New Zealand Journal of Marine and Freshwater Research abstracts
Attenuation and transport of atrazine and picloram in an alluvial gravel
aquifer: a tracer test and batch study
LIPING PANG
MURRAY E. CLOSE
Institute of Environmental Sciences & Research
P. O. Box 29 181
Christchurch, New Zealand
email: Liping.Pang@esr.cri.nz
Abstract A natural-gradient tracer experiment and laboratory
batch tests were conducted to study attenuation and transport of atrazine and
picloram in an alluvial gravel aquifer. An analytical transport model, AT123D,
was used to analyse the field data. Data analysis suggests that there was no
retardation and degradation of atrazine and picloram in the aquifer over a
distance of 90 m within a period of 49 h. In the batch tests with a
much longer time duration (194 days), atrazine concentrations significantly
decreased and picloram concentrations showed a small decrease. It is considered
that the rapid decrease in atrazine levels in the first 2 days was
sorption-dominated and the slow decrease subsequently was mainly because of
degradation and partially the result of slow sorption. If it is assumed that
the decrease in the first 2 days was all the result of sorption and it had
reached equilibrium, the estimated
Kd values are 0.04 ml/g for atrazine,
and 0.02 ml/g for picloram. Rates of atrazine degradation estimated from the
data after 2 days (slow rate of decrease) are 3.4 x 10
-3 per day
(equivalent half-life 204 days), and 3.0 x 10
-3 per day
(equivalent half-life 231 days), for total and chemical degradation,
respectively, assuming that there was no adsorption after 2 days. No
degradation rate could be determined from the picloram data of the batch tests
because of its highly noisy data and insignificant decrease in concentrations.
The significantly higher attenuation parameters derived from the batch tests
compared to those derived from the field data suggests that attenuation of
pesticides in the field is affected by other factors, such as aquifer
heterogeneity and preferential flow, and flow hydrodynamics etc., which should
be taken into account when applying laboratory-derived values to the field
conditions.
Keywords atrazine; picloram; degradation; retardation;
groundwater; alluvial gravel aquifer
M98039
Received 6 July 1998; accepted 9 November 1998
PDF file of entire paper: medium quality (1221K); (scanned from paper original: notes about this process)
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