Selenium exposure in subjects living in areas with high selenium

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Selenium exposure in subjects living in areas with high selenium
Environment International 40 (2012) 155–161
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Environment International
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / e n v i n t
Selenium exposure in subjects living in areas with high selenium concentrated
drinking water: Results of a French integrated exposure assessment survey
Barron Emmanuelle a, 1, Migeot Virginie a, b,⁎, Séby Fabienne c, Ingrand Isabelle b, Potin-Gautier Martine d,
Legube Bernard a, Rabouan Sylvie a, b
a
Université de Poitiers, Laboratoire de Chimie et Microbiologie de l'Eau, UMR CNRS 6008, 40, avenue du Recteur Pineau, 86022 Poitiers Cedex, France
Université de Poitiers, Faculté de Médecine et Pharmacie, 6 rue de la Milétrie, 86034 Poitiers Cedex, France
Ultra Traces Analyses Aquitaine, Hélioparc Pau Pyrénées, 2 avenue du Président Angot, 64053 Pau Cedex 9, France
d
Université de Pau et de l'Adour, Equipe de Chimie Analytique Bio-Inorganique et Environnement, UMR CNRS/UPPA 5254, avenue de l'Université, 64000 Pau, France
b
c
a r t i c l e
i n f o
Article history:
Received 23 December 2010
Accepted 10 July 2011
Available online 7 August 2011
Keywords:
Selenium
Drinking water
Monitoring
Intake
Toenail
France
a b s t r a c t
Background: Selenium is an essential element which can be toxic if ingested in excessive quantities. The main
human exposure is food. In addition, intake may be boosted by consumption drinking water containing
unusual high selenium concentration.
Objective: We measured the individual selenium level of people exposed to selenium concentration in
drinking water greater than the maximum recommended limit which is 10 μg/L.
Methods: We carried out a prospective cohort study on 80 adults (40 exposed subjects i.e. living in the
involved area and 40 non-exposed ones i.e. living elsewhere) in western France. We used three different
approaches: (1) direct measurement of ingested selenium by the duplicate portion method, (2) dietary
reconstitution with a food frequency questionnaire (FFQ) and (3) evaluation of the individual selenium status
by measuring the selenium content in toenail clippings. Analyses were performed by inductively coupled
plasma-mass spectrometry. The association between toenail selenium concentration and area of residence
was analyzed using linear regression with repeated measurements.
Results: We estimated selenium intake from FFQ at 64 ± 14 μg/day for exposed subjects as opposed to 52 ±
14 μg/day for the non-exposed ones. On the basis of 305 duplicate diet samples, average intake was estimated
at 64 ± 26 μg/day for exposed subjects. Area of residence (p = 0.0030) and smoking (p = 0.0054) were
independently associated with toenail selenium concentration.
Conclusion: Whatever method used for estimating selenium intake, the selenium level in this studied area
with high selenium concentrated drinking water is much lower than in seleniferous areas.
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Essentiality and toxicity of selenium for humans are well known
(Césarini 2004; Dodig and Cepelak 2004; Navarro-Alarcon and
Cabrera-Vique, 2008; Papp et al., 2009; Simonoff and Simonoff
1991; Tinggi 2008).
Insufficient intakes have been linked to serious health effects, such
as dilated cardiomyopathy in Keshan disease (Levander and Beck
1997; Liu et al., 2002; Yang and Zhou, 1994; Zhang et al., 2010) and
osteoarthritis in Kashin Beck disease (Suetens et al., 2001). These
⁎ Corresponding author at: Université de Poitiers, Faculté de Médecine et Pharmacie,
6 rue de la Milétrie, 86034 Poitiers Cedex, France. Tel.: + 33 549 454 359; fax: + 33 549
454 073.
E-mail addresses: [email protected] (B. Emmanuelle),
[email protected] (V. Virginie).
1
Present address: Université Victor Segalen, UFR Sciences Pharmaceutiques, FRE
CNRS 3396, 146 rue Léo Saignat, 3076 Bordeaux cedex, France.
0160-4120/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.envint.2011.07.007
disorders have been observed in areas with poor selenium soil (said to
be seleniprive). Minimal requirement is today estimated at 20 μg/day
(Thomson 2004).
