Heavy Metal Toxicity and Differential Effects on the Hyperglycemic Stress Response in the Shrimp Palaemon elegans |
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Authors: | S Lorenzon M Francese E A Ferrero |
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Affiliation: | (1) Shoreline S.c.ar.1., Area Science Park Padriciano 99, I-34012 Trieste, Italy, IT;(2) Department of Biology, University of Trieste, Via Giorgieri 7, I-34127 Trieste, Italy, IT |
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Abstract: | Agricultural and industrial activities cause heavy metal pollution of the aquatic environment. The sensitivity of crustaceans
to heavy metals is well documented. However, the hormonal and metabolic target of physiological functions affected by sublethal
toxicity and stress responses have been scarcely investigated. Exposure of Palaemon elegans to increasing concentrations of heavy metals dissolved in artificial sea water resulted in an order of toxicity tested by
LC50 for 96 h in intact and eyestalkless animals in which Hg is the most toxic, followed by Cd, Cu, Zn, and Pb. Eyestalkless animals
were found to be more sensitive than intact individuals. Heavy metals affect the blood glucose levels, yet manipulative stress
does not. The intermediate sublethal concentrations of Hg, Cd, and Pb produced significant hyperglycemic responses within
3 h, while the highest concentrations elicited no hyperglycemia in 24 h. In contrast, animals exposed to Cu and Zn showed
hyperglycemia even at high concentrations. This difference in response between Cu or Zn and the nonessential heavy metals
Cd, Hg, or Pb can probably be explained by the physiological roles of the former in crustaceans and by tolerance adaptations.
Involvement of the crustacean hyperglycemic hormone (cHH) was tested by routine bioassay on eyestalkless individuals; each
group was injected with a two-eyestalk-equivalent extract from control animals or from shrimp exposed to high concentrations
of Cd, Hg, Pb, or low concentrations of Cu or Zn. All showed a hyperglycemic response within 2 h. In contrast, extracts of
eyestalk removed from animals that had developed a full hyperglycemic reaction after exposure to low concentrations of Hg,
Cd, Pb, or high concentrations of Cu and Zn were depleted of cHH as shown by the attenuation of the response after injection
of the extracts into eyestalkless animals. This generalized and predictable sublethal response can be used as a quantitative
physiological biomarker for water quality monitoring assessment.
Received: 22 September 1999/Accepted: 9 March 2000 |
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