2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P48 APPLICATION OF DGT METhOD FOR
ASSESMENT OF AVAILAbILITy OF hEAVy
METALS TO PLANTS
Z. MLáDKOVá a , K. PEŠKOVá a,b , B. DOČEKAL b ,
H. DOČEKALOVá a and P. ŠKARPA c
a Department of Environmental Chemistry and Technology,
Faculty of Chemistry, Brno University of Technology, Purkyňova
118, 612 00 Brno, Czech Republic,
b Institute of Analytical Chemistry, Czech Academy of Science,
Veveří 97, 602 00 Brno, Czech Republic,
c Mendel University of Agriculture and Forestry, Faculty of
Agronomy, Zemědělská 1, 613 00 Brno, Czech Republic,
mladkova@fch.vutbr.cz
Introduction
At present time problems of toxic metal contamination
of soils are often solved. The form of metals present in the
environment is an important factor affecting their bioavailability.
Metals are often bound to various organic complexing
ligands as humic substances, which influences their mobility.
Therefore, studies of metal speciation are necessary for
understanding how metals can move in nature systems.
Leaching procedures are especially used for determination
of toxic metals concentration in soils. Simple leaching
procedures using aqua regia, ethylenediaminetetraacetic acid
(EDTA), nitric acid or sodium nitrate are usually recommended
and applied. However, leaching procedures give no
information about the metal fraction which is really available
for the root system of plants. Therefore, new approaches are
still being searched to obtain a better characterization of bioavailable
forms of metals and their transport in soils.
Recently an in situ technique capable of quantitatively
measuring labile metal species has been developed 1 . This
technique, known as diffusive gradients in thin films (DGT),
has been successfully used to measure the in situ concentrations
of metals in natural waters, sediments and soils and has
been shown to be a promising tool to assess metal phytoavailability
in a wide range of soils. The technique is based
on accumulation of solutes in a resin layer after passing through
a well-defined diffusive gel layer. The mass of solutes
accumulated in the resin during a period of deployment time
is measured.
The aim of this work was to assess the heavy metal
uptake of radish and to test the capability of DGT to predict
phytoavailability of the metals for this plant.
Experimental
S o i l T r e a t m e n t a n d L e a c h i n g
P r o c e d u r e s
Homogenized and sieved soil, which had been sampled
in Zabcice site, was used in the experiment. Content of
Cd and Cu extractable with nitric acid, acetic acid, EDTA,
sodium nitrate and water was determined in the soil according
to the recommendation of the Community of Bureau
of Reference (BCR) 2 and Gupta 3 . Portion of 6 kg of the soil
s428
was weight into each of 40 pots. Soil portions in individual
pots were spiked by adding solution of Cd and Cu, so that
the concentration of the metal in the soil was increased by
1 ppm Cd, 2 ppm Cd, 100 ppm Cu and 200 ppm Cu. The pots
with non-spiked soil portions served as control samples. After
3 months, leaching with the same agents was carried out
with artificially contaminated samples.
D G T E x p e r i m e n t
The gels for DGT were prepared according to the conventional
procedures (DGT Research, Ltd., Lancaster, UK) 4 .
The DGT piston probes were deployed at 24 ± 1 °C in each
soil sample in triplicate with the moisture content of 150 % of
maximum water holding capacity MWHC for 24 hours. After
elution of the resin gel with 1M HnO 3 , the accumulated mass
of Cd or Cu was determinated.
P o t E x p e r i m e n t
Radish (Raphanus sativa) was sown both in the control
and contaminated soils. Five plants of radish were grown in
each of four pots with the same soil sample. Six weeks after
sowing the radishes were harvested, rinsed with deionized
water; the root divided into the white inner part and the
red outer part and digested using the dry mode mineralizer
(APIOn). Dry matter content in both parts was determined
by drying samples in a oven at 105 °C.
D e t e r m i n a t i o n o f M e t a l s
Content of Cu and Cd was determined by electrothermal
atomic absorption spectrometry (ETAAS) employing Perkin-
Elmer Model 4110 Zeeman atomic absorption spectrometer.
Recommended conditions were applied.
Results
Concentration of Cd and Cu found in soil samples by
leaching with nanO 3 and water and in dry matter of radish
edible parts are summarized in Tables I and II. The test sample
was also characterized by other leaching agents. Content
of elements in this soil related to nitric acid, acetic acid
and EDTA leachate fractions was 49.1 ± 2.8; 45.5 ± 1.9;
11.8 ± 0.8 μg kg –1 Cd and 6.80 ± 0.50; 0.256 ± 0.051;
3.10 ± 0.17 mg kg –1 Cu.
The content of both metals is significantly higher in
contaminated soils as intended. The results show that added
metals are strongly bound to the soil matrix. The amount of
extractable Cd and Cu with nanO 3 reaches only 10 % and
even only 0.1 % of added metal, respectively. The concentrations
found by means of DGT technique are within 1–2
orders of magnitude lower than the concentrations in sodium
nitrate leachates for both metals.
The dry matter content was determined in both analyzed
parts of radishes. The red outer part and the white inner part
contained on average 11 % and 5 % of dry matter, respectively.
Cd and Cu concentration in both parts of radish increases
with increasing content of these metals in soils. The
Cd and Cu uptake in red outer part of radish is higher than