Parabens are used as anti-microbial preservatives in a range of consumer products, especially in cosmetics. In vitro and animal studies have shown weak estrogenic and other endocrine disrupting effects of parabens, including reduced testosterone levels in exposed male rats. The knowledge of paraben exposure, distribution and excretion in humans is limited. In this study we determined the concentration of five parabens; methyl-, ethyl-, n-propyl-, n-butyl- and benzylparaben in urine, serum and seminal plasma samples from 60 healthy Danish men. To conduct the study a sensitive and specific method using LC–MS/MS for simultaneous determination of the five parabens was developed for all three different matrices. Highest concentrations of the parabens were found in urine, wherein methyl-, ethyl-, n-propyl- and n-butyl parabens were measurable in 98%, 80%, 98% and 83% of the men, respectively. Benzyl paraben was only measurable in urine from 7% of the men. Methyl- and n-propyl parabens were also measurable in the majority of serum and seminal plasma samples, whereas the other parabens could only be detected in some of the samples. In all the three matrices significant correlations between the parabens were seen. Furthermore, urinary paraben concentrations correlate to the paraben concentrations in both serum and seminal plasma.
Parabens are a group of industrial chemicals, which during the last decade have been pointed out as possible endocrine disruptors. Some parabens have been shown to have weak estrogenic effects in vitro and in animal studies (Okubo et al., 2001; Byford et al., 2002; Darbre et al., 2002, 2003, 2004; Lemini et al., 2003; Pugazhendhi et al., 2005). Furthermore, studies have shown effects on the male reproductive system, resulting in the reduction of testosterone levels and mature sperm counts, in rats and mice after in utero exposure to some parabens (Oishi, 2001, 2002, 2004; Kang et al., 2002), whereas other studies could not confirm these effects (Hoberman et al., 2008; Taxvig et al., 2008). Recently it has been discussed whether parabens could have an adverse effect on the testis mitochondria function, followed by a decreased reproductive potential (Tavares et al., 2009).
In our daily life we are highly exposed to parabens owing to the wide use of parabens as anti-microbial preservatives in cosmetics such as skin-care and soap products, in pharmaceuticals and in some processed food products. The benefits are many; in general parabens are considered safe with low or no toxic effects, they have no taste or odor and are low-cost products (Soni et al., 2005; CIR Expert Panel, 2009). The most common used parabens are methylparaben (MeP), ethylparaben (EtP), n-propylparaben (n-PrP), iso-propylparaben (i-PrP), n-butylparaben (n-BuP), iso-butylparaben (i-BuP) and benzylparaben (BzP), and to increase the activity against microbial contamination in the host product, the parabens are often used in combination (CIR Expert Panel, 2009).
Humans are exposed to parabens via absorption through skin (Lobemeier et al., 1996; Akomeah et al., 2004; Janjua et al., 2007, 2008) and via the gastrointestinal tract after oral intake. Parabens are rapidly metabolized into mainly the harmless non-specific p-hydroxybenzoic acid and its respective glucuronic and sulfuric acid conjugates. Several in vitro, animal and a few human studies have shown that after oral intake almost the entire dose of parabens were excreted through urine as p-hydroxybenzoic acid and its conjugates (Soni et al., 2005; CIR Expert Panel, 2009). In contrast, following skin application more of the test doses were excreted in urine as the parent parabens in their free (unconjugated) or conjugated form (glucuronidated and sulphated) (Soni et al., 2005; Janjua et al., 2008; CIR Expert Panel, 2009). In a few human studies urinary, serum and breast tissue levels of the parent parabens have been used as biomarkers of exposure to the different parabens (Darbre et al., 2004; Ye et al., 2006a, 2006b, 2008; Janjua et al., 2007, 2008). Despite the rapid metabolization the levels of parent parabens, especially MeP and n-PrP, distributed to the different human matrices are not insignificant. Also rat studies have shown that parabens were distributed in their parent form to several different fluids and tissues before excretion (Soni et al., 2005) and even seem to accumulate in amniotic fluid (Frederiksen et al., 2008).
