Pharmaceuticals and Their Transformation Products in Hospital Effluents Before Reaching Urban Wastewaters Intended for Reuse: Characterisation, Management and Risks

During recent years, the issue of hazardous substances in wastewater has become a major concern with respect to both human health and environment. This has led to the launch of several studies into the monitoring of different aquatic environments (urban wastewaters, treated effluent, surface water, groundwater, drinkable water). In the last years, a particular interest was devoted to the monitoring of hospital wastewater in terms of either conventional pollutant or micropollutant concentrations and loads. With few exceptions, hospital effluents are considered to possess the same pollutant load as urban ones, and they are therefore discharged into the same sewage network and conveyed for co-treatment at the nearest municipal wastewater treatment plant (WWTP). Nevertheless, hospital effluents contain a great variety of toxic or persistent substances, due to laboratory and research activities as well as general hospital activity and excretion of medicines, generally occurring in concentrations ranging from ng/L to mg/L, while in urban wastewaters they are not present or they may occur at a lower level. Once pharmaceuticals are administered, their active substances are metabolized, but only to a certain extent. The unmetabolized fractions (varying between 10 and 95 %) are excreted, largely through the renal system (urine) and partially through the biliary system (faeces), depending on the nature of the compound and the individual in question. As a consequence, the residues join wastewater and enter the water cycle through the sewage system as unchanged substances (parent compounds), a mixture of metabolites, or conjugated with an inactivating compound attached to the molecule, whose fate in the environment will be governed by their characteristics (mainly: solubility, volatility, adsorbability, absorbability, biodegradability, hydrophilicity, lipophilicity, polarity and stability) as well as environmental conditions (temperature, pH, aerobic, anaerobic or anoxic conditions). On the basis of recent studies, it was found that antibiotics, analgesics/anti-inflammatories and steroid compounds are the therapeutic classes most abundantly administered in hospitals, followed by cardiovascular compounds, tranquilizers, anti-epileptic, beta-blockers, lipid regulators, anti-neoplastics and anaesthetics. Once in the sewage network, pharmaceuticals may embark on different pathways, perhaps exhibiting great stability and persistence in the environment, or perhaps being subjected to biological or chemical degradation, and/or sorption onto solids or other particles. In addition a release of some compounds may occur for some compounds, for instance the anti-epileptic carbamazepine whose concentration in the secondary effluent of a conventional wastewater treatment plant if often higher than in the influent. Four possible scenarios for the management and treatment of hospital effluent can be envisaged, namely: (a) direct discharge into a surface water body; (b) co-treatment in a municipal WWTP; (c) on-site treatment and subsequent discharge into a surface water body, and, finally, (d) on-site treatment prior to co-treatment at a municipal WWTP. The choice of the strategy to adopt should be based not only on economic constraints, but also on technical data, including assessment of the ecotoxicological risk posed by particular hospital wastewaters. Furthermore, different operational setups should be tested, in order to provide meaningful information about the financial aspects and overall risks associated with proposed future HWW treatment strategies. At the present time, most developing countries deal with hospital effluents by direct discharge into the environment without any treatment (option a from the list above); this unsurprisingly results in widespread contamination of the water cycle by both micro- and macropollutants. In contrast, in Europe and US, hospital effluents are discharged into the public sewage system and conveyed to municipal WWTPs (option b); these were originally built, and have more recently been upgraded, with the aim of removing nutrients (carbon, nitrogen and phosphorus compounds) and microorganisms and pollutants, which commonly arrive at the plant in concentrations of the order of several mg/L, or at least 105 CFU/100 mL, and are therefore not sensitive enough to remove micropollutants, typically present in quantities of μg/L, effectively. In contrast, option d promises the highest risk reductions but implies the highest costs; furthermore, in the case of a co-treatment at a municipal WWTP, HWW flow rates quite often amount to only a small percentage of the total influent flow rate. Consequently, although dilution of hospital effluents with urban ones usually results in a decrease in the PhC content in the final effluent (from μg/L to ng/L), the total load, that is to say the quantity released daily into the receiving water body, is not affected. It is evident, therefore that scenario c could be the best option, as an expensive, highly effective small-scale technology could eventually prove to be more eco- and cost effective than a relatively cheap large-scale solution with less effects on the diluted hospital effluent. All that being said, cost is not the only issue, and decision-makers also need to bear in mind several scientific considerations. Unfortunately, few studies have thus far looked into treatment and treatability of hospital effluents, and therefore the majority of PhC removal efficiency data reported are based on studies of urban wastewaters passing through conventional and (biological and chemical) advanced treatment plants. Attention has recently been focused on the risks posed by residual PhCs in the treated effluents, but ecotoxicological data are not always available for the single compounds under study, and even less is known about their behaviour as part of a mixture. Recently published environmental risk assessment of hospital effluents revealed that, the highest risk is posed by analgesics/anti-inflammatories (acetaminophen, ibuprofen, naproxen and salicylic acid) and antibiotics (ciprofloxacin, clarithromycin, erythromycin, ofloxacin and sulfamethoxazole), and the psychiatric drug fluoxetine, while 6 compounds (codeine, indomethacin, clenbuterol, atenolol, metoprolol and propranolol) pose a medium risk