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@PHDTHESIS{Vonberg:484062,
author = {Vonberg, David},
othercontributors = {Rüde, Thomas R. and Vanderborght, Jan},
title = {{A}trazine in the environment 20 years after its ban :
long-term monitoring of a shallow aquifer (in western
{G}ermany) and soil residue analysis},
volume = {293},
school = {RWTH Aachen},
type = {Dissertation},
address = {Jülich},
publisher = {Forschungszentrum Jülich GmbH, Zentralbibliothek},
reportid = {RWTH-2015-04985},
isbn = {978-3-95806-099-9},
series = {Schriften des Forschungszentrums Jülich. Reihe Energie
$\&$ Umwelt = Energy $\&$ environment},
pages = {1 Online-Ressource (149 Seiten) : Illustrationen,
Diagramme, Karten},
year = {2015},
note = {Druckausgabe: 2015. - Onlineausgabe: 2015. - Auch
veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2016; Dissertation, RWTH Aachen, 2015},
abstract = {Atrazine, one of the worldwide most widespread herbicides,
was banned in Germany in 1991 and in the European Union in
2004, due to findings of atrazine concentrations in ground-
and drinking waters exceeding the threshold value of 0.1 µg
L-1. Nevertheless atrazine and the metabolite
deethylatrazine were still detected in German aquifers more
than 10 years after its prohibition, often without any
considerable decreasing trend in groundwater concentration.
Because atrazine was already found to be persistent in soils
for more than two decades after the last application, the
hypothesis was raised that a continued release of atrazine
residues from the soil into groundwaters might sustain
atrazine groundwater concentrations on elevated levels. The
overall objective of this study was to investigate the
occurrence and concentration trends of atrazine and its main
metabolites in the groundwater-soil environment after the
prohibition of its use. Accordingly, in this study results
of i) 20 years of atrazine groundwater monitoring of a a
shallow aquifer in western Germany since its ban and ii)
atrazine soil residue analyses in the vadose zone of the
same study area 21 years after its ban are presented. The
phreatic Zwischenscholle aquifer located in the Lower Rhine
Embayment is exposed to intensive agricultural land use and
is highly susceptible to contaminants due to a shallow water
table. In total 60 observation wells (OWs) have been
monitored since 1991, of which 11 are sampled monthly today.
Descriptive statistics of monitoring data were derived using
the “regression on order statistics” (ROS) data
censoring approach, estimating values for nonquantifiable
values rather than substitute them by e.g. half of the limit
of quantification and taking the risk of biasing statistical
parameters. The monitoring data shows that even 20 years
after the ban of atrazine, the groundwater concentrations of
sampled OWs remain on a level close to the threshold value
of 0.1 µg L-1 without any considerable decrease. The
spatial distribution of atrazine concentrations is highly
heterogeneous with OWs exhibiting permanently concentrations
above the regulatory threshold on the one hand and other OWs
with concentrations mostly below the limit of quantification
(LOQ) on the other hand. Here atrazine concentrations show
upward, downward or approximately constant trends. The
deethylatrazine-to-atrazine ratio (DAR) was used to
distinguish between diffuse – and point-source
contaminations. A DAR around unity (slightly smaller for
thin vadose zones like for the investigated aquifer)
suggests a contamination of an aquifer by diffuse pathways,
resulting in significant metabolization of atrazine to
deethylatrazine due to a longer contact time to soil
microorganisms. Conversely, point-source contaminations
where the contaminant enters the aquifer directly by e.g.
macropore flow results in negligible deethylation and hence
a DAR close to zero. A global mean DAR value of 0.84 for the
monitoring data of the Zwischenscholle aquifer indicates
mainly diffuse contamination. Also most of the DARs for
single observation wells suggest mainly diffuse pollution,
except for one OW with a mean DAR of 0.02, clearly
indicating point-source contamination. Principle Component
Analysis (PCA) of the monitoring dataset demonstrated
relationships between the metabolite deisopropylatrazine and
its parent compound simazine but not with atrazine, and
deethylatrazine, atrazine, nitrate, and the specific
electrical conductivity. These parameters indicate diffuse
agricultural impacts on groundwater quality. The groundwater
monitoring findings point at the difficulty to estimate mean
concentrations of contamination for entire aquifers and to
evaluate groundwater quality based on average parameters.
