagrass Cymodocea nodosa, were investigated in İzmir Bay. Concentrations of radionuclides ²¹⁰Pb, ²²⁶Ra, ²³²Th, and ⁴⁰K were measured in samples of C. crinita and H. scoparia, whereas only ²¹⁰Pb and ⁴⁰K concentrations were determined in C. nodosa. In this study, ²¹⁰Pb concentrations ranged from 11.38 to 31.72 Bq/kg in C. crinita, 19.7–98.02 Bq/kg in H. scoparia, and 26.09–81.27 Bq/kg in C. nodosa. Elevated ²¹⁰Pb levels in H. scoparia and C. nodosa were observed predominantly during autumn and winter. The ²¹⁰Po/²¹⁰Pb activity ratios were found to range between 1.45 and 2.25 in C. crinita, 0.15–1.30 in H. scoparia, and 0.70–1.47 in C. nodosa. The antioxidant defense mechanisms in response to radiation-induced stress were examined in both macroalgae and seagrass samples, focusing on key biomarkers such as ascorbate peroxidase (APX), catalase (CAT), and proline. Correlation analyses were conducted between radionuclide concentrations and antioxidant activity. C. crinita exhibited a defense response to ²¹⁰Pb exposure similar to that of ²¹⁰Po, primarily through increased CAT enzyme activity. In C. nodosa, elevated ⁴⁰K levels were associated with enhanced proline and APX responses, while the accumulation of ²¹⁰Pb was met with a significant increase in proline-mediated antioxidant defense.