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Expanding world populations and economic growth with its necessary industries have placed a great burden on the environment (soil, water and air). In the past the environment was assumed to be infinite in its ability to absorb and remove the by-products of human populations (Sverdrup et al., 2003). However, waste discharges can and do exceed the ability of natural systems to flush themselves producing problems that cannot be ignored (Alley, 2007). There are many waste classes that are discharged into river systems but one which is of growing concern to the public and regulatory agencies due to its subtle, widely unknown nature of action in aquatic ecosystems and ever-increasing production and consumption uses are Pharmaceuticals and Personal Care Products (PPCPs) (Ozaki et al., 2008). PPCPs comprising of thousands of registered formulated end-use products which contain more than 3000 distinct bioactive chemical entities consist of prescription and over-the-counter therapeutic drugs (painkillers, antibiotics, contraceptives, beta-blockers, lipid regulators, tranquilizers, and impotence drugs), veterinary drugs, fragrances, cosmetics (skin care products, dental care products, soaps, sunscreen agents and hair care products), and numerous others (Water Encyclopaedia, 2009; Daughton, 2004; Ternes et al.,1998; Heberer et al., 1998; Hirsch et al., 1999; Qiting and Xiheng, 1988). The concentration of pharmaceuticals reaching the aquatic environment ranges from milligram/litre (mg/l) for some to nanogram/litre (Î¼g/l) for most. These present a significant environmental concern and evoke profound discriminating to elusive effects even at very low concentrations. Astonishingly, little is known about the numbers and types, trends of occurrence, the fate and transport of pharmaceuticals occurring in a large number of watersheds and municipalities (Daughton, 2003a).
Pharmaceutical concentrations in aquatic compartments such as soils, water column, sediments, flora and fauna increases yearly with the development of new pharmaceutical products which are more resistant to biodegradability by microbes and persist in the environment for many years. In aquatic systems, pharmaceuticals are typically associated with organic carbon (particulate and dissolved) and sediments. Sediment stores containing pharmaceuticals at appreciable amounts are "time bombs" which when suddenly released by hydrological processes such as flush events, pose a catastrophic treat to aquatic life and processes that mediate energy transfer and utilisation. Adsorption of pharmaceuticals to particulate and dissolved organic carbon, transportation and subsequent deposition to bottom sediments determines the fate of pharmaceuticals in most aquatic systems (Vähätalo et al., 2003). However, the removal of pharmaceuticals from overlying waters to the sediment is not necessarily direct, and pharmaceuticals may be biologically recycled by processes such as trophic transfer, bioturbation, bioaccumulation, and invertebrate migration.
Sediments differ from soils and rock from which it is obtained by exhibiting extensive microbial activity which modifies organic and inorganic components, and exhibit reduction and oxidation reactions resulting in surface coatings changes of the sediment grains (Baldwin et al., 2002). Aquatic ecosystem function and stability is governed by microbial metabolic transformation of organic matter through processes including photosynthesis, chemosynthesis and respiration. The stability of bed sediments is an important determinant of the biologically mediated energy flow through lotic ecosystems (Uehlinger et al., 2002). Aquatic ecologists have long been aware of the significant influence of sediment metabolism on overlying water (Grimm and Fisher, 1984). Hence, the study of sediment microbial metabolism is vital to understand ecosystem biomass and trophic structure, nutrient cycling and dynamics and the transportation and degradation of toxic chemicals in the aquatic ecosystem (Wetzel, 2001; Fallon et al., 1983). The total consumption of organic matter (particulate, dissolved and sediment) from autochthonous and allochthonous inputs within the sediment are indicated by extent of sediment microbial respiration (Vähätalo et al., 2003).
However, regardless of increasing knowledge about the numbers, population dynamics, biogeochemical activity of microbes, and the rates of production and turnover, an understanding of the entire subject of aquatic microbial ecology is an emerging frontier and in its infancy (Wetzel, 2001). Furthermore, the linkage between sediment microbial activity and the storage, subsequent remobilisation, entailment, metabolism and the consequent effects of many pharmaceutical compounds in sediments is poorly understood. There are only a few studies dealing with the potential range of effects of mixtures of pharmaceuticals, thus further toxicity studies is warranted to better understand the fate and effects of pharmaceuticals on a larger range of environmental matrixes including biosolids, soils and soil-biosolid types (Fent et al., 2006; Monteiro and Boxall, 2010).
