Factors controlling the bioavailability of methylmercury to fish.
Thesis information
Author:
Leaner, Joy JacqueliAdvisor(s):
Mason, Robert P.
Degree:
Ph.D.
School:
University of Maryland College Park.
Year:
2002.11.26
Full Abstract
Experiments were performed to determine the effect of thiolate organic compounds (cysteine, thiourea or thioglycolate) on the bioavailabity of CH 3Hg(II) to sheepshead minnows, Cyprinodon variegatus. These thiolate compounds effectively increased the bioavailability and uptake of CH3Hg(II) to the fish, at environmentally realistic concentrations. A composite of the CH3Hg(II) concentrations in the visceral organs of the fish, further highlighted the effect of the thiolates, where concentrations in the organs of the thiolate treatments were significantly higher than in the absence of the thiolate compounds.;As a contrast, the bioavailability and redistribution kinetics of CH 3Hg(II) was quantified in C. variegatus after a single dose of CH3Hg(II)-spiked flake food or green algae. Overall, CH 3Hg(II) uptake and redistribution to the tissues was similar irrespective of food source. Methylmercury was rapidly taken up into the intestinal tissue within hours after feeding, followed by a slow release to the blood and the other organs. The results of this study suggests that digestive processes may play an important role in controlling the bioavailability and uptake of CH3Hg(II) in fish.;The role of digestion in controlling the bioavailability of CH3 Hg(II) was investigated further by incubating the gastric and intestinal fluids of channel catfish Ictalurus punctatus, and Atlantic sturgeon Acipenser oxyrinchus, with CH3Hg(II)-spiked bloodworms or sediment. The CH3Hg(II) solubilized by the fluids was greater in the bloodworm than in the sediment incubations. Clear species-specific differences in the extent of CH3Hg(II) solubilized were observed, and was likely attributed to differences in amino acid content in the fluids of the fish, and suggests that the bioavailability of CH3Hg(II) to fish is likely controlled by the digestive processes.;As all solubilized CH3Hg(II) in the intestinal fluid of fish is available for uptake by the intestinal tissue, it is important to address the transport of CH3Hg(II) across the intestinal membrane of the fish. A number of ligands were used to determine CH3Hg(II) transport across the intestinal membranes of fish at 20 and 4°C, and revealed that CH3Hg(II) uptake occurs passive and active processes, and/or via an energy-dependent L-system amino acid carrier, depending on the form of the CH3Hg(II) complex.
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