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Keywords:

  • Pharmaceuticals;
  • Wastewater;
  • Groundwater;
  • Sorption;
  • Biodegradation

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

Pharmaceuticals and personal care products (PPCPs) have emerged as a group of potential environmental contaminants of concern. The occurrence of gemfibrozil, a lipid-regulating drug, was studied in the influent and effluent at a wastewater treatment plant (WWTP) and groundwater below a land application site receiving treated effluent from the WWTP. In addition, the sorption of gemfibrozil in two loam soils and sand was assessed, and biological degradation rates in two soil types under aerobic conditions were also determined. Results showed that concentrations of gemfibrozil in wastewater influent, effluent, and groundwater were in the range of 3.47 to 63.8 µg/L, 0.08 to 19.4 µg/L, and undetectable to 6.86 µg/L, respectively. Data also indicated that gemfibrozil in the wastewater could reach groundwater following land application of the treated effluent. Soil–water distribution coefficients for gemfibrozil, determined by the batch equilibrium method, varied with organic carbon content in the soils. The sorption capacity was silt loam > sandy loam > sand. Under aerobic conditions, dissipation half-lives for gemfibrozil in sandy loam and silt loam soils were 17.8 and 20.6 days, respectively; 25.4 and 11.3% of gemfibrozil was lost through biodegradation from the two soils over 14 days. Environ. Toxicol. Chem. 2012;31:550–555. © 2011 SETAC


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

The occurrence and fate of pharmaceuticals and personal care products (PPCPs) in the aquatic environment has been recognized as an emerging issue in recent years 1. In actuality, pharmaceuticals have been present in the environment for several decades 2. A wide variety of PPCPs has been detected in environmental samples at levels ranging from nanograms per kilogram up to grams per kilogram 3 as sensitive analytical methods have developed and both researchers and practitioners have recognized the need for more monitoring data. Although most PPCPs exist in the environment at trace levels, exposure to PPCPs is chronic, because they are discharged continuously from wastewater treatment plants 4. This chronic exposure has produced negative impacts on aquatic organisms 5–7.

Among the PPCPs frequently detected, acidic drugs represent an important group. Gemfibrozil (5-[2,5-dimethylphenoxy]-2,2-dimethyl-pentanoic acid, gemfibrozil, CAS: 25812-30-0) is an acidic drug and a lipid-regulating agent. Although the International Agency for Research on Cancer has classified it in group 3—not classifiable regarding its carcinogenicity to humans 8—gemfibrozil is considered to be a peroxisome proliferator 9. Lipid regulators are used widely and are one of the most common drug groups based on sales and prescriptions. Their widespread use suggests that they have the potential to occur commonly in wastewater and ultimately the environment. Pharmaceuticals and personal care products such as gemfibrozil enter wastewater treatment plants (WWTPs) via excretion with urine and feces as parent compounds, conjugated compounds, or metabolites 10. Removal of PPCPs from wastewater via WWTPs can be substantial (30–90%). However, several investigations 11, 12 have provided evidence that some PPCPs are not completely removed during conventional wastewater treatment and are not biodegraded. For example, Stumpf et al. 13 found the removal rate of gemfibrozil through a Brazilian sewage treatment plant varied from 16 to 46% 13, and Bendz et al. found gemfibrozil has been detected in effluents at 0.18 µg/L 14. Effluent from WWTPs is a significant source of PPCPs to waterways 15. Previously, gemfibrozil was found in surface waters in North America and Europe at about 0.75 µg/L and 1.5 µg/L, respectively 16.

The environmental risks associated with the presence of gemfibrozil in water are still unknown, and little information exists about the effect of gemfibrozil in aquatic organisms. Mimeault et al. 17 reported that gemfibrozil was taken up from water and concentrated in goldfish blood. Plasma testosterone levels were reduced by 49 and 72% compared with controls when goldfish were exposed to 1.5 and 1,500 µg/L of gemfibrozil in water.

