Expert answer:Water Pollution
Solved by verified expert:write a summary essay that: (1) Explains the issues related to pharmaceuticals (please limit your research to pharmaceuticals and not other substances) in waste water. Where do they come from? How widespread a problem is it? What kinds of things are found? (2) Can/are these chemicals effectively removed from the wastewater during processing? (3) Do they pose a risk to human health? Ecosystems? Do not use a Q&A format, write as an essay. Be sure to cite and reference all materials.
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Critical Reviews in Environmental Science and Technology
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http://www.informaworld.com/smpp/title~content=t713606375
Human Pharmaceuticals in Wastewater Treatment Processes
O. A. H. Jones a; N. Voulvoulis a; J. N. Lester a
a
Department of Environmental Science and Technology, Faculty of Life Sciences, Imperial College, London,
United Kingdom
Online Publication Date: 01 July 2005
To cite this Article Jones, O. A. H., Voulvoulis, N. and Lester, J. N.(2005)’Human Pharmaceuticals in Wastewater Treatment
Processes’,Critical Reviews in Environmental Science and Technology,35:4,401 — 427
To link to this Article: DOI: 10.1080/10643380590956966
URL: http://dx.doi.org/10.1080/10643380590956966
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Critical Reviews in Environmental Science and Technology, 35:401–427, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1064-3389 print / 1547-6537 online
DOI: 10.1080/10643380590956966
Human Pharmaceuticals in Wastewater
Treatment Processes
O. A. H. JONES, N. VOULVOULIS, and J. N. LESTER
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Department of Environmental Science and Technology, Faculty of Life Sciences, Imperial
College, London, United Kingdom
The presence of human pharmaceutical compounds in surface waters is an emerging issue in environmental science. In this study
the occurrence and behavior of human pharmaceuticals in a variety of wastewater treatment processes is reviewed. Although some
groups are not affected by sewage treatment processes others are
amenable to degradation, albeit incomplete. While water purification techniques such as granular activated carbon could potentially
remove these pollutants from wastewater streams, the high cost involved suggests that more attention should be given to the potential
for the optimization of current treatment processes, and reduction
at source in order to reduce environmental contamination.
KEY WORDS: fate, pharmaceuticals, pollution, sewage treatment
plants, wastewater
I. INTRODUCTION
The term “pharmaceutical” covers a wide-ranging class of compounds with
substantial variability in structures, function, behavior, and activity.27 Developed to elicit a biological effect, they are used in both humans and
animals to cure disease, fight infection, and/or reduce symptoms. Many
drugs are not fully metabolized in the body and so may be excreted to
the sewer system. Numerous pharmaceutical compounds have been shown
to pass through sewage treatment plants (STPs) and contaminate the aquatic
environment.9,15,19,20,33,38,56,64,67,72,90,94,115,117,120,126,131
Address correspondence to J. N. Lester, Department of Environmental Science and
Technology, Faculty of Life Sciences, Imperial College, London, SW7 2BP, UK. E-mail:
j.lester@imperial.ac.uk
401
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O. A. H. Jones et al.
The use of other organic pollutants, such as pesticides, has fallen in
recent years as new laws have been introduced to minimize their use.23
However, even if they should prove problematic, pharmaceuticals are unlikely to be restricted in this way, due to their beneficial human (and animal)
health effects and economic importance. Indeed, their use is expected to
grow with the increasing average age of the population and the publishing
of the human genome.25 They and their metabolites are therefore likely to
be found in the environment adjacent to human activity.107
The first reports of human drugs in the environment appeared in the
late 1970s,36,55 although it is not unreasonable to suppose that aquatic pollution from medicinal compounds dates back much further.63 The growing
importance worldwide of reducing potential impacts on water supplies has
ensured that this issue has been steadily gaining attention in recent years both
within the academic community and among the general public, although it
is only with the comparatively recent advent of more reliable and sensitive
analytical techniques that detailed research in this area has become possible.
