Selenium moderates mercury toxicity in free-ranging freshwater fish

Area of Science:

• Environmental toxicology
• Biochemistry
• Ecotoxicology

Background:

• Mercury (Hg) and selenium (Se) exhibit high affinity, influencing each other's bioavailability and toxicity.
• The tissue Se:Hg molar ratio is critical in determining Hg toxicity and Se's protective role.
• Metallothionein (MT) is a sensitive biomarker for metal-induced toxicity.

Purpose of the Study:

• To investigate the effects of Hg and Se levels on metallothionein (MT) induction in brown trout.
• To determine if increased tissue Se:Hg molar ratios and Se levels influence MT demands.
• To assess the protective role of Se against Hg toxicity in a Se-depauperate environment.

Main Methods:

• Analysis of Hg and Se levels in free-ranging brown trout from Lake Mjøsa, Norway.
• Quantification of metallothionein (MT) as a biomarker for metal exposure.
• Statistical assessment of the relationship between tissue Se:Hg molar ratios, Se levels, and MT induction.

Main Results:

• The Se:Hg molar ratio and tissue Se levels were key factors in assessing metal exposure and MT levels.
• Mercury in molar excess over selenium was a stronger inducer of MT synthesis than Hg levels alone.
• Elevated Se:Hg ratios indicated a protective effect of Se against Hg toxicity.

Conclusions:

• The tissue Se:Hg molar ratio is a more accurate indicator of Hg toxicity than Hg levels alone.
• Selenium plays a significant protective role against mercury toxicity in aquatic organisms.
• Considering Se's protective effects is crucial for assessing Hg risks to wildlife and human health.