Ecotoxicological evaluation of selected pharmaceuticals to Vibrio fischeri and Daphnia magna before and after photooxidation process
Graphical abstract
Introduction
The growing consumption and production of pharmaceuticals and personal care products (PPCPs) have resulted in their frequent presence in the waste water and environment (Marugan et al., 2012). The main route of the PPCPs introduction into the environment is the disposal of treated and untreated domestic or hospital waste water. The second environmental source is leaching, connected with the application of medicines as growth enhancers in the animal breading (Ellis, 2006, Sanderson et al., 2004). The low effectiveness of PPCPs waste water׳ conventional treatment is the result of (i) minimal interaction of PPCPs with the organisms in activated sludge, (ii) toxicity of PPCPs to the water organisms and (iii) low biodegradability of PPCPs during common waste water treatment (Schnell et al., 2009, Zhang et al., 2008).
PPCPs presence was noted in the ground and surface water at levels ranging from ng/L to μg/L (Qin et al., 2012). The commonly used treatment methods are not sufficient in the PPCPs removal, and new techniques are nowadays developed and widely tested (Gultekin and Ince, 2007). The confirmed high utility of photocatalysis for the removal of many organic pollutants from water (Czech et al., 2013), air (Paz, 2010) or soil (Carp et al., 2004) is connected with the oxidation of all contaminants into CO2, H2O and simple inorganic acids using mainly TiO2 as photocatalyst and UV irradiation at ambient temperature and pressure (Chong et al., 2010).
The main aim of the photocatalysis is the removal of targeted pollutant, expressed mainly as the decrease of pollutants׳ concentration with time of treatment, c/c0, where c is concentration determined at time t, c0 is initial concentration of studied pollutant. This approach however has not answer the question if the observed decrease is the result of the total mineralization of studied pollutants. Generally, the photocatalytically treated waste water contains the mixture of organic compounds being the products of partial oxidation or reaction of by-products. These mixtures are characterized by unknowing toxicity both for the microorganisms of activated sludge or water organisms in the environment. The environmental impact of these products is not established. Some of them are recognized as Endocrine Disrupting Compounds that modifies the hormonal and homeostatic systems of the organisms disturbing growth or reproduction (Manusadzianas et al., 2003).
For the evaluation of the removal of toxic compounds during waste water treatment, the ecotoxicological tests can be used as a useful tool (Fisher et al., 2010). Bioassays are sensitive, quick and reliable. Beside unquestionable advantages, fast tests may be characterized by low answer from tested organizms. They usage is preferd for the substances soluble in water that react quickly and caused a quick response. The great popularity of Daphtoxkit FTM (with Daphnia magna as tested organism) and Microtox® (Vibrio fischeri) is connected with their unquestionable advantages (Sponza, 2006). Zooplankton (in particular the genus Daphnia) is frequently used in ecotoxicological tests because this is one of the most sensitive organisms to toxic chemicals and this organism occupies a central position in the lentic food chain (Bervoets et al., 1996, Naddy et al., 2007). Bacteria V. fischeri is another organism commonly accepted in toxicity test that is internationally recognized and standardized as ISO (2007) (Libralato et al., 2010). Microtox® is though a widespread acute test as it is very sensitive, reproducible, possesses high discriminant power for organic and inorganic pollutants.
The ecotoxicological tests are frequently used to determine the impact of contaminants on living organisms (Fisher et al., 2010, Manusadzianas et al., 2003, Naddy et al., 2007). However, their application in the qualitative analysis of photocatalytically treated waste water containing PPCPs is quite occasional (Marugan et al., 2010, Schnell et al., 2009). Generally, many PPCPs are considered to be toxic for the water organisms and their toxicity to non-target organisms may occur even at concentrations lower than expected due to synergistic effects between the different toxicants (Marugan et al., 2012). Though it seems to be extremely important to combine the results of the photocatalytic decomposition of some typed PPCPs with the toxicity tests.
As the model pollutants compounds belonging to different therapeutic class drugs: an analgesics and anti-inflammatory drug Diclofenac (DCF), β-blocker Metoprolol (MT) and antimicrobial agent Chloramphenicol (CPL) were selected. These compounds were chosen because of their frequent presence in the water. DCF was detected in surface waters at the concentrations ranging from 0.001 to 0.5 μg/L (Ternes, 1998) representing low acute toxicity: EC50 (concentration that causes 50% of effect) was varied from 11 mg/L to 72 mg/L (Table 1). The second typed PPCPs was MT that was detected in the surface water at the levels 0.05–0.15 μg/L (Kasprzyk-Hordern et al., 2007). CPL is nowadays mainly used in the veterinary practice because of confirmed cytotoxicity to bone marrow in vitro. The surface water concentrations of CPL were reaching to 0.56 μg/L (Hirsch et al., 1999) and the toxicity is described at the broad levels ranging from 20.68 mg/L using V. fischeri to even 1 g/L for D. magna (Table 1).
Though the main objectives of this work were:
- 1)
to estimate the efficacy of photocatalytic oxidation in terms of enhanced biodegradability,
- 2)
to compare the results of two widely used biotests: Daphtoxkit FTM and Microtox® referring to the treated model waste water containing PPCPs,
- 3)
to confirm the utility of photocatalysis as environmentally friendly method of waste water decontamination.
Section snippets
Reagents
All pharmaceuticals: diclofenac (CAS No. 15307-86-5), chloramphenicol (CAS No. 56-75-7) and metoprolol (CAS No. 51384-51-1) were purchased from Sigma-Aldrich, Poland. Model waste water was prepared using diclofenac sodium salt, chloramphenicol or metoprolol. The compounds were typed as the representatives of different therapeutic classes of drugs: anti-inflammatory drugs, antibiotics and β-blockers, respectively.
Photooxidation of PPCPs
The photocatalytic oxidation was conducted using ca. 5 g of 19 nm TiO2 (anatase, SBET
Daphtoxkit
The results of untreated solutions containing selected PPCPs was presented in Table 2 and Fig. 1. D. magna showed higher sensitivity to the presence of pollutants than V. fischeri. The response of D. magna exposed for 48 h was similar to 24 h exposition (expect MT: EC50 48 h is 15% lower than after 24 h) (Fig. 1A to C). It may indicate that the mechanism of toxicity is quick. The highest EC50 (concentration that caused 50% immobilization of D. magna or reduction of V. fischeri bioluminescence)
Conclusions
According to the conducted studies it can be concluded that (1) photocatalysis is very efficient method of the decrease of model waste water contamination by PPCPs, their mineralization, degradation and detoxicification, (2) photocatalysis may be proposed as the polishing or post-treatment method of PPCPs removal from model waste water, (3) generally during treatment there were observed compounds with lower toxicity in comparison to initial pollutant, but that general statement needs to be
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