In summary, it is often difficult to obtain accurate PCR efficiency, which results in possible erroneous estimation of transgene copy number from qPCR. In this study, we present a novel qPCR approach, named standard addition qPCR, to accurately determine transgene copy number. The strategy is to add known amounts of standard DNA to test samples to change fluorescence intensity and Ct values, which is similar to standard addition in quantitative chemical analysis. In this assay, the estimation of PCR efficiency can be bypassed, which is not the case in the previously mentioned approaches. Among the many types of pharmaceuticals, antibiotics receive particular attention concerning their risk to the natural environment. Antibiotics are widely prescribed worldwide, and thus are expected in receiving waters. Their presence in the aquatic environment is of concern as they are potentially harmful to organisms there. They are thought to foster bacterial resistance, for example. Not surprisingly, recent studies on the occurrence of micropollutants in the environment include antibiotics. Several field campaigns have reported fluctuations of pharmaceutical concentrations in receiving waters, the magnitude of which varies with location and substance. Roig reported an extensive overview of different field campaigns focused on antibiotics and other pharmaceuticals in surface waters, including Wastewater Treatment Plant influent and effluent. Since the temporal variation of pharmaceutical concentrations is a supplementary pressure on aquatic system preservation, understanding of such variations is an important challenge in environmental assessment and management. Antibiotics are present in both urban and rural environments. For the latter, their concentrations are often driven by veterinary use. In urban settings, antibiotic concentrations in wastewater result from ambulatory and hospital consumption. As a consequence, consumption data are needed to estimate their concentration. Several studies attempted to estimate wastewater pharmaceutical concentrations using sales data and the Predicted Environmental Concentration Model. These studies were not focused on short-term fluctuations as they considered only annual sales data. At present, no study has considered seasonality in consumption of antibiotics in urban settings. Here, we first investigated seasonality of antibiotic concentrations in wastewater based on monthly sales data and the PEC model. Second, the fraction of antibiotics originating from hospitals in the total load found in 
wastewater was examined, again based on monthly consumption. The study considered nine substances – azithromycin, ciprofloxacin, clarithromycin, clindamycin, metronidazole, norfloxacin, ofloxacin, sulfamethoxazole and trimethoprim – using data for the city of Lausanne, Switzerland. These monthly dry weather wastewater data were provided by Lausanne public authorities. A seasonal trend can be observed with higher volumes in summer than in winter. Similar behaviour in WTP dry weather monthly flow volumes was observed in other studies. In our approach, we considered only hospitals or clinics performing acute somatic treatments, as such establishments dispense antibiotic prescriptions. The study is based on data from ambulatory sales and hospital dispensaries. These data are considered as accurate measures of consumption. Antibiotics are prescription drugs, and are pathology-specific.
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