Speciation of hepatic Zn in trout exposed to elevated waterborne Zn using X-ray absorption spectroscopy.
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.
Beauchemin
Suzanne
S
Environment Group, Mining and Mineral Sciences Laboratories, Natural Resources Canada, 555 Booth Street, Ottawa, Ontario, K1A 0G1. sbeauche@nrcan.gc.ca
Hesterberg
Dean
D
Nadeau
Jennifer
J
McGeer
James C
JC
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*
D014873:Water Pollutants; D013455:Sulfur; D015032:Zinc