The fate of PPCPs in soils is attracting more attention, particularly with respect to water recycling through the land application of treated wastewater and the possibility of groundwater contamination 18. Microbial degradation is considered an important removal pathway for pharmaceuticals in the environment, especially for those compounds resistant to photodegradation and/or hydrolysis. However, measurements of degradation rates for PPCPs in soils are less common than in water. In addition, few investigations have focused on the mobility, especially the sorption behavior, and plant uptake potential of gemfibrozil in soils. Assessments of the biological availability and trophic transfer potential of PPCPs in soil environments are important with regard to the risks associated with water reuse and recycling. With regard to gemfibrozil, a few studies have examined its persistence in natural water 19 and sediment 20. However, soil fate data are lacking.

The objectives of the present study were to monitor the variation in gemfibrozil concentrations in influent and effluent from a WWTP and groundwater below a land application site (LAS) over one year. The goals were to assess the sorption behavior of gemfibrozil in two soil types, and to determine the biodegradation potential of gemfibrozil in a sandy loam and silt loam soil under aerobic conditions.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

Chemicals and reagents

Gemfibrozil (purity >98%) was purchased from Sigma-Aldrich. Relevant chemical properties of gemfibrozil are shown in Table 1. High-performance liquid chromatography (HPLC)-grade acetonitrile and ethyl acetate were obtained from Fisher Scientific. Ultrapure water (>18 MΩ) was prepared by a Barnstead NANOpure infinity ultrapure water system. Standard solutions of gemfibrozil were prepared in 100% acetonitrile.

Table 1. Physical and chemical properties of gemfibrozil (5-(2,5-dimethylphenoxy)-2,2-dimethyl-pentanoic acid)
FormulaStructureMolecular weightWater solubility (mg  ·  L−1)Log KowpKa
  • a

    Hassan et al. 45.

  • b

    Westerhoff et al. 46.

C15H22O3
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250.329.10a4.77b4.7b

Occurrence of gemfibrozil

Wastewater samples were collected from a wastewater reclamation plant in a municipality in Texas. The community's water consumers can be characterized as residential (85%), small commercial (10%), municipal (4%), and other user classes (1%), including industrial, schools, wholesale, and irrigation. The wastewater reclamation plant treats approximately 21 million gallons of wastewater per day and has an average daily flow design capacity of 31.5 million gallons.

Groundwater samples were collected from an LAS associated with the wastewater reclamation plant. The LAS was 6,000 acres of irrigated farmland for tertiary treatment of wastewater effluent. The LAS was seeded with forage grasses, cotton, and legume plant species in an effort to use the nitrogen present in the effluent. The LAS soils were classified as slightly alkaline loams with more than 40% sand and low organic matter (<2%). There were four sampling points named after the monitoring well codes: well A, well B, well C, and well D. Wells B and D were wells located outside the area of pivot irrigation; wells A and C were under center pivot irrigation systems 21. Water samples were collected quarterly from March to December, 2010. Groundwater samples were collected from a tap at each well. Samples were stored in 1-L amber glass bottles on ice during transport to the laboratory and refrigerated at 4°C until extraction and analysis.

Wastewater and groundwater samples were first filtered through 10-cm P5 filter paper (Fisher Scientific) to remove suspended solids. The pH of the filtrate was adjusted to pH 2 with concentrated hydrochloric acid. A 6-cc, Oasis HLB solid-phase extraction cartridge was conditioned successively with 5 ml methanol and 10 ml Milli-Q water (adjusted to pH 2 with hydrochloric acid). Two hundred milliliters of wastewater or 500 ml groundwater was loaded onto solid-phase extraction cartridges at approximately 3 ml/min. The cartridge was then washed with 2 ml of 10% methanol in water. The cartridge was dried for approximately 10 min, and then eluted with 5 × 2 ml of ethyl acetate. Eluates were evaporated to approximately 500 µl under a gentle stream of nitrogen. The sample was brought to 1 ml volume with acetonitrile and analyzed by HPLC with ultraviolet (UV) detection. We tested the efficiency of this method by spiking gemfibrozil at 100 µg/L into water samples. Recoveries of gemfibrozil using this extraction method for wastewater (n = 3) and groundwater (n = 3) matrices were 93 ± 2.1% and 92 ± 1.3%, respectively.

