Cadmium accumulation,distribution and elimination in the bivalve Macoma balthica: Neither metallothionein nor metallothionein-like proteins are involved |
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| Institution: | 1. Department of Environmental Management, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran;2. Iranian National Institute for Oceanography and Atmospheric Science (INIOAS), No. 3, Etemadzadeh St., Fatemi Ave., Tehran 1411813389, Islamic Republic of Iran;3. Young Researchers and Elites Club, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran;4. Department of Environmental Science, Faculty of Environment and Energy, Science and Research Branch, Islamic Azad University, Tehran, Iran;1. University of Crete, Biology Department, 70013 Heraklion, Crete, Greece;2. Hellenic Centre for Marine Research, Institute of Oceanography, 71003 Heraklion, Crete, Greece |
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| Abstract: | Accumulation and elimination of cadmium was investigated in the tellinid clam, Macoma balthica (L.). Accumulation of Cd was linear in soft tissues (0·35 μg g−1 day−1 dry weight) throughout a 29-day exposure period at 100 μg Cd litre−1. Loss of Cd, measured after transfer of experimentally-contaminated clams to clean seawater, was exponential and relatively slow (biological half-time, 70 days). In contrast, Cd uptake onto the shell of Macoma was characteristic of saturation kinetics, indicative of physical adsorption processes. Amounts of Cd accumulated by the shell were low, and the elimination rate rapid (half-time, 7 days) compared with soft tissues.Gel chromatographic profiles of cytosol extracts from control and experimental groups of M. balthica revealed that most of the Cd was bound to high molecular weight ligands, an unusual feature in bivalve molluscs. Although the proportion of cytosolic Cd associated with very low molecular weight ligands is small (< 15%) this pool may be important in regulating Cd fluxes in Macoma during uptake and elimination phases. No evidence was found of metallothionein (or similar metal-binding protein) involvement in Cd accumulation and storage in either field or laboratory exposed clams.The metabolism of Cd in M. balthica is different from that reported for other bivalve groups in several respects. In particular, the relatively slow rate of Cd accumulation in Macoma may be an important adaptive advantage for survival in contaminated areas and may compensate for the absence of a recognised detoxifying (MT) system in this species. |
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