Antibiotics - University of Washington



Pharmaceuticals in Drinking Water: An Overview

By Steven Drangsholt, Lesley Leggett, Jennifer Parker,

Ching-Yu Peng, and Kelly Stumbaugh

Introduction

The extensive use and disposal of pharmaceuticals worldwide leads to their presence in wastewater and surface water; eventually, pharmaceuticals find their way into drinking water supplies. Researchers and scientists have detected prescription and over-the-counter (OTC) drugs, antibiotics, and synthetic hormones in aquatic systems. Detection of these chemicals is limited by current technology; low levels of many compounds are not detectable, but are likely to occur in water. While the ecologic and human health effects of pharmaceuticals in aquatic ecosystems and drinking water are not fully known, evidence suggests that chronic low-level exposure may be harmful. Pharmaceutical residues in drinking water may cause effects such as contributing to antibiotic resistance of human pathogenic bacteria, reproductive effects, and increased cancer risk. Conventional drinking water treatment techniques are inefficient at removing most pharmaceuticals; other available treatment options may be more effective.

Prescription and Over-the-Counter (OTC) Drugs

Every year, thousands of prescription and OTC drugs are used. Most are ingested and metabolized by the body before being excreted to sewage. Unused or expired drugs are commonly flushed down the toilet and enter sewage without being metabolized. There are numerous classes of prescription and non-prescription drugs. Whether or not these compounds reach water sources used for drinking water depends on several factors: stability, biodegradability, and water solubility. While prescription and non-prescription drugs are detected in sewage effluents and drinking water, these substances are found at low-levels. Typical concentrations in the ng/L-(g/L (ppt-ppb) range. A 2002 USGS study, which sampled many U.S. streams, reported detection frequencies of 32% and 81% for prescription and non-prescription drugs, respectively (toxics.).

Prescription drugs used in high doses have a much higher probability of entering and persisting in water sources. Blood lipid regulators are the most commonly and widely detected prescription drugs in receiving waters. Due to the high doses used in humans (often grams per day) there is very high input of blood lipid regulators into the environment. Clofibric acid is an active metabolite of lipid regulators and is formed when the drug is metabolized within the body. In Europe, this compound has been detected in groundwater (4 (g/L), lakes (1-9 (g/L), and in drinking water (270 ng/L). The annual input into the North Sea has been estimated to be as much as 50-100 tons (Daughton and Ternes, 1999). This compound is persistent in the environment, which also contributes to its widespread detection (Daughton and Ternes, 1999). Effects from exposure to clofibric acid at low levels in not known.

Other prescription drugs are known to cause reproductive, mutagenic, and teratogenic effects in various aquatic organisms. Beta-blockers (anti-hypertensive drugs) produce the metabolites metroprolol and propranolol, which have been detected in sewage effluents at concentrations 1 (g/L in sewage effluent and at lower concentrations in surface water. While these drugs are used at very high levels, they may be less stable in the environment; photolysis can degrade ibuprofen. Acetaminophen is another commonly used OTC drug and has been detected in sewage effluent at concentrations of 6 (g/L. It is not detected in drinking water, most likely, because it is efficiently removed during the drinking water treatment process. Other non-prescription drugs that are highly prevalent in sewage effluent are caffeine and nicotine (Daughton and Ternes, 1999). The effects of chronic low-level exposure to drugs, whether prescription or over-the-counter, is unknown.

Antibiotics

As the quantity and distribution of antibiotic resistance genes increases in microbial populations, attempts are being made to identify the factors contributing to the rapid spread of resistance. Infiltration of antibiotics and other antimicrobials into the aquatic environment has the potential to be a significant part of the resistance problem. Antibiotics have the opportunity to enter water bodies and come in contact with bacteria through their direct release in sewage and from animal wastes. Through drinking water, in particular, antibiotic residues are able to come into direct contact with humans, which may be a cause for concern in terms of spreading resistance genes to human bacterial flora. This action could have serious implications for treating bacterial infections in the future.

A variety of antibiotics have been detected in wastewater effluents, surface waters, and drinking source waters (Kolpin et al., 2002). Researchers have detected low level concentrations of fluoroquinolone (Vieno et al., 2007), macrolide and quinolone antibiotics (Ye et al., 2006) in finished drinking water despite the lack of research into the presence of antibiotics in drinking water. Antibiotic resistance in bacteria is encouraged by the presence of low concentrations of antibiotics (Jørgensen and Halling-Sørensen, 2000). Low doses allow the bacteria to survive in the presence of antimicrobials without being eliminated; thereby, giving them the opportunity to adapt and develop resistance. Though little is known about the causal connection between the occurrence of resistant bacteria and the low environmental concentrations of antibiotics (Hirsch et al., 1999), it is plausible that the presence of aquatic antibiotics would generate bacterial resistance.

Synthetic Hormones and Other Endocrine Disrupting Chemicals

Concerns about trace levels of synthetic hormones and other endocrine disrupting chemicals in the environment have increased because evidence of endocrine disruption has been found in wildlife. In particular, aquatic wildlife that lives downstream of wastewater discharges. This situation has translated into concerns about the possible human health effects of consuming drinking water contaminated with trace levels of such hormones. Research has found endocrine disrupting chemicals in aquatic systems worldwide. Though current human epidemiological data is inconclusive (Falconer et al., 2006), it is plausible that health effects from trace levels of hormones may exist based on the known health effects of these compounds found in animal studies.

