Removal of alkylphenols and polybromodiphenylethers by a biofiltration treatment plant during dry and wet-weather periods

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1 1591 IWA Publishing 2012 Water Science & Technology Removal of alkylphenols and polybromodiphenylethers by a biofiltration treatment plant during dry and wet-weather periods S. Gilbert, J. Gasperi, V. Rocher, C. Lorgeoux and G. Chebbo ABSTRACT This paper investigates the occurrence of alkylphenols (APs) and polybromodiphenylethers (PBDEs) in raw wastewater during dry and wet-weather periods, and their removal by physico-chemical lamellar settling and biofiltration techniques. Due to in-sewer deposit erosion and, to a lesser extent, to external inputs, raw effluents exhibit from 1.5 to 5 times higher AP and PBDE concentrations during wet periods compared with dry ones. The lamellar settler obtains high removal of APs and PBDEs under both dry and wet-weather flows (>53% for Σ 6 AP and >89% for Σ 4 PBDE), confirming the insensitivity of this technique to varying influent conditions. Indeed, despite the higher pollutant concentrations observed in raw effluents under wet-weather flows, adjusting the addition of coagulant flocculent allows for efficient removal. By combining physical and biological processes, the biofiltration unit treats nutrient pollution, as well as Σ 6 AP and Σ 4 PBDE contamination (58 ± 5% and 75 ± 6% respectively). Although the operating conditions of the biofiltration unit are modified during wet periods, the performance in nutrient pollution, APs and light PBDE congeners remains high. Nevertheless, lower efficiency has been noted in nitrogen pollution, i.e. no denitrification occurs, and BDE-209 (not removed during wet-weather periods). In conclusion, this study demonstrates that the combination of both techniques treats AP and PBDE pollution efficiently during dry periods, but that they are also suitable for stormwater treatment. Key words alkylphenols, biofiltration, physico-chemical settling tank, polybromodiphenylethers, stormwater, wastewater treatment plant S. Gilbert J. Gasperi (corresponding author) C. Lorgeoux G. Chebbo LEESU (UMR MA 102 Université Paris-Est, Agro ParisTech), 6 8 avenue Blaise Pascal, Champs-sur-Marne, Marne-la-Vallée Cedex 2, France gasperi@u-pec.fr V. Rocher SIAAP, Direction du Développement et de la Prospective, 82 avenue Kléber, Colombes, France INTRODUCTION The European Water Framework Directive requires Member States to achieve a good ecological and chemical status in surface waters by To assess the chemical status of water bodies, a list of chemicals is monitored and maximum thresholds in surface waters (Environmental Quality Standards for 33 substances, EQS) have been set. Wastewater, stormwater and combined sewer overflows are potential sources of pollutants in the receiving waters, conveying a large spectrum of organic contaminants. Among them, alkylphenols (APs) and polybromodiphenylethers (PBDEs) are listed as priority substances and can affect the receiving waters, due to their endocrine disrupting properties. Alkylphenols are mostly used in industrial applications but their occurrence in the environment derives primarily from alkylphenol ethoxylate biodegradation. The latter group includes nonylphenol and octylphenol polyethoxylates (NPnEOs and OPnEOs), with n as the number of ethoxy units. NPnEOs, which account for about 80% of alkylphenol ethoxylates, were widely used as surfactants and as additives in plastics, personal care products, lubricants, etc. (OSPAR 2001; Ying et al. 2002). OPnEOs were mostly used as emulsifying agents for polymer synthesis and, to a lesser extent, in textile and leather auxiliaries, pesticides and water-based paint (OSPAR 2003). In this article, APs will refer to alkylphenol and their ethoxylates. PBDEs are brominated flame retardants added to polyurethane foams i.e. insulating material used in upholstery and the construction industry, and to electrical and electronic equipment (ECB 2000, 2007). Nowadays, the use of these chemicals is regulated. doi: /wst