Sorption of gemfibrozil

Two types of natural soils, a sandy loam and a silt loam, were used in sorption experiments. The sandy loam soil was an agricultural soil (no exposure to wastewater) collected from Terry County (West Texas, USA) and is similar to the soil type at the LAS, whereas the silt loam soil was a garden soil (no exposure to wastewater) from Harlan County (South Central Nebraska, USA). Ottawa sand (average grain size 0.32 mm; Fisher Scientific) served as a reference sorbent. Physicochemical properties of the soils and sand are listed in Table 2. For calculation purposes, the organic carbon content of the sand was assumed to be 0.1%. Both soils were sieved (4 mm) prior to use.

Table 2. Physicochemical properties of the test soils and sand
 Sand (%)Silt (%)Clay (%)Organic carbon (%)pH
  • a

    Assumption.

Sandy loam7410161.3 ± 0.068.3
Silt loam3454122.5 ± 0.17.0
Sand100000.1a7.0

Sorption experiments were conducted by the batch equilibrium method. Working solutions of gemfibrozil in 0.01 M CaCl2 were prepared to obtain desired concentrations within the range of 0.1 to 5 mg/L. The ratio of sorbent mass to solution volume was 1:2 for both soils and 1:1 for sand. Sorption tests were conducted in 40-ml glass vials. Each treatment included three replicates. Control samples (no sand or soil) were included in each treatment to account for any sorption to the vials or losses from volatilization (we did not observe any losses of gemfibrozil through these processes). A blank for each soil and sand and a control for each concentration were prepared as specified by OECD guidelines 22.

Soil and sand solutions were equilibrated for 24 h on a shaker (250 rpm). Based on preliminary studies (data not shown), 24 h was an adequate equilibration time for gemfibrozil sorption. Although the soils and sand were not sterilized, there was no significant loss of gemfibrozil during 24 h from biological degradation. After equilibration, the pH of the soil and sand solutions was adjusted to 2 by adding hydrochloric acid, solutions were centrifuged for 10 min (2,000 g), and 1 ml supernatant was collected and analyzed by HPLC.

The relationship between gemfibrozil mass in solution and gemfibrozil mass on the sorbent was modeled using the Freundlich equation, S = KfC1/n, where S is the concentration of chemical in the solid phase (µg/g), Kf is the Freundlich constant, C is the concentration of chemical in solution (µg/ml), and 1/n is a power function. When the value of 1/n = 1, the isotherm becomes a linear equation, S = KdC, where Kd is the sorption coefficient (ml/g). KOC was calculated from the experimentally determined Kd and organic carbon content of the sorbent: KOC = (Kd/percentage of organic carbon) × 100.

After the conclusion of the sorption experiments, the sample vials containing the soils and sand were used to determine desorption of gemfibrozil. Five milliliters of 0.01 M CaCl2 was added to each vial and then equilibrated for 24 h on an orbital shaker. Solutions were centrifuged for 10 min (2,000 g), and 1 ml supernatant was collected and analyzed by HPLC.

Biodegradation of gemfibrozil

Biodegradation experiments 23 were conducted using the two soil types described previously. Ten grams of sandy loam or silt loam soil was added to 40-ml glass vials. Soil samples were spiked with 0.5 ml of a 25 µg/ml gemfibrozil standard in acetonitrile. Sterile Milli-Q water (2 ml) was added to adjust soil moisture to 30% field capacity and distribute the test chemical. The headspace of sample vials was sparged with breathing-quality air. Triplicate samples were incubated in the dark at room temperature. Triplicate killed (autoclaved) controls were also incubated at the same time. The concentrations of gemfibrozil were monitored after incubation periods of 0, 3, 7, and 14 days. At each time point, the sample was extracted with 20 ml acetonitrile by shaking (250 rpm) for 2 h. After shaking, solutions were centrifuged for 10 min (2,000 g), and the supernatant was evaporated to 2 ml, and then analyzed by HPLC. Short-term spike-recovery studies indicated 93 ± 2.0% extraction efficiency for gemfibrozil in both the sandy loam and the silt loam soils.

