Determination of selected acidic pharmaceutical compounds in wastewater treatment plants
Date
2017
Authors
Madikizela, Lawrence Mzukisi
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Abstract
This research was directed towards the environmental monitoring and assessment of the most used non-steroidal anti-inflammatory drugs (NSAIDs) which are naproxen, ibuprofen and diclofenac. The work involved the development and application of sensitive techniques for the quantification of naproxen, ibuprofen and diclofenac in the South African aquatic environment. Based on this information, a multi-templates molecularly imprinted polymer (MIP) was synthesized and applied alongside the commercial available sorbent (Oasis MAX) in the solid-phase extraction (SPE) of target compounds from water samples. The extracted compounds were then quantified using high performance liquid chromatography (HPLC).
MIP was synthesized by applying a bulk polymerization approach at 70 ͦ C where all target compounds were used as multi-templates. Other reagents used in synthesis were 2-vinyl pyridine, 1,1’-azobis-(cyclohexanecarbonitrile), ethylene glycol dimethacrylate and toluene as functional monomer, initiator, cross-linker and porogenic solvent, respectively. Synthesis of a non-imprinted polymer (NIP) under similar reaction conditions as MIP was carried out with the omission of templates.
Techniques employed in characterization of MIP and NIP were Fourier transform infrared spectroscopy (FTIR), Brunauer, Emmett and Teller (BET) method, CHNS analyzer, zeta potential, cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and x-ray diffraction. Monomer-template interactions were investigated using molecular dynamics.
The performance of the MIP was evaluated based on its ability to selectively extract target compounds in organic (acetonitrile, acetone, chloroform and toluene) and aqueous media. The extraction capacity of the MIP in organic solvents for naproxen, ibuprofen and diclofenac increased from high polarity to low polarity solvents. In a low polarity solvent (toluene), the extraction capacity achieved for naproxen, ibuprofen and diclofenac were 14.4, 11.0 and 14.0 mg/g, respectively. In this case, the selectivity of the MIP where gemfibrozil was employed as the
competing species was evident. Selectivity of the MIP collapsed during the adsorption of naproxen, ibuprofen and diclofenac from water using gemfibrozil and fenoprofen as competitors. This resulted in high extraction efficiencies for target compounds and competitors, however, both gemfibrozil and fenoprofen were easily desorbed from the MIP using weak organic solvent due to lack of molecular recognition.
During the binding sites characterization, the best fit of pseudo-second-order implied a chemisorption of all target compounds onto MIP sorbent. The data also fitted well in Langmuir isotherm which meant that the adsorption of target pharmaceuticals occurred on the homogeneous binding sites of the MIP.
Optimized adsorption conditions in water such as MIP amount of 50 mg, extraction time of 10 min, sample pH of 2.5 and sample volume of 10 mL were applied for the selective adsorption of naproxen, ibuprofen and diclofenac in contaminated wastewater and river water. In WWTP influent, naproxen recovery was 38%, whereas ibuprofen and diclofenac were 69% and 87%, respectively.
MIP was further used as a selective adsorbent in solid-phase extraction (SPE) of three drugs from environmental samples. The selectivity of the MIP in environmental samples was compared to that of the commercially available Oasis MAX sorbent. The application of molecularly imprinted solid-phase extraction (MISPE) reduced matrix effects and improved the sensitivity of the analytical method. In this case, the detection limits for naproxen, ibuprofen and diclofenac were 0.2, 1 and 0.6 μg/L, respectively. When deionized water was spiked with 5 and 50 μg/L of target compounds, recoveries greater than 80% were obtained.
Thereafter, the developed MISPE was applied for selected acidic drugs from environmental samples. Environmental samples were collected from urban (Durban) and semi-urban/rural areas (Ladysmith) of KwaZulu-Natal Province in South Africa. The most abundant compound in the environment was ibuprofen. In river water samples from Durban, the maximum concentrations found for naproxen, ibuprofen and diclofenac were 6.8, 19 and 9.7 μg/L, respectively. The maximum amounts found for the same drugs in Ladysmith river samples were generally lower
with naproxen, ibuprofen and diclofenac detected at 2.8, 6.7 and 2.6 μg/L, respectively. The same trend was observed in wastewater.
Further work on the monitoring of acidic compounds in wastewater was conducted using Oasis MAX as the SPE sorbent prior to HPLC analysis. All target compounds were detected in Kingsburg and Umbilo WWTPs located in Durban surroundings. The influent and effluent concentrations detected were in the ranges of 6.4 to 69 μg/L and 0.6 to 4.2 μg/L, respectively. Further to this, the removal efficiency of the target compounds during the WWTP process in Kingsburg and Umbilo was in the range of 69 to 97%.
The extent of pollution in the environment was further assessed by the monitoring of ketoprofen and triclosan in wastewater and river water using SPE with Oasis HLB sorbent and HPLC. Traces of both compounds ranging from 1.2 to 9.0 μg/L were detected in wastewater. The maximum concentrations found in river water were 2.0 and 0.9 μg/L for ketprofen and triclosan, respectively.
Overall, the analytical methods implemented in this work were highly accurate, precise and sensitive. The synthesized MIP was highly selective and its application in environmental studies led to the development of a less expensive analytical method. This work also gives the overview of the extent of water pollution caused by acidic pharmaceuticals in various water matrices.
Description
A thesis submitted to the Faculty of Science, University of the
Witwatersrand in fulfilment of the requirements for the degree of
Doctor of Philosophy. November 2016.
Keywords
Citation
Madikizela, Lawrence Mzukisi (2017) Determination of selected acidic pharmaceutical compounds in wastewater treatment plants, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/22741>