BARBARA GWOREK*, MAREK BOROWIAK**, JOANNA KWAPISZ*
EFFECT OF ZEOLITE-BEARING ROCKS
UPON INACTIVATION OF CADMIUM IN SOILS
^Department o f Soil Science, Warsaw Agricultural University - SGGW Institute of Industrial Chemistry in Warsaw
INTRODUCTION
The fate o f trace elem ents that accumulate in soils in an uncontrolled way is to a large extent conditioned by physical and chem ical properties o f both so ils and the elem ents them selves. Cadmium has been shown to be m ost rapidly m obilized in an experim ent aimed at determining the behaviour o f heavy metals (Cu, Pb, Zn and Cd) introduced into arable soils o f diverse origin [Dudka 1989; Piotrow ska
1985].
D espite that cadmium is not needed for the plant growth, it is exceptionally easily taken up by both root system s and leaves. Generally, plants are capable o f taking up cadmium proportionally to its concentrations in the soil [G worek 1993; Piotrow ska 1985]. Human and animals ingest cadmium m ostly together contam i nated food and accum ulate it in kidneys and liver in particular, though it was found that cadmium may be to a som e extent excreted. B ecause o f its m obility in the food chain, cadmium has been allocated to the category o f potentially highly threatening elem ents.
The present work was aimed at determining the possibility o f using a natural zeolite-bearing rock to im m obilize cadmium in the soil, i.e. to reduce cadm ium quantities which enter the food chain. The effect o f cadmium inactivation in soils w as evaluated by com paring its content in plants grown with the zeolite additive with those in control plants.
MATERIALS AND METHODS
In order to establish the extent o f cadmium inactivation by zeolite additive, a three-year long pot experim ent was carried out in a glasshouse in four replicates. Soil material for laboratory tests was sampled from upper horizons ( 0 - 2 0 cm ) o f anthropogenic soils o f the Upper S ilesia Industrial R egion, from the m unicipalities o f S zop ienice and Jaworzno. Both areas lie within the impact o f large industrial agglom erations and, locally, are also influenced by waste dumps.
L o ca lity pH Hh Ca M g К N a С N Cd [m g/kg] H 20 KC1 [m e / 100 g] [%] S z o p ie n ice 6.6 6 .2 2 .1 0 4 8 .7 8 6 .8 0 0 .6 4 1.52 4 .0 5 0 .2 8 4 3 .0 4 Jaw orzn o 5.5 5.0 1.95 7.93 2.08 0 .7 4 3.88 1.67 1.14 4 .7 4 C h y lic e 6 .0 5.8 2 .0 0 8 .1 0 1.10 0 .8 0 1.94 1.04 0 .5 4 0 .8 2
Additionally, tests with simulated cadmium contam ination were performed using topsoil taken from the study field o f the Warsaw Agricultural University in C hylice. To this soil, 20 mg Cd per kg soil dry w eight in the form o f C d (N 03 ) 2
were added. B asic chem ical properties o f the soils are given in Table 1. The soils have been classified to the respective soil texture groups: soils from S zop ienice and Jaworzno - heavily loam y sand, and those from C hylice - light loam.
The amounts o f soils taken for the experim ent corresponded to 1.5 kg soil o f dry w eight. B efore filling in the pots, macroelem ents were added to the soil in the quantities recom m ended by the agrotechnical requirements o f plants under culti vation. At the same time zeolite-bearing rock was added as pellets o f 1-3 mm in diameter at the rate o f 2% o f the soil weight. The rock is in 90% built o f clinoptilolite [(K, Na, l/2 C a )20 A120 3 1 0 S i02 8H20 ] . Anthropogenic and
artificially contaminated soils without any addition o f natural zeolite-bearing rock were used as reference.
Oat o f var. Dragon, beetroot o f var. Red Ball and perennial ryegrass (L olium
p e re n n e ) were sown directly to the pots. T w o-w eek old seedlings o f lettuce o f var.
