Mobile GC/MS has opened new ways to assess contaminated sites and search
for unknown sources of hazardous compounds. However, in order to produce
analytical results within a few minutes, efficient on-site GC/MS analysis requires
quick and simple customized methods for sample introduction. Therefore the
work within the SFB project was focused on the following subjects:
For the screening of microbiological degradation of polycyclic aromatic
hydrocarbons (PAHs) in agar media a thermal microdesorption method was
developed. Organic analytes contained in the media can either be directly
desorbed using a high energy laser pulse, or at first sampled with a fine glass
capillary for subsequent thermal desorption. This unique system offers precise
sampling and anlysis on the media at different locations and therefore enables
characterization of a complete biological process.
In the course of microbiological degradation often very polar metabolites are
formed. Since several of these substances are difficult to analyse by gas-
chromatograph, the applicability of alkylation reactions to organic hydroxy and
acidic compounds inside the GC-injection chamber was investigated. It was
found that several metabolites could be methylated in situ by adding small
amounts of tetramethyl ammonium hydroxide to the media samples. This way
hydroxynaphtoic acid, a known PAH-metabolite has been detected in media
supplied from collegues of the SFB 188 project B1.
A particularly simple method has been developed for the analysis of volatile
organic soil gas constituents. Sampling is effected using subsurface probes
consisting of slitted stainless steel tubing lined inside concentrically with tubular
glass. The probes were evaluated within the remediation of contaminated soil
and proved to be well suited for monitoring volatiles in conjunction with mobile
GC/MS analytics.
To determine low concentration of volatiles at the ground surface a large volume
dynamic headspace method has been developed. From a 6 liter sampling
container the gas from a 1kg soil sample is collected using adsorption cartridges
for subsequent thermal desorption GC/MS. In addition to the low typical limits of
detection in the range µg/kg, the integration effect of the large sampling volume
has been proven to return more reliable quantitative analyses.
A new membrane probe has been developed for GC/MS water monitoring. A
silicone based permeation membrane separates and accumulates traces of
volatile organics directly from the aqueous solution. After the sampling time of 5-
10min the membrane is thermally desorbed. Now the accumuated analytes are
released and flushed to the GC-column with carrier gas. The non intrusive probe
allows consecutive GC/MS analyses in 10-15min intervals. Field tests including
the analysis of bioreactor fluid have verified the applicability of the device.
Automated sample preparation reduces both sources of error and time required
for liquid extract soil analyses. For this purpose an dedicated robotic system has
been constructed. It performs the task of weighing the sample, adding both
solvent and internal standard, and the extraction. For the injection of the sample
into the GC-inlet a pipetting device that uses oneway glass capillaries has been
developed. This unit statistically provides a much improved accuracy and
precision to the quantitative analysis.
While the already completed developments and optimizations have led to a
substantial improvement in mobile GC/MS analytical technology, new goals have
been set for the next research period:
Embedded in the principal concept of the SFB and in close cooperation with
other projects investigations on organic analysis, synthesis and electrochemistry
are carried out. These main topics are specified as follows:
Analysis: The chemical structure of soluble and extractable products of
secondary reactions which are produced during treatment of contaminated
material or during microbial degradation are identified. These investigations
involve aspects of efficiency control of decontamination techniques developed in
other projects of the SFB and thus may include the quantification of selected
compounds before and after treatment as well as investigations of processes of
remobilization.
Synthesis: The synthesis of non commercial substances which serve as
reference samples for structural proof of identified compounds or which may be
used as starting materials in other projects is an important component within the
context of the SFB. Included are syntheses of 13C-labelled compounds which are
needed in project D6 to investigate the mechanisms of fixation of xenobiotics
which cause so-called bound residue problems. In the syntheses of naphthalene,
phenanthrene and fluoranthene the label will be introduced at positions which are
expected to be transformed to carbonyl- or carboxylic groups during ring
cleavage reactions induced by degradation processes. The compounds may
react with the matrix at the labelled site which is supposed to be followed up by
13C NMR spectroscopy in project B4.
Electrochemistry: Electrochemical investigations will aim at optimising conditions
for the dechlorination of polychlorinated biphenyles (PCB), of polychloro
naphthalenes (PCN), polychloro biphenylethers (PSCE) and chlorophenols as
well as of selected insecticides. Main subjects will be the optimization of
conditions for the use of aqueous systems and scale up of the reaction.
Batchreactors, discontinuous cascades, or continuous flow cells will be tested.
The investigations will be carried out in close cooperation with project A1.
Target of this research is to gain insight into the quantitative and qualitative
aspects of pollutants and their metabolites chemically bound to soil constituents.
Analytical and methodical procedures are developed necessary to evaluate the
effort of remediation and decontamination treatments in future. We could
demonstrate the presence of covalent bonds between contaminants and soil
humic matter. The ongoing work focuses on respective linkages stable enough
to resist hydrolysis. The majority of soil bound pollutants is expected to exist
within this field of ether and carbon-carbon linkages.
