Removal of pharmaceuticals during wastewater treatment and environmental risk assessment using hazard indexes

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Abstract

In a long term study, which covered 4 sampling periods over three years, a total number of 84 samples, specifically 28 influent, effluent, from seven WWTP located in the main cities along the Ebro river Basin (North East of Spain), as well as receiving river waters, were analyzed to assess the occurrence of 73 pharmaceuticals covering several medicinal classes. Results indicated that pharmaceuticals are widespread pollutants in the aquatic environmental. Linking the calculation of removal rates with half-lives, assuming that compound degradation followed pseudo-first order kinetics, suggested that conventional wastewater treatments applied at the seven WWTP were unable to completely remove most of the pharmaceuticals under study. The evaluation of compound degradability, in terms of half-lives, is an important task to discuss integrated solutions for mitigation of pollutants entry into the water cycle. High half-lives observed for the majority of pharmaceuticals in WWTP suggest that, in order to enhance compound degradation, higher hydraulic retention times should be required.

The wide spectrum of substances detected in receiving river waters indicates that WWTP outlets are major contributors of pharmaceuticals in the aquatic environment. However, municipal wastewater treatment represents an obligatory and final treatment step prior to their release into the aquatic media, since load of pharmaceuticals in outlets were considerably reduced after treatment.

Finally, hazard posed by pharmaceuticals in both surface and effluent wastewaters was assessed toward different aquatic organisms, (algae, daphnids and fish). The overall relative order of susceptibility was estimated to be algae > daphnia > fish. Results indicate that no significant risks could be associated to the presence of pharmaceuticals in those matrices, indicating that reduction of compound concentration after wastewater treatment as well as dilution factor once pharmaceuticals are discharged in receiving river water efficiently mitigate possible environmental hazards.

Introduction

In the European Union (EU) around 3000 different PhACs are used in human medicine belonging to different medicinal classes. Thus, their main route into the aquatic environment is ingestion following excretion and disposal via wastewater. After administration, pharmaceuticals can be excreted, primarily via urine and faeces, either as an unchanged parent compound or in the form of metabolites or as conjugates of glucuronic and sulphuric acid. Besides these WWTP discharges into the environment, that are usually a consequence of their incomplete removal (Petrovic et al., 2005), other environmental exposure pathways of PhACs are manufacturing and hospital effluents, land applications (e.g., biosolids and water reuse), concentrated animal feeding operations (CAFOs), and direct disposal/introduction to environment (Daughton and Ternes, 1999).

Several studies reported on the limited degradability of pharmaceuticals under conventional treatments applied in the WWTPs (Radjenovic et al., 2007, Carballa et al., 2005), suggesting that their upgrade and implementation of advanced treatment technologies are required to achieve high-quality treated effluents (Radjenovic et al., 2009).

While most of northern European WWTPs include tertiary wastewater treatments, in Spain only primary and secondary treatments are performed, where the second one is based on conventional activated sludge, and tertiary treatments are seldom applied. Consequently, there is a need to assess the limitations of current wastewater treatment processes, as well as to evaluate which operational parameters would play a key role regarding pharmaceutical removal.

Selection of target analytes, which will be included in the analytical methods applied in monitoring programs, should be based on the sales and practices of each country (according to national sales figures and health system), compound pharmacokinetics (the percentage of excretion as non-metabolized substance), occurrence in the aquatic media (data taken from similar studies) as well as on data provided by environmental risk assessment approaches, which link the calculation of predicted environmental concentrations (PEC) with toxicity data in order to evaluate which compounds are more liable to pose an environmental risk for aquatic organisms (Bound and Voulvoulis, 2006, Castiglioni et al., 2004, Cooper et al., 2008).

