There is a lack of knowledge in environmental pollution of the anthropogenic contaminants in wastewater and surface water. Several organic compounds merit special attention, because of their potential risk to the aquatic environment. Therefore, gas chromatography–mass spectrometry-based screening analyses were performed in order to identify anthropogenic organic contaminants and to reveal information on the structural diversity of individual compounds and to characterize their environmental behavior. Wastewater samples from wastewater treatment plants in Germany, representing various capacities, and surface water samples from corresponding receiving waters were analyzed. Numerous substances were identified in the samples. Several compounds were treated inadequately during wastewater treatment, and their identification in surface waters highlights their potential impact on the aquatic environment. Contaminants were selected according to available information about their environmental relevance (e.g. persistence, bioaccumulation potential), their possible application or usage and their occurrence within the environment. Based on the results of this study, it is recommended that non-target screening analyses be undertaken to identify the structural diversity of anthropogenic organic contaminants and that further investigations of specific anthropogenic compounds be undertaken as a high priority.

INTRODUCTION

In recent years an increasing number of emerging pollutants have been detected in surface waters. The majority of these substances, such as pharmaceuticals, surfactants, biocides, personal care products, plasticizers and flame retardants, is mainly present in treated and untreated wastewater which is discharged into surface waters (e.g. Ricking et al. 2003a, 2003b; Fatta et al. 2007). Hence, many organic compounds which are not eliminated during wastewater treatments are discharged into receiving waters. A broad range of significant anthropogenic contaminants have been investigated in wastewater treatment plants (WWTPs) and corresponding surface waters in recent years (e.g. Schwarzbauer et al. 2002; Schwarzbauer & Ricking 2010; Dsikowitzky et al. 2015). Analyses of discharges from urban WWTPs revealed a broad range of pollutants with high structural diversities and several compounds which play a substantial role in the contamination of the environment. These anthropogenic contaminants need special attention, because of their potential risk to the aquatic environment. A challenge is that the knowledge of organic contaminants in surface water systems is incomplete. This can be addressed through screening analyses, which are powerful tools to obtain information on the current levels of pollution. Gas chromatography and mass spectrometry (GC/MS) analyses are widely established for target screenings (e.g. Schwarzbauer & Heim 2005) and non-target screenings (e.g. Schwarzbauer & Ricking 2010) of organic contaminants.

The aim of this study was to identify the structural diversity of anthropogenic organic contaminants in the effluent stream at WWTPs and in the receiving surface waters with focus on identifying organic substances that might trace anthropogenic emissions of specific sources within the system. Non-target-screening analyses by GC/MS were used to collect information on organic compounds in terms of their structural variety and to characterize their environmental behavior. Contaminants were selected based on the available information on their environmental relevance (e.g. persistence, bioaccumulation potential), their possible application or usage and their occurrence within the environment. In order to identify a wide variety of anthropogenic contaminants and to differentiate between common and specific anthropogenic contaminants found in wastewater and surface water, samples from three representative WWTPs in Germany, representing various capacities, were analyzed and selected compounds were subsequently quantified.

EXPERIMENTAL APPROACH

Chemicals and reagents

To prevent and to reduce the potential for sample contamination, only glass and metal materials were used in the laboratory. The materials were cleaned ultrasonically and were rinsed with acetone and n-hexane prior to extraction. Solvents were purchased from Merck, Germany, and were pre-cleaned by rectification. Purity was tested by gas-chromatographic (GC) analyses. Anhydrous sodium sulfate (Na2SO4) and hydrochloric acid (32%) were purchased from Merck, Germany. For quality assurance, procedural blank analyses were processed in the same manner as the water samples. No contamination of the blank samples by the target compounds was identified.

Sampling

In 2015 water samples were collected in Germany from three urban WWTPs of various capacities (from 35,000 up to 1,000,000 equivalent population (EP)) once. WWTP A was sampled at the end of January 2015, WWTP B was sampled in March 2015 and WWTP C was sampled in May 2015. The characteristics of the WWTPs are summarized in Table 1. The purification of wastewater in these WWTPs is undertaken in three treatment steps, namely: mechanical, biological and chemical treatment. In the first purification step (mechanical) approximately 20% to 25% of solids and suspended matter are removed. In the second purification step (biological) biological processes or rather microbiological degradation processes are used for decomposition of polluted wastewater. In the third purification step abiotic chemical reactions such as oxidation and precipitation are used. In the municipal WWTPs they are used primarily for the removal of phosphorus by precipitation reactions, to avoid the eutrophication of the receiving water. At each WWTP, samples were taken from the influent streams, sewage water before biological treatment and from the effluent streams. Additionally, four samples per WWTP were collected from the receiving surface waters with three sampling locations downstream and one location upstream of the WWTP outfall. Water samples from the WWTPs were collected by automatic samplers over a period of 24 hours and placed into polyethylene canisters. Afterwards, these samples were transferred into pre-cleaned 1.2 L aluminum bottles with Teflon-lined screw caps. Water samples from the receiving waters were collected using a telescope sampler with a stainless-steel beaker. Samples were taken midstream at a depth of approximately 20 cm and placed into pre-cleaned 1.2 L aluminum bottles with Teflon-lined screw caps. All samples were stored in the dark at a temperature of 4°C until sample preparation.