However, analytical data of monthly sampled single
observation wells provide adequate information to
characterize local contamination and evolutionary trends of
pollutant concentration. For atrazine soil residue analysis
three soil cores reaching down to the groundwater table
(approximately 3 m below soil surface) were taken in an
agricultural field where atrazine was applied prior to its
ban. It is uncertain if atrazine was applied in total two or
three times with a recommended dose of 0.96 kg ha-1. Eight
layers were separated (0-10 cm, 10-30 cm, 30-60 cm, 60-100
cm, 100-150 cm, 150-200 cm, 200-250 cm, 250-300 cm) for
atrazine residue analysis and soil parameters (grain size
distribution, pH, cation exchange capacity (CECeff) and
organic carbon content). Soil samples of each layer were
extracted using accelerated solvent extraction (ASE) and
analyzed by LC-MS/MS analysis. Prior to this analysis, a
method validation was conducted to find optimum extraction
parameter combinations. For all extractions a methanol/water
(4:1, v/v) solvent was used. The highest quantifiable
atrazine extraction yield amongst all extraction parameter
combinations between 100°C and 135°C and 100 bar, 150 bar
and 207 bar was obtained for 100°C and 207 bar. Atrazine
yields were generally higher for higher pressures. Possibly
the higher pressure facilitates soil matrix penetration by
the solvent. Extractions using 135°C and the highest
pressure of 207 bar resulted in quantified concentration of
atrazine 31 $\%$ lower than those using 100°C. Probably,
the higher extraction temperature lead to an increased
co-extraction of soil-matrix compounds, which caused a
quenching effect and hence less quantifiable atrazine.
Extracted atrazine concentrations of the different layers of
the soil cores ranged between 0.2 µg kg-1 and 0.01 µg kg-1
for topsoil and subsoil, respectively. Averaged residual
atrazine accounts for 0.01 $\%$ of the applied mass in the
top layer and 0.07 $\%$ in the total soil profile (for in
total 3 applications). However, the calculation can only be
treated as a conservative estimate, because spatial
information of atrazine field applications and the correct
number of applications (2 or 3 times) are not available. A
complete and instantaneous remobilization of atrazine
residues from the unsaturated zone, leaching to and mixing
with the entire groundwater body would result in a mean
groundwater concentration of 0.002 µg L-1. In contrast,
considering local atrazine groundwater contamination below
an atrazine residue area by a complete instantaneous
remobilization of the latter and vertical mixing with the
groundwater body below, atrazine groundwater concentrations
would be 0.068 µg L-1. Based on the first scenario, long
term leaching of aged atrazine residues from the vadose zone
seems to marginally contribute to sustaining average
groundwater concentrations of the Zwischenscholle aquifer,
which remained constantly close to the threshold limit of
0.1 µg L-1 even 20 years after the ban of atrazine. In
contrast, the second scenario shows that ongoing local
leaching of atrazine from soil residues might result in
locally elevated atrazine groundwater concentrations, what
might be reflected by the high spatial variability in
atrazine groundwater concentrations in the investigated
aquifer. A conservative estimate suggests an atrazine
half-life value of approximately 2 years for the soil zone,
which is significantly higher than the highest atrazine
half-life values found in literature (433 days [1.19 years]
for top soil). This value only can be taken as rough
orientation and most probably underestimates the atrazine
half-life time in this soil, because i) non-extractable
atrazine could not be included in the calculation and ii)
the first two applications were executed before 1991
(information of the exact time of application is missing)
and iii) for aged atrazine residues and increased resistance
to biodegradation, atrazine degradation in soils rather
follows multi-rate kinetics than assumed first order
kinetics, what could result in an overestimation of decay
rates. These findings show that atrazine persistence in the
field might be distinctively higher than predicted assuming
first-order degradation kinetics and using half-life values
obtained from lab experiments which reach a maximum of 433
days for topsoils. Generally, literature values for the
organic carbon normalized distribution coefficient (KOC) and
dissipation half-life value for atrazine show a wide range
between 25 and 600 L Kg 1 and a few days up to 433 days.
Until now there is a lack of the understanding of how
herbicide degradation rates vary according to spatial
heterogeneity of soil properties. Furthermore, important
determining factors influencing degradation like microbial
ecology and its spatial variability have been neglected so
far for pesticide fate predictions. Accordingly, the
accuracy of model predictions of catchment scale atrazine
behavior on the long-term based on first-order-kinetics and
standard laboratory-derived sorption parameter values may be
not reliable. Thus the risk of long-term adverse
environmental effects may be higher than estimated. In
consequence, there is a need for more realistic pesticide
risk assessments and regulation procedures besides standard
models for pesticide fate predictions. Finally, considering
the key finding that the persistence of particular
pesticides in groundwater may be highly underestimated by
pesticide fate predictions based on laboratory short-term
studies, contaminant monitoring in the groundwater-soil
environment remains of highest importance, to i) detect
potential groundwater contaminations, ii) re-consider
pesticide fate predictions, iii) limit or ban the use of
contaminants frequently exceeding thresholds and iv) treat
drinking water adequately.},
cin = {532220 / 530000},
ddc = {550},
cid = {$I:(DE-82)532220_20140620$ / $I:(DE-82)530000_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
urn = {urn:nbn:de:hbz:82-rwth-2015-049853},
url = {https://publications.rwth-aachen.de/record/484062},
}
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