2 1592 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology The occurrence of APs and, to a lesser extent, of PBDEs in wastewater, as well as their removal by conventional activated sludge wastewater treatment plants (WWTP) has been documented well (Song et al. 2006; Clara et al. 2007; Clarke et al. 2010). However, there is a lack of data regarding the removal of these chemicals by more compact wastewater treatment technologies, such as lamellar settling tank and biofiltration (aerated or nonaerated submerged biological filters). These technologies are attractive due to their compactness, modularity and short hydraulic retention time. Moreover, lamellar settling is becoming a popular technology for urban stormwater management. More recently, a new approach that consists in directly treating wet-weather flows within the connected WWTP was proposed. This situation requires the WWTP operating configuration to be rapidly adapted to wetweather flows. Lamellar settling and biofiltration offer these technical advantages. This study pursues three objectives. The first aims at providing data on the quality of raw effluents under dry and wet periods, by investigating AP and PBDE concentrations. The second objective is to examine the performance of the lamellar settler and the biofiltration unit during dry-weather flows (DWF), corresponding to the optimal operating conditions, regarding routine wastewater parameters, APs and PBDEs. Finally, the third, which is an evaluation of the performance of both techniques during wet-weather flows (WWF). To achieve these objectives, the Seine-Centre WWTP (Paris, France) was considered. METHODS Seine-Centre WWTP description and sampling points Seine-Centre WWTP receives 240,000 m 3 /d (2.8 m 3 /s) of wastewater from 800,000 inhabitant-equivalents. It is operated by the public agency of Paris conurbation sewage treatment (SIAAP). Raw sewage is pre-treated by screening and sand/grease catcher. Primary sedimentation is performed in a physico-chemical lamellar settler: coagulant (causing destabilization of colloidal particles) and polymers (promoting floc formation) are injected into the influent wastewater, prior to entering the flocculation zone and the lamellar clarifier. The biological treatment consists of a three-stage submerged biofiltration unit (Figure 1(a)). The first stage (up to 24 Biofor filters) is aerated and designed for carbonaceous pollution removal. In the second stage (up to 29 Biostyr filters), a nitrifying biomass oxidizes ammonia pollution into nitrates. In the third stage (up to 12 Biofor filters), non-aerated, a denitrification process takes place (with the addition of methanol as carbon substrate for bacteria). The final effluent is then released into the River Seine. During wet-weather periods, the plant changes its operating mode to treating higher flows, up to 735,000 m 3 /d (8.5 m 3 /s). On the one hand, more settlers are running (four under DWF and up to nine under WWF) and on the other, the biological treatment is split into two paths (Figure 1(b)): 70% of the flow is successively treated through stages 1 and 2 (treatment of carbonaceous and ammonia pollution), while 30% is treated through stage 3 only, which becomes aerated (treatment of carbonaceous pollution only). Three sampling points were considered (Figure 1): raw effluents (RE), settled effluents (SE) and final effluents (FE). Samples were collected using automated and refrigerated (4 W C) samplers, taking the usual precautions with organic pollutants (sampling in glass bottles, plastic tubing coated with Teflon). 24-h composite samples were collected under DWF, while sampling time under WWF varied between 2 and 3 hours, depending on the rain event characteristics. A total of five campaigns under dry and wet-weather periods were carried out between January and July The stormwater proportion was calculated for each sample, Figure 1 WWTP configuration under (a) dry-weather flows (DWF) and (b) wet-weather flows (WWF).