Despite the discussion and concern in recent years about the possible endocrine disrupting effects of parabens and development of analytical methods for quantification of parabens in human urine and serum (Ye et al., 2006b, 2008), the knowledge about human exposure, distribution and excretion of parabens are limited. The aim of this study has been to investigate the distribution and excretion of five commonly used parabens (MeP, EtP, n-PrP, n-BuP and BzP) in human urine, serum and seminal plasma. The study group consisted of 60 young and healthy Danish men, and an analytical method using LC–MS/MS was developed for the analyses of the parabens in all three matrices. To our knowledge, the data presented here is the first to report parabens measured in human urine, serum and seminal plasma samples collected from the same individuals.
Materials and methods
Urine, blood and semen samples were obtained from 60 young and healthy Danish men participating in a study on male reproductive health. Mean anthropometric data for the population group were: age, 19.7 years (range: 18.2–26.2 years); height, 182.4 cm (range: 164.3–197.1 cm); weight, 77.0 kg (range: 60.3–100.0 kg); and body mass index (BMI), 23.1 kg/m2 (range: 19.0–31.5 kg/m2). All participants gave their written consent after having received written and oral information about the study. The study was approved by the ethical committee for the Copenhagen municipality (ref. nos.: KF 01-117/96 and KF 01-292/98 with amendment on 19 January 2006). All samples were collected in clinic, December 2006, in connection with a physical examination. The three different samples from each of the men were obtained within maximum one hour.
Sample Collection and Storage
From each participant a blood sample was drawn from the cubital vein and serum was obtained by centrifugation for 10 min at 2000g and subsequently aliquoted for hormone and chemical analyses. Semen samples were obtained by masturbation and preserved at 37°C until liquefaction had occurred. After aliquots were taken out for routine clinical assessments of semen quality parameters, the remaining sample was immediately centrifuged for 30 min at 2000g (Jorgensen et al., 2002) and the supernatant consisting of cell-free seminal plasma were used for chemical analyses. For the analyses of parabens aliquots of urine, serum and seminal plasma were transferred into 4 ml glass screw-cap vials. To avoid possible enzyme activity in serum and seminal plasma samples after collection, these samples were added 1.2M phosphoric acid, 100μl and 200μl per 1.0ml serum, and seminal plasma, respectively, before storing at −20°C. Spot urine samples were collected in polyethylene cups and aliquots of each urine sample was transferred to 20 ml glass scintillation vials with tops packed with aluminum foil. All urine samples were stored at −20°C until analysis. From surplus human serum and seminal plasma collected over time from different inhouse studies, and human urine sampled from colleagues, who consciously avoided exposure to parabens before the sampling, one pool of each matrices were made and used for the calibration of standards and as control material in the validation of the present method.
Reagents and Standards
MeP, EtP, n-PrP, n-BuP and BzP were purchased from Fluka (distributed by Sigma–Aldrich, Brøndby, Denmark) and deuterium-labeled methylparaben (D4-MeP) was obtained from CDN Isotopes (Quebec, Canada). Phosphoric acid, glacial acetic acid, formic acid and sodium dihydrogen phosphate dihydrate were obtained from Merck (Darmstadt, Germany). Acetonitrile, methanol, ammonium acetate and sodium sulfate were all obtained from J.T. Baker. Both Merck and T.J. Baker chemicals were distributed by Bie & Berntsen A/S (Rødovre, Denmark). Ethyl acetate was obtained from BDH Laboratories Supplies (Poole, England and distributed by VWR International, Rødovre, Denmark). 4-Methylumbelliferone, 4-methylumbelliferyl-β-D-glucuronide and 4-methylumbelliferyl sulfate were obtained from Sigma–Aldrich (Brøndby, Denmark). β-Glucuronidase (Escherichia coli K12) and aryl-sulfatase were obtained from Roche Diagnostics (Mannheim, Germany). Milli-Q water was cleaned in a Millipore System (Synthesis A10). Solid-phase extraction (SPE) cartridges (Strata XL; 200 mg, 3 ml) were obtained from Phenomenex (Allerød, Denmark). All chemicals were of analytical or HPLC grade and all chemicals, solutions and laboratory wares were checked for contamination with parabens before use.
