Issue 3

ABSTRACT
Pollution from metals and metalloids of the environment of Greece seemed to attract many
researchers and elemental pollutants in air, soil and water have been determined and studied
systematically during the last decade. The most recent of these studies, concerning the last
five years (2003 to 2008), were reviewed and the major problems of the occurrence of heavy
metals in the country’s environment were pointed out.
Regarding the atmospheric environment, the chemical characterization of particulate matter of
the big Greek cities attracted the interest of many authors. Heavy metals and As represented
an important fraction of the particulate matter of the atmosphere of Greek cities, with
increased content in inhalable fraction.
In addition, many works studied the metal content of soil and plants of the Athenian forests,
among with agricultural soils from the countryside. Copper, Fe and Cd were identified as the
most accumulated metals that may pose a long-term threat to soil and aquatic environment.
Most of the reviewed articles concerned the aquatic environment. Rivers and coastal
environment of northern Greece presented increased levels of metals and arsenic, reflecting
the transboundary and local agricultural and industrial activities. Marine environment nearby
the big cities was found reasonably polluted.
Therefore the presented results reflected the human activities: urban areas were reasonably
found more polluted (however without severe exceedence of the regulated values), compared
with the less populated regions. On the contrary, drinking water of the urban populated areas,
due to proper treatment, conformed to the regulated values.

The present work concerns the investigation of the chemical kinetics of H2S selective
oxidation into elemental sulfur, by gas absorption and chemical reaction in Fe3+·(ΝΤΑ)
aqueous solutions. By using initial reactivity data, priority is given to the study of intrinsic
kinetics i.e. to avoid interactions with ligand degradation and the presence of sulfur. A wetted
wall gas-liquid reactor was employed under a batch-recycle regime. The conversion of Fe3+ to
Fe2+ chelate was determined over the pH range ca. 3–6, temperature range ca. 30–60°C and
a short overall per run contact time of phases. The penetration theory was used for the
evaluation of intrinsic reaction rate constant and enhancement factor. Activation energy
values determined from the pertinent Arrhenius plots fall in the range, Εa=17.2– 22.8 kcal
mol-1. These values compare satisfactorily with the value Εa=24 kcal mol-1 obtained from a
similar kinetic study performed in a bubble column reactor and indicates a chemical reaction
control of the overall gas absorption phenomenon. Enhancement factors varied in the
respective ranges Ε =2.7–7.5 (pH=3), E=3.2–14.1 (pH=4), E=5.9–17.0 (pH=5), και Ε=6.7–
20.1 (pH=6) indicating a substantial increase of the mass transfer coefficient due to chemical
reaction. For the experimental conditions applied in this study the following kinetic correlation
was validated:

Heterogeneous photocatalysis is an advanced oxidation process (AOP) which has been
widely studied by numerous researchers in the world and is used to degrade or remove a
wide range of pollutants in water and air.
The photocatalytic oxidation and mineralization of phenol in aqueous catalyst suspensions of
titanium dioxide (TiO2) Degussa P25 (80% anatase, 20% rutile) has been carried out in a
helical reactor. The photodegradation was investigated using two kinds of high pressure
mercury irradiation lamps one emitting at 254 nm (15 Watts) and the other emitting at 365 nm
(400 Watts). The effects of the recirculation flow, source of withdrawal, initial phenol
concentration, amount of catalyst, suspension pH and light intensity on photodegradation of
phenol were investigated. These parameters were studied to find the optimal conditions for a
complete and fast oxidation of this organic compound.
Kinetic experiments were performed at 32 oC over a range of phenol concentrations from 2.5
to 25 mg l-1, a range of TiO2 concentrations from 0.1 to 1 g l1, a range of suspensions pH from
3 to 9. The helical reactor was operated under a continuous flow-mode.
Results showed that photodegradation is an effective method for the removal of phenol from
wastewaters. The efficiency of the process depends strongly on the experimental conditions.
The amount of catalyst, UV irradiation time, pH and light intensity were important parameters
in the degradation process. The rate constants for the different parameters (TiO2, phenol
concentration) were evaluated. Kinetic studies showed that titanium dioxide photocatalyst P25
was very active in phenol degradation; we observed that 99% of pollutant was degraded after
6 hours of UV irradiation; furthermore, we observed that phenol degradation was more
effective under acidic conditions than alkaline. The kinetics were described by the Langmuir-
Hinshelwood (L-H) kinetic model. An overall pseudo-first order kinetic constant has been
calculated for phenol conversion and values obtained in acidic pH are higher than those
calculated for basic pH media.

Phytoremediation is a low cost alternative solution to soil contamination compared with
traditional removal and/or disposal techniques. One of the phytoremediation technologies is
the phytovolatilization, whereby the contaminant is not primarily accumulated in above-ground
tissues, but is instead transformed by the plant into the atmosphere. The detoxification of
highly toxic organmercurial compounds and subsequent volatilization of elemental mercury is
a unique example for the successful phytoremediation based on genetic engineering
approach. For mercury removal techniques we constructed a dicistronic construct containing
the bacterial mercury detoxification genes merA and merB under the control of the
Arabidopsis Actin2 promoter and terminator. The resulted construct was introduced to
Agrobacterium competent cells using heat shock transformation method. In the mean time,
we germinated tobacco (Nicotiana tabacum var. Gold leaf) seeds on MS media and infected
leaf discs of 6-8 weeks tobacco seedlings with Agrobacterium containing Ti plasmid harboring
merA/merB dicistronic construct. The results showed that about 90% of tobacco seedlings
were carrying the mer genes. Tobacco seeds were collected from wild type and transgenic
lines and tested for mercury resistance. The results showed that transgenic plants are
resistant to both Phenyl Mercuric Acetate (PMA) and HgCl2. The root length and dry weight of
wild and transgenic seedlings growing on both media amended with mercury compounds and
media without mercury (control) were scored. The results showed that the root lengths and
dry weight of the transgenic lines are significantly higher by 60 and 17-folds, respectively,
compared to wild type. The results showed clear evidence that the transgenic plants are
resistant to both organic and inorganic mercury compounds and can be used to clean up
mercury contaminated sites.