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Believe it or not, commonly ingested pharmaceuticals and even human hormones are ending up in your drinking water supply. One or more OWCs(outside water cone) were found in 80% of the 139 streams sampled for this study. The high overall frequency of detection for the OWCs is likely influenced by the design of this study, which placed a focus on stream sites that were generally considered susceptible to contamination (i.e. downstream of intense urbanization and livestock production). In addition, select OWCs (such as cholesterol) can also be derived from nonanthropogenic sources.

Furthermore, some of the OWCs were selected because previous research (28) identified them as prevalent in the environment. Thus, the results of this study should not be considered representative of all streams in the United States. Only eight antibiotics and five other prescription drugs were not detected in the samples analyzed. Measured concentrations were generally low (median detectable concentrations generally <1 íg/L,), with few compounds exceeding drinking water guidelines, health advisories, or aquatic-life criteria. The concentration of benzo[a]pyrene exceeded its maximum contaminant level (MCL) of 0.2 íg/L at one site and bis(2-Ethylhexyl)phthalate concentrations exceeded its MCL of 6.0 íg/L at five sites. In addition, aquatic-life criteria were exceeded for chlorpyrifos t a single site.

However, many of the 95 OWCs do not have such guidelines or criteria determined. In fact, much is yet to be known about the potential toxicological effects of many of the OWCs under investigation. For many OWCs, acute effects on aquatic biota appear limited because of the low concentrations generally occurring in the environment. More subtle, chronic effects from low-level environmental exposure to select OWCs appear to be of much greater concern.

Such chronic effects have been documented in the literature. In addition, because antibiotics are specifically designed to reduce bacterial populations in animals, even low-level concentrations in the environment could increase the rate at which pathogenic bacteria develop resistance to these compounds. The 30 most frequently detected compounds represent a wide variety of uses and origins including residential, industrial, and agricultural sources. Only about 5% of the concentrations for these compounds exceeded 1 íg/L. Over 60% of these higher concentrations were derived from cholesterol and three detergent metabolites (4-nonylphenol, 4-nonylphenol monoethoxylate, and 4-nonylphenol ethoxylate). The frequent detection of cotinine, 1,7-dimethylxanthine, erythromycin-H2O,and other OWC metabolites demonstrate the importance of obtaining data on degradates to fully understand the fate and transport o fOWCsin in the hydrologic system.

In addition, their presence suggests that to accurately determine the overall effect on human and environmental health (such as pathogen resistance and genotoxicity) from OWCs, their degradates should also be considered. The presence of the parent compound and/or their select metabolites in water resources has previously been documented for OWCs as well as other classes of chemicals such as pesticides. Many of the most frequently detected compounds were measured in unfiltered samples. Thus, their frequencies of detection may be somewhat higher because concentrations being measured include both the dissolved and particulate phases, whereas concentrations measured by Methods 1-3 include just the dissolved phase. For example, about 90% of the coprostanol discharged from sewage effluents has been shown to be associated with particulate matter.

Thus, the concentration and frequency of detection for select compounds would likely have been reduced if sample filtration had taken place. Variations in RL also influence the frequency of OWC detection. For example, the detection of 4-nonylphenol would likely have been much greater if an order of magnitude lower RL (similar to other OWCs)could have been achieved. The effect of RL on frequencies of detection is more clearly demonstrated by the comparison of concentrations of select compounds that were measured using multiple analytical methods. To obtain a broader view of the results of this study, the 95 OWCs were divided into 15 groups based on their general uses and/or origins. The data show two environmental determinations: frequency of detection and percent of total measured concentration for each group of compounds.

These two views show a vastly different representation of the data. In relation to the frequency of detection, there were a number of groups that were frequently detected, with seven of the 15 groups being found in over 60%of stream samples. However, three groups (detergent metabolites, plasticizers, and steroids) contributed almost 80% of the total measured concentration. For those groups of compounds that have received recent public attention namely antibiotics, nonprescription drugs, other prescription drugs, and reproductive hormones, nonprescription drugs were found with the greatest frequency. Antibiotics, other prescription drugs, and reproductive hormones were found at relatively similar frequencies of detection. The greater frequency of detection for nonprescription drugs may be at least partially derived from their suspected greater annual use compared to these other groups of compounds.

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When toxicity is considered, measured concentrations of reproductive hormones may have greater implications for the health of aquatic organisms than measured concentrations of nonprescription drugs. Previous research has shown that even low-level exposure (<0.001 íg/L) to select hormones can elicit deleterious effects in aquatic species (7, 46, 47). Mixtures of various OWCs were prevalent during this study, with most (75%) of the streams sampled having more than one OWC identified. In fact, a median of seven OWCs was detected in these streams, with as many as 38 compounds found in a given stream water sample. Because only a subset of the 95 OWCs was measured at most sites collected during the first year of the study, it is suspected that the median number of OWCs for this study is likely underestimated.

Although individual compounds were generally detected at low levels, total concentrations of the OWCs commonly exceeded 1 íg/L. In addition, 33 of the 95 targets OWCs are known or suspected to exhibit at least weak hormonal activity with the potential to disrupt normal endocrine function, all of which were detected in at least one stream sample during this study. Although previous research has also shown that antibiotics, other prescription drugs, and nonprescription drugs can be present in streams, this study is the first to examine their occurrence in a wide variety of hydro-geologic, climatic, and land-use settings across the United States. Much is yet to be learned pertaining to the effects (particularly those chronic in nature) on humans, plants, and animals exposed to low-level concentrations of pharmaceuticals and other OWCs.

Furthermore, little is known about the potential interactive effects (synergistic or antagonistic toxicity) that may occur from complex mixtures of these compounds in the environment. Finally, additional research also needs to be focused on those OWCs not frequently detected in this stream sampling. Select OWCs may be hydrophobic and thus may be more likely to be present in stream sediments than in stream water. For example, the low frequency of detection for the tetracycline (chlortetracycline, doxycycline, oxytetracycline, tetracycline) and quinolone (ciprofloxacin, enrofloxacin, norfloxacin, sarafloxacin) antibiotics are not unexpected given their apparent affinity for sorption to sediment. In addition, select OWCs may be degrading into new, more persistent compounds that could be transported into the environment instead of (or in addition to) their associated parent compound.

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