Preparation of Standards
Stock solutions of each of the native paraben standards and the labeled standard D4-MeP were prepared in volumetric flasks by dilution with 50% acetonitrile to a concentration of 100 μg/ml. Mixtures of all native parabens were prepared from the stock solutions and diluted with 10% acetonitrile to a range of working solutions (0.1–10.0 μg/ml). D4-MeP was diluted with 10% acetonitrile to a final working solutions of 200 ng/ml.
Enzymatic Hydrolysis and SPE of Samples
After thawing, samples were mixed and aliquots of 500 μl were added 1.5 ml 2 M ammonium acetate buffer, pH 6.5 each. 20 μl of the 200 ng/ml D4-MeP solution were then added to all samples as internal standard. Subsequently, 20 μl 100 ng/ml 4-methylumbelliferyl β-D-glucuronide and 20 μl 100 ng/ml 4-methylumbelliferyl sulfate were added to all samples for the control of enzyme reaction (Ye et al., 2006b). Immediately before the incubation 15 μl of a freshly prepared enzyme mixture containing 5 μl β-glucuronidase and 10 μl aryl-sulfatase was added to all the samples, mixed and incubated for 90 min at 37°C in a shaking water bath. The reaction was terminated by adding 1 ml of 3.6 M phosphoric acid.
All samples were purified by the automated SPE (Aspec XL, Gilson, Middleton, USA). The SPE cartridges were preconditioned with 1 ml acetonitrile, 1 ml milli-Q water and 1 ml 0.15 M ammonium acetate buffer, pH 2–3. Subsequently samples were applied to the columns and the tubes were rinsed with 3 ml 0.15 M ammonium acetate also applied to the columns. Before elution the cartridges were washed with 2 ml of 1% phosphoric acid followed by 2 ml of 10% acetonitrile. The compounds were eluted with 1.5 ml pure acetonitrile followed by 1.5 ml ethyl acetate. The eluates were evaporated to dryness (45°C, 5–15 p.s.i. N2) and the residues of total metabolites were resuspended in 200 μl of resuspension solution (1% formic acid in 60% acetonitrile/water).
Preparation of Calibration and Quality Control Samples
All calibration and quality control material were prepared in the three pools of respectively urine, serum and seminal plasma and treated exactly as the real samples as described above. The pools were dispensed into 500 μl aliquots. Pool aliquots for blank (unspiked) samples and calibration samples were deconjugated and purified by SPE and subsequently the calibration samples were spiked with the native paraben solutions to a final concentration of 0.5, 2.0, 10, 50, 100 and 500 ng/ml. Before deconjugation and SPE purification, pool aliquots for quality control were added the native paraben solutions to final concentrations of 5, 10 and 50 ng/ml. An extra set of quality control samples was prepared to determine the SPE recovery; these samples were not added D4-MeP to final concentration of 10 ng/ml until after deconjugation and SPE. All calibration and quality control material were stored at −20°C until use. As solvent blank samples, 2000 μl 2 M ammonium acetate buffer was used and treated as described above.
For all detection and quantification of analytes, a high performance liquid chromatograph (LC) (Surveyor, ThermoFinnigan, San Jose, CA, USA) coupled with a tandem mass spectrometer (MS/MS) (Finnigan TSQ Quantum Ultra triple quadrupole mass spectrometer, Thermo Electron Corporation, San Jose, CA, USA) was used in combination with the X-calibur software program. The LC–MS/MS system was equipped with an electrospray ion source (ESI) and was running in negative mode. The injection volume was 20 μl on a Synergi 4U fusion-RP 80A column (75 × 2.0 mm × 4 μm) (Phenomenex, Anschaffenburg, Germany) equipped with a filter (frit ss blk, A 120 × , 5 μm pore size from Upchurch Scientific distributed by Mikrolab, Aarhus, Denmark) in front of the column. The flow rate was 300 μl/min and the column temperature was 25°C. Solvents were A: 0.1% acetic acid in water and B: 0.1% acetic acid in acetonitrile. Table 1 shows the solvent programming and Figure 1 shows MS transitions. The optimized MS/MS interphase settings used were: spray voltage, 3000 V; sheath gas (N2) pressure, 55 psi; auxiliary gas (N2) pressure, 10 psi; capillary temperature, 350°C; collision gas (Ar) pressure, 1.0 mTorr; tube lens offset, 80 V; and for the formation of the product ions the collision energy was set to 20 V.
