Environmental Engineering Reference
In-Depth Information
tissues and sediments were manual, but today there are
several commercially available automated CVAAS analyti-
cal systems. The EPA has promulgated several CVAAS meth-
ods for determination of total Hg in solid environmental
matrices, including EPA 245.5
Determination of Mercury in
Sediment by Cold Vapor Atomic Absorption Spectrometry
(in
EPA 1994), EPA 245.6
Determination of Mercury in Tissue by
Cold Vapor Atomic Absorption Spectrometry
(in EPA, 1994),
EPA 7470
Mercury in Liquid Waste—Manual Cold Vapor Tech-
nique
(EPA, 1993), and EPA 7471
Mercury in Solid or Semi-
solid Waste (Manual Cold-Vapor Technique)
(EPA, 2007). The
CVAFS technique described previously for aqueous samples
can also be used for solid phases if very high sensitivity is
required. A small aliquot of a strong acid digest of the solid
is spiked into a purging system in a manner identical to
that used for the preparation of a standard curve.
Researchers have been using multiple collectors (MC-ICP-
MS) tuned to specifi c Hg isotopes to determine variation
in Hg isotopic ratios that may be used to determine the ori-
gin of Hg in the environment (Hintelmann and Lu, 2003;
Foucher and Hintelmann, 2006; Blum and Bergquist, 2007).
X-RAY SPECTROSCOPY
X-ray fl uorescence (XRF) is convenient because the sample
preparation is minimal, analysis is quick and nondestruc-
tive and it is indifferent to the chemical or physical state
of the analyte. However, it is less sensitive than AAS and
neutron activation analysis (NAA). Typical detection limits
of x-ray techniques are in the ppm range. The sensitivity
can be improved by preseparation and preconcentration of
Hg (D'Silva and Fassel, 1972; Bennun and Gomez, 1997).
In vivo determination of Hg was investigated and applied
(O'Meara et al., 2000). Synchrotron radiation XRF has suc-
cessfully been applied to biologic monitoring using hair.
Its advantage is in studying Hg dynamics in a small sam-
ple (Shimijo et al., 1997). X-ray absorption spectroscopy
(XAS), in particular extended x-ray absorption fi ne struc-
ture (EXAFS) spectroscopy has been applied for Hg specia-
tion in Hg-bearing mine wastes (Kim et al., 2004).
THERMAL DECOMPOSITION
A relatively new analytical method for the determination of
total Hg in solids uses direct thermal decomposition, pre-
concentration by amalgamation onto gold and detection
by CVAAS (Hall and Pelchat, 1997; Cizdziel, et al., 2002;
Lowery et al., 2007). The method uses complete combus-
tion of solid samples in an oxygen carrier gas to release Hg
vapor instead of the chemical reduction step used in most
liquid-based analyzers. The combustion process does not
require the conversion of Hg to mercuric ions, so lengthy
sample pretreatments are unnecessary. Sample analysis is
rapid, and automated systems are commercially available.
Because chemical reduction is not used, there is no need for
sample digestion. This method has been promulgated as EPA
Method 7473 (EPA, 1998a). This method can also be applied
to liquid samples such as industrial wastes, but is not sensi-
tive enough for ambient environmental water samples.
ELECTROCHEMICAL METHODS
An electrochemical method using chronopotentiometric
stripping analysis on gold fi lm electrodes for the determi-
nation of total mercury in fi sh and shrimp was described
by Augelli et al. (2007). They achieved a detection limit of
5 ng/g, which is comparable to methods based on CVAA.
Other Total Mercury Analytical Methods
NEUTRON ACTIVATION ANALYSIS
INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION
SPECTROMETRY
NAA can be performed as nondestructive instrumental NAA
(Dams et al., 1970; Das and van der Sloot, 1976) or radio-
chemical NAA (Kosta and Byrne, 1969; Byrne and Kosta,
1974). k
0
standardization instrumental NAA (k
0
-INAA)
is now available and can be used on a routine basis
(Ja ´imovi ´ and Horvat, 2004). Good agreement of the
results obtained by k
0
-INAA with other methods was
observed in environmental samples such as soil, sediments,
and sewage sludge with elevated Hg values (
ICP-MS has been increasingly used in Hg research stud-
ies and has been demonstrated to be a very powerful
tool (Hintelmann and Ogrinc, 2003). Although standard-
confi guration ICP-MS is not suffi ciently sensitive for the
analysis of many solid matrix environmental samples,
specialized sample introduction systems that introduce Hg
in the form of gaseous species into a dry plasma greatly
reduced the occurrence of memory effects, which was one
of the major problems for the effective use of ICP-MS ini-
tially. ICP-MS can achieve absolute detection limits of less
than 100 pg of Hg. Moreover, the capability of ICP-MS to
take advantage of special isotope-dilution methods makes
this technique suitable for very precise and accurate mea-
surements. In addition, multiple stable tracer experiments
to study the fate of Hg species in the environment and bio-
logic systems are available for the investigation of multiple
transformation processes simultaneously (Demuth and
Heumann, 2001; Stoichev et al., 2004; Tseng et al., 2000).
1 mg/kg), while
at lower concentrations agreement is good in the absence
of major interferences in k
0
-INAA. In biologic samples
(plants, algae, and tissues) the agreement is satisfactory at
concentrations higher than 0.05 mg/kg. The sensitivity of
k
0
-INAA largely depends on the presence of other elements
that interfere with the gamma line of
203
Hg. k
0
-INAA may
suffer from spectral interferences and, when plastic irra-
diation vials are used, from volatilization losses. Therefore,
the use of standard reference materials of known chemi-
cal composition close to those of the samples should be