Given the lack of data on the relationship between pharmaceutical sediment contamination and sediment metabolism, intensively diverse fluvial sediment research would provide a good opportunity to extensively record and contribute information to this growing this discipline of study.
1.2 Research Aim and Objectives
The successful completion of research needs on pharmaceuticals could lead to many outcomes some spanning a wide spectrum of disciplines and aspects of society (Daughton, 2004). This study aims to quantify the effects of the most widely used pharmaceuticals in the in the UK namely Propanolol, Ibuprofen, Diclofenac, Erythromycin and Mefenamic acid as single and multiple stressors of sediment respiration. Each of these pharmaceuticals based on aquatic toxicity data from the literature were highly persistent and the PEC: PNEC ratio (Table 2.31 and 2.32) were comparatively high or exceeded 1 ngl-1 in the aquatic environment of the UK indicating their environmental risk and potential hazards. The specific objectives of this research are to:
Determine the dose-effect relationship of single pharmaceutical compounds on sediment respiration
Determine the dose-effect relationship of a mixture of pharmaceutical compounds on sediment respiration
Though this experiment would be conducted under aerobic conditions, results from this experiment would provoke critical laboratory and field research needed to quantify the attenuation of pharmaceuticals under anoxic and saturated conditions.
2.1 Pharmaceuticals and Personal Care Products (PPCPS): An Emerging Contaminant
Ferrer and Thurman (2003) defines emerging contaminants (ECs) as "compounds that are not currently covered by existing regulations of water quality, that have not been previously studied, and that are thought to be a possible threat to environmental health and safety". ECs include pharmaceuticals and personal care products (PPCPs), surfactants, new pesticides and pesticide metabolites, plasticizers, flame retardants, insect repellents, disinfection by-products, endocrine-modulating compounds, nanoparticles, industrial chemicals (new and recently recognized) and biological metabolites and toxins and pathogens (Table 2.1 and 2.2) (Hudkin, 2005; Snow et al., 2008). ECs can be classified as organic or inorganic solids, volatile or nonvolatile, biodegradable or intractable, dissolved, suspended or settleable, liquids or gas, or as one of these mixed with, absorbed onto or dissolved in another and of animal, mineral or vegetable origin (Alley, 2007).
The most abundant class of EC compounds belong to the PPCP class (TerziÄ‡ et al., 2009). PPCPs comprise thousands of registered formulated end-use products which contain more than 3000 distinct bioactive chemical entities which are ubiquitous pollutants, owing their origins in the environment to their worldwide everyday usage and disposal (Daughton, 2004). Each PPCPs consists of a bioactive substance (usually in low concentration) that are mainly simple to complex organic substances, mixed with a number of auxiliary substances that are designed to be biologically active and to cause very specific effects (Palace et al., 2002). PPCPs in the environment have no geographic boundaries or climatic-use limitations, hence, are discharged wherever people live or visit, regardless of the time of year (Daughton, 2003a; 2003b).
2.2 PPCP Consumption in the UK
Annual production of PPCPs exceeds 1-106 million tonnes worldwide (Daughton and Ternes, 1999). There are approximately 2,000 and 3000 active substances licensed for use in the European and the UK markets respectively with many of them already being detected in surface water (Jones et al., 2001; Perazzolo et al., 2010). Records of drug use in the UK in terms of number of prescription items issued kept by the Department of Health (for prescribed drugs) and the Proprietary Association of Great Britain (for over the counter medicines) indicates the most used pharmaceuticals by weight in England in 2000 (Table 2.3) (Fatta et al., 2007) to range from over 10 tons to over 100 tons per year (Paracetamol, Metformin hydrochloride and Ibuprofen) (Jones et al., 2002). However, this type of data is often of little use when trying to estimate the amount of drugs and drug metabolites that may find their way into watercourses as the actual quantity of each of the numerous commercial drugs that is ingested/disposed is unknown, contrasting sharply with pesticides in which usage is much better documented and controlled (Jones et al., 2002). Such data can be used as a tool for ranking priorities on the basis of high volume and high activity pharmaceuticals in the UK (ibid.).
