Pharmaceuticals

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Pharmaceuticals include "a wide-ranging class of compounds with substantial variability in structures, function, behavior, and activity" that are developed to elicit a biological effect in both humans and animals in order to cure disease, fight infection, and/or reduce symptoms.^[1] Pharmaceutical drugs are manufactured and sold by the pharmaceutical industry. However, drugs may be both natural and synthetic (consider caffeine, which is present both in coffee and the over-the-counter drug Excedrin).

Drug Classifications

Pharmaceuticals are classified into drug classes based on either active ingredients or how they are used to treat particular conditions.^[2] An individual drug may fall into one or more drug classes. In the U.S., there is no one single classification system that is universally used.

Pollution of Pharmaceuticals in the Environment

Because humans and animals often do not fully metabolize pharmaceuticals in their body, they can excrete drugs or their breakdown products, which may the enter the environment.^[3] This phenomenon was first cited in the 1970s, but it may have occurred before then. Scientists now estimate that "most if not all urban wastewater is contaminated with medicinal compounds, differing only in the type and abundance of the substances present."^[4]

Human waste goes into sewage treatment plants, where water is treated and released as effluent. Any pharmaceuticals separated from the water end up in sewage sludge, and if they are not naturally broken down during treatment processes, they then follow the sewage sludge to wherever it is disposed of, whether that is a landfill or a farm field. One study concluded:^[5] "The occurrence and fate of pharmaceutically active compounds (PhACs) in the aquatic environment has been recognized as one of the emerging issues in environmental chemistry. In some investigations carried out in Austria, Brazil, Canada, Croatia, England, Germany, Greece, Italy, Spain, Switzerland, The Netherlands, and the U.S., more than 80 compounds, pharmaceuticals and several drug metabolites, have been detected in the aquatic environment Several PhACs from various prescription classes have been found at concentrations up to the μg/l-level in sewage influent and effluent samples and also in several surface waters located downstream from municipal sewage treatment plants (STPs). The studies show that some PhACs originating from human therapy are not eliminated completely in the municipal STPs and are, thus, discharged as contaminants into the receiving waters." The study notes that several pharmaceuticals have been detected in groundwater samples in Germany, but to date, very few have been found in drinking water.

Breakdown of Pharmaceuticals

Over more than a decade, scientists have examined how various pharmaceuticals behave when they are excreted by humans and animals and sent to wastewater treatment plants and/or released into the environment. One study noted that "Many of the more commonly used drug groups (for example antibiotics) are used in quantities similar to those of pesticides and other organic micropollutants, but they are not required to undergo the same level of testing for possible environmental effects. The full extent and consequences of the presence of these compounds in the environment are therefore largely unknown and the issue as a whole is ill-defined. Although these compounds have been detected in a wide variety of environmental samples including sewage effluent, surface waters, groundwater and drinking water, their concentrations generally range from the low ppt to ppb levels."^[6]

Anti-Tumor Drugs

One study on the ability of drugs to biodegrade focused on anti-tumor agents, which are often "known to be carcinogenic, mutagenic, teratogenic, embryotoxic or fetotoxic."^[7] The study used two methods of testing, a closed-bottle test (CBT) and a Zahn-Wellens test (ZWT), and the drugs 5-fluorouracil (5-FU), cytarabine, and gemcitabine. They found that 5-fluorouracil did not break down in either test. Gemcitabine biodegraded between 42% and 50%, depending on the testing method used and the length of time of the test period. The last drug, cytarabine, broke down by 50% in 20 days and 80% in 40 days using the CBT, but using the ZWT method, it biodegraded more than 95% after a few days. A later study looked at the anti-tumor drug ifosfamide and found that there was no biodegradation at all, nor was the drug absorbed by sewage sludge.^[8] In other words, when ifosfamide enters a wastewater treatment plant, it likely ends up in effluent.

Antibiotics

A 1999 study examined the biodegradability of the antibiotics cefotiam, ciprofloxacin, meropenem, penicillin G, and sulfamethoxazole as well as their toxicity to bacteria.^[9] The study aimed to see how much of these drugs were breaking down in wastewater treatment plants as well as what effect they might have on creating antibiotic-resistance in bacteria. Of the drugs, only penicillin G biodegraded, and it did so only partially (35% in 40 days). The study concluded "Therefore, antibiotic drugs emitted into municipal sewage may affect the biological process in sewage treatment plants (STPs), and they may persist in the aquatic environment and contribute to the increasing resistance of pathogenic bacteria."

In 2000, another study examined the antibiotics ciprofloxacin, ofloxacin, and metronidazole to see if they biodegraded and if their genotoxicity (i.e. ability to damage DNA, potentially causing mutations or cancer) was eliminated. None of the drugs broke down and their genotoxicity was not eliminated.^[10]

A 2004 study looked at the ability of 18 antibiotics to biodegrade in a closed bottle test.^[11] The antibiotics tested were: Amoxicillin, Benzylpenicillin sodium salt, Ceftriaxone disodium, Cefuroxime sodium salt, Chlortetracycline hydrochloride, Clarithromycin, Clindamycin, Erythromycin, Gentamicin sulfate, Imipenem, Metronidazole, Monensin sodium salt, Nystatin, Ofloxacin, Sulfamethoxazole, Tetracycline, Trimethoprim naphthoate, and Vancomycin hydrochloride. The study concluded: "None of the antibiotics was readily biodegradable. Elimination in the environment by other mechanisms may happen, but will not completely mineralize the active compounds. The results of CFU determination showed that some of antibiotics have an inhibitory effect on the bacterial population. Our findings underline the need for more detailed investigating effects on antibiotics in the environment."

Other Drugs

A 2001 study composted the gout medication Probenecid and the now illegal drug Methaqualone (Quaalude) to see if they were biodegraded during composting. Both were reduced to "acceptable" soil concentrations after 6 and 14 weeks of composting, respectively.^[12]