Directives set by the US Food and Drug Administration (FDA) stipulates that an environmental risk assessment (ERA) should be part of the approval procedure of new medical substances (Cooper et al., 2008). However, few of these substances have been subjected to a complete ERA, because, in most cases, predicted environmental concentrations lie below the proposed cut-off values, fixed by these directives, making further ecotoxicological studies unnecessary. The current US and European regulatory guidance requires new pharmaceuticals to undergo standard acute toxicity tests (to algae, Daphnia magna and fish) if the predicted or measured environmental concentration (PEC or MEC) of the active ingredient is > 1 µg/L for the US legislation or 10 ng/L, according to the European threshold safety value, set by the European Medicines Agency (EMEA). For compounds whose PEC exceed these values, as a second tier in the ERA procedure, predicted no-effect concentrations (PNEC) are extrapolated by dividing E(L)50 values, (which are obtained from standard toxicity tests), by an assessment factor of up to 1000 in the EU (Cooper et al., 2008). If the quotient between the PEC or MEC and PNEC is lower than 1 (MEC or PEC/PNEC < 1), no further assessment is necessary (Cooper et al., 2008).

Over recent years, Spain has raised its position in the world and the European pharmaceutical market. It was the eighth largest world market in 2005, whereas the following year, it took up the fifth position in Europe's top pharmaceutical markets (www.farmaindustria.es; IMS Health). Such high consumption may lead to the conclusion that the problematic associated with aquatic contamination by pharmaceuticals may be an important issue that needs to be assessed and, since data regarding contamination of Spanish aquatic systems is still sparse, it is necessary to set up surveys at national or basin scale.

In the light of these concerns, the aim of the present study was to identify the loads of pharmaceuticals discharged into the aquatic environment through municipal wastewater effluents in the region of the Ebro river basin (North East of Spain). Therefore, the occurrence of 73 pharmaceuticals of major human consumption, which are listed in Table 1, was determined in both influent and effluent wastewaters from seven WWTP located in the main cities along the basin, as well as in their subsequent receiving river waters (see Fig. 1). Both removal rates and half-lives were evaluated for each compound, in all WWTP, in order to overview their biodegradability, as a consequence of the effectiveness of treatments currently applied in Spanish WWTP.

Finally, established hazard indexes were calculated in order to assess the risk towards different aquatic organisms (algae, daphnids and fish). Such indexes were obtained through the ratio between MECs in both effluent and river waters and PNECs, which were derived from acute toxicity data (EC50) from the literature. Such quotients could be used as an indicator of the possible ecotoxicological risks posed by the concentrations of pharmaceuticals detected in the aquatic environment in the area under investigation.

Section snippets

Pharmaceutical standards

All standards used were of high purity grade (> 90%). Compounds with number 1–5 and 16 (see Table 1) were kindly supplied by Jescuder (Rubí, Spain). Compounds with number 4, 6–8, 10, 11, 13, 14, 15, 17, 18, 21, 24–27, 29, 30, 31–52, 54, 55–64, 68–73 were purchased from Sigma-Aldrich (Steinheim, Germany). Compounds with number 21, 27, 29, 30, 31, 32, 57 and 64 were provided as hydrochloride, 33 as hydrate, 18 as sodium salt, 56 as tartrate, 70 as dehydrate, 73 as citrate, 68 as maleate and 40 as

Wastewater monitoring

It is well documented that WWTPs are major contributors of pharmaceuticals in the aquatic environment, since important loads are discharged into river waters through effluent wastewaters. This statement is supported by the information given in Table 3, which shows total loads of target pharmaceuticals in treated wastewaters that are afterwards discharged in receiving river waters. For each WWTP and sampling period, loads were calculated by multiplying total concentrations (addition of

Acknowledgments

This work has been supported by the EU project AQUATERRA (GOCE 505428) and by the Spanish Ministry of Science and Education Project CEMAGUA (CGL2007-64551). M Gros acknowledges her grant from the MSyE under the EVITA project (CTM2004-06265-C03-01). Merck is acknowledged for the gift of LC columns and Waters Corporation for the SPE cartridges. Staff from the WWTP are also acknowledged for their kindness and cooperation during the sampling.

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