In this article the term “drugs” is taken to exclude both natural and
synthetic hormones. While these compounds are an important subgroup of
pharmaceuticals, there is already an abundance of work available in the
literature on this topic4,11,14,61,80−83,95,121,124,130
From published occurrence data, it seems probable that most if not
all urban wastewater is contaminated with medicinal compounds, differing only in the type and abundance of the substances present.24 The
existence of drugs in surface waters9,15,19,20,33,38,56,67,72,90,94,115,117,120,126,131
groundwater,1,21,32,58,89,99,103,108 and even marine systems18,115 has also been
confirmed. It is probable that the presence of these compounds stems primarily from the consumption and use of such products rather than from
manufacturing.35
Medicinal compounds are generally excreted after being partially or
completely converted to water-soluble metabolites,29,42,92,98 but a significant
amount of the original substance may also be excreted unchanged.57 This
has previously been regarded as inconsequential because of the dilution received in the sewerage system. However, recent studies on pharmaceutical
residues (primarily in Germany) have demonstrated that elimination of high
to medium polar pharmaceuticals in municipal STPs is often incomplete,
ranging between 60 and 90%.116,117,120 One of the most comprehensive studies of this type was performed by Kolpin et al.72 who chronicled the detection of over 95 organic chemicals in U.S. streams and rivers. Measured
concentrations from this study were generally low (nanograms per liter) and
rarely exceeded drinking-water guidelines, drinking-water health advisories,
or aquatic-life criteria, although it is worth noting that no such guidelines
have been established for the majority of pharmaceutical compounds detected. The detection of multiple organic pollutants was relatively common
in this study, with a median of 7 and as many as 38 compounds being found
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Pharmaceuticals in Wastewater Treatment Processes
403
in a given water sample. These results demonstrate the importance of obtaining data on metabolites as well as parent compounds in order to fully
understand the fate and transport of individual pollutants in the hydrological
cycle.
Compounds having relatively short half-lives would likely survive in
only the freshest of sewage sludge samples,7 but it is important to understand the fate and behavior of these compounds during wastewater
treatment in order to assess the likely concentration of contaminants in
sludges and effluents, and hence their potential contribution to the pollution of the environment. Some drugs may be removed from wastewater
by adsorption onto solids, but can then enter the aquatic environment, in
particular groundwaters, via sludge application to land, landfilling, or soil
erosion. There have been many reviews on the topic of environmental pollution by drug compounds,6,25,44,50,64,96 all of which note that no quantitative
data were found on concentrations of pharmaceuticals in sewage sludge
or soil amended with sewage sludge, although some modeling has been
attempted.65,70 This is surprising, considering that this is a potential route
for lipophilic substances to the terrestrial environment. However, it is most
probably a consequence the extreme difficulty in extraction and analysis of
pollutants from sludge samples on a quantitative basis.70,101,106
II. DEGRADATION WITHIN STPs
A. Biodegradation
There is an obvious potential for biological degradation (aerobic/anaerobic
by micro-organisms) of drug substances leading to a reduction of the parent
compounds and/or their metabolites during wastewater treatment.128 Some
biodegradation may also occur during in-pipe transport to the STP, but most
will probably occur in the secondary stage of treatment when the compound
is exposed to large concentrations of micro-organisms. Biodegradation tests
can be performed following test protocols such as the closed bottle test
(OECD 301D)78 or the Zahn–Wellens test (OECD 302B).77 In general, these
tests are carried out with several hundred milligrams of a substance as the
carbon source. Therefore, they give answers for only fairly extreme conditions, which, despite their intention, simulate only the maximum potential
and not the most probable environmental outcome. Therefore, conclusions
on the degradability of drugs in STPs from these tests are of limited value
and further research is necessary.76
Al-Ahmad et al.2 assessed the biodegradability of the clinically important antibiotics cefotiam, ciprofloxacin, meropenem, penicillin G, and sulfamethoxazole using the closed bottle test (CBT). None of the test compounds met the criteria for ready biodegradability. Of all the compounds
studied, only penicillin G was found to be biodegradable to some degree,
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O. A. H. Jones et al.
with approximately 27% being removed after 28 days. Even when the test was
prolonged to 40 days, the removal rate was only increased to 35% indicating
the compound was relatively stable.
