The Effects of Mercury Exposure on Intracellular Distribution of Mercury, Copper and Zinc in Skeletonema costatum (Grev.) Cleve

Abstract

The effects of exposure to low concentrations of HgCl2 on the intracellular levels of Cu, Zn and Hg in S. costatum grown in artificial seawater were determined. An attempt was made to determine whether Hg-induced synthesis of metallothionein-like substance could be responsible for sequestering heavy metals in a diatom. Short-term exposure to 1.84 nM HgCl2 resulted in a reduced growth rate and cell density, possibly due to the toxic effects of Hg which mainly accumulated in the high MW pool. Pre-exposure to 1.84 nM HgCl2 prior to exposure at 5.53 nM HgCl2 resulted in a lower accumulation of Hg in the high MW pool. Exposure to 0.37 nM HgCl2 was sufficient to alter the levels and distribution of intracellular Cu and Zn. Upon Hg exposure, Zn levels decreased in high and low MW fractions but gradually increased in the medium MW pool. Cu slightly increased in the high MW pool but remained constant in the medium and low MW pools in relation to total intracellular levels. The increase of Zn in the medium MW pool, in Hg-exposed cultures, the low levels of Cu and Zn in the medium MW fractions, and the absence of aromatic amino acids, as determined by the 280 nm absorbance profiles, suggest that metallothionein may play a role in storage or detoxification of heavy metals in S. costatum. High levels of Cu and Zn in the low MW pool may indicate that a substance of lower MW than usually reported for metallothionein-like substance also may play a role in the storage and detoxification of heavy metals in S. costatum.