Mercury accumulation, speciation, and temporal trends in Atlantic Stingrays (Hypanus sabinus)

Area of Science:

• Environmental toxicology
• Marine biology
• Biogeochemistry

Background:

• Mercury (Hg) in aquatic sediments can be converted to toxic methylmercury (MeHg) by microbes.
• Atlantic stingrays (Hypanus sabinus) inhabit diverse western North Atlantic coastal areas.
• Mercury dynamics and speciation in stingrays are poorly understood.

Purpose of the Study:

• Quantify total Hg and Hg species (Hg(II), MeHg) in Atlantic stingrays.
• Examine Hg concentrations in relation to stingray size and tissue type.
• Assess potential Hg bioaccumulation and demethylation in stingrays.

Main Methods:

• Collected muscle and liver tissues from 29 Atlantic stingrays in Florida's Indian River Lagoon (2012-2013).
• Lyophilized and homogenized tissues.
• Analyzed total Hg, Hg(II), and MeHg using a direct mercury analyzer.

Main Results:

• Total Hg concentrations in muscle were positively correlated with stingray disk width.
• Mean total Hg was higher in muscle (0.56 ± 0.30 mg/kg dw) than liver (0.23 ± 0.19 mg/kg dw).
• Liver methylmercury comprised 31-99% of total Hg; Hg liver/muscle ratio <1 suggests limited hepatic demethylation.
• Total Hg in muscle has decreased since 1994, indicating reduced bioavailable Hg in the IRL.

Conclusions:

• Atlantic stingrays in the IRL exhibit lower Hg concentrations than those causing toxicity in fish, though elasmobranch thresholds are unclear.
• Hg levels in stingray muscle have declined over 20 years.
• Reduced bioavailable Hg in the Indian River Lagoon ecosystem is suggested.