W onder o f Volburg were also used in the experiment. During the grow ing season all plants were watered daily with redistilled water up to 60% o f the m aximum field water capacity. Foliar dressings o f nitrogen at the rate o f 0.1 g N /kg soil dry w eight were given to lettuce during the third w eek o f growth w hile to oat and ryegrass during the tillering phase. Three crops o f lettuce were grown su ccessively in the same pots. After 6 w eeks all plants were cut. Plant material, except for oat
straw, grains and glum es, was washed with tap water and, subsequently, rinsed with redistilled water. W ashed material was then dried at 60° C, ground and ashed in a m uffle furnace at 480°C. The ash thus obtained was dissolved in 20% HC1.
Soil sam ples were sieved through 1 mm sieve and ashed at 480°C , then digested in 20% HC1 for 30 min. Cadmium content in plant and soil mineralisates was determined directly by A A S technique.
RESULTS
The effect o f zeolite-bearing rock upon cadmium content in plants cultivated on anthropogenic soils is presented in Table 2. Leaves and roots o f su ccessive lettuce crops grown on the soil from Szopienice contained, respectively, from 21.4 to 39.3 m g/kg o f d.w. and from 34.3 to 74.2 mg/kg d.w. W hereas in the su ccessive crops o f lettuce grown on the soil from Jaworzno, the respective quantities amounted from 3.9 to 4.9 m g/kg d.w. Considerably higher cadmium content in the reference lettuce grown on the soil from S zopienice relative to that o f the reference lettuce from Jaworzno results from higher soil cadmium levels in Szopienice.
T A B L E 2. M ean (± S D ) cadm ium content [m g/k g o f d. w .] in lea v es and roots (n = 12) o f plants cu ltivated on anthrop ogen ic so ils w ith and w ithou t z eo lite add itive
Plants part C o m b i nation S z o p ie n ic e Jaw orzno C ontrol Z N w o % C ontrol Z N W O% L ettuce L e a v es I 4 9 .3 ± 8 .3 2 4 .7 ± 3 .4 4 9 .8 4 .6 ± 1 .8 2 .9 1 0 .9 3 5 .9 II 3 8 .8 ± 6 .9 2 8 . 1±3.2 2 7.3 4 .9 ± 1 .2 1 .0 1 0 .6 7 8 .9 III 2 1 .4 ± 2 .4 1 0 .3 ± 2 .7 4 8 .2 3 .9 ± 1 .3 1 .0 1 0 .4 73.1 R o o ts I 3 4 .3 1 4 .2 2 7 .2 ± 3 .0 2 0 .6 6 .3 1 1 .4 3 .3 1 1 .1 4 7 .8 II 7 4 .2 ± 5 .7 3 0 .9 1 6 .2 4 1 .6 8 .0± 2.1 3 .9 1 0 .8 5 0 .9 III 4 7 .2 ± 4 .2 1 9 .2 ± 2 .7 59.1 5 .4 1 1 .9 2 .3 1 0 .9 5 7 .4 R y eg ra ss H arvest I 1 1.3± 1.2 6 .3 ± 1 .0 4 4 .2 4 .3 1 0 .9 3.7 Ю .9 13.9 II 6 .2 ± 0 .9 4 .3 ± 0 .8 3 0.6 2 .8 1 0 .3 1.2Ю .04 57.1 III 8 .6 ± 1 .0 4 .2 1 0 .6 51.1 3 .0 1 0 .7 2 .0 Ю .0 6 33.3 R o o ts 3 7.3± 2.1 18.2± 2.3 5 1 .2 2 0 .3 1 2 .3 1 6 .2 1 1 .9 2 0 .2 Oat Straw 9 .6 ± 1 .3 3 .6 ± 0 .7 62.5 2 .6 1 0 .6 0 .9 Ю .0 4 Grain - - - 0 .9 1 0 .0 6 0 .4 Ю .0 2 G lu m es 1 0 .7 ± 2 .1 2 .7 ± 0 .6 74.8 1.710.1 1.0Ю .06 R oots 3 4 .2 ± 3 .6 13,4+ 2,4 60.8 6 .3 1 1 .3 2 .2 Ю .0 9 B e et L e a v es 3 7 4 ± 3 .4 2 0 .3 ± 4 .0 4 5 .7 8 .7 1 1 .6 5 .6 1 1 .2 R o o ts 2 9 .8 ± 2 .0 1 8.2± 3.7 38.9 6 .2 1 1 .2 5 .0 1 1 .9
Control - no additive o f zeolite-bearing rock; ZN - treatment with zeolite additive; WO - percent reduction o f cadium relative to the control.
