Toxicity of REEs, Th, and U: A Biodisponibility, Cytotoxicity, and Bioaccumulation Assessment in Marine Sediment

In this work, bioaccessibility tests for rare earth elements (REEs), Th, and U in marine sediment were carried out, in addition to complementary tests for cytotoxicity and bioaccumulation for the elements La, Ce, Eu, and Gd. The evaluation of human health risk through dermal absorption and oral ingestion was performed using the hazard quotient (HQ). According to the gastric digestion simulation (SBET), it was observed that the elements Ce and Nd exhibited higher absorption capacities in the human body (> 2 µg g^-1). La and Sc presented intermediate concentrations (close to 1 µg g^-1), while the remaining elements displayed concentrations below 0.5 µg g^-1. In the gastrointestinal digestion extraction stage (PBET), all the elements maintained a similar absorption capacity to that observed in SBET, except for the absorption of Y which increased. The results of the bioaccumulation test conducted with fibroblast cells (L929) indicated that La and Eu had a 25% probability of intracellular accumulation. The cell viability test, with exposure to a standard REEs, Th, and U solution in 2% v v^-1 HNO₃ medium (until 100 μg mL^-1) and an aqueous solution of La₂O₃, Gd(NO₃)₃, Ce(NO₃)₃, and Eu₂O₃ (until 1000 μg mL^-1), did not demonstrate cytotoxic effects on fibroblast cells. Considering the ingestion hazard quotient (HQ_ing) and dermal hazard quotient (HQ_derm) obtained, it was suggested that there is no significant risk of non-carcinogenic effects (< 1). However, they had higher HQ_ing values compared to HQ_derm, indicating that REEs pose more significant risk to human health through oral ingestion absorption than dermal absorption.