Histopathological analysis of nauplii under different forms of mercury stress.

Inorganic mercury (Hg) and methylmercury (MeHg) have emerged as global pollutants owing to their long-term environmental stability and bioaccumulation. These heavy metals enter aquatic systems via industrial emissions, coal combustion, and natural processes, posing a serious threat to ecosystems and human health. This study assesses the impact of Hg and MeHg on the growth and development of brine shrimp () nauplii by analyzing the histopathological effects on their tissues. Brine shrimp nauplii from the Bohai Bay in China were selected as the study subjects and exposed to 1 μmol/L solutions of HgCl₂ and MeHgCl. Tissue sections were continuously taken at different immersion times. After staining with the standard hematoxylin-eosin (HE) method, the tissue morphology of brine shrimp nauplii under different forms of Hg stress was observed under a light microscope. The results showed that MeHg exhibited significantly greater toxicity to brine shrimp nauplii than Hg. Under the same exposure time, the MeHg group exhibited more pronounced epithelial cell damage, nuclear material disorder, and nucleoplasm diffusion outside the nucleus than the HgCl₂ group. This finding provides an important theoretical support for further research into the toxicological mechanisms of MeHg and Hg, and highlights that the toxic effects of methylmercury on aquatic organisms.