Alfred Y.C. Tong

TiO2-assisted photodegradation of pharmaceuticals — a review

AbstractPharmaceutical compounds have been detected in the environment and potentially arise from the discharge of excreted and improperly disposed medication from sewage treatment facilities. In order to minimize environmental exposure of pharmaceutical residues, a potential technique to remove pharmaceuticals from water is the use of an advanced oxidation process (AOP) involving titanium dioxide (TiO2) photocatalysis. To evaluate the extent UV/TiO2 processes have been studied for pharmaceutical degradation, a literature search using the keywords ‘titanium dioxide’, ‘photocatalysis’, ‘advanced oxidation processes’, ‘pharmaceuticals’ and ‘degradation’ were used in the ISI Web of Knowledge TM, Scopus TM and ScienceDirect TM databases up to and including articles published on 23 November 2011. The degradation rates of pharmaceuticals under UV/TiO2 treatment were dependent on type and amount of TiO2 loading, pharmaceutical concentration, the presence of electron acceptors and pH. Complete mineralization under particular experimental conditions were reported for some pharmaceuticals; however, some experiments reported evolution of toxic intermediates during the photocatalytic process. It is concluded that the UV/TiO2 system is potentially a feasible wastewater treatment process, but careful consideration of the treatment time, the loading and the type of TiO2 (doped vs. undoped) used for a particular pharmaceutical is necessary for a successful application (198 words).

UV-induced photodegradation of oseltamivir (Tamiflu) in water

Environmental context Oseltamivir (Tamiflu) is widely used to prevent and treat influenza but conventional wastewater processes involving sedimentation and biotic oxidation do not appear to significantly remove it from sewage, leading to its discharge into the environment. A range of advanced oxidation processes (AOPs) involving photolysis of aqueous solutions of oseltamivir with UV alone, UV/H2O2 and UV/H2O2/FeII is demonstrated to lead to photodegradation of oseltamivir to products with no ecotoxicity observed. These AOPs may therefore offer potentially environmentally friendly sewage water treatment options. Abstract Aqueous solutions of the antiviral drug oseltamivir phosphate (OSP, Tamiflu, (3R,4R,5S)-ethyl 4-acetamido-5-amino-3-(pentan-3-yloxy)cyclohex-1-enecarboxylate) were degraded using advanced oxidation processes (AOPs) involving photodegradation with UV alone, UV/H2O2 and UV/H2O2/FeII (photo-Fenton reaction). The photodecay of the parent OSP in all three cases followed first-order kinetics with respective rate constants of 0.21, 1.56 and 1.75 min–1 at 20°C in pH 7 phosphate-buffered Milli-Q water. The rate of UV/H2O2 photolysis in the presence of 2-methylpropan-2-ol was significantly slower with an approximate first-order rate constant of 0.13 min–1 suggesting the involvement of •OH in the degradation process. NMR spectroscopy, mass spectrometry and high-performance liquid chromatography (HPLC) with UV diode array detection were used to identify the crude photoproduct as the hydroxylated OSP derivative (3S,4R,5S)-ethyl 4-acetamido-5-amino-2-hydroxy-3-(pentan-3-yloxy)cyclohexanecarboxylate that occurs by an unknown mechanism. OSP and this crude photoproduct demonstrated no effect on the survival of Quinquelaophonte sp. over 96 h.

Determination of trace metal concentrations in ginseng (Panax Quinquefolius (American)) roots for forensic comparison using Inductively Coupled Plasma Mass-Spectrometry

The trace metal content of roots of samples of the American ginseng natural herbal plant species (Panax quinquefolius) was investigated as a means of differentiating between this species grown on Wisconsin and New Zealand farms, and from Canadian and Chinese sources. ICP-MS measurements were undertaken by ashing samples of the roots and then digestion with conc. HNO3 and H2O2. There was considerable variation in the concentrations of 28 detectable elements along the length of a root, between different roots, between different farms/sources and between different countries. Statistical processing of the log-transformed concentration data was undertaken using principal component analysis (PCA) and discriminant function analysis (DFA). Although PCA showed some differentiation between samples, a much clearer discrimination of the Panax quinquefolius species of ginseng from the four countries was observed using DFA. 88% of the variation between countries could be accounted for by only using discriminant function 1 while 80% of the remaining 12% of the variation between countries is accounted for by discriminant function 2. The Fisher Classification Functions classify 98% of the 87 samples to the correct country of origin with 97% of the cross-validated cases correctly classified. The predictive ability of this DFA model was further tested by constructing 100 discriminant models each using a random selection of the data for two thirds of the 87 sampled ginseng root tops, and then using the resulting classification functions to determine correctly the country of origin of the remaining third of the cases. The mean success rate of the 100 classifications was 92%. These results suggest that measurement and statistical analysis of just the trace metal content of the roots of Panax quinquefolius promises to be an excellent predictor of the country of origin of this ginseng species.

