C - Lublin

In this paper AT sorption by surface horizon of hydromorphous soil from
natural riparian wetland (Brittany, France) was studied. Special attention has been
paid to modifications of soil properties under the influence of earth worms
(Aporrectodea giardi) by soil ingestion and their effect on atrazine adsorption. To
investigate the effect of possible AT-soil interactions on bioavailability of AT and
on kinetics of its biodegradation, laboratory experiments were performed under soil
slurry conditions with a model well-characterized AT-degrading bacterium
Pseudomonas sp. strain ADP (Mandelbaum et al. 1995). Worm casts were
laboratory prepared by Aporrectodea giardi (Lumbricidae). Soil used for casts
production was sampled from 20 cm top layer from studied soil profile (PF7).
Deposited casts were sampled from the soil surface every 24 hs.
Carbon (total and organic) content in samples was determined with Shimadzu
TOC-5050A equipment. Composition of humic substances was determined in the
accordance with the method of Ponomareva & Plotnikova (1980). Cation exchange
capacity and exchangeable bases content were obtained by ammonium acetate
method with 1:10 solid: liquid ratio and pH 7. Mineralogical composition of bulk
soil samples and their clay fractions was determined by X-ray diffractometry.
Atrazine (AT) stock solution of 30mg/l for adsorption experiments was
prepared in mineral water (Volvic, France). Adsorption of AT was carried out
using batch-equilibration technique at 25°C in darkness. 1 g of solid was agitated
for 24h with 10 ml of 3, 6, 9, 12, 15, 18, 21, 24, 27 and 30 mg/l AT. After
adsorption, supernatants were passed through solid phase extraction cartridges
“Oasis” HLB, and AT was extracted with methanol.
For biodegradation experiments, Pseudomonas sp. strain ADP was grown in
100-ml portions of Trypticase Soy broth in 500-ml Erlenmeyer flasks incubated at
30°C at 200 rpm. The cells were harvested after 15 hs of culture. Extracts obtaind
from adsorption and biodegradation experiments were analyzed by HPLC analysis
(Perkin Elmer series 200) with a UV detector (λ= 225nm). A mixture of
acetonitrile with acetate buffer was used as the mobile phase (30/70 V/V).
Earthworms change visibly the properties of the parent soil. Worm casts
are characterized by lower pH, are enriched in organic carbon, clay fraction, have
larger CEC and exchangeable Ca content. Bulk cast sample is higher in C, HA,
HA/FA ratio, degree of humification (ΣC HA /C) in a comparison with parent soil.
Clay fraction of cast sample contains less C, lower proportion of humic acids, and
is characterized by smallest HA/FA ratio and degree of humification in a
comparison with clay fraction separated from parent soil. This is, probably,
connected to the preferential ingestion of slightly decomposed organic fragments.
Both soil and cast are characterized by similar mineralogical composition of
clay fractions: predominantly muscovite (30-45 %) – kaolinite (35-40 %)
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