Environmental Engineering Reference
In-Depth Information
have also been successf ully used followed by A A S. HPLC has
proven of use with reductive amperometric electrochemical
detection, UV detection, inductively coupled plasma emis-
sion spectrometric detection, or AAS detection. NAA has
been used for MMHg determinations in fi sh, blood, and
hair samples after suitable preseparation procedures.
Graphite furnace AAS has also been used for the fi nal deter-
mination of MMHg in toluene extracts to which dithizone
was added. An anodic stripping voltammetry technique has
been developed for determination of MMHg. However, the
method has never been used for environmental samples.
Methylmercury has also been extracted into dichlorometh-
ane (CH
2
Cl
2
). This was then evaporated down to 0.1 mL
and subjected to GC with an atmospheric pressure active
nitrogen detector (Horvat, 1996). An enzymatic method for
specifi c detection of organo-mercurials in bacterial cultures
has been developed. It is based on the specifi c conversion
of MMHg (no other methyl-metallo groups are enzymati-
cally converted) to methane by organo-mercurial lyase.
Ethyl and phenylmercury can also be detected (Baldi and
Fillipelli, 1991).
satisfactory yields, whereas ethylmercury is only partly
extracted. No suitable extraction techniques have been
found for methoxyethylmercury and ethoxyethylmercury
in soils (due to decomposition of these compounds under
acidic conditions) (Horvat, 2005).
Fractionation of Mercury in Soils
and Sediments
Frequently, for the purpose of risk assessment, it is impor-
tant to understand the relative availability of the forms of
Hg present in a soil or sediment sample. The biogeochemi-
cal and especially the ecotoxicologic signifi cance of Hg
input is determined by its specifi c binding form and cou-
pled reactivity rather than by its concentration in the solid
material. Consequently, these are the parameters that have
to be determined in order to assess the potential for Hg
transformation processes (such as methylation, reduction,
and demethylation) and to improve data for environmen-
tal risk assessment. EPA Method 3200 (EPA, 2005)—
Mercury
species fractionation and quantifi cation by microwave-assisted
extraction, selective solvent extraction and/or solid phase extrac-
tion—
uses sequential extraction and separation procedures
to differentiate mercury species that are present in soils and
sediments into four distinct fractions: extractable organic
mercury, extractable inorganic mercury, semimobile mer-
cury, and nonmobile mercury. Hg pyrolysis followed by
AAS detection was developed to distinguish among cinna-
bar-bound Hg, metallic Hg, and matrix-bound Hg (Biester
et al., 1999; Bloom et al., 2003). Alternative approaches
used for Hg fractionation are based on sequential extrac-
tions and leaching to provide information on the solubility
and reactivity of Hg. A sequential extraction method devel-
oped by Bloom et al. (2003) consists of six steps that extract
increasing recalcitrant forms of Hg, including water-sol-
uble, “human stomach acid”—soluble, organo-chelated,
elemental Hg, mercuric sulfi de, and residual fraction. An
additional step was incorporated into this scheme in order
to provide information on the volatilization potential of
Hg present in soil (Kocman et al., 2004). An alternative
approach to Hg speciation in soils has been described by
Cattani et al. (2008) based on HPLC-ICP-MS quantifi cation
of a diffusive gradient in thin-fi lm fractionation. The tech-
nique is designed to quantify inorganic Hg and organo-Hg
(e.g., methyl, ethyl, and phenyl Hg) species. Issaro et al.
(2009) reviewed the extractants used to speciate mercury
in soils and sediments. They found a lack of consensus
between the existing methods and argued for a standard
protocol and appropriate standard reference materials.
Other Organo-Mercurials
Among other organo-Hg species currently of interest,
ethylmercury (EtHg) is a compound that requires further
attention because it is still used in thiomerosal for
preservations of vaccines. It is important to analyze EtHg
in vaccines, in wastewater from waste treatment plants in
industries using EtHg, as well biologic samples in order
to understand EtHg uptake, distribution, excretion, and
effects. In principle, methods developed for MMHg can
also be used for EtHg, except in protocols using derivatiza-
tion by ethylation. In such cases propylation is recom-
mended (Logar et al., 2004).
Only a few investigations concerning the determination
of other organo-mercurials used in agriculture and for other
purposes have been reported (Horvat and Schroeder, 1995).
Methoxyethylmercury and ethoxyethylmercury have been
examined by thin-layer chromatography (TLC) and GLC. It
would appear that the only method that can separate and
measure many of the compounds simultaneously is HPLC
with UV detection (Hempel et al., 1992; Hintelmann and
Wilken, 1993). It offers several advantages. The separa-
tion of the compounds is performed at ambient tempera-
tures; hence, thermal decomposition does not occur. It
offers the possibility to separate less volatile or nonvola-
tile species such as mersalyl acid or the aromatic organo-
mercurials, that usually present a problem for GLC. It is,
however, very important to isolate these compounds from
environmental samples quantitatively. Methylmercury and
ethylmercury can easily be isolated from soils by extrac-
tion from acidifi ed samples. Several extraction agents have
been tested in order to release organo-mercurials from
soils. Methylmercury and phenylmercury can be extracted
by potassium iodide-ascorbic acid and oxalic acid with
Use of Mercury Isotopic and Radiochemical
Tracers
In order to understand the fate and transformation of Hg
in the environment, it is necessary to assess the potential
for Hg transformation rates under various environmental