Table 2.1 Classes of emerging contaminants
Source: de Alda et al. (2003)
Table 2.2 Emerging potential waterborne pathogens
Mycobacterium avium intracellulare
(Source: Nwachcuku and Gerba, 2004)
Table 2.3 The 25 most used pharmaceuticals by weight in England in 2000
Amount used per
Detected in UK environment
Treatment of ulcerative colitis
H2 receptor antagonist
Anti-inflammatory and Analgesic
Figures relate to the Health Authority where the prescription was dispensed not where it was prescribed.
The weight of the chemical dispensed is based on Defined Daily Dose (DDD) information. Note that the DDD data do not cover all individual drugs. The ''coverage'' column indicates for each chemical the percentage of the prescriptions dispensed where DDD data are held. For example, the weight of aspirin dispensed is based on only 8% of prescription items dispensed.
Source: Jones et al. (2002)
Although largely unknown, there is evidence that large quantities of prescription and non-prescription drugs are never consumed and many of these are undoubtedly disposed down toilets or via domestic refuse (Greenwood, 2008). A survey conducted in UK households revealed that two-thirds (63.2%) discard PPCPs in household waste, with the remainder returning them to a pharmacist (21.8%), emptying them into the sink or toilet (11.5%) or taking them to municipal waste sites (3.5%) that sometimes have special waste facilities (Bound and Voulvoulis, 2005).
2.3 Sources and Occurrence of Pharmaceuticals in the Environment
Pharmaceuticals may enter the environment through the disposal of unused or expired medications or partially metabolized excrement from humans or animals on a continuous basis via agricultural run-off and aquaculture effluents (commercial animal feeding operations and surface application of manure and biosolids), sanitary sewer from hospitals and residents, industrial discharges, leaching municipal landfills or after wastewater treatment processes, which are generally not designed to remove them (Daughton, 2003a; Daughton, 2003b; Ellis, 2006; Alley, 2007) (Figure 2.1). During wastewater treatment, the processes acting on pharmaceuticals, metabolites and their conjugates (e.g. Bromochloroacetic acids, Chloral Hydrate, Haloacetonitriles, Trihalomethanes, Cyanogen Chloride, Carboxylic acid, Aldoketoacids and Aldehydes) (Richardson, 2003; Hemminger, 2005) are not fully understood and there are conflicting reports on their biodegradability (95% to <10%) (Jones et al., 2002; Snyder, 2008; Bolong et al., 2009). The elimination efficiency of PPCPs in wastewater treatment plants is still a matter of intensive research though some have already been well-described in the literature (Ahel et al., 1994; Larsen et al., 2004; Clara et al., 2005; Hudkin, 2005; Lindqvist et al., 2005; Phillips et al., 2005; Molinari et al. 2006; Gultekin and Ince, 2007; Santos et al., 2007).
Figure 2.1 Sources, pathways, and sinks of pharmaceuticals in the environment (Kummerer, 2001)
Laboratory and field experiments indicate the persistence of pharmaceuticals in aquatic environments (Lin and Reinhard, 2005). Conceptually, pharmaceuticals in the aquatic environment can be viewed as residing in one of four pools: (i) dissolved in the water column; (ii) associated with suspended sediments; (iii) deposited in bed sediments; or (iv) incorporated into the biota (Fig. 2.2). Water and sediment chemistries and biological activity control the exchange of pharmaceuticals between each of the pools in the water body.