Operation and Quality Control Procedure
For validation of the method accuracy the recoveries of the SPE and recoveries of native standards spiked in pools of urine, serum and seminal plasma were determined. Analytical batch for urine, serum or seminal plasma, respectively, included five repeated sequences of a solvent blank sample, a blank pool sample and the quality control pools spiked with 5, 10 and 50 ng/ml of the native paraben solution. In the same five sequences pool samples spiked with 10 ng/ml of the native parabens and to which the D4-MeP solution (20 μl, 200 ng/ml) was added after SPE were also included to enable the determination of SPE recovery. The method accuracy was expressed as the percentage of expected levels measured in the quality control samples spiked before deconjugation and purification (spike recovery). Furthermore the SPE recovery was determined by calculating the percentage difference in concentration between quality control samples added the labeled standard D4-MeP before deconjugation and purification and quality control samples to which D4-MeP was added after deconjugation and purification.
For validation of the inter- and intra-day precision of the method, each analytical batch included two solvent blank samples, and for each of the three matrices six pool samples; two blank pools samples, two pools spiked with 5 ng/ml and two pools spiked with 50 ng/ml of the native parabens. These quality control samples were evenly distributed among the unknown urine, serum and seminal plasma samples.
In all, daily urine, serum or seminal plasma sample batches, series of calibration samples were analyzed before and after the unknown samples and the quality control samples. In addition, a solution of 4-methylumbelliferone (20 ng/ml) was analyzed once or twice in every batch. A typical daily sample batch contained from 50–80 samples including calibration samples.
Data Analysis and Statistics
The X-calibur software was used for automatic selection and integration of ions of analytes and internal standards in all chromatograms. Peaks were corrected manually if necessary. Only peaks with a signal-to-noise ratio ≥3 were integrated. The ratios between of the peak areas in samples (calibration, control and unknowns) and the corresponding internal standards were calculated and the average calibration curve weighted by the reciprocal of the standard amount (1/x) was constructed in the X-calibur program. For the quantification of control and unknown samples the y-intercept of the linear calibration curve were set to 0 in order to adjust for possible background levels present in the serum pool used to prepare the calibration samples. Thus the concentration in unknown samples were calculated as the area ratios divided by the slope of calibration curve. All validation data were expressed as means±SD or as the relative SD (RSD∼(SD/mean) × 100). The limit of detection (LOD) was calculated as 3S0, where S0 was the value of the SD as the concentration approaches zero. S0 was determined as the point where the best-fit line of the SD of five repeated sets of the lowest four standards versus the known standard concentration cross the y-intercept (Blount et al., 2000). To describe the levels of parabens in the urine, serum and seminal plasma samples, 25th, median (50th), 75th percentiles and the maximum concentration were computed. To analyze for correlations between the different parabens in each matrices and between the single parabens in different matrices Spearman correlations were computed. In some of the samples the paraben concentration was below LOD and in others the concentration was not detectable. For correlation analyses all data were included and not detectable data were all set to 0.01, which was half of the lowest LOD. P-values<0.05 were considered as statistically significant. All statistical analyses were carried out using SPSS (SPSS for Windows, version 17.0, SPSS Chicago, IL, USA).
Method Characteristics and Validation
Extracted ion chromatograms of a urine pool sample spiked with 50 ng/ml of the native paraben standards, their retention times and precursor/product ions in negative mode [M–H]− are shown in Figure 1. The precursor/product ion pair for D4-MeP (not shown) was m/z 155 → 96 and D4-MeP had retention time analog to MeP.
The concentrations of all parabens were calculated in relation to D4-MeP, as this was the only commercially available internal standard of the parabens at the time when analyses were carried out. Owing to matrix effects in especially serum and seminal plasma, all calibration samples were prepared in the same matrix as the unknown samples, urine, serum and seminal plasma, respectively. The endogenous levels of the analytes in the pooled matrices were for most of the analytes <1 ng/ml except the concentration of MeP in the serum pool which was 11.0 ng/ml. However, the calibration curves of standards spiked in urine, serum or seminal plasma all gave good linearity (correlation coefficients (r2)>0.99) in the full measurement range (0.5–500 ng/ml).