Table 1

Characteristics of WWTPs studied

WWTP Capacity [EP] Annual flow [m3/y] Type of sewage Average flow of receiving water [m3/s] 
WWTP A 1,000,000 180,000,000 Municipal and industrial 175 
WWTP B 35,000 4,000,000 Municipal 2.0 
WWTP C 500,000 25,000,000 Municipal 1.4 
WWTP Capacity [EP] Annual flow [m3/y] Type of sewage Average flow of receiving water [m3/s] 
WWTP A 1,000,000 180,000,000 Municipal and industrial 175 
WWTP B 35,000 4,000,000 Municipal 2.0 
WWTP C 500,000 25,000,000 Municipal 1.4 

Water samples from the WWTPs were comparable with one another because variations and fluctuations in pollutant concentrations were smoothed by analyzing 24-hour mixed samples of wastewater.

Liquid–liquid extraction

Prior to extraction water samples were filtered through pre-cleaned Whatman glass fiber filters without binder (MN GF-5 Ø 50 mm, 0.45 μm pore diameter). All water samples were extracted using a sequential liquid–liquid extraction procedure described by Franke et al. (1995). The general preparation scheme is displayed in Figure 1. The extraction procedure involved three extraction steps which were applied to 1 L samples. The first two extraction steps used 50 mL of n-pentane and dichloromethane, respectively, with 5 minutes of shaking of each 1 L water sample. In the first step n-pentane was added to a 1 L aliquot and was shaken for 5 minutes. The same procedure was applied then to the solvent dichloromethane for steps two and three. After acidification with hydrochloric acid (32%), pre-cleaned by extraction with n-hexane, to pH 2, the procedure was performed again using dichloromethane (step three). After three extraction steps and separation into the phases, the extracts were concentrated by rotary evaporation and dried by filtration with 1 g anhydrous sodium sulfate (Na2SO4). Extracts from steps one and two were spiked with 50 μL of surrogate standard solution consisting of d10-benzophenone (c = 19.8 ng μL−1). Extracts from step three were derivatized with diazomethane (see ‘Derivatization and fractionation’ section) and spiked with 200 μL of surrogate standard solution, respectively. All extracts from steps one and two were concentrated to 50 μL and extracts from step three were concentrated to 200 μL final volume at ambient temperature.
Figure 1

Analytical procedure used for non-target-screening analyses of wastewater and surface water samples.

Figure 1

Analytical procedure used for non-target-screening analyses of wastewater and surface water samples.

Derivatization and fractionation

Acidic compounds in the third extract (volume of 1 mL) were methylated prior to GC/MS by the addition of a diazomethane solution (0.2 to 0.4 mL). After derivatization the extract was reduced to a final volume of 200 μL by rotary evaporation at ambient temperature.

GC/MS analyses

GC/MS analyses were performed using a Finnigan Trace MS mass spectrometer(Thermo Fisher Scientific, Massachusetts, USA) linked to a MegaSeries 5160 gas chromatograph (Carlo Erba HRGC 5160 Mega Series, Milan, Italy) equipped with a ZB-Multi-Residue-2 capillary column (30 m × 0.25 mm I.D. × 0.25 μm film) (Phenomenex, Aschaffenhausen, Germany). Chromatographic conditions were as follows: 1 μL sample was injected at 270 °C injector temperature in splitless mode (splitless time 1 min). The helium carrier flow rate was set at 1 mL min−1. The oven temperature program started at 60 °C (3 min isothermal time) and was heated at a rate of 5 °C min−1 to 300 °C (20 min isothermal time). The mass spectrometer was operated in electron impact ionization mode (EI + , 70 eV) with a source temperature of 200 °C scanning from 35 to 700 amu at a rate of 1.5 scans s−1. Quantification was based on integration of characteristic ion chromatograms (see Table 2) and an external four-point-calibration using reference substances. If reference material was not commercially available, then response factors of chemically similar substances were then used for quantification (see Table 2). A surrogate standard was used for the correction of inaccuracies of sample and injection volume.

Table 2

Quantified compounds with characteristic ions (m/z: mass-to-charge ratio) and surrogate standard

Compound Characteristic ions [m/z] 
4-Chloro-4′-hydroxybenzophenonea 121 
232 
Triphenyl phosphate 170 
326 
Cotinine 98 
176 
Nicotine 133 
161 
Hexa(methoxymethyl)melamine 207 
267 
2-Ethylhexyl p-methoxy cinnamateb 161 
290 
Chlorophene, 2-benzyl-4-chlorophenol 140 
218 
Propofolc 163 
178 
Carbamazepine 193 
236 
Lidocaine 86 
234 
Diclofenac 214 
309 
d10-Benzophenoned 110 
192 
Compound Characteristic ions [m/z] 
4-Chloro-4′-hydroxybenzophenonea 121 
232 
Triphenyl phosphate 170 
326 
Cotinine 98 
176 
Nicotine 133 
161 
Hexa(methoxymethyl)melamine 207 
267 
2-Ethylhexyl p-methoxy cinnamateb 161 
290 
Chlorophene, 2-benzyl-4-chlorophenol 140 
218 
Propofolc 163 
178 
Carbamazepine 193 
236 
Lidocaine 86 
234 
Diclofenac 214 
309 
d10-Benzophenoned 110 
192 

aQuantified with internal calibration.

bResponse factor value determined from structurally related compound α-tocopherol acetate.

cResponse factor value determined from structurally related compound 2,5-dimethylphenol.

dSurrogate standard.