Analytical methods

High-performance liquid chromatography with UV detection was used to determine gemfibrozil in all sample matrices. An Alltech® Prevail C18 column (25 cm × 4.6 mm i.d., 5 µm) was used for separation. The mobile phase was 80:20:0.05 acetonitrile:water:trifluoroacetic acid. The flow rate was 1.0 ml  ·  min−1. Detection wavelength was 200 nm. The detection limit for gemfibrozil in water and soils was 0.01 mg/L and 0.1 mg/kg.

Although HPLC/UV can be considered somewhat ambiguous for forensic measurements of PPCPs in environmental samples, the technique is very reliable for PPCP measurements in samples from controlled laboratory experiments in which determination and quantification of known compounds are desired. To determine and account for potential matrix effects and coeluting compounds, the analytical method was developed using wastewater samples spiked with the test compound similar to previous studies in our laboratory 21. All analyses met predetermined performance-based quality assurance criteria for calibration linearity (r2 = 0.99) and recovery (80–120%). Nonetheless, identification of the test compound based solely on UV detection and without second column confirmation is acknowledged as a potential limitation to the work reported herein.

Statistical analysis

Statistical analyses were performed by using SPSS Version 11 (for IBM). Data comparisons were conducted using analysis of variance. Significant differences between treatments were determined by a least significant difference test.

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

Gemfibrozil in wastewater and groundwater

The concentrations of gemfibrozil found in wastewater and groundwater samples are provided in Table 3. Gemfibrozil was present in all wastewater samples from March to December, 2010, but concentrations varied between quarterly samples. Gemfibrozil concentrations were highest in September: 63.8 µg/L in the influent and 15.3 µg/L and 19.4 µg/L in separate effluent stations. In contrast, gemfibrozil concentrations were lowest during the fourth quarter. Although we expected some variation in quarterly gemfibrozil concentrations likely because of use, we did not anticipate the order-of-magnitude greater concentrations observed during the third quarter. Concentrations of gemfibrozil in the effluent were less than those in the influent during the same quarter, which suggests that gemfibrozil can be partially removed from wastewater during the treatment process. Concentrations of gemfibrozil in the effluent ranged from 0.08 to 19.4 µg/L. Bendz and coworkers 14 found gemfibrozil effluent concentrations (0.18 µg/L) within that range. Several investigators have shown that many PPCPs do not fully degrade during municipal wastewater treatment 4, 24, 25. The percentage of change in gemfibrozil concentration from wastewater treatment has been reported to vary between 16 and 69% 13, 26. There was a difference in gemfibrozil concentration in effluent between station I and station II. In general, the removal efficiency for gemfibrozil in station I was better than that in station II; station I has an extra treatment process (chlorination). Snyder et al. 27 reported that some pharmaceuticals can be oxidized using chlorine; however, oxidation does not result in complete mineralization (oxidation to carbon dioxide and water), so gemfibrozil and/or its metabolites may still be detected in the effluent.

Table 3. Concentrations (µg/L) of gemfibrozil in wastewater samples from a wastewater treatment plant and groundwater samples below a land application sitea
Sampling dateWastewaterGroundwater
Bar rack (influent)Station I (effluent)Station II (effluent)Well AWell BWell CWell D
  • a

    ND = not detected; — = no sample.

