2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P93 FACTORS INFLuENCING ThE SORPTION
bEhAVIOuR OF hERbICIDE ACETOChLOR
IN SOILS AND SEDIMENTS
LEnKA ZEMAnOVá, EDGAR HILLER and ZOLTán
KRASCSEnITS
Comenius University in Bratislava, Faculty of Natural
Sciences, Department of Geochemistry, Mlynská dolina,
842 15 Bratislava, Slovak Republic,
zemanoval@fns.uniba.sk
Introduction
Acetochlor (2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6methylfenyl)acetamide)
is a selective systematic herbicide
used in the production of maize, soybean and other crops 1 .
Ability to predict its mobility in the environment is of major
importance as US EPA has classified acetochlor as a probable
human carcinogen 2 .
The aim of this study was to investigate the sorption and
desorption of acetochlor in various types of natural sorbents
(soils, bottom and river sediments). The attention was paid to
the effect of soil/sediment properties on acetochlor sorption
and desorption.
Experimental
C h e m i c a l s a n d S o r b e n t s
Experiments were conducted with analytical grade acetochlor
(purchased from Sigma Aldrich Kft.), a relatively
non-polar compound (logK ow = 2.5) with water solubility
223 mg dm –3 at 20 °C 1 .
Eight surface soils (denoted as A1–8) were collected
from cultivated sites in Slovakia. Moreover, one soil collected
from C horizon at the depth of 2 m (SS), three bottom
sediments (BS1–3), and two river sediments (RS1–2) were
used. Basic properties of the soils and sediments studied are
shown in Table I.
S o r p t i o n / D e s o r p t i o n E x p e r i m e n t s
Sorption experiments were conducted using a batch
equilibration method, with two initial concentrations of acetochlor
used (1 and 10 mg dm –3 ). The acetochlor concentration
in supernatant solutions after equilibration was measured
using high performance liquid chromatography with ultraviolet
detection (HPLC-UV) in the national Water Reference
Laboratory for Slovakia (Bratislava).
Desorption experiments followed immediately after
the sorption experiments with an initial concentration of
10 mg dm –3 .
Results
Sorption coefficients for acetochlor are given in Table II.
TOC was found to be the main soil/sediment property correlating
with the extent of acetochlor sorption (r = 0.774;
P < 0.01). Strong affinity of acetochlor to soil organic matter
was reported also by other researchers 2,3 .
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Table I
Properties of soils and sediments used in the study
TOC [%] C HA /C FA Clay [%] pH (H 2 O) CaCO 3 [%]
A1 4.59 1.09 11.13 6.93 1.40
A2 1.92 1.12 15.32 7.99 2.00
A3 0.89 0.72 22.08 6.76 0.30
A4 2.49 1.07 9.08 7.86 12.2
A5 1.21 1.16 5.75 6.32 n.D.
A6 1.19 1.53 11.00 7.96 2.74
A7 0.48 0.90 0.60 5.76 0.20
A8 1.57 1.12 37.20 6.11 n.D.
SS 0.60 0.95 4.05 8.20 4.10
RS1 2.46 0.42 2.16 7.17 0.30
RS2 3.46 0.87 1.89 7.22 3.60
BS1 3.05 0.89 6.41 7.56 3.80
BS2 1.64 1.62 7.85 7.46 2.20
BS3 6.39 0.78 2.03 6.45 n.D.
The relationship between K d and total organic carbon
content was improved after excluding the soil A8 from the
data set (r = 0.902; P < 0.001). This could be explained by the
significantly higher clay mineral content (especially smectites)
of this soil as compared with other sorbents. Previous
studies of the sorption of organic pollutants in soils have
shown that in soils with the high clay mineral/organic matter
ratio, the mineral fraction can play an important role in binding
organic compounds such as pesticides 4 .
The humic/fulvic acid ratio (C HA /C FA ) is one of the
characteristics of the soil organic matter quality 5 . The results
of this study showed a positive correlation between the
K oc and the C HA /C FA ratio (r = 0.578; P < 0.05). Its signifi-
Table II
Sorption coefficients of acetochlor (Kd and Koc) and percentage
of acetochlor desorbed (P des )
Initial concentration Initial concentration
C 0 = 1 mg dm –3 C 0 = 10 mg dm –3
K d K oc K d K oc P des
[dm 3 kg –1 ] [dm 3 kg –1 ] [dm 3 kg –1 ] [dm 3 kg –1 ] [%]
A1 7.108 155 5.871 128 12.0
A2 3.248 169 2.537 132 27.9
A3 1.358 152 1.036 116 37.5
A4 3.406 137 2.635 106 19.1
A5 2.109 174 1.551 128 35.6
A6 3.344 281 2.999 252 23.0
A7 1.018 212 0.840 175 34.3
A8 6.265 399 5.145 328 27.7
SS 1.062 177 0.918 153 41.0
RS1 3.463 141 2.579 105 27.0
RS2 4.218 122 3.353 97 22.5
BS1 3.020 99 3.081 101 26.4
BS2 3.854 235 3.378 206 26.2
BS3 6.577 103 5.491 86 16.0