IONIC REGULATION RESPONSE OF MACROBRACHIUM AMAZONICUM TO ACUTE MERCURY EXPOSURE UNDER DIFFERENT PH AND DISSOLVED ORGANIC CARBON CONDITIONS

Abstract

Mercury contamination in aquatic ecosystems is a concern due to its toxic effects on local fauna, interfering with osmoregulation and ionic homeostasis in aquatic organisms. The Amazonian shrimp (Macrobrachium amazonicum), a key species in freshwater and estuarine ecosystems, is frequently used as a model organism in ecotoxicological studies. This study evaluated the impact of acute mercury exposure (220 ng L⁻¹ HgCl₂, 24 h) on enzymatic activities related to ion regulation under different pH conditions (4 and 7) and in the absence or presence of dissolved organic carbon (DOC, 10 mg L⁻¹) from the Rio Negro (Manaus, Brazil). The enzymes analyzed were Na⁺/K⁺ ATPase, V-type H⁺ ATPase, and carbonic anhydrase in shrimp (n = 10; weight: 0.12 ± 0.002 g; length: 5.4 ± 0.13 cm). Enzymatic activities were compared between control groups and mercury-exposed groups across four treatments: pH 7, pH 7 + DOC, pH 4, and pH 4 + DOC. Although some numerical variations were observed, no statistically significant differences were found between the groups for any of the enzymes. These results suggest that, under the tested conditions, acute mercury exposure did not affect the osmoregulatory and ion-regulating enzymatic activities of M. amazonicum, indicating a possible influence of pH and/or DOC on the metal’s bioavailability