Effect of a chelating agent (EDTA) on zinc uptake and regulation by Palaemon elegans (Crustacea: Decapoda)

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Abstract
The littoral prawn Palaetnon elegans Rathke regulates the body concentration of zinc at higher external zinc concentrations in the presence of EDTA. The dissolved zinc concentration in artificial sea water corresponding to the threshold of regulation breakdown changed from ca. 100 μg Zn 1-1 (ca. 1.53 μmol Zn 1-1) without EDTA, to ca. 316 μg Zn 1-1 (ca. 4.8 μmo1 Zn 1-1) in the presence of 8.6μmol EDTA 1-1 at 10 °C. The regulated body Zn concentration remained unchanged at 77–79 μg Zn g-1 dry wt with or without EDTA. Increased levels of EDTA in the medium decreased the rate of uptake of labelled zinc by P. elegans. The presence of 3 μmol EDTA 1-1 decreased the mean Zn uptake rate of prawns in 100 fig Zn 1-1 (ca. 1.53 μmol Zn 1-1) from 2.9 to 0.25% of total body Zn g-1 day"1 at 10 °C. The increased ability of P. elegans to regulate zinc in the presence of EDTA may be explained by the reduced bioavailability of the zinc-EDTA complex for uptake. There is marked individual variation in the rate of uptake of labelled zinc in prawns, even in the presence of the same concentration of zinc or zinc-EDTA.
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