2010 Mar 35.553.854.39NDNDNDND
2010 Jun 36.261.780.13NDNDNDND
2010 Sep 863.815.319.46.865.695.292.28
2010 Dec 83.470.080.930.750.110.13

Gemfibrozil was not detected in any groundwater sample below the LAS during the first and second quarters but was detected in the third and fourth quarters. Gemfibrozil in groundwater likely comes via leaching from the LAS soil, which is continually receiving treated wastewater effluent, and all effluent samples contained gemfibrozil. Runoff and subsurface transport are important processes for movement of PPCPs from soil to groundwater 28. The extent of PPCPs in groundwater can be affected by sorption and biodegradation 29, 30. The third and fourth quarters could be characterized as periods of low evapotranspiration. In such instances, more water (treated effluent) is available to leach through the soil profile 31, potentially leading to higher concentrations in groundwater. Introducing PPCPs to the soil environment through irrigation is potentially an important exposure route in semiarid zones, where recycled wastewater can be a primary source of irrigation water 32. Groundwater samples in the third quarter had the highest concentrations of gemfibrozil, consistent with the high gemfibrozil concentrations observed in the wastewater influent and effluent during the same period.

Gemfibrozil was detected in most water samples at levels ranging from 0.08 to 63.8 µg/L. Mimeault et al. 33 addressed the potential of an environmentally relevant waterborne concentration of gemfibrozil (1.5 µg/L) to induce oxidative stress in goldfish. Zurita et al. 34 used the immobilization of Daphnia magna to investigate toxic effects of gemfibrozil; a no-observed-adverse-effect level of 30 µM (7,500 µg/L) and a mean effective concentration of 120 µM (30,000 µg/L) for gemfibrozil after 72 hr were observed. These concentrations are well above the water concentrations that we observed.

Sorption and desorption

A better understanding of sorption is needed to identify the main processes influencing the fate of PPCPs in soils irrigated with reclaimed wastewater. Results of the batch experiments showed that sorption isotherms for gemfibrozil were essentially linear over the range of concentrations tested (Fig. 1). Gemfibrozil sorption was highest in the silt loam and lowest in the sand, which was consistent with organic carbon content being the primary soil component for sorption. Sorption of PPCPs to soils has been shown to be influenced by organic sorbents 35–37; adsorption is generally higher in soils with higher carbon contents. According to a sorption classification system provided by the U.S. Environmental Protection Agency (U.S. EPA) 38, sorption of gemfibrozil in silt loam soil was moderate, and sorption of gemfibrozil in sand and sandy loam was low.

thumbnail image

Figure 1. Sorption isotherms for gemfibrozil in sand, sandy loam, and silt loam soils.

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Isotherm data for gemfibrozil in sand and soils are presented in Table 4. Freundlich constants (Kf) and Kd values were consistent with the isotherms. We observed the highest Kd value (9.2 ml/g) for gemfibrozil in the silt loam soil. A total of 1/n exponents for the sand, sandy loam, and silt loam indicated that there was some variation from linearity, although the linear regression coefficients for the isotherms (r2) were all ≥0.94. Organic carbon-normalized sorption coefficients (log KOC) were similar for the three sorbents, although there was more variation than expected. Other soil factors beyond organic carbon content, such as cation exchange, cation bridging at clay surfaces, surface complexation, and hydrogen bonding, could affect sorption of pharmaceuticals in soils 39.

Table 4. Sorption coefficients for gemfibrozil to sand, a sandy loam, and a silt loam soil
SorbentFreundlich equationLinear equation
Kf1/nr2Kdr2Log Koc
Sand0.240.680.960.120.942.08
Sandy loam1.310.831.001.061.001.91
Silt loam12.381.370.979.20.992.57

In addition to soil type and characteristics, sorption coefficients for chemicals depend largely on the physicochemical properties of the chemical. Gemfibrozil is an acidic substance (pKa 4.7). At most environmental pHs (pH 5–9), it will exist primarily in an ionized (anion) form and not interact with soil components 19, because soils have little anion exchange capacity. Urase and Kikuta 40 reported that the water–sludge partition coefficient (Kp) of acidic pharmaceuticals such as gemfibrozil was increased under acidic conditions, whereas the effect of pH on Kp was small for those substances that do not have acidic functional groups.

