An experimental ecotoxicological model and its application to the behavioral study of inorganic mercury (HgCl$_2$) in the environment

The aim of this research was to study the accumulation and transfer process of a contaminant (mercury) within an ecosystem. The study was led with a laboratory-conceived ecotoxicological model including two basic factors: biotic and abiotic, and was performed with inorganic mercury (HgCl$_2$). The chosen method was an interactive model (experimental ecosystem) with three compartments: water, natural sediment and air. The influence of pH and temperature on the behavior of mercury in two compartments, water and air (basic model) were first studied, and then the sediment and fish (Scardinius erythrophtalmus) were included. The mercury determination in various mediums was carried out with a laboratory prototype based on the principle of cold vapor flameless spectrometric atomic absorption developed by Livardjani et al. [1]. It was conceived in order to make direct analyses in the air and the water, as well as in the sediment and fish after mineralization. The measurement and mineralization conditions were optimized so as to obtain higher sensitivity and accuracy (90 ng per m$^3$ of air, 15 pg in absolute weight). In an acid medium (${\rm pH < 5}$), mercury remained stable in the water, but its concentration decreased as pH and temperature increased. However, in the presence of sediment (pH 7.2), all the mercury disappeared, and was fixed onto the sediment. In the fish, a maximum level of mercury accumulation was reached after 10 days of exposure, and did not vary thereafter, no matter how long the exposure time lasted