RESULTS AND DISCUSSION

Generally, two groups of compounds were differentiated. The first group comprised contaminants appearing throughout the wastewater and surface water systems and which have a high environmental stability accompanied by a widespread distribution while the second group was specific contaminants which characterize surface water impacted by wastewater.

GC/MS non-target screening analyses applied to wastewater and surface water revealed a broad range of compounds. More than 270 compounds can be present in municipal wastewater, which highlights the high structural diversity of organic contaminants and the importance of considering this diversity in environmental assessments. However, not all contaminants are environmentally relevant and, therefore, a preselection of contaminants for a more detailed investigation was undertaken. Based on this preselection the following discussion will characterize the most interesting and important anthropogenic contaminants detected not only in wastewater but also in impacted surface waters.

The preselection of compounds was based on their structural properties and their anthropogenic usage. The list of 85 preselected substances is given in Table 3. Out of this group a subset of 11 substances were considered for quantification. Their corresponding molecular structures are illustrated in Figure 4.

Table 3

Selected compounds including their application and/ or origin and their occurrence in wastewater and surface water samples from three WWTPs (A, B and C) marked by x

Compound A
 
B
 
C
 
In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 
Natural fragrances 
trans-1,10-Dimethyl-trans-9-decalinol                     
 2H-1-benzopyran-2-one, coumarin                     
 Diisopropyltrisulfide                    
 Dipropyltrisulfide                
 Hexathiepan                   
Synthetic fragrances  
 Galaxolide, HHCB  
 Tonalide, AHTN             
 4-Oxoisophorone, 2,6,6-trimethyl-2-cyclohexene-1,4-dione                     
 Methyl dihydrojasmonate        
Plasticizers 
 Triphenyl phosphate, TPP                  
 Tributylphosphate, TBP    
 Triethylphosphate, TEP               
 Tris(butoxyethyl)phosphate                     
 Tris(2-butoxyethyl)phosphate                  
 Tris(2-chloroethyl)phosphate, TCEP                
N-Ethyl-2-methyl-benzenesulfonamide, NEBS                
N-Butyl benzene, BBSA        
 Tributylcitrate                     
 Acetyl, itroflex A               
 Acetyltriethyl                    
 Ethyl citrate, Citroflex 2       
 Triacetin                 
Ingredients of personal care products 
 4-iso-Propyl-m-cresol, Biosol                     
 Hexadecyl-2-hexyl decanoate, Schercemol 1688              
N,N,N0,N0-tetraacetylethylenediamine, TAED                 
 Tricaprylin                    
 Hexahydro-4,7-methano-1H-indenol                  
 2-Ethylhexyl p-methoxy cinnamate, Parsol MCX°              
 Methoxybenzoic acidm                     
 1,3-Dicyclohexylurea                   
 Bumetrizole                                         
Flame retardants 
 Tris(2-chloroisopropyl)phosphate, TCPP  
 Tris(1,3-dichloroisopropyl)phosphate, TDCPP, Fryol FR2                 
Physiologically active substances and metabolites 
 DEET, N,N-diethyl-m-toluamide        
 Caffeine            
 2,6-Di-iso-propylphenol, propofol°          
 Carbamazepine°    
 Lidocaine°             
 Nicotine°                   
 Cotinine°                   
 Diclofenacm,°       
 Diclofenac amide                     
 Ibuprofen                
 1,4: 3,6-Dianhydro-2,5-di-O-methyl-d-glucitol              
 2-((2,6-Dichlorophenyl)amino)phenylethanol                     
 6-Methoxy-2-naphthylacetic acidm              
 4-Chloro-1-methoxy-2- (phenylethyl) benzene                     
 Chloroindole                    
 2,6-Dimethylphenyl                    
 Dipyrone                     
 Chlorophen°                   
 4-Chloro-4′-hydroxybenzophenone°                  
 1H-indole-2,3-dione, isatin, indole derivative                    
 Isopropylbenzoic                     
Vitamins and metabolites 
α-Tocopherol acetate, vitamin-E-acetate               
 2-Hydroxy-3-methyl-1,4-naphthalindion, phthiokol                     
Pesticides and metabolites 
 Terbutryn              
 3-iso-Propyl-5-methylphenyl methylcarbamate, ITC, promecarb                    
 5-Chloro-1,10-phenanthroline                     
 2,6-Di-tert-butyl-4-nitrophenol        
Technical industrial application/origin 
 1-Hydroxycyclohexyl phenyl ketone, Irgacure 184  
 2,2-Dimethoxy-1,2-diphenylethanone, DMPA                
 Oxodecanoic acidm                     
 Oxododecanoic acidm                     
p-Chlorbenzotrichloride, 1-chloro-4-(trichloromethyl)benzene                     
 2,6-Diethoxytetrahydropyrane                  
 Methyl 2-benzoylbenzoate                     
 2-Ethylhexyl-2-ethylhexanoate                     
 Phlorobutyrophenone                 
 Bisphenol A                    
N,N-Dimethyl-1-tetradecanamine, dimethyl myristamine                     
N,N-Di-iso-propylacetamide                     
 2,6-Dichloraniline                    
 2,3-Diethyl-2,3-dimethylsuccinonitril                     
N,N-Diethylaniline                    
N,N-Dibutylformamide          
 Hexa(methoxymethyl)melamine, HMMM°                
S-Methyl dimethylthiocarbamate                     
 Benzothiazole             
 2-Methylthiobenzothiazole                     
 Benzenesulfonic anilide            
 Cyclohexyl isocyanate                    
 Cyclopentylethanone,                     
 Citric acidm                   
 Triphenylphosphine oxid, TPPO                   
Compound A
 
