title: Speciation of hepatic Zn in trout exposed to elevated waterborne Zn using X-ray absorption spectroscopy.
abstract: The long-term impacts of chronic metal exposure for aquatic biota are not well understood, partly due to a lack of understanding of metal speciation within tissues. The objective of this study was to determine hepatic Zn speciation of rainbow trout (Oncorhnychus mykiss) exposed to Zn-enriched water in relation to unexposed (control) fish,through direct analysis of freeze-dried liver samples using synchrotron X-ray absorption spectroscopy (XAS). Juvenile rainbow trout (n=30) were exposed to Zn in a two-step process, 200 microg L(-1) for 14 days, followed by 370 microg L(-1) for 23 days. Thirty other trout were grown in a control treatment (10 microg Zn L(-1)). At the end of the experiment, three liver samples per treatment were collected, freeze-dried, ground, and mixed homogeneously. Although Zn concentration was higher in the Zn-exposed livers than in the control livers (22.32 vs 13.73 mg kg(-1), respectively; p < 0.05), Zn speciation was similar for both groups. Extended X-ray absorption fine structure (EXAFS) spectroscopy indicated that Zn was coordinated to 4 sulfur atoms with an average Zn-S bond distance of 2.31 +/- 0.02 A. Sulfur K-XANES analysis confirmed that S was predominantly in reduced organic form analogous to cysteine. Our results are consistent with previous evidence for Zn(II) bonding to S in metallothionein proteins. These results suggest that the mechanisms for dealing with the extra load of bioaccumulated Zn in high exposure conditions were the same as in the control group.
authors.affiliation: Environment Group, Mining and Mineral Sciences Laboratories, Natural Resources Canada, 555 Booth Street, Ottawa, Ontario, K1A 0G1. sbeauche@nrcan.gc.ca
authors.forename: Suzanne
authors.initials: S
authors.lastname: Beauchemin
authors.forename: Dean
authors.initials: D
authors.lastname: Hesterberg
authors.forename: Jennifer
authors.initials: J
authors.lastname: Nadeau
authors.forename: James C
authors.initials: JC
authors.lastname: McGeer
mesh_terms: D015502:Absorptiometry, Photon; D000818:Animals; D008099:Liver / Q000737:chemistry; D017686:Oncorhynchus mykiss; D013455:Sulfur / Q000737:chemistry; D014018:Tissue Distribution; D014873:Water Pollutants / Q000493:pharmacokinetics*; D015032:Zinc / Q000737:chemistry* / Q000493:pharmacokinetics*
chemical_list: D014873:Water Pollutants; D013455:Sulfur; D015032:Zinc