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Mercury in pilot whales: possible limits to the detoxification process
F Caurant1, M Navarro, J C Amiard
1ISOMer, Nantes, France.
The Science of the Total Environment
|July 16, 1996
Summary
Pilot whales accumulate high levels of cadmium and mercury, yet show remarkable tolerance. Detoxification primarily involves mercury-selenium complexes in the liver, though this process is limited in some individuals and poses a potential risk.
Area of Science:
- Marine Mammal Toxicology
- Environmental Chemistry
- Biogeochemistry
Background:
- Pilot whales (Globicephala melas) are known to accumulate significant levels of cadmium and mercury.
- These heavy metal concentrations often exceed those found in other marine mammals.
- Despite high accumulation, pilot whales exhibit notable tolerance to heavy metals, with no apparent widespread toxic effects.
Purpose of the Study:
- To investigate the cellular distribution and detoxification mechanisms of mercury in pilot whales.
- To identify the role of specific proteins and biochemical pathways in heavy metal tolerance.
- To assess potential toxicological risks associated with mercury accumulation in this species.
Main Methods:
- Analysis of liver samples for cellular mercury distribution.
- Identification and quantification of mercury-binding proteins, including metallothionein-like proteins.
- Determination of molar ratios between mercury and selenium to elucidate detoxification pathways.
- Comparison of mercury speciation (organic vs. inorganic) in different tissues (liver and muscle).
Main Results:
- Mercury was predominantly bound to the insoluble fraction of liver cells, indicating metallothionein-like proteins play a minimal role in its detoxification.
- A high molar ratio of mercury to selenium suggests the formation of mercury-selenium complexes as the primary detoxification mechanism, leading to mercury demethylation.
- Mercury in the liver was mainly inorganic, while muscle tissue showed a higher proportion of organic mercury.
- Detoxification appeared limited in lactating females and individuals within a specific school.
Conclusions:
- Pilot whales utilize a mercury-selenium complexation pathway for detoxification, primarily in the liver.
- The observed limitations in detoxification in certain individuals or groups may be linked to dietary shifts.
- These limitations present a potential toxicological risk for pilot whale populations, particularly under specific environmental or physiological conditions.