Abstract
The tolerance of Perna viridis to a high inorganic mercury (Hg) exposure was determined based on its accumulation, depuration and distribution. The Hg accumulation of the mussel was conducted for a 4-day semi-static exposure at a ‘very’ high Hg concentration (100 ig/L). None of the mussels died after the experimental period, indicating that the elevated level of inorganic Hg exposure was not toxic to P. viridis. Following the 4-day exposure, the Hg concentrations were higher in the gill and byssus than in the mantle, foot, gonad and muscle (with bioconcentration factor values being between 13 and 625). The Hg distribution among the different soft tissues after 11 days of depuration was almost similar with that after Hg exposure. The high Hg levels found in the byssus and different soft tissues after the depuration indicated that Hg accumulated in the different ST was tightly bound to metallothionein and it was not easily mobilized. The Hg distribution in the byssus and in the different soft tissues could be due to their differing capacities for Hg accumulation and depuration. Since the soft tissues of P. viridis can accumulate inorganic Hg in high concentrations after exposing to a ‘very’ high level of inorganic Hg, it has a high bioaccumulative capability and a high tolerance to inorganic Hg. The mussel byssus was found to have the highest depuration rate coefficient, indicating that it could act as one of the excretion routes for Hg and it can be proposed as a sensitive biomonitoring material for Hg. The fecal materials released by the mussel had elevated levels of Hg, indicating that the mussels acted as a Hg retention mechanism in the coastal ecosystem.
Highlights
Of the total high inorganic mercury (Hg), methyl-Hg is the most toxic form of Hg from the human health point of view
The results indicated that fecal materials produced by P. viridis contained more than 100,000 ng/g Hg during the accumulation periods
The higher levels of Hg (121-365 ng/g) in the fecal materials during the experimental period than in day 0 (48 ng/g) might be due to the algae fed to the mussels once in every two days containing some contaminated Hg. These levels were significantly (P< 0.001) lower than those in the exposed mussels that were higher than the detection limit set by the Hg model MA-1S. These results showed the ability of P. viridis to accumulate Hg at elevated levels in the byssus and in the different soft tissues without signs of mortality when the mussels were exposed to elevated levels of inorganic Hg (100 μg/L)
Summary
Of the total Hg, methyl-Hg is the most toxic form of Hg from the human health point of view. Exposing the mussels to an elevated level of metal under laboratory condition could provide information on the bioaccumulative capability for the metal and its tolerance to the high metal level. We looked into the metal accumulation by P. viridis exposed to a ‘very’ high level of inorganic Hg from the dissolved solution phase of seawater since the bioavailability of inorganic Hg had been demonstrated to be mainly from the dissolved phase (Davies and Pirie, 1978; Eganhouse and Young, 1978). The objective of this study was to determine the tolerance and the accumulation, depuration and distribution of 100 μg/L inorganic Hg exposure under laboratory conditions
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