But, selenium can also be toxic if ingested in excessive quantities in
the long run (i.e. in seleniferous area). The most frequent symptoms
described are skin and scalp lesions, nails and hair abnormalities
including loss (Hira et al., 2004; Srivastava et al., 1995; Thérond et al.,
1997; Yang and Zhou, 1994).Yang and others have monitored
selenium exposure and clinical symptoms of subjects living in
seleniferous area. They proposed, for safety, a maximum safe daily
dietary intake at 400 μg/day (Yang and Zhou 1994).
Health effects of intermediate levels of intake are less certain
therefore conflicts rise up about the optimal intake (Combs 2005;
Dodig and Cepelak 2004; Fairweather-Tait et al., 2010a; NavarroAlarcon and Cabrera-Vique 2008; Rayman et al., 2008).
The World Health Organization (WHO) has set the No Observed
Adverse Effect Level (NOAEL) at 240 μg/day (4 μg/kgBW/day) and has
recommended consequently a maximum upper limit of 10 μg/L for
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B. Emmanuelle et al. / Environment International 40 (2012) 155–161
selenium in drinking water (which corresponds to about 10% of the
NOAEL) (WHO 1996). This limit of 10 μg/L has been adopted in the
European regulations (Directive 98/83/CE — 03.11.98) and translated
into French law (Ministère de la santé et des solidarités 2007).
The major source of selenium is food but intake from beverage is
highly neglected (Rayman, 2008). Most of drinking water concentrates selenium less than 1 μg/L (Conde and Sanz Alaejos 1997).
However when water gets down through particular geological
formations (i.e. rich in selenium), selenium content can be increased.
La Vienne, western France, is the case where eight drinking water
stations, supplying 40,000 to 55,000 inhabitants contain up to 40 μg/L of
selenium (Barron et al., 2009). We carried out a study to quantify
selenium intake of Vienne inhabitants using three different approaches:
(1) direct measurement of ingested selenium by the duplicate portion
technique, dietary reconstitution based on a food frequency questionnaire (FFQ) and the use of a biological marker.
2. Material and methods
2.1. Study design
We carried out a prospective cohort study over 9 months (October
2005 to July 2006).
2.2. Study population
We recruited 80 subjects: 40 “exposed” adults, i.e. living in the
studied area for at least 2 years, and 40 “non-exposed” subjects, i.e.
living outside the studied area for at least 2 years. The exposed group
was representative of the residents in terms of age, sex and socioprofessional status. The subjects in both groups were matched for the
same criteria. All participants gave written informed consent.
Exclusion criteria were taking a selenium supplement and intending
to leave the area within the coming year. Participants completed a
pre-inclusion questionnaire, four food frequency questionnaires
(FFQ) (one per season) and a health questionnaire. They provided
two samples of toenail clippings (Slotnick and Nriagu 2006). The
exposed group also provided a duplicate of what they had eaten and
drunk over 2 days per season. The study was approved by the relevant
ethics committees, which advocate that all data remain confidential
and anonymous.
2.3. Data collection
All data collected and the sampling strategy were evaluated in a
pre-test involving three subjects over two consecutive days.
2.3.1. Self-administered questionnaires
The pre-inclusion questionnaire was administered to collect sociodemographic data (age, sex, occupation, income level, educational level,
place and length of residence, intention of moving), anthropometric
measurements (weight, height) and selenium supplement ingestion.
The FFQ (24-hour recall), adapted from a questionnaire validated in
France, enabled us to estimate both total and fractionated (i.e. food vs.
drinking water) selenium intake (Guilbert and Perrin-Escalon 2002).
A health questionnaire was developed from two questionnaires
validated in France (Guilbert et al., 2000; CREDES Centre de Recherche
d'Etude et de Documentation en Economie de la Santé 2004). The
main categories of data collected were current and previous medical
pathology, lifestyle habits such as smoking status, alcohol consumption and physical activity, and Duke health profile (Guillemin et al.,
1997).
2.3.2. Toenail clippings
We collected toenail clippings twice during the study to measure
selenium level (van den Brandt et al., 1993a). The first sampling was
performed three months into the study and the second at the end of
the study (i.e. 6 months after the first collection).