3 1593 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology based on its conductivity and the theoretical conductivities of raw sewage and runoff (hypothesis min: 1,150 and 150 μs/cm respectively for wastewater and runoff, hypothesis max: 1,150 and 75 μs/cm, respectively). This estimation leads to a stormwater proportion in wet-weather flow effluents varying from 10 to 70%. Analysis of wastewater quality parameters, APs and PBDEs Wastewater quality parameters These parameters include total suspended solids (TSS), chemical and biological oxygen demands (COD and BOD 5 ), ammonia nitrogen (NH þ 4 ), nitrates (NO 3 ), nitrites (NO 2 ) and orthophosphates (PO 3 4 ). They were analyzed by the SIAAP analytical laboratory for each sample (RE, SE and FE), according to the French Afnor standards ( Dissolved organic carbon was also analyzed. AP and PBDE analysis The analytical method is here briefly described but is available in detail in Gilbert (2011). Afterfiltering, the dissolved phases (1 L for PBDEs; from 100 ml to 250 ml for APs) are spiked with AP deuterated standards (n-op-d17 and NP1EO-d2) and PBDE quantification internal standards (BDE-77, BDE-181 and BDE C). They are then extracted within 24 h by solid phase extraction (Oasis HLB for APs and C18 Chromabond for PBDEs). For the particulate phase, the collected particles (about 100 mg) previously spiked with similar standards are microwave extracted with 20 ml of dichloromethane/ methanol (90:10, v/v) over a 30 min-cycle. After a silica gel clean-up for both dissolved and particulate phases, the PBDE fraction is treated with activated copper and the AP fraction is spiked with internal standards (4-n-NP and n-np1eo). APs are analyzed by liquid chromatography coupled with tandem mass spectrometry in multiple reaction monitoring mode, while PBDEs are analyzed by gas chromatography coupled with mass spectrometry in selected ion monitoring mode. Both quantifications are performed using internal calibration curves. The overall calibration is verified with a calibration check standard analysis every 10 samples and a deviation lower than 20% is accepted. Experimental and analytical blanks are also monitored regularly to assess external contamination. RESULTS AND DISCUSSION Individual total concentrations of APs (six congeners) and particulate concentrations of PBDEs (four out of nine congeners detected) in raw, settled and final effluents are given in Figure 2. The mean value ± standard deviation (n ¼ 5) are illustrated for dry and wet periods. Raw effluent quality: AP and PBDE concentrations During dry periods, total Σ 6 AP concentrations in raw effluents range from 2,706 to 3,573 ng/l, while total Σ 4 PBDE concentrations lie within the ng/l range. Generally, these concentrations are in the lower range of the literature values. This may be due to the high dilution of wastewater by parasitic water (street-cleaning water, infiltration and leakage from the drinking water network) within the Parisian network (Gasperi et al. 2008). For APs, concentrations are nevertheless close to those reported by Loos et al. (2007). For PBDEs, concentrations appear 10 times lower than those quoted by Song et al. (2006) in South Korea but similar to those reported by Clarke et al. (2010) in Australia, probably as a result of the geographic disparities in the use of PBDE commercial mixtures. The daily PBDE and AP loads were calculated based on the flow rate, their concentration in the raw wastewater and the number of equivalent inhabitants (1 eqhab equals to 12 g of Total Kjeldahl Nitrogen per day). It was found equal to 1,127 ± 124 μg/day/eqhab for Σ 6 AP and 33 ± 13 μg/day/ eqhab for Σ 4 PBDE. Whatever the period considered, nonylphenolic compounds are predominant (about 90% of total APs), compared with octylphenolic compounds, which is in agreement with their general use. Regarding PBDEs, BDE-209 is predominant to a large extent. The other congeners can be divided into three groups: BDE-47, BDE-99 and BDE-100, found at levels between 1 and 8 ng/l; BDE-153, BDE-183 and BDE-154, at concentrations lower than 1 ng/l; and finally BDE-28 and BDE-205 seldom and never detected, respectively. APs are mainly found in the particulate phase during dry periods (12 69% and 46 76% for octyl and nonylphenolic compounds, respectively). This trend is stronger during wet periods (42 72% and 63 89% for octyl and nonylphenolic compounds, respectively). Due to their higher hydrophobicity (5 <Log Kow <12), PBDEs are strongly bonded with particles and their particulate phase accounts for 78% to 97% for BDE-47 and BDE-99 respectively. In fact, these two congeners were the only ones to be regularly

