Stable ‘Non-Traditional’ Isotopes - Application of Geochemical Tracers to Fluvial Sediment - page 118

Unlike many other trace metals, Zn is not a highly toxic element, but there is
considerable interest in the use of Zn isotopes as a tracer because (1) they may be
applied to determine the source of Zn from a wide range of materials including
mining and refining products and wastes, steel processing plants, coal-fired power
plants, vehicles, urban waste incinerators, car tires, and other constituents in urban
runoff (Chen et al. 2008 ), and (2) Zn is often associated with Cd and Pb in natural
and anthropogenic materials, and therefore Zn isotopes also may be of use in deter-
mining the provenance of these trace metals. It is also related to the fact that they
may provide information on contaminant sources when other more commonly used
isotopic systems fail (as detailed below).

5.2.1 Use of Zn Isotopes as Contaminated Sediment Tracers

To date the use of Zn isotopes as a contaminant tracer in near surface environments
has been limited, particularly within riverine systems. Nonetheless, recent studies
(e.g., Sivry et al. 2008 ; Cloquet et al. 2008 ; Chen et al. 2008 ;Bird 2011 ; Aranda
et al. 2012 ) suggest that Zn isotopes hold considerable promise because the iso-
topic composition of specific anthropogenically produced materials can, at least in
some cases, be distinguished from that found naturally in rocks, sediments, soils,
etc. The ability to differentiate between natural and anthropogenic sources of Zn
is aided by relatively small variations in

66 Zn values (

ʴ ∼

) in ore, sediments,
and biota (Maréchal et al. 1999 , 2000 ; Maréchal and Albaréde 2002 ; Cloquet et al.
2008 ), and the measurable fractionation of Zn by various physical and biological
processes, including those used in industry. Industrial Zn fractionation is dominated
by the mass-dependent processes of evaporation, condensation, and electroplating.
During ore smelting, for example, the evaporation of Zn and Cd is likely to release
isotopically light isotopes in the exhaust, whereas isotopically heavy Zn and Cd will
remain within the smelting residue (Mattielli et al. 2009 ; Sivry et al. 2008 ). Similarly,
electroplating may result in relatively light electroplated Zn (and presumably Cd) in
comparison to the parent solution (Bullen 2011 ; Kavner et al. 2008 ). Once released
into the surrounding environment, fractionation may occur at low temperatures by
a range of processes including biogenic uptake by micro-organisms and other biota
(Stenberg et al. 2004 ; Weiss et al. 2005 ), diffusion (Rodushkin et al. 2004 ), adsorp-
tion onto inorganic and organic surfaces (Weiss et al. 2005 ; Pokrovsky et al. 2005 ),
ion exchange (Maréchal and Albaréde 2002 ), and mineralization (Mason et al. 2005 ;
Wilkinson et al. 2005 ) (Table 5.1 ).
Much of the work on Zn isotopes to date has focused on sourcing Zn from
atmospheric sources (Luck et al. 1999 ; Sonke et al. 2002 , 2008 ; Cloquet et al. 2006 ;
Dolgopolova et al. 2006 ; Weiss et al. 2007 ; Gioia et al. 2008 ; Mattielli et al. 2009 ;
Bigalk et al. 2010a ; Thapalia et al. 2010 ; Juillot et al. 2011 ). Thapalia et al. ( 2010 ), for
example, examined changes in the flux and sources of Zn to Lake Ballenger located
in a highly urbanized area near Seattle, Washington. Of primary interest was the
atmospheric deposition of Zn from a smelter located approximately 53km upwind

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