B
 
C
 
In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 
Natural fragrances 
trans-1,10-Dimethyl-trans-9-decalinol                     
 2H-1-benzopyran-2-one, coumarin                     
 Diisopropyltrisulfide                    
 Dipropyltrisulfide                
 Hexathiepan                   
Synthetic fragrances  
 Galaxolide, HHCB  
 Tonalide, AHTN             
 4-Oxoisophorone, 2,6,6-trimethyl-2-cyclohexene-1,4-dione                     
 Methyl dihydrojasmonate        
Plasticizers 
 Triphenyl phosphate, TPP                  
 Tributylphosphate, TBP    
 Triethylphosphate, TEP               
 Tris(butoxyethyl)phosphate                     
 Tris(2-butoxyethyl)phosphate                  
 Tris(2-chloroethyl)phosphate, TCEP                
N-Ethyl-2-methyl-benzenesulfonamide, NEBS                
N-Butyl benzene, BBSA        
 Tributylcitrate                     
 Acetyl, itroflex A               
 Acetyltriethyl                    
 Ethyl citrate, Citroflex 2       
 Triacetin                 
Ingredients of personal care products 
 4-iso-Propyl-m-cresol, Biosol                     
 Hexadecyl-2-hexyl decanoate, Schercemol 1688              
N,N,N0,N0-tetraacetylethylenediamine, TAED                 
 Tricaprylin                    
 Hexahydro-4,7-methano-1H-indenol                  
 2-Ethylhexyl p-methoxy cinnamate, Parsol MCX°              
 Methoxybenzoic acidm                     
 1,3-Dicyclohexylurea                   
 Bumetrizole                                         
Flame retardants 
 Tris(2-chloroisopropyl)phosphate, TCPP  
 Tris(1,3-dichloroisopropyl)phosphate, TDCPP, Fryol FR2                 
Physiologically active substances and metabolites 
 DEET, N,N-diethyl-m-toluamide        
 Caffeine            
 2,6-Di-iso-propylphenol, propofol°          
 Carbamazepine°    
 Lidocaine°             
 Nicotine°                   
 Cotinine°                   
 Diclofenacm,°       
 Diclofenac amide                     
 Ibuprofen                
 1,4: 3,6-Dianhydro-2,5-di-O-methyl-d-glucitol              
 2-((2,6-Dichlorophenyl)amino)phenylethanol                     
 6-Methoxy-2-naphthylacetic acidm              
 4-Chloro-1-methoxy-2- (phenylethyl) benzene                     
 Chloroindole                    
 2,6-Dimethylphenyl                    
 Dipyrone                     
 Chlorophen°                   
 4-Chloro-4′-hydroxybenzophenone°                  
 1H-indole-2,3-dione, isatin, indole derivative                    
 Isopropylbenzoic                     
Vitamins and metabolites 
α-Tocopherol acetate, vitamin-E-acetate               
 2-Hydroxy-3-methyl-1,4-naphthalindion, phthiokol                     
Pesticides and metabolites 
 Terbutryn              
 3-iso-Propyl-5-methylphenyl methylcarbamate, ITC, promecarb                    
 5-Chloro-1,10-phenanthroline                     
 2,6-Di-tert-butyl-4-nitrophenol        
Technical industrial application/origin 
 1-Hydroxycyclohexyl phenyl ketone, Irgacure 184  
 2,2-Dimethoxy-1,2-diphenylethanone, DMPA                
 Oxodecanoic acidm                     
 Oxododecanoic acidm                     
p-Chlorbenzotrichloride, 1-chloro-4-(trichloromethyl)benzene                     
 2,6-Diethoxytetrahydropyrane                  
 Methyl 2-benzoylbenzoate                     
 2-Ethylhexyl-2-ethylhexanoate                     
 Phlorobutyrophenone                 
 Bisphenol A                    
N,N-Dimethyl-1-tetradecanamine, dimethyl myristamine                     
N,N-Di-iso-propylacetamide                     
 2,6-Dichloraniline                    
 2,3-Diethyl-2,3-dimethylsuccinonitril                     
N,N-Diethylaniline                    
N,N-Dibutylformamide          
 Hexa(methoxymethyl)melamine, HMMM°                
S-Methyl dimethylthiocarbamate                     
 Benzothiazole             
 2-Methylthiobenzothiazole                     
 Benzenesulfonic anilide            
 Cyclohexyl isocyanate                    
 Cyclopentylethanone,                     
 Citric acidm                   
 Triphenylphosphine oxid, TPPO                   

In: sampling point in the inlet of the WWTP, InBio: sampling point in the influent of the biological stage of the WWTP, Out: sampling point in the effluent of the WWTP, R1: sampling point in the receiving water 10 m upstream of the WWTP, R2: sampling point in the receiving water 0 m downstream of the WWTP, R3: sampling point in the receiving water 500 m downstream of the WWTP, R4: sampling point in the receiving water 1,000 m downstream of the WWTP, mwas identified in its methylated form due to the derivatization, °was identified and quantified with reference material.