Chemical and pyrolytical methods are applied to characterize soil bound residues
in various samples. The amount of released pollutants is determined using
gaschromatography and massspectrometry. Knowledge of the modes of linkages
brings along information on the formation processes as e.g. biocatalytic coupling.
Model experiments are conducted to gain data on the basic mechanisms of the
build-up of soil bound residues. Results of this experiment are tested on their
validity in natural systems. Moreover, the relation between mobility and release
of soil bound residues and diagenetic alteration of humic matter is investigated.
Focus is thereby aimed at the estimation of the transport of humic bound organic
pollutants into the ground water system.
Pertaining to this partial project was the development of an leaching apparatus,
with which the fact of mobility of non polar organic contaminants can be
determined. Leaching procedures for organic contaminants, which have been
done so far, have not given any satisfying results because essential factors like
ground structure, texture class, poresize distribution etc., were not considered
during the tests.
Therefore a way has been developed, in which undisturbed material appropiate
to the field situation, or disturbed, under specific storing conditions condensed,
material can be checked. It is also possible to check the different factors of
transporting the contaminants by altering the test variations and conditions. In
this way of testing, the water flows under unsaturated conditions through the
contaminated soil. The contaminants are transported by the percolating water
and pass trough a quartz-silt layer, where they will be enriched. At the end of the
test the hydrocarbon content of the quartz-slit layer can be determined. With this
method the essential parameters which determine a mobilizing of non polar
organic contaminants in soils, will be fulfiled.
For comparison with real leaching conditions field tests are made by using soil
columns in subsurface lysimeters with material of different texture class and oil
contaminations between 0.2 and 7.5 weight percent. With the help of the
lysimeters the influence of the texture class and the level of the contaminations
on the amount of leached contaminats and percolating water could be measured
under normal weather conditions.
The results of the lysimeter tests, as well as the labratory tests show, that in soil
containing oil, in which the hydrocarbons do not move in a phase, the various
aspects of mobility depend on numerous facts.
First it has to be determined that the content of hydrocarbon in the percolating
water is often higher than its solubility, without creating an oil slick on the
watersurface in the collecting bottles. Therefore the transport of the oil has to be
done in a dissolved and emulsified form.
The drag-out of hydrocarbons per litre of percolating water will shrink at lower
temperatures. Since the viscosity of the oil will rise at lower temperatures, it is
more difficult for the percolating water to separate the oil from the soil
aggregates and to transport it with the percolating water.
The drag-out of hydrocarbons per litre of percolating water will rise with the size
of the contaminations. But for a risk assessment of contaminated sites the
freights of leached contaminants is decisive. The drag-out will be determined by
the content of hydrocarbons and the amount of percolating water. The quantity
of percolating water depending varies on the texture class and the size of the
contamination in a wide range. The transportation of contaminants does not rise
in any case with increasing contamination. The water repellency, as well as the
changed water retention capacities of the soil through oil determine the amount
of percolating water. The water repellency of the soil material leads to a
reduction of the percolating water. On the field lysimeters this is expressed by an
overflow of rainwater, and during the laboratory percolation by a reduced water
conductivity. With a loamy, diesel contaminated material the water retention
capacity rises and therefore reduces the amount of trickled water.
Examining over a year the hydrocarbon leaching, neglecting the temperature
factor, the mobility of hydrocarbons depends in the first place upon the texture
class. In loamy soil the leachability compared to a sandy soil is reduced. The
viscosity of the oil plays a minor role. Modification of the leached contaminants
takes place through changes in the volume of the soil pores and a variation of
the water conductivity.
At the new project D7 the question for the leachability and remobilization of
contaminants after a biological treatment of contaminated soil will be answered.
At the biological treatment of soil fast convertible organic matter will be added
and organic contaminants will be reduced. Thereby the organic matter will be
altered qualitatively and quantitatively. At a reconstruction of the cleaned material
the natural conditions of the site will alter the material. This leads to a
decompostion of the organic matter, connected with an translocation of soil
compounds and a remobilization of combined contaminants or metabolites
(bound residues).
In a subsurface lysimeter should be measured the shifting within the pools of
organic matter, the mobilization of different combined contaminants at the
reduction of the soil organic matter. Besides there will be determined the
influence of dissolved organic compounds on the solubility of heavy metals.
The leachability and reduction of contaminants should be simulated in laboratory
tests. The results will be compared with the lysimeter tests. The examination of
the soil genesis includes the discription of the soil organic matter, the
translocation of soil compounds within the soil profile, the soil structure and the
chemical properties of the soil. The leachates will be analysed on dissolved
organic matter, released contaminants and metabolites and non organic
compounds.