Z eolite-rock addition reduced cadmium content in leaves o f lettuce grown on the soil from S zop ienice by 2 7 .3 ^ 9 .8 % and in roots by 2 0.6-59 .1 % , whereas in the lettuce grown on the soil from Jaworzno these reductions ranged, respectively, from 35.9 -7 8 .9 % and 4 7.8-57.4% . As far as leaves are concerned, the highest percent reduction in cadmium content induced by the zeolite additive was observed in the first crop o f lettuce grown on the soil from Szopienice, w hile in the lettuce on the soil from Jaworzno - in the second crop. In the roots the highest reduction in cadmium content was found in III crop o f lettuce grown on soils from both S zop ien ice and Jaworzno.
The advantage o f using natural zeolites for a partial removal o f ex cess cadmium from the trophic chain was also corroborated by the results o f analyses o f the three harvests o f grass. In the grass grown on the anthropogenic soils, the reduction in cadm ium content in the leaves was from 3.9 to 57.1 %, w hile in the roots - from 21.2 to 51.2% (Table 2).
The experim ents with oat have shown that plants grown in the presence o f natural zeolite additives contain less cadmium not only in vegetative organs but also in the generative ones relative to the control plants. This was evidenced by
Jaworzno with and without the zeolite additive. On the other hand, it was im p ossib le to assess the zeolite effect on soils from S zop ienice due to the fact that oat eared but no grains were developed. In general, the reduction in cadm ium content, regardless the treatment, amounted to: in oat grain - 55.5% , in straw - 62.5% and 65.3% , in glum es -4 1 .2 % and 74.8% and in roots - 60.8% and 65.3% relative to the control (Table 2). It was also found that the amounts o f cadm ium in beetroot leaves and roots decreased when the plants were grown on soils with zeolites in com parison with the control, regardless the degree o f soil contam ina tion. This reduction was 35.6% and 45.7% in the leaves and 19.4% and 38.9% in the roots.
The results o f tests with simulated cadmium contamination o f soils are given in Table 3. The percent reduction o f cadmium content due to zeolite additive in plants cultivated on artificially contaminated soils was generally higher than in those cultivated under comparable regim es on anthropogenic soils. The decrease in cadm ium content in leaves o f su ccessive lettuce crops amounted from 62.3 to 81.4% w hile in roots - from 53 to 72.3% . The addition o f 20 m g Cd per kg o f soil dry weight, in an easily soluble form, did not affect the process o f grain setting in oat. The decrease in cadmium content in the respective parts o f oat cultivated on soils with the natural zeolite additive, as compared to the control, amounted to: in straw - 4 6 .9 % , in grain -4 3 ,8 % , in g lu m e s-5 2 .2 % and in ro o ts-6 1 .5 % . Sim ilar decrease in cadmium uptake was found in beetroots cultivated with zeolite
T A B L E 3. M ean (± S D ) cadm ium contcnt [m g/kg o f d. w .] in lea v es and roots o f lettuce cu ltiv a ted on so ils artificially contam inated with and w ithout zeo lite add itive
Parts o f plants C om b in ation Control Z N W O% Lettuce L ea v es I 3 2 .9 ± 2 .7 1 2 .4 ± 1 .4 62.3 II 5 8 .1 ± 3 .4 1 0.8± 2.0 8 1 .4 III 5 8 .1 ± 3 .1 11.3 ± 1 .7 80.5 R oots I 8 0 .1 ± 5 .7 3 7 .6 ± 2 .4 5 3 .0 II 1 3 3 .4 ± 5 .2 3 4 .7 ± 2 .3 7 3 .9 III 1 2 2 .9 ± 3 .4 3 4 .0 ± 3 .0 7 2.3 R ey grass H arvest I 10.4± 2.4 4 .3 ± 0 .9 5 8 .6 II 8 4 + 2 .1 3 .8 + 1 .2 5 4.8 III 2 5 .3 ± 3 .2 5.2+1.1 7 9 .4 R oots 8 0 .0 ± 5 .6 3 9 .2 ± 3 .4 5 1 .0 Oats Straw 3 3 .2 ± 2 .8 1 7 .6 ± 1 .9 4 6 .9 Grain 13.0± 3.0 7 .3 ± 1 .4 4 3 .8 G lu m es 2 4 .3 ± 4 .3 1 1.6± 0.9 5 2 .2 R oots 9 7 .0 ± 8 .2 3 7 .3 ± 2 .7 61.5 B eet L ea v es 146 .0 ± 1 2 .3 5 8 .4 ± 3 .4 6 0 .0 R oots 4 0 .0 ± 6 .7 2 1 ,7 ± 2 .2 4 5 .7 Denotations as in Table 2.