4 1594 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology Figure 2 AP total concentrations and PBDE particulate phase concentrations (ng/l) in raw (a), settled (b) and final effluents (c) under dry (grey) and wet (white) periods. quantified in the dissolved phase, with concentrations reaching 0.9 ng/l. During rainy periods, the average concentrations significantly increase, from two to five times for most APs and from 1.5 to 3 times for PBDEs (Figure 2). This is due to the higher TSS concentrations in WWF raw effluents (Table 1), as well as higher contents in particles (from two to three times for APs and twice for BDE-209). As demonstrated by Gasperi et al. (2010a), the TSS concentration increase is related to in-sewer deposit erosion, which Table 1 Wastewater parameter removal in the settler, and mean concentration ± standard deviation in raw (RE) and settled effluents (SE) under DWF and WWF (n ¼ 5) TSS (mg/l) COD (mg O 2/L) BOD 5 (mg O 2/L) PO 4 3- (mg P/L) DWF WWF DWF WWF DWF WWF DWF WWF RE 252 ± ± ± ± ± ± ± ± 0.9 SE 20 ± 3 39± ± ± ± ± ± ± 0.1 % 92± 2 89± 7 58± 4 75± ± 7 79± 9 73± 2 87± 4

5 1595 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology contributes to 47 to 69% of TSS measured in WWF. For APs, no clear relationship was observed between their concentration and the rain event characteristics, nor was there any relationship between AP concentrations and the proportion of stormwater, suggesting that in-sewer processes may play a predominant role. For light PBDEs, the particulate phase concentration tends to increase with the proportion of stormwater. External inputs such as atmospheric inputs and urban surface leaching should be considered. PBDEs may partly come from atmospheric deposition. They are found at high levels in aerosols, up to 1,700 ng/g for Σ 8 PBDEs, according to Muresan et al. (2010). Similarly, Björklund (2010) reported significant AP concentrations in runoff and identified vehicles and concrete as major sources. Efficiency of the physico-chemical lamellar settler under dry and wet-weather flows Wastewater quality parameters Whatever the rain event considered, the efficiency of the lamellar settler remains high (>81% for TSS and PO 4 3 and >60% for COD and BOD 5 ), suggesting its insensitivity to varying influent conditions, obtaining steady results in each campaign. Removal, observed during wet periods, even becomes slightly higher than that observed during dry periods (Table 1). Higher removal can be partially explained by higher TSS and organic matter concentrations under WWF compared with DWF (Table 1). Another explanation lies in the adjustment of the amount of coagulant flocculent added to the wastewater (ratios increase from 10 to 20%). A higher orthophosphate removal, which is directly related to coagulant input, confirms this hypothesis. Dissolved pollution (dissolved organic carbon and NH 4 þ )is only slightly removed (<30%). Alkylphenols and polybromodiphenylethers As AP and PBDE are mainly particulate-bound in raw effluents, high total removal is obtained in the settler for PBDEs (>89% for Σ 4 PBDE) and, to a lesser extent, for APs (>53% for Σ 6 AP, Figure 3). As for routine wastewater parameters, the pollutant removal observed during wet periods is slightly higher than that observed during dry periods (or at least equal), confirming the insensitivity of the settler to varying influent conditions. No clear relationship was found between the removal and the proportion of stormwater, suggesting that the quality of the effluent does play a major role in pollutant removal. For PBDEs, a similar behaviour is observed for each individual congener between both periods, and seems to be well correlated to TSS removal for lighter congeners. The removal of nonylphenolic compounds is generally higher (57 89%) and that of OP is significantly lower. In the latter compound, a marked difference is observed between DWF (14 44%) and WWF (52 66%). In settled effluents, the particulate phase proportion has drastically decreased. For APs, it does not exceed 30% for dry periods and 60% during wet periods. For PBDEs, it is markedly reduced for BDE-47 and BDE-99 but is still over 30%. Despite low concentrations in the dissolved phase, an average removal of 42% is observed under DWF for BDE-47 and BDE-99; it reaches 62% under WWF. Regarding APs, removal in the dissolved phase is low (around 20%) and it fluctuates. The removal of these pollutants in the dissolved phase might be related to colloid removal in the settler, as suggested by Song et al. (2006) regarding certain PBDE congeners. Although the physico-chemical lamellar settler removes a significant part of APs and PBDEs, their concentrations in settled waters reach respectively 904 ± 641 ng/l (Σ 6 APs) and 14 ± 5 ng/l (Σ 4 PBDEs). Moreover, concentrations observed under WWF remain higher compared with DWF, except for OP. Figure 3 Total AP and PBDE removal (%) in the lamellar settler under dry and wet periods.