2.3.3. Duplicate diet portions
Exposed subjects duplicated everything they ingested over two
entire days (Gay 2000) in each season. A meeting was organized to
explain the context, objective and schedule of the study (Kazutoshi et
al., 2003; Kazutoshi et al., 2004). Each participant received compensation (15 euros) for each duplicate day (Lightowler and Davies
2002).
2.4. Data analysis
2.4.1. Food frequency questionnaire (24-hour recall)
Based on this questionnaire, the daily selenium intake was
reconstituted by adding together the amount contained in each
item of food (or in beverage). The selenium content of foods was
calculated from the French table of selenium concentration of foods
(Leblanc et al., 2005). The selenium content of water was fixed at
1 μg/L for subjects in the non-exposed group (Simonoff and Simonoff
1991) and at the median selenium concentration of the municipal
water supply system for the exposed group (Barron et al., 2009). The
weight of each portion of food was defined from nutritional
recommendations (GPEM/DA 1999). The liquid quantity was defined
as 150 mL/glass.
2.4.2. Duplicate diet portions and toenail clipping samples
2.4.2.1. Sample preparation. All solutions were prepared with ultrapure
water (18.2 MΩ cm) obtained from a Millipore Milli-Q water purification system (Bedford, MA, USA). After collection, toenail clippings were
cleaned to minimize external contamination. Each set of clippings was
sonicated first in a detergent [triton ×100, 1%, Sigma-Aldrich (SaintLouis, MO, USA)] and then in ultrapure water. Between these two steps,
the clippings were rinsed three times in ultrapure water. They were
then air-dried for several days and placed in a dry place for 24 h to
ensure uniform humidity between samples. Duplicate diet portions
were collected in polythene containers cleaned in 10% nitric acid and
rinsed in ultra pure water before use. These samples were kept in a cool
place until their preparation for analysis (household refrigerator,
transport to laboratory in cool boxes and subsequent storage in a
cold room [5± 2 °C]). At the laboratory, inedible parts were first
discarded (e.g. bones, fruit stones) and then food and drinks were
weighed. Food and drink corresponding to the same day were mixed
together using a grinder (Bermixer B2000, 4400 W Electrolux).
Subsamples (about 30 g) were collected, weighed and stored at
−20 °C before lyophilisation (Freeze-Dryer Christ Alpha).
2.4.2.2. Sample digestion. Duplicate diet and toenail samples were
digested using a graphite heating block system (DigiPREP system with
temperature control [SCP Science, Quebec, Canada]). For duplicate diet
portions, 1 g of sample was accurately weighed in a 50 mL polypropylene tube. Four milliliters of HNO3 (Baker-INSTRA, 70%) were then
added and this mixture was left overnight before the addition of 2 mL of
H2O2 (Baker analyzed, 30%), obtained from Baker (Phillipsburg, NJ,
USA). The tubes were then tightly sealed with a polypropylene screw
cap and heated from room temperature to 45 °C within 20 min. This
temperature was maintained for 40 min. A further temperature rise to
80 °C was then effected, again within 20 min, and this temperature was
maintained for 220 min. After cooling, digests were diluted to 50 mL
with ultrapure water before total selenium analysis. For duplicate diet
portion samples, all digestions were performed in duplicate (independent aliquots). For nail samples, 2 mL of HNO3 were added to the
collected sample (about 100–200 mg) and this mixture was left
overnight before the addition of 0.5 mL of hydrogen peroxide. Digestion
was performed using the same temperature program as described
B. Emmanuelle et al. / Environment International 40 (2012) 155–161
above for food samples, except that the step at 80 °C lasted for 40 min
instead of 220 min, because this was easily enough time to dissolve nail
clippings. Finally, samples were diluted to 10 mL with ultrapure water
before total selenium analysis. For nail samples, only one digestion per
sample was performed because of the small quantity. For each digestion
run, two blanks and two Certified Reference Materials (CRMs) with a
matrix close to that of the samples under study were processed at the
same time as the real samples: bovine muscle BCR 184 (0.3 g) (IRMM
[Geel, Belgium]) and dogfish muscle DORM-2 (0.2 g) (NRCC [Ottawa,
Canada]) for digestion of food-based samples and 2 replicates of hair
sample BCR 397 (0.1 g) (IRMM [Geel, Belgium]) for nail samples. Since
there was no CRM for nail clippings, a keratin-based hair sample with a
very similar matrix was used.