Degradation of pharmaceuticals in wastewater

The majority of the human pharmaceuticals that have been detected in the natural environment have arisen though their discharge in parent or metabolized forms into sewage wastewater which is then treated to various levels of purification to progressively lower the concentrations of pharmaceuticals before discharge of effluent into an aquatic environment. This chapter will introduce a range of physical, biological, and chemical remediation techniques that are the basis of three key wastewater treatment steps—primary, secondary, and tertiary sewage treatment processes. Examples are given of different types of specific processes such as primary sedimentation, secondary biological oxidation, tertiary membrane filtration, and advanced oxidation processes. These are illustrated with the results of both field and laboratory studies of these wastewater treatment processes applied to the degradation and removal of some common pharmaceuticals including paracetamol, diclofenac, ibuprofen, β-blockers, oseltamivir, and fluoxetine. Finally, the effect of the natural organic matrix present in all wastewater on pharmaceutical removal and degradation is briefly considered.

2 – Prescribing practices

The specific pharmaceuticals that are used globally are governed by access policies (availability, costs, etc.). These policies have a significant impact on the types and volumes of pharmaceuticals that are consumed. These access policies can also make it difficult to quantify the volumes of particular pharmaceuticals that are used. A large body of literature has reported patient behavior that will impact on whether these medications are actually used. Variable adherence rates to medications for a plethora of reasons all contribute to pharmaceuticals that need to be disposed of. An increasing consumer pressure for pharmaceuticals also drives consumption with follow-on consequences for their ultimate disposal.

9 – Summary and Conclusions

The prescription and disposal of pharmaceuticals and their detection in the environment are summarized. The likely environmental impacts and methods to degrade pharmaceuticals in wastewater treatment processes are reviewed along with legislative measures to control their discharge. Suggestions are made for areas of future research in this field.

Impact of pharmaceuticals on the environment

The occurrence of pharmaceuticals in sewage effluents, surface water, groundwater, and drinking water is widely recognized as a potential global environmental issue. There is a dearth of data available to fully characterize these risks of pharmaceuticals in the environment and their potential impacts. Current ecotoxicology methodologies used to assess the risk of chemicals are not always suitable to fully characterize the hazards posed by pharmaceuticals that show a diversity of physicochemical characteristics, environmental fate and behavior, and unique mechanisms of toxicity. To address the complexity of this challenge requires new approaches and frameworks that ensure a cohesive use of resources and expertise. Alternative approaches to assess the potential environmental risks such as the integration of current knowledge on the persistence, bioaccumulation, and toxicity are being used to assign a risk score to pharmaceuticals so that they can be prioritized. However, caution is warranted when using those ranking methods as they may not always accurately assess risk. Examples of risk assessments derived from current best information on paracetamol, fluoxetine, and diclofenac suggest no evidence for immediate alarm arising from the environmental presence and persistence of these pharmaceuticals.

Detection and presence of pharmaceuticals in the environment

The generally very low concentrations of pharmaceutical species in natural environments make both their identification and quantitation very difficult particularly as they often occur as complex mixtures in a background matrix of uncharacterized natural organic matter. This situation has improved significantly with recent developments in analytical techniques involving preconcentration of analytes, their separation from the background matrix, and their sensitive detection and quantitation using mass spectrometric techniques. This chapter will introduce aspects of the sequential steps in the measurement process of sample collection, storage, extraction and preconcentration, separation by high-performance/pressure chromatography, and then detection and quantitation by mass spectrometry. A summary will be given of a range of concentrations of common pharmaceuticals measured in different natural aquatic environments.

Regulatory practices to control the discharge of pharmaceuticals into the environment

Approaches to lessen the real or potential adverse impact of pharmaceutical residues on the environment can include regional or national legislative controls at each step in their life-cycles beginning with their prescription and subsequent disposal, degradation in wastewater treatment processes, and limits on the their allowed concentrations in effluent discharged into the environment. There is no global agreement on unified legislation to cover all of these control aspects and instead different countries have slowly introduced their own legislation at both the regional and national levels to cover various parts of these control aspects. This situation is illustrated by some of the major legislative acts that have been introduced to control the usage and discharge of pharmaceuticals into the environment in the United States and Canada, the European Union, China, Japan, Australia, and New Zealand. Of particular relevance is the concept of a mixing zone for a receiving environment and how this is currently legislated under the Resource Management Act (RMA) in New Zealand.

Disposal of unused medications

A significant proportion of the pharmaceuticals supplied by pharmacies are unused for many reasons and accumulate before ultimately needing disposal. In this chapter, the disposal of pharmaceuticals is discussed, and it is noted that appropriate disposal of pharmaceuticals is not always available; it can be cost prohibitive and selecting the most appropriate method of disposal is not always a simple decision. Take-back programs provide an opportunity for consumers to return unwanted and unused medications and provide a public awareness profile of the magnitude of the problems; however, these can be resource intensive, and again, disposal of the pharmaceuticals collected can incur additional costs