6 1596 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology Table 2 Wastewater parameter removal in the biofiltration unit, and mean concentration ± standard deviation in settled (SE) and final effluents (FE) under DWF and WWF (n ¼ 5) TSS (mg/l) COD (mg O2/L) BOD5 (mg O2/L) NH4 þ (mg N/L) DWF WWF DWF WWF DWF WWF DWF WWF SE 20 ± 3 39± ± ± ± ± ± 1 26± 12 FE 6 ± 1 8± 1 38± 2 23± 4 10± 3 5± 1 6± 2 2± 1 % 70± 7 72± ± 3 72± ± 5 84± ± 7 88± 17 Efficiency of the biofiltration unit, under dry and wet-weather flows Wastewater quality parameters By combining physical and biological processes, the biofiltration can effectively treat carbonaceous, nitrogenous and phosphorus pollution during both weather periods (Table 2). A significant part of TSS is also eliminated in the biofiltration unit, leading to TSS concentrations lower than 10 mg/l. The TSS removal occurs mainly in the first stage of the biofiltration (Gasperi et al. 2010b). As shown by standard deviations, higher removal variability is observed during wet periods for most parameters. However, no clear trend appeared between removal and storm event characteristics. Concentration of organic matter (COD and BOD 5 ) in the final effluent is significantly lower under WWF compared with DWF (Table 2). This finding is partly related to lower (but highly variable) concentrations in settled effluents but it may also result from the change of the biofiltration operating configuration. Despite this modification, its efficiency remains high, even for NH 4 þ.it actually seems that the modified operating conditions only affect the denitrification process, i.e. nitrate concentration in the final effluent reaches 4.5 ± 2.2 mg N/L under DWF vs 16 ± 5 mg N/L under WWF. Alkylphenols and polybromodiphenylethers On the whole, APs are well removed during biological treatment during dry and wet periods (58 ± 5% and 68 ± 20% respectively, for Σ 6 APs). PBDEs are seldom quantified in the dissolved phase of the final effluent. Hence, the results discussed here correspond to the particulate phase only. Light congeners (BDE-47, BDE-100 and BDE-99) are efficiently removed from the particulate phase during both periods (from 44 to 87%, Figure 4). In contrast, BDE-209 is strongly removed during dry periods (75 ± 6%) but weakly removed during wet periods. The removal of this compound in the particulate phase is lower than 15% and can be negative (from 14% and 125%). Despite the successful TSS removal, this result is mainly explained by the higher BDE-209 content in final effluents under WWF (2.2 ± 0.4 mg/kg) compared with particles found in settled effluents (0.10 ± 0.06 mg/kg). Today, no clear explanation can be provided and further investigation is needed. A high removal of APs in the particulate phase is observed within the biofiltration unit: it ranges from 45 to 97%, except for OP. A strong correlation between TSS removal and AP and PBDE particulate phase removal is noticed during dry periods. In the final effluents, AP particulate phase does not exceed 17 and 43% under DWF and WWF respectively. Regarding dissolved pollution, APs are Figure 4 AP total removal (%) and PBDE particulate phase removal (%) in the biofiltration unit under dry and wet periods.

7 1597 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology well removed (55 ± 5% under DWF and 62 ± 19% under WWF). Among the different processes occurring within the biofiltration unit (volatilization, sorption and biodegradation), sorption probably plays a key role, as suggested by Song et al. (2006). Besides, these authors claim that the decrease of dissolved PBDEs during an activated sludge biological treatment could be due to their partitioning and settling with biomass. Regarding APs, sorption, and to a lesser extent, biodegradation are the main processes occurring within biofiltration. CONCLUSION This study was designed to provide information regarding AP and PBDE contamination levels in raw effluents, as well as to evaluate the performance of physico-chemical lamellar clarification and biofiltration during dry and wetweather periods. This study primarily emphasizes the fact that rainy periods enhance AP (two to five times) and PBDE (1.5 to 3 times) concentrations in raw effluents, confirming the need to treat wet-weather flows. This increase is mainly due to in-sewer deposit erosion and, to a lesser extent, to external inputs such as atmospheric sources and leaching of urban areas. The physico-chemical lamellar settler obtains high AP and PBDE removal, due to their partitioning. During wet periods, this removal is