2.4.2.3. Sample analysis. Total selenium was analyzed in all the digested
extracts by inductively coupled plasma-mass spectrometry (ICP-MS)
(Agilent model 7500ce, Tokyo, Japan) using a spectrometer equipped
with an octopole reaction cell. For sample introduction, a microconcentric nebulizer (Glass Expansion, Romainmotier, Switzerland) was
fitted with a double-pass Scott spray chamber (2 °C). ICP-MS
measurement conditions (nebulizer gas flow, RF power and lens
voltage) were optimized daily using a multi-element solution (Li, Y and
Tl). Selenium detection was achieved after removing the Ar2+
interferences using H2 reaction gas (octopole bias −18 V; quadrupole
bias −17 V) in the octopole reaction cell. Appropriate Internal Quality
Control (IQC) parameters were used to evaluate the validity of the
analytical process and to check that no outliers occurred during routine
analysis sequences. Quantification of total selenium was performed
using the standard additions method to avoid any matrix effect and
this procedure was regularly performed during analysis (every 10
samples); CRMs were also regularly analyzed throughout the analytical
sequence. Their use enabled us to validate and control the method on a
routine basis (Shewhart control charts). Detection limits were
estimated at 1.5 μg kg−1 and 2.2 μg kg−1 (dw) for food and toenail
samples, respectively, based on the International Union of Pure and
Applied Chemistry's harmonized definitions. Quantification limits were
estimated at 4.5 μg kg−1 and 7.0 μg kg−1 (dw) for food and toenail
samples, respectively. Repeatability, as estimated from analysis of 6
different digested aliquots and expressed as % relative standard
deviation, ranged from 1 to 2%.
The amount of selenium in a duplicated day was calculated by
taking the mean of the content obtained from two different
mineralizations of the same duplicate portion. Intake was standardized by body weight as recommended by Kroes et al. (2002).
However, this standardization is not systematically performed in
the literature, because studies from public establishments such as
hospitals, canteens and army barracks do not collect the weight of
subjects providing duplicate portions. For the purpose of making
comparisons, our results were also expressed in μg/day.
2.5. Statistical analysis
We estimated that to demonstrate a difference in toenail
selenium concentration corresponding to a difference in selenium
intake of 32 μg/day between the exposed and non-exposed populations (Longnecker et al., 1993), it would be necessary to include 40
subjects in each group (allowing for a significance of 5%, a power of
80% and a loss to follow-up of 20%). Results are expressed as mean ±
standard deviation.
Normal distribution of data was verified using the Kolmogorov–
Smirnov test. Thus, we carried out log transformations for selenium
intake and selenium toenail concentration and calculated geometric
means and corresponding 95% confidence intervals (CI). We used
Student's t-test for matching data for quantitative variables and
McNemar's test for qualitative variables. Differences were considered
significant at the level of p ≤ 0.05. We checked the correlation
157
between the two methods of intake estimation (FFQ and duplicate
diet portions) using Pearson's correlation coefficient.
The dependent variable was toenail selenium concentration (from
toenail clippings collected at the end of the study). The variable of
interest was the subject's place of residence. The independent
variables were educational level (elementary, college, secondary,
university or equivalent), household size (≤2 persons, N2), smoking
status (smoker, non-smoker), alcohol use (at least twice a week,
maximum once a week), physical activity (at least once during the
two previous weeks, less), body mass index (b20, 20–24, 25–30, N30),
Duke score (Guillemin et al., 1997), annual frequency of homeproduced and locally produced food consumption (N5; [4–5]; [2–3];
b2) corresponding to the sum of the frequency of consumption
recorded for each season (i.e. 0 = maximum once a week; 1 = maximum 3 times a week; 2 = maximum every day), and total selenium
intake (average of the results from the four seasons as estimated by
FFQ). To perform our analysis, we used SAS's PROC MIXED procedure
for repeated measures to take into account the seasonal effect.