Kümmerer and Al-Ahmad77 used the CBT and the modified Zahn–
Wellens test (ZWT) to examine the biodegradability of the widely used antitumor agents 5-fluorouracil, cytarabine, and gemcitabine. 5-Fluorouracil was
not biodegradable in either of these tests. Gemcitabine was biodegraded by
42% in the CBT, but prolonging the test period to 40 days only improved
this to 45%. Cytarabine was also partially biodegraded in the CBT (50%). In
the ZWT, the biodegradation of gemcitabine was also 50% but only after an
adaptation period of 20 days, which is not normally included in such tests.
Prolonging the test to 40 days improved the degree of biodegradation to 80%,
and in the ZWT the biodegradability was over 95%.
Henschel et al.54 investigated the biodegradability of paracetamol and
methotrexate and the two drug metabolites salicylic acid and clofibric acid.
Their results were in agreement with other studies and demonstrated that salicylic acid and (to a lesser extent) paracetamol were biodegradable, whereas
clofibric acid and methotrexate were not.
Kümmerer78 studied the biodegradability of three clinically important
antibiotics (ciprofloxacin, ofloxacin, and metronidazole) and found none
of the compounds were biodegraded. As a consequence the genotoxicity
of these compounds (as measured by the SOS chromotest) remained unaffected after treatment. A more comprehensive review of antibiotics in the
environment is available in Hirsch et al.57 This article describes the analysis of various water samples for 18 antibiotic substances, from several
groups, including macrolid antibiotics, sulfonamides, penicillins, and tetracyclines. Both STP effluents and surface-water samples were frequently contaminated with sulfamethoxazole and roxithromycin (a degradation product
of erythromycin) at concentrations up to 6 µg L−1 . The highest concentrations detected for tetracyclines and penicillins were 50 and 20 ng L−1 , respectively. Except for two sites, no contamination by antibiotics was detected from a large number of groundwater samples that were taken from
agricultural areas in Germany. This suggests that contamination of groundwater by antibiotics from veterinary applications is relatively minor. Other
drugs that have been investigated for their biodegradability include ifosfamide and cyclophosphamide.79,112 Both of these compounds exhibited
poor biodegradability in the CBT and the ZWT as well as in laboratory-scale
activated sludge plants.
Degradation may also occur during bank filtration, if it is used. Heberer
et al.52 found clofibric acid, phenazone, propyphenazone, diclofenac, ibuprofen, and fenofibrate, and two metabolites, N -methylphenacetin (probably
originating from phenacetin) and also a derivative of clofibric acid at concentrations up to the micrograms per liter level in groundwater samples taken
from beneath a drinking-water treatment plant. These contaminants were
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Pharmaceuticals in Wastewater Treatment Processes
405
found to leach from the neighboring sewage contaminated surface water by
bank filtration through the subsoil.53
Molecules with long, highly branched side chains are generally less
amenable to biodegradation than unbranched compounds with shorter side
chains.105 Unsaturated aliphatic compounds are generally more accessible to
biodegradation than saturated analogues or aromatic compounds with complicated aromatic ring structures and sulfate or halogen groups.101 Examples
of the latter are the x-ray contrast media. Since these compounds are exclusively utilized in human medicine, contaminated STP effluents are presumably the sole sources for these compounds in the aquatic environment. The
occurrence of four iodinated x-ray contrast media (diatrizoate, iopamidol,
iopromide, and iomeprol) in eight German STPs was examined by Ternes
et al.120 These compounds were found to be ubiquitously distributed in the
raw sewage and were not significantly degraded or absorbed during the
sewage treatment processes and so remained in the aqueous phase. The
concentrations of diatrizaote, iopromide, and iomeprol frequently exceeded
1 µg L−1 in the raw sewages, and these were found at comparable concentrations in the final effluents, with the maximum concentration measured being
15 µg L−1 for iopamidol.
A similar study by Steger-Hartmann et al.111 demonstrated that while
these compounds are not readily biodegradable, iopromide was amenable
to photodegradation. The resulting degradation product (5-amino-N ,N bis(2,3-dihydroxypropyl)-2,4,6-triiodo-N -methyliso-phthalamide) also exhibited a faster rate of photolysis than the parent compound and was further
degraded in a test system simulating surface-water conditions. However, the
predicted environmental concentration (PEC) in surface water was still high
at 2 µg L−1 .