The relevant substances were classified into groups according to their application. These groups comprise: natural fragrances, synthetic fragrances, plasticizers, ingredients of personal care products, flame retardants, physiologically active substances, vitaminoids, pesticides and compounds with known technical industrial application or origin. It should be also noted that in addition to the selected compounds many more organic compounds were detected, including terpenoids, steroids, aliphatic and aromatic carboxylic acids, as well as fatty acid esters.

Common contaminants

Several common water contaminants that frequently occur in these samples were identified. Some molecular structures are illustrated in Figure 2. The polycyclic musk compounds galaxolide (4,6,6,7,8,8-hexamethyl-1,3,4,6,7,8-hexahydrocyclopenta[g]isochromene; HHCB) and tonalide (1-(5,6,7,8-tetrahydro-3,5,5,6,8,8-hexamethyl-2-naphthalenyl)ethanone; AHTN) are well known fragrances. Both compounds have been identified frequently in municipal wastewater in partially high concentrations (Dsikowitzky et al. 2002; Ricking et al. 2003a, 2003b; Bester 2004; Zhou et al. 2009; Schwarzbauer & Ricking 2010). Due to their extensive use in numerous detergents, cleaning agents and cosmetics and their high bioaccumulation potential, because of lipid solubility and persistence, these musk compounds are distributed widely and can be referred to as environmentally relevant contaminants. While galaxolide was detected in both wastewater and surface water samples, tonalide was detected only in wastewater samples. This highlights a better degradation and elimination of tonalide compared to galaxolide during wastewater treatment or to the enrichment of tonalide in particulate material by its preferential adsorption to particulate material in the fluviatile environment (Winkler et al. 1998).
Figure 2

Molecular structure of selected common contaminants.

Figure 2

Molecular structure of selected common contaminants.

One synthetic fragrance is methyl dihydrojasmonate. Methyl dihydrojasmonate is commonly synthesized from 2-pentyl-2-cyclopenten-2-one and is mainly used in personal care products such as deodorants (about 65–86%) (Frosch et al. 2002). The compound has a log Kow value of 3.0 (Simonich et al. 2000). This substance has been detected in wastewater and surface water samples. Thus, it appears that methyl dihydrojasmonate is widespread. Two further compounds of physiologically active substances are carbamazepine and N,N-diethyl-m-toluamide (DEET). Carbamazepine is an antiepileptic drug and is known to enter the surface water systems through WWTP effluent discharges due to very low elimination rates during wastewater treatment (7%) (Ternes 1998). Accordingly, carbamazepine has been identified in numerous studies of WWTP effluents and in surface waters (Ternes 1998; Dsikowitzky 2002; Heberer 2002; Schwarzbauer & Heim 2005) and was also continuously detected in this study. Due to its ecotoxicological effects, carbamazepine has a high environmental relevance. DEET belongs to the category of insect repellents. This contaminant is conveyed in WWTP effluent discharge into surface water systems, resulting in its widespread occurrence (e.g. Franke et al. 1995; Kolpin et al. 2002; Dsikowitzky et al. 2004). In this study DEET was identified in wastewater samples and in a few surface water samples. With respect to its environmental fate and relevance a slight toxic effect on aquatic organisms (for acute Daphnia toxicity an EC-50 (half maximal effective concentration) value of ≥56 mg L−1 has been specified by Juno Limited (2014)) as well as a log Kow value around 2.4 and a bioconcentration factor (BCF) value around 40 have been noted.

Specific contaminants

In addition to the more common wastewater constituents numerous further compounds have been detected in singular analyses of selected samples of wastewater and surface water impacted by WWTP effluent discharges. Some of these compounds are candidates for more specific environmental assessments since they have been reported very rarely as environmental contaminants. The phosphorus-organic compounds triphenyl phosphate (TPP), tris(butoxyethyl)phosphate (TBEP) and tris(2-chloroethyl)phosphate (TCEP) are typical representatives of plasticizers (molecular structures are given in Figure 3). TPP, TBEP and TCEP are mainly used as plasticizers in polymers to improve their elasticity (Rahman & Brazel 2004). Additionally, they are used as flame retardants for example in electronic equipment, as additives in hydraulic fluids, lubricating oils and in paints and adhesives (e.g. Carlsson et al. 2000; Marklund et al. 2005). As one example of their toxicological effects, TPP is known to inhibit the formation of white and red blood cells in human blood and, therefore, to weaken the immune system (e.g. Saboori et al. 1991; Carlsson et al. 2000). Furthermore, it has been reported that TPP may cause contact dermatitis in humans (Carlsen et al. 1986). Overall TPP has a high acute toxicity on aquatic organisms with LC-50 (median lethal dose) values from 0.4 to 1.1 mg L−1 (Marklund et al. 2005). The chronic toxicity for daphnia has a NOEC (no observed effect concentration) of 0.1 mg L−1 (Van der Veen & de Boer 2012). As further environmentally relevant parameters, TPP exhibits a log Kow value of 4.59 (Fisk et al. 2003) and a BCF value of 113 (Van der Veen & de Boer 2012).
Figure 3

Formula structure of TPP, TBEP and TCEP.