Independent variables were included in the initial regression model if
they were associated with selenium toenail concentration at a pvalue b 0.20. From the initial regression model, variables were selected
using a stepwise descending process. We tested the first-order
interactions in the final model. We captured data derived from
questionnaires with EPI-Info version 3.3.2. The controls and statistical
analysis were performed using SAS for Windows, version 8.0 (SAS
Institute Inc., Cary, NC, USA).
3. Results
3.1. Study population
Eighty volunteers were selected to participate in the study. One non-exposed
subject left the study. Data from his matched exposed subject were excluded from the
analysis. Analyses were thus performed on 78 subjects. The distribution of age, sex and
occupational group within the exposed group and the local residents was similar. Mean
age was the only independent variable to differ significantly between the two study
groups (Table 1).
3.2. Daily selenium intake
3.2.1. Estimation from FFQ
Selenium intakes from food observed in exposed and non-exposed subjects over
the four seasons are shown in Fig. 1. We observed no significant difference between the
two groups (0.70 ± 0.18 μg/kgBW/day vs. 0.74 ± 0.25 μg/kgBW/day respectively,
p = 0.53) (equivalent to 48 ± 12 μg/day vs. 50 ± 14 μg/day) (Table 2). We observed
no seasonal effect (p = 0.07).
We observed a significant difference in selenium intake from drinking water
between the two groups as shown in Fig. 2 (0.23 ± 0.13 μg/kgBW/day vs. 0.024 ±
0.010 μg/kgBW/day respectively, p b 0.0001). Thus, selenium intake from water
represented on average 24% (0–57) of total intake for exposed subjects as opposed
to only 3% (1–8) for non-exposed subjects.
Finally, we estimated total selenium intake (from food and beverage) from the FFQ
at 0.94 ± 0.22 μg/kgBW/day for the exposed group (64 ± 14 μg/day) and 0.77 ±
0.25 μg/kgBW/day (equivalent to 52 ± 14 μg/day) for the non-exposed group.
3.2.2. Estimation from duplicate diet portions
We collected 305 duplicate diet portions. Samples provided by one subject were
excluded because of systematic and obvious disregard of quantities. Average intake was
0.94 ± 0.37 μg/kgBW/day (0.25–2.73) (64 ± 26 μg/day). The correlation coefficient
between intake estimated by FFQ and by duplicate diet portions was calculated at
0.36 (p b 0.0001).
3.3. Toenail selenium concentration
Toenail selenium concentration according to the characteristics of the 78
participants is shown in Table 3. The multivariate analysis showed that area of
residence (p = 0.0030) and smoking (p = 0.0054) were independently associated with
toenail selenium concentration (Table 4) without interaction (p = 0.50). We estimated
the difference in toenail selenium concentration between exposed and non-exposed
subjects at 70 μg/kg (95% CI [27; 110]) and between smokers and non-smokers at
− 111 μg/kg (95%CI [− 201; −33]) (Table 4).
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B. Emmanuelle et al. / Environment International 40 (2012) 155–161
Table 1
Socio-demographic characteristics, anthropometric characteristics and lifestyle habits
of the 78 participants by area of residence.