Preliminary studies showed that desorption equilibrium time for gemfibrozil was 48 h in sandy loam and 24 h in silt loam (data not shown). Desorption of gemfibrozil was higher than expected in both soil types, especially the sandy loam. Gemfibrozil desorption values were 19.7 ± 3.35% and 9.2 ± 0.58% in sandy loam and silt loam soil, respectively. The desorption results indicate that the sorption of gemfibrozil to soil was partially reversible and inversely related to soil organic carbon content. This helps to explain partially the groundwater data.

Biodegradation

Biodegradation experiments indicated that gemfibrozil behaved differently in the two soil types (Fig. 2). Some loss of gemfibrozil was observed in the killed controls over 14 days (13.1% loss in the sandy loam and 16.1% in the silt loam), suggesting that gemfibrozil can be degraded abiotically. Araujo et al. 19 concluded that sunlight plays an important role in the degradation of gemfibrozil in the environment; however, in our laboratory study, there was little chance of photodegradation, because test vials were wrapped with aluminum foil and incubated in the dark. Gemfibrozil does not contain functional groups that typically hydrolyze under environmental conditions. The only remaining possibility for the implied loss of gemfibrozil in the killed controls is incomplete extraction.

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Figure 2. Dissipation curves for gemfibrozil in sandy loam and silt loam soils under aerobic condition.

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Not considering the abiotic losses of gemfibrozil in the soil, biological degradation of gemfibrozil over the 14 days was 25.4 and 11.3% in the sandy loam and silt loam soil, respectively. These values were significantly different from controls (p < 0.05). Calculated half-lives for gemfibrozil in sandy loam and silt loam soil were 17.8 and 20.6 days, respectively. Gemfibrozil exhibited a slightly shorter half-life in sandy loam than in silt loam soil, although the difference was not statistically significant (p > 0.05). Kunkel and Radke 20 concluded that the half-life for gemfibrozil in (aerobic) sediment was 10.5 d, whereas no degradation was observed in bed sediment (mostly anaerobic). Ying et al. 41 reported that triclocarban and triclosan can be biodegraded in aerobic soil but will persist longer in anaerobic soil. Biodegradation of veterinary antibiotics in water was significantly slower in tests conducted in the absence of oxygen compared to tests with oxygen 42. The half-life of gemfibrozil in biosolids-amended agricultural soil was 231 ± 4 d 43. Notable difference in the persistence for gemfibrozil observed for our soils versus the biosolids-amended agricultural soil may be that the biodegradability of some compounds decreases when they are introduced into soils in the form of biosolids 44; the application matrix had very significant effects on the rates of biodegradation. Another reason for the difference may be that a mixture of pharmaceuticals might be more persistent than individual compounds.

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

Gemfibrozil was detected in the influent and effluent of a WWTP. In addition, gemfibrozil was occasionally found in groundwater below an associated LAS. These observations indicate that gemfibrozil is not completely removed by the wastewater treatment process and, under conditions of low evapotranspiration, can move through soil to groundwater. However, the concentrations of gemfibrozil detected in groundwater were very low compared with those in the effluent, indicating that the land application process is generally effective at removing gemfibrozil. Gemfibrozil had a moderate tendency to sorb to silt loam soil and a low tendency to sorb to sandy loam soil. Desorption of gemfibrozil from both soils was greater than expected. The degradation half-lives for gemfibrozil were 17.8 and 20.6 days in sandy loam and silt loam soils, respectively. It is hoped that these data will aid in understanding the fate of PPCPs in the environment, in particular the widely used drug gemfibrozil.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

This research was supported in part by a grant from the U.S. EPA to the Water Law and Policy Center, Texas Tech University School of Law.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. MATERIALS AND METHODS
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
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