Figure 3

Formula structure of TPP, TBEP and TCEP.

Phosphorus-organic compounds have been formerly identified as being present in wastewater samples. Hence phosphorus-organic compounds, especially TCEP, have been reported widely by several authors in river water (e.g. Ishikawa et al. 1985; Bohlen et al. 1989; Hildebrandt 1995), in WWTPs (Paxéus 1996; Metzger & Möhle 2001) and in wastewater (Paxéus 1996; Metzger & Möhle 2001). Comparable data are measured in this study. However TCEP was only detected in the receiving water of one WWTP. In general these compounds have large effects on aquatic organisms at low concentrations (Kuhlmann 1991) and TCEP has a high persistence.

A remarkable constituent from the second group of substances, the personal care products, is 2-ethylhexyl p-methoxy cinnamate which is a UV filter with application in sun screening agents (molecular structure see Figure 4). This lipophilic compound (log Kow value is about 5.92) was used in 1991 in 67% of all light-protection agents (Ternes et al. 2003) and is one of the most common UV filters worldwide. Additionally, besides usage in sun screening agents, it is a constituent for product preservation in many other cosmetic products such as washing lotions (Klammer 2006). A previous study by Schlumpf et al. (2001) revealed that 2-ethylhexyl p-methoxy cinnamate has estrogenic effects. EC-50 for acute daphnia toxicity is 0.57 mg L−1 and NOEC is at 0.04 mg L−1 (Sieratowicz et al. 2011). The 2-ethylhexyl p-methoxy cinnamate was identified sporadically in a limited number of wastewater and river water samples. Another UV protector detected in the investigated wastewaters was bumetrizole (2-(5-chlor-2H-benzotriazol-2-yl)-4-methyl-6-(2-methyl-2-propanyl)phenol), also known as an intermediate in the synthesis of UV light absorbers for polyester fibers. Due to its UV-absorbing properties bumetrizole is used as sunscreen agent in cosmetics but also for the protection of plastics (e.g. PET (polyethylene terephthalate) bottles) (ChemLin 2015; Iordanidis et al. 2015). Noteworthy is that bumetrizole was solely detected in the influent of one WWTP, with a capacity of 1,000,000 EP, and the treatment of both municipal and industrial wastewater. Further, two anesthetics were identified, propofol and lidocaine (molecular structures are given in Figure 4). Propofol is an intravenous anesthetic with a rapid onset of action after infusion and is known for a low patient recovery time of 2 minutes (NIH 2015). Propofol was also tested for application in veterinary medicine for various species (GholipourKanani & Ahadizeh 2013). The log Kow value of this lipophilic compound is 3.79 (NIH 2015) and the BCF value is 357 (SciFinder 2015). The acute toxicity for goldfish LC-50 has been determined to be 6.34 mg L−1 (GholipourKanani & Ahadizeh 2013). Lidocaine is a local anesthetic for use in human and veterinary medicine. As an ingredient in ointments it is used for local analgesia. In addition, it is used as an anti-arrhythmic agent for the treatment of cardiac arrhythmias (NIH 2015). The log Kow value is 2.44. Lidocaine is also classified as harmful to aquatic organisms with an EC-50 value for acute toxicity of daphnia of 61 mg L−1. Both anesthetics have been reported rarely in surface waters and wastewaters (Rúa-Gómez & Püttmann 2012). In this study, lidocaine occurred sporadically in wastewater and surface water of three WWTPs. Propofol has been detected in both sewage water and surface water samples and occurred mainly in wastewater samples and isolated in surface water samples, pointing to an inefficient removal during wastewater treatment. One further substance is 4-chloro-4′-hydroxybenzophenone which is known to be an intermediate for the synthesis of fenofibrate, a lipid lowering agent. Its molecular structure is displayed in Figure 4. This compound is used not only for the preparation of pharmaceutical products but also as a component in synthetic perfumes (Montes-Grajales & Olivero-Verbel 2015). Regarding its environmental relevance, the log Kow value is 0.93 indicating a high hydrophilicity (U.S. Pharmacopeia 2015) and to the authors' knowledge there is no information about toxicity or environmental behavior. In this study 4-chloro-4′-hydroxybenzophenone was identified sporadically in wastewater and at one river water sampling point only for the WWTP with a capacity of 35,000 EP.
Figure 4

Molecular structures of selected quantified compounds.

Figure 4

Molecular structures of selected quantified compounds.