Age (years)
Length of residence (years)
Exposed (n = 39)
Mean ± SD
Mean ± SD
p
50.5 ± 13.0
27.7 ± 19.2
52.7 ± 15.0
27.7 ± 18.5
0.0011
0.33
n (%)
n (%)
p
1.00
19 (48.7)
19 (48.7)
19 (48.7)
19 (48.7)
1 (2.6)
1 (2.6)
4 (10.3)
2 (5.1)
8 (20.5)
5 (12.8)
3 (7.7)
15 (38.5)
1 (2.6)
2 (5.1)
5 (12.8)
1 (2.6)
8 (20.5)
4 (10.3)
3 (7.7)
15 (38.5)
2 (7.4)
7 (25.9)
9 (33.3)
9 (33.3)
12
3 (8.6)
13 (37.1)
12 (34.3)
7 (20.0)
4
6 (17.7)
13 (38.2)
8 (23.5)
7 (20.6)
5
15 (38.5)
10 (25.6)
9 (23.1)
5 (12.8)
0
22 (56.4)
17 (43.6)
22(56.4)
17 (43.6)
2 (5.1)
20 (51.3)
14 (35.9)
3 (7.7)
1 (2.6)
20 (51.3)
17 (43.6)
1 (2.6)
10 (25.6)
29 (74.4)
0
3 (8.1)
34 (91.9)
2
21 (56.8)
16 (43.2)
2
18 (48.7)
19 (51.4)
2
6 (16.2)
31 (83.8)
2
9 (24.3)
28 (75.7)
2
1.00
0.42
0.51
1.00
0.63
0.092
0.63
0.55
1
.5
0
selenium intake from food
(µg/day/kg body weight)
1.5
Sex
Male
Female
Socio-professional category
Farmer
Shopkeeper
Executive
Professional
White-collar worker
Blue-collar worker
Other
Retired
Income level
450 b income ≤ 1000 euros
1000 b income ≤ 2000 euros
2000 b income ≤ 3000 euros
N 3000 euros
Missing data
Educational level
Elementary
College
Secondary
University or equivalent
Missing data
Household size
1–2 people
≥3 people
BMI (kg/m−2)
b 20
20 ≤ BMI b 25
25 ≤ BMI b 30
≥30
Tobacco
Smoker
Non-smoker
Missing data
Alcohol consumption
Maximum once a week
At least twice a week
Missing data
Physical activity
At least one activity
No activity
Missing data
Non-exposed (n = 39)
spring
summer
exposed
autumn
winter
unexposed
Fig. 1. Distribution of selenium intake from food as estimated from the food frequency
questionnaire stratified by season and exposure.
4. Discussion
This survey studied selenium status among residents exposed to
high selenium concentrated drinking water. Whatever method used
for estimating selenium intake, the selenium level in this studied area
is much lower than in seleniferous areas (Hira et al., 2004; Longnecker
et al., 1991). This study is the first one to combine three different
methods of measuring selenium exposure in a French population.
Estimation of daily selenium intake provides valuable insight into
the amount of selenium ingested by the subjects (Longnecker et al.,
1991).
The FFQ did not show any difference between food intakes in the
two groups. This data may indicate that subjects had no particular
eating patterns explaining a particular selenium level (for example,
high consumption of fish or meat). As well as other studies, we found
no seasonal variation (Swanson et al., 1990; Taylor et al., 1987). On
the contrary, intakes from drinking water were significantly different
between the two groups. In the non-exposed subjects, these intakes
were negligible as in the general population (Barclay et al., 1995;
Santé, 1986; WHO 1996). Estimation of total intake was similar to
French (about 45 μg/day) and English populations (between 38 and
57 μg/day) (AFSSA., Agence Française de Sécurité Sanitaire des
Aliments, 2004). In the exposed subjects, drinking water consumption
explained increase in total selenium intake. Nevertheless, this intake
remained lower than in an American population (between 74 and
126 μg/day) with the same method (AFSSA., Agence Française de
Sécurité Sanitaire des Aliments, 2004). It is also lower than in a
selenium-rich area of India where the population had selenium
toxicity signs (on average 475 μg/day for men and 632 μg/day for
women) (Hira et al., 2004).
Duplicate portion sampling is the right method because it reflects
actual selenium intake (Kroes et al., 2002; Lightowler and Davies
2002). The average selenium intake in the exposed subjects was lower
than the recommended level of 1 μg/kgBW/day (Martin 2000) and
lower than the toxicity threshold fixed by WHO (4 μg/kgBW/day)
(NOAEL) (WHO 1996). These values were comparable with those
determined in France (66 μg/day) (Noel et al., 2003) and in other
European studies (Murphy et al., 2002; Robberecht et al., 1994).
The correlation between the two methods of intake estimation
was acceptable. The FFQ does provide a good measure of average
selenium intake. However, it resulted in a lower standard deviation
than the duplicate portions method, neglecting the extreme values.
The duplicate portion sampling remains the reference method but
requires time and effort. It requires also an accurate and reliable
method of measurement, which is difficult to achieve in the case of
selenium. In the SU.VI.MAX study (Hercberg et al., 2004), the use of
models or visual images (photographs) of food eaten led to the
publication of the first manual of photos for the estimation of
quantities. The use of such a manual might have improved the
accuracy of the estimation of weights of portions and hence of
selenium intake, but would have made the study more cumbersome.