Endocrine disrupting chemicals fall into two broad classes: synthetic pharmaceutical hormones (oral contraceptives, hormone replacement therapy drugs, and steroids) and anthropogenic chemicals (pesticides, industrial chemicals, and manufactured plastics). Synthetic pharmaceutical hormones enter wastewater after being metabolized by humans. Anthropogenic chemicals enter aquatic systems though industrial point source discharges or indirect pathways. In general, endocrine disrupting compounds are lipophilic; concentrations would be expected to be reduced during water treatment processes through sorption (Daughton and Ternes, 1999). However, concentrations of estrogens in wastewater, although reduced during treatment, can still be found at detectable levels post-treatment (Falconer et al., 2006). The drinking water process used will determine its removal efficiency.

Removal of Pharmaceuticals in Drinking Water

According to a recent studies, the conventional drinking water treatment processes (e.g., coagulation and sand filtration) that effectively reduce the amount of natural organic matter (NOM) and turbidity were inefficient for the removal of pharmaceuticals found in the source water (Vieno et al., 2007 and Kim et al., 2007). Coagulation and the subsequent sedimentation eliminated pharmaceuticals by only 3%. Rapid sand filtration following coagulation and sedimentation eliminated an additional 10% of the pharmaceuticals (Vieno et al., 2007).

According to present knowledge and available technology, oxidation by ozone, adsorption to activated carbon (either powered or granular), and separation by membranes are the most promising methods for the removal of pharmaceuticals (Vieno et al., 2007, Kim et al., 2007 and Stackelberg et al., 2007). Ozonation showed an average removal efficiency of 75%. Removal efficacy is a function of the contaminant structure and ozone dose. When the ozone dose was 1.0-1.3 mg/L of O3 (typical dose applied in drinking water treatments), it was sufficiently high to remove most of the pharmaceuticals to below their limit of quantifications. Ozone is a very selective oxidant and reacts preferentially with unsaturated bonds and aromatic rings substituted by electron donor groups (e.g., OH, NH2, and OCH3). Amine functionalities are structural components of many pharmaceuticals, such as beta blockers and fluoroquinolones antibiotics, making these compounds highly reactive with ozone (Vieno et al., 2007).

The average removal efficiency of pharmaceuticals by granular activated carbon (GAC) treatment is 75%. Removal capacity is limited by contact time, competition from natural organic matter, contaminant solubility, and carbon type. During GAC filtration, adsorption occurs mainly by hydrophobic interactions, but also ion exchange processes may take place. Adsorption through hydrophobic interactions tends to increase with an increasing octanol-water partition coefficient (Kow) value of a substance. The more hydrophobic pharmaceuticals have been reported to be more efficiently eliminated by GAC filtration (Vieno et al., 2007 and Stackelberg et al., 2007). Reverse osmosis (RO) and nanofiltration (NF) membranes provide effective barriers for rejection of pharmaceuticals. Both RO and NF membrane processes showed excellent removal rates (95%) for the pharmaceuticals (Kim et al., 2007).

Conclusions

Many classes of pharmaceuticals have made their way into water bodies worldwide. Current exposure levels to humans via drinking water are not well characterized, but evidence indicates that a variety of pharmaceuticals are present at low levels in drinking water. Additionally, while the human health effects of drug residues in drinking water are not well understood, animal studies suggest that these chemicals may be harmful to humans. Further research is needed to better quantify the efficiency of different drinking water treatment methods in order to reduce possible health hazards.

References

Daughton CD, and Ternes TA. Pharmaceuticals and personal care products in the environment: agents of subtle change? Environmental Health Perspectives 1999, 107(6), 907-938.

Falconer IR, Chapman HF, Moore MR, Ranmuthagala G. Endocrine-disrupting compounds: a review of their challenge to sustainable and safe water supply and water resuse. Environmental Toxicology 2006, 10, 181-191.

Hirsch R, Ternes TA, Haberer K, and Kratz L. Occurrence of Antibiotics in the Aquatic

Environment. The Science of the Total Environment 1999, 225, 109-118.

Jørgensen, SE and Halling-Sørensen B. Drugs in the Environment. Chemosphere 2000, 40, 691-699.

Kim SD, Cho J, Kim IS, Vanderford BJ, and Snyder SA. Occurrence and removal of pharmaceuticals and endocrine disruptors in South Korean surface, drinking, and waste waters, Water Research 2007, 41, 1013-1021.

Kolpin DW, Furlong ET, Meyer MT, Thurman EM, Zaugg SD, Barber LB, and Buxton HT. Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in U.S. Streams, 1999-2000: A National Reconnaissance. Environmental Science and Technology 2002, 36, 1202-1211.

Stackelberg PE, Gibs J, Furlong ET, Meyer MT, Zaugg SD, and Lippincott RL. Efficiency of conventional drinking-water-treatment processes in removal of pharmaceuticals and other organic compounds. Science of the Total Environment 2007, 377, 255–272.

U.S. Geologic Survey. Pharmaceuticals, Hormones, and Other Organic Wastewater Contaminants in U.S. Streams. USGS Fact Sheet FS-027-02, June 2002. .

Vieno NM, Härkki H, Tuhkanen T, and Kronberg L. Occurrence of pharmaceuticals in river water and their elimination in a pilot-scale drinking water treatment plant. Environmental Science and Technology 2007, 42, 5077-5084.

Ye Z, Weinberg HS, and Meyer MT. Trace analysis of trimethoprim and sulfonamide, macrolide, quinolone, and tetracycline antibiotics in chlorinated drinking water using liquid chromatography electrospray tandem mass spectrometry. Analytical Chemistry 2007, 79(3), 1135-1144.

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