Two nitrogen-containing compounds with interesting molecular properties (refer Figure 4) were identified but were reported formerly only very rarely as aquatic pollutants. The acaricide 2,6-di-tert-butyl-4-nitrophenol (DBNP) belongs to the group of pesticides and is particularly suitable for combating mites and ticks (miticide) (e.g. Vesselinovitch et al. 1961; Deichmann & Gerarde 1964). The compound was identified additionally as a derivative of 2,6-di-tert-butylphenol (DBP) (Alexander et al. 2001). DBP is included as an antioxidant in lubricating oil (turbine oil 2190 T-EP), e.g. used by the US Navy submarine fleet (Alexander et al. 2001). The oil mist containing DBP is nitrified to DBNP (Alexander et al. 2001). DBP-containing lubricating oils are also used in other applications, where similar processes of nitrification can occur: firstly the oxidation of ammonia to nitrite and secondly the oxidation that converts nitrite to nitrate. Hence, DBNP can be discharged via wastewater into surface water systems. So far toxicity tests have been carried out only on rats. To the authors' knowledge there are no investigations of its aquatic toxicity so far. In this study, DBNP was identified in both wastewater and surface water samples but the occurrence is more dominant in surface water than in wastewater. Thus, a dominant discharge of DBNP into surface water systems from the WWTPs was not evident. The second nitrogen-containing compound, hexa(methoxymethyl)melamine (HMMM, molecular structure see Figure 4), is a technical additive used in melamine resins as well as in paints and plastics for coatings of cans, coils and cars as a crosslinking agent (Dsikowitzky & Schwarzbauer 2015) and is mainly present in industrial discharges to a WWTP. The occurrence of HMMM demonstrated the contribution of industrial wastewater discharges to surface water. With a log Kow value of 1.61 HMMM is dominant in the water phase; HMMM has an acute fish and daphnia toxicity, but values for the classification of its toxicity on aquatic organisms are currently not available (e.g. Labunska et al. 2012; Dsikowitzky & Schwarzbauer 2015). In a previous study of river water samples in Germany HMMM was detected in surface water samples with concentrations up to 880 ng L−1 (Dsikowitzky & Schwarzbauer 2015). The main pathway for HMMM is industrial discharges, especially from the automotive industry in the form of process waters (Dsikowitzky & Schwarzbauer 2015). In this study, HMMM has been identified only in one WWTP and river water system for the city with a population of above 1 million.

Quantitative data for selected organic contaminants

The wastewater and surface water samples collected from WWTPs of different sizes and characteristics showed a great variety of substances from different substance classes. The substances occurred in all WWTPs of varying capacities from small and large areas. Effluent samples hold a special position because they clearly indicated the level of treatment of organic contaminants by WWTPs. However, if substances were detected in the effluent and were not detected in surface water samples downstream of the WWTP outfall, then it was concluded that the adsorption on particulate matter and/or extensive dilution prevented laboratory detection. Specific elimination rates for a WWTP depend on the technical capabilities of the WWTP. Current wastewater treatment methods do not remove substances effectively (Cizmas et al. 2015). The occurrence of the substances in the WWTPs and surface water systems did not follow systematic patterns; substances did not occur evenly in wastewater and surface water samples. Eleven compounds were selected for quantitative analyses (refer Table 4). The preselection was based on their specific molecular properties, their representation of the structural diversity of organic contaminants in wastewater (refer Figure 4) and also on their environmental relevance, e.g. due to ecotoxicological risks. The spectrum of substances which were selected was representative of different substance groups, including physiologically active agents, plasticizers and flame retardants, ingredient of personal care products and substances with technically industrial application. These substances may result from emissions of medical, industrial and agricultural activities and households.

Table 4

Quantification of selected compounds

Compound A
 
B
 
C
 
In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 
Physiologically active substances and metabolites 
 Nicotine        77 17      160       
 Cotinine        81 53      98       
 Propofol 21 78 57   16  96 130 40  32 15 <10 54 17      
 Carbamazepine 64 150 120  31 23 26 62 54 67  330 87 89  82 66 66 85 160 190 
 Lidocaine  66   170  16     95 34   79  24  66 62 
 Diclofenacm 160 500 1,300   100 73 210    670 330 33 830 800 240 14  38 86 
 Chlorophene        1,000 1,400 1,500            
 4-Chloro-4′-hydroxybenzophenone1 60 200 210         150          
Plasticizers and flame retardants 
 Triphenyl phosphate, TPP 220 30 30       62            
Ingredients of personal care products 
 2-Ethylhexyl p-methoxy cinnamate <10 <10 15 <10 <10 <10   <10    <10         
Technical industrial application 
 Hexa(methoxymethyl)melamine, HMMM 3,100 12,000 4,900  98 170 240               
Compound A
 
B
 
C
 
In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 In InBio Out R1 R2 R3 R4 
Physiologically active substances and metabolites 
 Nicotine        77 17      160       
 Cotinine        81 53      98       
 Propofol 21 78 57   16  96 130 40  32 15 <10 54 17      
 Carbamazepine 64 150 120  31 23 26 62 54 67  330 87 89  82 66 66 85 160 190 
 Lidocaine  66   170  16     95 34   79  24  66 62 
 Diclofenacm 160 500 1,300   100 73 210    670 330 33 830 800 240 14  38 86 
 Chlorophene        1,000 1,400 1,500            
 4-Chloro-4′-hydroxybenzophenone1 60 200 210         150          
Plasticizers and flame retardants 
 Triphenyl phosphate, TPP 220 30 30       62            
Ingredients of personal care products 
 2-Ethylhexyl p-methoxy cinnamate <10 <10 15 <10 <10 <10   <10    <10         
Technical industrial application 
 Hexa(methoxymethyl)melamine, HMMM 3,100 12,000 4,900  98 170 240               

Concentration in ng L−1.

In: sampling point in the inlet of the WWTP, InBio: sampling point in the influent of the biological stage of the WWTP, Out: sampling point in the effluent of the WWTP, R1: sampling point in the receiving water 10 m upstream of the WWTP, R2: sampling point in the receiving water 0 m downstream of the WWTP, R3: sampling point in the receiving water 500 m downstream of the WWTP, R4: sampling point in the receiving water 1,000 m downstream of the WWTP, mwas identified in its methylated form due to the derivatization, 1was quantified by internal calibration.

