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The beneficial use of herbicides on pastures to increase crop yields is offset by
associated risks from chemical runoff contaminating environmental waters. Most commonly
used methods to remove residues from environmental waters are ineffective, while some
produce degradation by-products which can also affect the environment. The successful use
of polymer inclusion membranes (PIMs) as a simple remediation method to remove pyridine
herbicides, such as picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxyIic acid), and related
herbicides from an aqueous environment was reported. An optimum PIM composition of
25 wt%CTA, 30 wt% Aliquat 336 and 45 wt% NPOE was used to transport picloram with
an initial flux of 294 (± 14) * 10 8 mol.m 2.s 1 and transport efficiency of 95 ± 1%. The PIM
was reused in five consecutive transport cycles with a negligible change in flux during later
cycles. The results indicate that PIMs provide a potential alternate method for the removal of
troublesome herbicides fr om environmental waters.
Degradation products from herbicides are considered emerging contaminants and
studies on effective removal methods from environmental waters are limited. The successful
tiansport of 4-amino-2-chloropyridine (ACP) as a model degradation product of pyridine-
based herbicides using PIMs was demonstrated. An optimal membrane composition of
20wt%CTA,
40 wt% Aliquat
and
40wt%NPOE
producing
an
initial
flux
of
413 (± 7) 10 8 mol.m“2.s 1 and 98 ± 1% transport efficiency was identified. Preferential
transport of ACP, involving the formation of aggregates with the carrier, over picloram was
noted. The results indicate the opportunity for future investigations of the extraction and
transport of degradation products of pyridine-based herbicides using PIMs.
The use of natural compounds from plants as active chemicals for various
applications is regarded as a “green chemistry approach” because of die reduced risk of
contaminating the environment. However, there are limited investigations on the use of iplant-based compounds as components in PIMs. Anacardic acid (AA) derived from cashew
nut shell liquid was investigated as a “green cationic carrier’’ for some representative organic
compounds.
An
20 wt% dodecanol
optimal
and
membrane
composition
40 wt% NPOE
of
producing
30 wt% CTA.
an
initial
10 wt% A A.
flux
of
364 (± 16) x to x mol.m 2.s 1 and transport efficiency of 98 ± 1% for the transport of ACP as
a model compound was demonstrated. The results were comparable with using a commercial
carrier, bis-(2-ethylhexyl) phosphoric acid. The membrane also displayed effective
competitive transport of ACP, paraquat and diquat with an average transport efficiency of
97±l%. Therefore, the potential use of plant derived natural compounds as “green
chemicals” in membranes is an exciting novel development and worthy of further
investigations.
PIMs have emerged as a powerful tool for the pre-treatment of samples because of
their versatility and easy fabrication. The optimal membranes were tested for the pre
concentration of picloram, ACP. paraquat and diquat as representative compounds from a
low initial concentration of 500 pg/L in samples of natural water. The effective pre
concentration of the compounds was indicated by the significant increase in HPLC signal
intensities of the post-concentrated samples. The results indicate the suitability of PIMs as an
alternate method of sample pre-treatment and the potential for fabrication and application in
passive sampling devices.
The results from this thesis indicate the potential of PIMs as a viable method to
remove and measure problematic herbicides and degradation products from natural waters
using commercial and “green” carriers. However, more investigations simulating real-world
conditions, such as long-term use of similar membrane chemistry in hollow fibre extractors
and passive sampling devices, are needed to fully demonstrate this exciting potential.
Statement of Authorship
Except where reference is made in the text of the thesis, this thesis contains no
material published elsewhere or extracted in whole or in part from a thesis accepted for the
award of any other degree or diploma. No other person’s work has been used without
acknowledgment in the main text of the thesis. This thesis has not been submitted for the
award of any degree or diploma in any other tertiary institution. |
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