Mercury biomagnification in a tropical black water, Rio Negro, Brazil

Area of Science:

• Environmental Science
• Ecotoxicology
• Aquatic Ecology

Background:

• Amazon basin populations rely on fish as a primary nutritional source.
• Methylmercury (MMHg) bioaccumulates in fish, posing a human health risk.
• Fish MMHg concentration and consumption levels determine human exposure risk.

Purpose of the Study:

• To assess total mercury (Hg) levels in various fish species from the Rio Negro basin.
• To investigate the relationship between fish feeding strategies, weight, and Hg concentration.
• To compare Hg levels in fish from the Rio Negro with established safe consumption limits.

Main Methods:

• Collected 951 fish samples across nine locations in the Rio Negro basin.
• Analyzed total Hg concentrations in fish representing different trophic levels (herbivorous, detritivorous, omnivorous, piscivorous).
• Examined correlations between fish weight, Hg concentration, water pH, Hg concentration, and dissolved organic carbon (DOC).

Main Results:

• Hg concentrations varied significantly among species, with piscivorous fish exhibiting the highest mean concentrations (688.90 ng/g).
• Sixty percent of piscivorous fish exceeded the safe human consumption limit of 500 ng/g.
• Positive correlations between fish weight and Hg were observed in piscivorous species (Serrasalmus spp., Cichla spp., Pimelodus spp.), while negative correlations were found in some non-piscivorous species (Potamorhina latior, Leporinus spp.).

Conclusions:

• Fish feeding strategy is a key determinant of mercury bioaccumulation in the Rio Negro.
• Piscivorous fish represent a significant pathway for mercury exposure in humans consuming Rio Negro fish.
• Naturally occurring mercury sources contribute to high fish Hg levels in the Rio Negro, irrespective of mining activities.