These substances include nicotine, cotinine, propofol, carbamazepine, lidocaine, 4-chloro-4′-hydroxybenzophenone and TPP. 4-chloro-4′-hydroxybenzophenone and TPP have been investigated very scarcely, e.g. TPP was reported as an environmental contaminant by Rodil et al. (2005). Concentrations ranged between the limit of quantification from <10 ng L−1 up to 12,000 ng L−1 (for hexa(methoxymethyl)melamine). The concentrations of these compounds in wastewater samples were from 16 to 220 ng L−1 and in surface water samples from 14 to 330 ng L−1.

Nicotine and its metabolite cotinine were identified in two WWTPs, with low concentrations in the influents ranging from 20 to 80 ng L−1. These concentration levels are 40 times lower than detected by Buerge et al. (2008). Propofol was detected only in the effluent of one WWTP, with a capacity of about 500,000 EP. In the downstream surface water samples the concentration of propofol decreased downstream of the WWTP outfall due to high dilution effects and adsorption on particulate matter. Guitton et al. (1997) described the metabolism of up to 10% of propofol into 2,6-diisopropyl-1,4-quinol. For this reason the rate of the elimination of the unchanged propofol is about 90% (Kümmerer 2001). Propofol and its metabolite are supposed to be biodegradable in WWTPs (Kümmerer 2001). Carbamazepine concentrations in wastewater were up to 150 ng L−1. These concentrations are far below the predicted non-effect concentration of 420 ng L−1 (Zhang et al. 2008). Studies from Clara et al. (2004) showed 10 times higher concentrations. For the compound diclofenac even low concentrations were present. Similar diclofenac concentrations in wastewater, ranging from 50 to 500 ng L−1, were identified by Moreira et al. (2015) and Cabeza et al. (2012). However, even higher values of up to 1,300 ng L−1 were detected in the effluent of the WWTP with a capacity of 1,000,000 EP. Chlorophene values were in range of 1,000 to 1,500 ng L−1 and occurred in one WWTP, with a capacity of 32,000 EP. The concentrations are higher than the concentrations identified by Kasprzyk-Hordern et al. (2009) in one WWTP in 2007. HMMM was detected in effluent in one WWTP, with a capacity of 1,000,000 EP, and in surface water downstream of the WWTP outfall with high concentrations ranging from 98 to 12,000 ng L−1. High concentrations of HMMM were also detected in Hessian river systems by Eberhard et al. (2015). Their data indicated that the contamination of surface water results mainly from surface water runoff and industrial wastewater. In contrast, 2-ethylhexyl p-methoxy cinnamate was detected below or next to the limit of detection of 10 ng L−1. That corresponds to detections in wastewater and surface water from Negreira et al. (2010).

Differences between the WWTPs

Finally, the appearance and quantitative data of individual contaminants can be discussed with respect to the different characteristics of the wastewater treatment plants. WWTP A is the only WWTP to receive and treat industrial wastewater. These contributions are indicated by only some very few substances; in particular HMMM and TPP appeared in relevant concentrations. However, these two contaminants were detected only in samples from inside WWTP A. For all other substances identified in this study either the contaminant was detected sporadically or there was a widespread occurrence in at least two WWTPs pointing to contamination profiles in WWTPs with generally low specificity.

WWTP C has a slightly different characteristic regarding the relative water flows. On the one hand the annual sewage flow in relation to its capacity is approximately 25% to 45% in comparison to WWTP A and WWTP B. This might suggest higher concentrations in WWTP C, but the quantitative data for compounds appearing in all WWTPs (e.g. carbamazepine or diclofenac) did not support this contention because a systematic higher concentration level in WWTP C is not evident. Furthermore, the ratio of sewage water flow to water flow in the receiving water differs also for WWTP C when compared to WWTP A and B; namely, it is 10 to 20 times higher. However, corresponding lower concentrations of WWTP C derived contaminants in the river samples were not observed at sampling locations downstream of the WWTP C outfall.

CONCLUSIONS

Screening analyses are highly important for the evaluation of the environmental pollution caused by multiple anthropogenic organic contaminants. Non-target screenings of wastewater from WWTPs of varying capacities and from corresponding receiving waters were conducted and identified a broad range of organic pollutants. Various load profiles were identified depending on the capacity of the WWTP, the flow rates of receiving waters and individual treatment procedures. The identified compounds were classified into common and specific anthropogenic substances and were assigned to a group based on their application and usage. Specific contaminants which were detected in all wastewater and surface water samples did not follow systematic patterns in frequency or occurrence. The selected specific compounds have been reported very rarely as environmental pollutants and are clearly candidates for more specific assessments to characterize their long-term ecotoxicology. The spectrum of contaminants was not related to typical characteristics of the WWTPs like capacity or water flow.

Based on the results of this study, it is recommended that non-target screening analyses be undertaken to identify the structural diversity of anthropogenic organic contaminants and that further investigations on specific anthropogenic compounds be undertaken as a high priority.

ACKNOWLEDGEMENTS

The authors would like to thank the operators of the wastewater treatment plants for their support and assistance.

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