T A B L E 4. M ean (n = 1 2 ) cadm ium content [m g/kg o f d. w .] in anth rop ogen ic so ils after c o m p le ting the experim en t
T reatm ent L ocality
S z o p e n ice Jaw orzno
C ontrol S 4 2 .4 4 .0 T 4 2 .3 4.1 0 4 1 .9 3.9 В 4 1 .3 3.8 Natural z eo lite S 3 6.9 3.1 ad d itive T 3 6 .2 3.0 0 34.3 2.8
в
34.3 2.7 R ed u ction o f Cds
13.0 2 2.5 to control T 14.4 26.8о
18.1 28 .2в
16.9 28.9D enotations: S - treatment with lettuce, T - treatment with rcygrass, О - treatment with oat, В - treatment with beetroot
additive, the contents o f cadmium being reduced, respectively, in leaves by 60% and in roots by 45.7% . A decrease was found in the soil Cd content after com pleting the experim ent with the highest reduction coefficien t for soils from Jaworzno (Table 4). In general, the greatest reductions in cadmium content in soils with the zeolite additive were observed in the treatments with oat and beetroot and, subsequently, in those with ryegrass and lettuce. The m agnitude order o f coefficien ts o f Cd content reduction for respective plants cultivated on soils from S zop ienice was as follow s: 18.1, 16.9, 14.4 and 13.0% w hile that for Jaworzno soils - 28.2, 28.9, 26.8 and 22.5% .
DISCUSSION
The results o f analyses o f m ono- and dicotyledonous plants grown on both anthropogenic and artificially contaminated soils have shown that cadmium accum ulation was the highest in plant roots, smaller in the vegetative plant parts and, it was the sm allest, in the generative ones. The above results point out to the existen ce o f biological barriers in plants which reduce the transport o f ex cess cadmium to the generative organs. The action o f the above barriers consists in binding heavy metals by proteins and in depositing the com pounds thus established within intracellular spaces or in the cells [Gworek 1993; Kabata-Pendias, Pendias 1993; Piotrowska 1985]. The results o f a m any-year-long study corroborate the fact that the highest contents o f cadmium are to be found in the second crop o f lettuce grown on anthropogenic soils [Gworek 1993]. M oreover, studies by other authors have shown that cadmium content in grain increases with the increase in the level o f soil Cd [Gambuś 1993; Gworek 1993; Piotrowska 1985]. It was assum ed that the migration o f cadmium to the above ground plant parts occurs in the phase o f grain developm ent [Dudka 1989].
decreasing the excess cadmium in the trophic chain within the system: soil - plant - animal - man by adding the natural zeolite-bearing rock. The addition o f zeolite to the Cd contaminated soils contributed significantly to decreasing cadmium levels in plants relative to the control. The decreased uptake o f cadmium by plants is conditioned by the soil sorption capacity and ion exchange p ossibilities o f zeolites [Borowiak et al. 1983; Brogowski 1987; Czupyrna et al. 1986; G worek
1992a,b].