The LOD was determined for the parabens in all three matrices (Table 2). Under the condition that 500 μl of sample were purified and resolved in 200 μl after purification (resulting in a 2.5-fold concentration), LODs were ≤0.41 ng/ml for all the parabens in all matrices.
Very good SPE and spiked recoveries were obtained for nearly all parabens in all three matrices (Table 2). The method accuracy ranged from 85% to 110% with SD below 10 for most of the parabens. Most important was that acceptable recoveries could be obtained in the lowest spike level of the parabens (5 ng/ml) in serum and seminal plasma, because very low concentrations of the parabens were expected in real-life serum and seminal plasma samples. In the lowest spike level only the spike recovery of EtP (79.7%) and n-PrP (82.7%) in serum and EtP (78.0%) in seminal plasma were lower than 85%.
The precision of the method was determined by repeated measurements of 24 urine, 18 serum and 14 seminal plasma quality control samples spiked in a low and a high level of the analytes. The spiked quality control samples were measured over a period of 2 months in respectively 12, 9 and 7 different batches (Table 3). The RSD expressed in percentage reflecting the intra- and inter-day variability, ranged from 2.8% to 29.2%. In general, the highest RSD values were found among the parabens in the low spike level, which could be caused by the use of D4-MeP as labeled standard for all the parabens. However, the RSD values were below 10% for most of the analytes in all three matrices, which demonstrated a good precision of the method over time.
Parabens Levels in Human Samples
Urine, serum and seminal plasma from 60 young Danish men were analyzed and the total levels of parabens (sum of unconjugated, deglucuronidated and desulfated parabens) were determined (Figure 2). All parabens except BzP were measurable in most of the urine samples, with MeP excreted in urine in highest amounts (median=17.7 ng/ml) (Table 4). The urinary excretion of n-PrP, EtP and n-BuP were about 5, 10 and 100-fold lower, respectively. In a few of the urine samples the concentration of MeP was higher than the linear range of the calibration curves. These samples were re-analyzed after two or four-fold dilution to ensure that the concentration was correctly determined.
In serum and seminal plasma the levels of all the parabens were much lower than in urine (Table 4). In serum MeP and n-PrP were detected in most of the samples, whereas the levels of the other parabens only were above LOD in few of the samples. Apart from BzP, the other four parabens were detected in several of the seminal plasma samples but with very low median levels below 1.00 ng/ml. Also in serum and seminal plasma was MeP observed in highest concentration followed by n-PrP.
Correlations Between Parabens and Matrices
Highly significant positive correlations were observed between all four parabens excreted in urine, all with P-levels <0.001. In Figure 3a the correlation between MeP and the three other parabens are shown. In serum MeP and n-PrP were >LOD in most of the samples and a significant correlation between them was observed (Figure 3b). EtP was only >LOD in 18 samples; however, the concentration of EtP in serum also correlates significantly to the MeP concentration (Figure 3b). No other correlations between the parabens in serum were observed. Similar to urine, MeP, EtP, n-PrP and n-BuP in seminal plasma all were significantly correlated to each other. In Figure 3c the correlations of MeP to the other measurable parabens in seminal plasma are shown.
Urine, blood and seminal fluid were sampled from each of the men within 1 h and for those parabens that could be measured the concentration correlates significantly between the three different matrices (Figure 4a–d).
All of the analyzed parabens except BzP were found in most of the 60 urine samples from the young Danish men. BzP is the most hydrophobic of the parabens we analyzed for and it is possible that the lack of BzP in urine could be due to it being excreted in urine as the water soluble but non-specific metabolite p-hydroxybenzoic acid rather than in its parent form. However, also in serum and seminal fluid were the BzP levels <LOD in the majority of the samples indicating that the exposure to this parabens is much lower than the other parabens. For MeP, EtP and n-PrP the maximum levels measured were more than 50–100-fold higher than the average levels measured suggests a wide range of exposure among participants.
Compared with previous studies of urinary concentration of parabens in US male and female adults (Ye et al., 2006a) the median urinary concentration of the parabens were in general about 2.5-fold lower in our Danish men, except of EtP, which was twice as high in the Danish men. This may represent a country difference in use of parabens between the USA and Denmark. However, the US study also included women, whereas our study did not, and thus the difference in excretion pattern may also reflect a difference in exposure between women and men.