Fig. 2.2 Diagram of pharmaceutical interaction in the aquatic system (Adapted from Baldwin et al. (2002)). The arrows in the diagram signify the exchanges between each of the pharmaceutical 'pools'. Arrow A - Addition of pharmaceuticals into any of the four defined pools of a water body (river reach or lake) from upstream inputs. Arrows B and C - Adsorption and desorption exchanges occur between the dissolved pool and the sediment bound pools. Arrow D - Sedimentation and re-suspension exchanges pharmaceuticals between the bed sediment and the suspended sediment pools. Arrow E - Incorporation of pharmaceuticals into the biological pool from the dissolved pool through the growth of bacteria, algae, and aquatic plants. This is further transferred along the food chain. Direct excretion (arrow E) or mineralization during decomposition of organic matter and following the death of organisms (arrows F to C and G to B) releases pharmaceuticals from the biological pool (bed and in suspended sediments) back to the dissolved pool.
Although there has been no systematic monitoring for the presence of pharmaceuticals in the aquatic environment of the UK, the data available indicate that the concentrations in surface waters will be very low (Jones et al., 2002). A comprehensive study conducted by the U.S. Geological Survey (USGS) on 139 streams found 80% of them to contain PPCP agents in low concentrations (Kolpin et al., 2002). About 70-80 % of drugs administered in fish farms end up in the environment with drug concentrations of antibacterial activity are found in the sediment underneath fish farms (Halling-Sorensen et al., 1998).
The environmental risks of pharmaceuticals, generally identified in soils, plant and animal tissues, groundwater, surface and drinking water in concentrations of parts per billion (Âµg/l) to parts per trillion (ng/l) (Hemminger, 2005) have captured the attention of scientists and the public, especially in the more developed western countries of North America, the United Kingdom, and Europe (Halling-Sorensen et al., 1998; Kolpin et al., 2002; Larsen et al., 2004).
Astonishingly, little is known about the numbers and types, and trends of occurrence of pharmaceuticals in a large number of watersheds and municipalities even though medications have been in the environment for as long as long as they have been used commercially (Daughton and Ternes, 1999). However, research over these past years in the UK which is primarily focused on the environmental occurrence and effects of endocrine disrupting compounds and antibiotics have accrued evidence that the concentrations of some pharmaceuticals detected in streams and rivers are likely to pose some treat to health and aquatic health (Thiele-Bruhn, 2003). The limited amount of research on pharmaceuticals is in most part probably due to the little experience in environmental issues by human health agencies regulating pharmaceuticals whose actions are practically unknown and their control is an ongoing challenge (Jones et al., 2002). Another reason for this general lack of data is that, until recently, there have been few highly selective and sensitive analytical methods capable of detecting pharmaceutical compounds at low concentrations which might be expected in the environment (Daughton, 2003a; Derksen et al. 2004). These analytical procedures have detection limits, for instance ranging from 0.01 to 0.20 ngl-1 for ibuprofen and 17-ethinylestradiol respectively (Möder et al., 2007). Table 2.4 shows the minimum and maximum concentrations of pharmaceutical compounds detected in the aquatic environment of the United Kingdom.
Where the predicted environmental concentrations (PEC) of pharmaceuticals exceed 0.01 Î¼gl-1 further aquatic fate and effect studies are conducted to access the risk (Jones et al., 2002). The study of Jones et al (2002) concluded that the predicted no-effect concentration (PNEC) based on aquatic toxicity data from the literature is available for a few pharmaceuticals and the PECs for the 25 most used pharmaceuticals (Table 2.5) in the aquatic environment in England exceeded 1 ngl-1 with the PEC: PNEC ratio exceeding one for Paracetamol, Amoxycillin, Oxytetracycline and Mefenamic acid. Some probable invalid assumptions such as no metabolism or breakdown of the drug within man or the sewage system, drug being evenly distributed in usage over time and space, and the non adsorption of pharmaceuticals to organic or inorganic colloidal material or bacterial biomass in sewage treatment works or natural water were made during the study. However, the PEC: PNEC values estimated for these pharmaceuticals in the environment is considered uncertain or conservative estimates of risk by some researchers because of
Table 2.4 Detected pharmaceutical compounds in the aquatic environment of the United Kingdom