Some degradation of iopamidol in activated sludge has also been observed with 85% being transformed into two metabolites.68 Degradation of
the same compound in river water was even more significant, with a half-life
of 3.1 days. However, for other, similar compounds such as diatrizoate the
half-life was longer, suggesting there is potential for some compounds to
reach rivers and lakes. Although of low toxicity, x-ray contrast media may
contribute significantly to the absorbable organic halogen compound (AOX)
load in receiving waters. This is of concern because of the high persistence,
mobility, and potential of these substances to biotransform to toxic breakdown products.
It is also possible that the biota of a STP may gradually become acclimatized to certain chemicals and therefore may degrade them more effectively given time.132 For instance Zwiener et al.133 investigated the biological degradation of pharmaceutical residues (clofibric acid, ibuprofen,
diclofenac). In this study both a pilot sewage plant and biofilm reactors operating under oxic and anoxic conditions were run as model systems for
municipal sewage treatment, with synthetic sewage and pharmaceuticals in
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O. A. H. Jones et al.
concentrations of 10 µg L−1 . Clofibric acid displayed persistence in all cases.
The pilot sewage plant and the anoxic biofilm reactor showed comparable
results for diclofenac and ibuprofen, which both were partially degraded.
A high degree of degradation was found for ibuprofen in the oxic biofilm
reactor, which was attributed to adaptation of the biofilm to the residue. This
effect has also been show to occur for other compounds, for example, nitrilotriacetic acid, where a period of acclimatization has been shown to be
required before biodegradation can begin.102 In addition, the phenomenon
of co-metabolism—the oxidation and degradation of nongrowth substrates
by micro-organisms—is well documented.45,46
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B. Deconjugation
Pharmaceutical compounds are often metabolized in the liver, and as a consequence gluconoride and sulfate conjugates of the parent drugs are excreted.98
Conjugates of other organic compounds such as steroid hormones have been
shown to be readily deconjugated in domestic wastewater and within STPs
due to the large amounts of β-glucuridase enzyme present (produced by the
fecal bacterium Escherichia coli).10 It seems probable that gluconoride and
sulfate conjugates of drug compounds will be degraded by the same process.
The effect will be to increase the excreted contribution of the active drugs
to sewage and effluents.117
C. Partitioning
Partitioning between the aqueous and organic biomass phases is a key component in determining the ultimate concentrations of organic pollutants.49
Compounds with high log K ow values are known to sorb to sludge,84 while
substances with lower values are more likely to stay in the aquatic phase, depending on the individual compound,40 and substances sorbing to solids may
also be remobilized if they are not strongly bound. It is also well known that
bacterial, algal, and fungal cells are capable of adsorbing and accumulation
organic pollutants.10 The activated sludge biomass is able to adsorb organic
pollutants such as lindane, and adsorption of these compounds generally
fits the Freundlich isotherm. There is a good correlation between compound
adsorption and the octanol/water partition coefficient. However, since most
drugs are soluble with low log K ow and K oc values, they exist primarily in
the aqueous phase and transfer to sewage sludge is probably of only minor
concern for the majority of compounds.
There are few studies in the literature detailing potential sorption interactions of drug compounds. Hua et al.60 studied the removal of chemical oxygen demand (COD), micro-organisms, and selected pharmaceutical
compounds by trickling wastewater through a sandy soil from the Rhine
valley in glass columns. The sewage contained low concentrations of at
least 10 different pharmaceuticals and x-ray media. Some of the compounds
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Pharmaceuticals in Wastewater Treatment Processes
407
were removed by adsorption onto sand and/or biodegradation. The rate
of removal varied from complete (e.g., ibuprofen and naproxen), to almost none, for several x-ray contrast media. Some of the compounds
were removed as effectively by this method as by conventional sewage
treatment.
Jones et al.65 estimated physicochemical values for the top 25 pharmaceuticals in England in 2000 using a computer model. Of the top 25 compounds, 16 had low predicted sorption potential and were thought unlikely
to bind to sludge solids. Five compounds had medium sorption potential
and two (quinine sulfate and mefenamic acid) …
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