ECOTOXICOLOGICAL EFFECTS OF MERCURY IN MACROBRACHIUM AMAZONICUM UNDER THE INFLUENCE OF PH AND DISSOLVED ORGANIC CARBON: GENOTOXIC ASSESSMENT IN AMAZONIAN BLACKWATER

Abstract

Mercury contamination in Amazonian blackwater rivers, such as the Rio Negro, which is rich in dissolved organic carbon (DOC), represents an environmental threat due to the toxicity and bioaccumulation of this metal. This study evaluated the short-term (24 h) effects of exposure of the Amazonian shrimp Macrobrachium amazonicum (n = 10; weight: 0.12 ± 0.002 g; length: 5.4 ± 0.13 cm) to HgCl₂ (220 ng L⁻¹, CONAMA 357/2005 permissible limit) under four experimental conditions (pH 7, pH 7 + DOC, pH 4, and pH 4 + DOC). Total mercury concentrations were measured in water and shrimp muscle. Lipid peroxidation (LPO) and DNA damage analyses were also performed. The presence of DOC increased mercury persistence in the water (independently of pH), but without bioaccumulative effects in muscle tissue (0.0013 ± 0.000095 mg kg⁻¹). Analysis of lipid peroxidation levels in the hepatopancreas revealed no statistically significant differences among experimental groups (P = 0.359). In contrast, DNA damage assessment showed significant differences between exposed groups and controls (P < 0.001). Even at the legal limit, HgCl₂ caused DNA damage in M. amazonicum after 24 h of exposure, without increases in LPO or muscle bioaccumulation. Altogether, these findings indicate a relevant sublethal effect, with potential impairment of the organism’s defenses, and demonstrate that mercury toxicity is modulated by the natural components of Rio Negro water