even slightly improved, thus confirming the insensitivity of this technique to varying influent conditions. This is explained by higher pollutant concentrations in raw effluents, as well as by the adjustment of the amount of coagulant flocculent added to the settler. By combining physical and biological processes, the biofiltration unit obtains high removal of the dissolved (39 80% for Σ 6 AP) and particulate pollution (from 45 to 97% for APs, except for OP and from 44 to 87% for PBDEs, except for BDE-209 during a wet period). Indeed, the configuration changes under wet-weather periods do not influence removal of most wastewater quality parameters and organic pollutants, except for nitrogen pollution (no denitrification occurs) and BDE-209 (not removed during wet-weather periods). In conclusion, this study highlighted the high performance of both lamellar clarification and biofiltration techniques, whose combination appears suitable for stormwater treatment. If the treatment of raw effluents during wet periods within the connected WWTP seems to be technically efficient in limiting stormwater discharges into the receiving waters, one should keep in mind that this solution requires high levels of investment in terms of infrastructure and maintenance. ACKNOWLEDGEMENTS The authors would like to thank SIAAP (Ms Briand and Rechdaoui) and LEESU (Mr Leroy, Saad and Segor) for their technical support and their active participation in sampling campaigns. REFERENCES Björklund, K Substance flow analyses of phthalates and nonylphenols in stormwater. Water Science and Technology 62 (5), Clara, M., Scharf, S., Scheffknecht, C. & Gans, O Occurrence of selected surfactants in untreated and treated sewage. Water Research 41, Clarke, B. O., Porter, N. A., Symons, R. K., Marriott, P. J., Stevenson, G. J. & Blackbeard, J. R Investigating the distribution of polybrominated diphenyl ethers through an Australian wastewater treatment plant. Science of the Total Environment 408, ECB 2000 European Union Risk Assessment Report: diphenyl ether, pentabromo deriv. In: 1st Priority List. European Chemicals Bureau, Office for Official Publications of the European Communities, Luxembourg, Volume 5. ECB 2007 Review on production process of décabde used in polymeric applications in EEE and assessment of the availibility of potential alternatives to decabde. In: 1st Priority List. Joint Research Centre, European Chemicals Bureau, Office for Official Publications of the European Communities, Luxembourg, Volume 16. Gasperi, J., Kafi-Benyahia, M., Lorgeoux, C., Moilleron, R., Gromaire, M. C. & Chebbo, G Spatial variability of the pollutant load conveyed by dry weather flows within the Parisian combined sewers. Urban Water Journal 5, Gasperi, J., Gromaire, M. C., Kafi, M., Moilleron, R. & Chebbo, G. 2010a Contributions of wastewater, runoff and sewer deposit erosion to wet weather pollutant loads in combined sewer systems. Water Research 44, Gasperi, J., Rocher, V., Gilbert, S., Azimi, S. & Chebbo, G. 2010b Occurrence and removal of priority pollutants by lamella clarification and biofiltration. Water Research 44, Gilbert, S Removal of polybromodiphenylethers, alkylphenols and their ethoxylates during wastewater treatment. PhD Thesis, Paris, 289 pp. (in French). Loos, R., Hanke, G., Umlauf, G. & Eisenreich, S. J LC MS MS analysis and occurrence of octyl- and nonylphenol, their

8 1598 S. Gilbert et al. Treatment of wastewater under dry and wet-weather flows Water Science & Technology ethoxylates and their carboxylates in Belgian and Italian textile industry, waste water treatment plant effluents and surface waters. Chemosphere 66, Muresan, B., Lorgeoux, C., Gasperi, J. & Moilleron, R Fate and spatial variations of polybrominated diphenyl ethers in the deposition within a heavily urbanized area: case of Paris (France). Water Science and Technology 62 (4), OSPAR 2001 Nonylphenol/nonylphenolethoxylates. In: Hazardous Substances Series. OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic, London. OSPAR 2003 Octylphenol. In: Hazardous Substances Series. OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic, London. Song, M., Chu, S. G., Letcher, R. J. & Seth, R Fate, partitioning, and mass loading of polybrominated diphenyl ethers (PBDEs) during the treatment processing of municipal sewage. Environmental Science and Technology 40, Ying, G. G., Williams, B. & Kookana, R Environmental fate of alkylphenols and alkylphenol ethoxylates a review. Environment International 28, First received 5 September 2011; accepted in revised form 22 December 2011