In the above respect, the sorption capacity o f zeolites may be superior to that o f the soil humus [Breck 1974]. O w ing to their specific intracrystalline structure, the above minerals behave as a sort o f sieves at the m olecular level though their action in the soil is restricted to sorption o f ions and m olecules less than 1 nm in
diameter [Borowiak et al. 1983].
On the basis o f this study it was found that the introduction o f natural zeolites to soils contaminated with cadmium resulted in a more profound decrease in cadmium content in the above ground parts than in the roots. It was also dem on strated that there is a possibility for dim inishing the amounts o f cadmium in the generative organs o f giants. This is proven by a 43.8 and 55.5% decrease in Cd content in oat grain [C eliscev and C elisceva 1981] performed an experim ent on the effect o f simulated Cd contamination and diverse additives o f natural rock containing clinoptilolite upon the plant growth. In the experim ent a decrease in Cd content was found in the green mass sampled at diverse stages o f oat d evelop ment and, especially, in its grain. In the latter the decrease was as much as 70%. An earlier study with the use o f synthetic zeolites enabled to attain a similar or even better effects that resulted from a higher sorption capacity o f the synthetic zeolites.
The analysis o f cadmium content in soils after 6 months o f soil conditioning
with natural zeolite-bearing rock pointed out to a decrease from 13.0 to 18.1 % in cadmium level for the soil from Szopienice and from 22.5 to 28.9% for the soil from Jaworzno (Table 4). One o f the reasons o f the higher decrease in the case o f soils from Jaworzno may be their lower pH. Generally, more m obile cadmium forms are to be found in the environments having low er pH, since under those conditions cadmium may be easily entering the processes o f sorption and ion exchange.
CONCLUSIONS
The study performed allow s the follow in g conclusions:
1. The introduction o f zeolite-bearing rock into the cadmium contam inated soil, in the amount o f two per cent o f soil dry w eight resulted in 19.4-81.4% decrease in the Cd level in plants grown on the soil. Considering generative organs o f plants the reduction was 43.8 and 55.5%.
2. In general, a higher drop in cadmium content in plants as a consequence o f the application o f natural zeolites, was found in regim es with simulated Cd contam ination as compared to the plants cultivated on the polluted soils. 3. After a lapse o f 6 months, the addition o f natural zeolite-bearing rock to the
13.0 to 18.1% w hile in the case o f Jaworzno - this decrease was contained within the limits 22 .5-28.9% .
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WPŁYW ZEOLITÓW SKAŁOTWÓRCZYCH
NA UNIERUCHOMIENIE KADMU W GLEBACH
*Katedra Gleboznawstwa SGGW w Warszawie, **Instytut Chemii Przemysłowej w Warszawie
STRESZCZENIE
W dośw iadczeniach w azonow ych badano w pływ naturalnej skały zeolitonoś- nej na zm niejszenie pobierania kadmu przez rośliny uprawiane na glebach zanie czyszczon ych . Zastosowana do dośw iadczeń skała zeolitonośna zawiera około 90% klinoptilolitu. W prowadzenie do gleb w ym ienionej skały w ilości 2% w ago- w ych w stosunku do suchej masy gleby spow odow ało obniżenie zawartości kadmu w roślinach na niej uprawianych w granicach 19.4-81.4% w porównaniu z roślinami kontrolnymi (sałata, rajgras, ow ies, buraki). D ziałanie naturalnych zeolitów w glebie antropogenicznej przez 6 m iesięcy spow odow ało spadek ilości
kadmu w glebie. Spadek ten wahał się od 13.0 do 28.9% w zależności od pH gleby.
D r hab. B a rb a r a G w o rek D e p a r tm e n t o f S o il S cien ce
W a rsa w A g ric u ltu ra l U n iv e rsity (S G G W ) R a k o w iec k a str. 2 8 /3 0 , 0 2 -5 2 8 W arsaw , P o la n d