As far as we know parabens have never before been measured in human seminal plasma. Traces of parabens in seminal plasma were expected, because our previous rat study showed that parabens were distributed to several fluids and tissues (Frederiksen et al., 2008). However, it was a surprise that several of the parabens could be detected in seminal plasma, and for n-PrP and n-BuP the levels were even higher in seminal plasma than in serum. Adverse effects of PrP and BuP on male reproduction such as decreased serum testosterone, sperm concentration and motility of the spermatozoa have been observed in animal studies (Oishi, 2001, 2002, 2004; Kang et al., 2002; CIR Expert Panel, 2009), whereas MeP and EtP do not seem to have the same effects. We cannot say whether the parabens we measured in seminal plasma derived from fluids coming from the testis together with the spermatozoa and thus reflect a direct exposure of the testis or whether they derived from seminal fluid coming from the accessory glands. But irrespective of the route, it is concerning that we in seminal plasma observed relatively high concentration of n-PrP and that a high number of samples also contained measurable levels of n-BuP, as these two parabens are suspected to affect male reproduction (Oishi, 2001, 2002). In a previous study we found a higher concentration EtP and n-BuP in rat amniotic fluid compared to maternal serum. Furthermore the concentration in amniotic fluid was proportional with dose, whereas the concentration in maternal serum were similar in all dose groups suggesting that continuous exposure during pregnancy maybe lead to an accumulation of the parabens in amniotic fluid (Frederiksen et al., 2008). We speculate whether parabens also accumulate in seminal plasma and whether seminal plasma paraben concentrations, especially n-PuP and n-BuP, may have any impact on sperm quality in adult men as seen in rodents (Oishi, 2001, 2002). Further studies of the correlation between paraben exposure and male reproductive parameters such hormone levels and semen quality are needed to answer this questions.
Significant positive correlations between the different parabens were observed, indicating that men, who are exposed to high levels of one of the parabens, are likely to also have relatively high exposure to the other parabens. This may be owing to the fact that parabens often are used in combination in consumer products (CIR Expert Panel, 2009). However, the question remains whether a general higher urinary excretion of parabens seen in some men is truly due to higher exposure. Considering that parabens are believed to rapidly metabolize into the non-specific metabolite p-hydroxybenzoic acid, an alternative explanation for a general higher urinary excretion of parent parabens in some men might be that these men have a less effective paraben metabolism.
Also between the three different matrices we did observe significant positive correlations between the paraben concentrations. This indicates that urinary paraben levels can be used as a biomarker for the circulating levels of parabens. As urine in general contained higher levels of parabens and is easier to sample, it appears to be the preferred matrix to study human exposure. Our results show, however, that serum or seminal plasma parabens levels also could be used as biomarker of paraben exposure.
The levels of parabens we measured in urine, serum and seminal plasma from healthy, young Danish men presumably reflect only a fraction of human parabens exposure, as most of the parabens taken up are believed to be rapidly metabolized into harmless and unspecific metabolites. The fraction of the parent compound of parabens excreted in urine may depend on the route of exposure. Uptake of parabens through skin may thus result in more parent compound avoiding degradation in the liver before urinary excretion compared with oral uptake. The presence of parent compounds in the three different human matrices nevertheless indicates that parabens-uptake results in the exposure of human tissues to the potentially harmful parent compounds.
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For skilled technical assistance, the authors thank Ole Nielsen, Department of Growth and Reproduction, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark. The instrumental equipment was financially supported by Velux Fonden and this work was supported by the Danish Research Agency (Grant no. 2107-05-0006) and the Lundbeck Foundation (j.nr. 124/05).
The authors declare no conflict of interest.
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Cite this article
Frederiksen, H., Jørgensen, N. & Andersson, AM. Parabens in urine, serum and seminal plasma from healthy Danish men determined by liquid chromatography–tandem mass spectrometry (LC–MS/MS). J Expo Sci Environ Epidemiol 21, 262–271 (2011). https://doi.org/10.1038/jes.2010.6
- endocrine disruptor
- human urine
- human serum
- seminal plasma
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