In this study, we also chose to measure the selenium concentration
in toenail clippings, which was significantly higher in exposed than
non-exposed subjects. However, whatever group, the values were
comparable to French (median [5th–95th percentile]: 620 μg/kg
[440–910]) (Goulle et al., 2009) and European subjects (between
500 and 700 μg/kg) (Bergomi et al., 2002; Krogh et al., 2003; van den
Brandt et al., 1993a). They were lower than in Canada, in USA (mean
[5th–95th percentile]: 844 μg/kg [654–1110]) (Satia et al., 2006; Xun
et al., 2011) and in the seleniferous area of South Dakota whose
population however presented no signs of selenium toxicity (between
806 and 3824 μg/kg) (Longnecker et al., 1991). Thus, statistically
significant differences were not clinical significant. Other biological
markers such as blood selenium concentration, could have been used
(Hambidge 2003; Laclaustra et al., 2009; Mayne 2003). But nails are
biological tissues easy to collect and keep; they are widely used in
B. Emmanuelle et al. / Environment International 40 (2012) 155–161
159
Table 2
Distribution of selenium intake as estimated from food frequency questionnaire.
Non-exposed (n = 39)
−1
−1
Food (μg/kgBW /day )
Beverage (μg/kgBW−1/day−1)
Exposed (n = 39)
Mean ± SD
Adjusted mean⁎ ± SD
Mean ± SD
Adjusted mean⁎ ± SD
Difference mean
95% CI
p
0.74 ± 0.25
0.028 ± 0.011
− 0.1551 ± 0.0164
− 1.5825 ± 0.0380
0.70 ± 0.18
0.24 ± 0.13
− 0.1696 ± 0.0164
− 0.7170 ± 0.0380
− 0.0145
0.8655
− 0.0615; 0.0324
0.7565; 0.9744
0.53
b 0.0001
⁎ Adjusted on season
.6
.4
.2
0
selenium intake from beverage
(µg/day/kg body weight)
.8
epidemiological studies (Cardoso et al., 2010; Longnecker et al., 1991;
Steevens et al., 2010; Swanson et al., 1990) and correlation with
intake has been demonstrated in volunteers taking selenium
supplements (Longnecker et al., 1993). Nevertheless, the usefulness
of a biological marker depends upon the existence of an accurate and
reliable method for its chemical analysis. It also requires an
understanding of the confounding factors that need to be taken into
account in the analysis of the results. Hunter and others observed that
selenium concentration in toenails decreased with age (Hunter et al.,
1990). This could be responsible of an underestimation of selenium
concentration in exposed group which is older. But, the age difference
between the two groups was less than five years. With the exception
of Hunter's study, most of the studies show there is no link between
age and toenail selenium concentration (Krogh et al., 2003; Morris et
al., 2006; Satia et al., 2006; Swanson et al., 1990; van den Brandt et al.,
1993a).
We found that smoking led to a diminution of selenium
concentration in toenail clippings, this finding being consistent with
other studies (Hunter et al., 1990; Krogh et al., 2003; Morris et al.,
2006; Swanson et al., 1990; van den Brandt et al., 1993b; Xun et al.,
2011). Some authors have demonstrated a relationship between the
diminution of selenium concentration and the number of cigarettes
smoked (Hunter et al., 1990). Several hypotheses have been put
forward to explain this finding: lower levels of intake in the diet,
higher levels of antioxidant metabolism provoked by an increased
production of free radicals, an effect of tobacco consumption on the
incorporation of selenium into the nail matrix or increased excretion
of selenium caused principally by its forming a complex with
cadmium (Kayan et al., 2009; Krogh et al., 2003; van den Brandt et
al., 1993a).
However, whatever method for estimating selenium intake is
used, it clearly cannot take into account the fraction assimilated. In
fact, only a part of ingested selenium is assimilated by the organism.
This amount can vary widely as a function of several factors
including selenium speciation, nature of the food and meal composition (Cabanero et al., 2004; Dumont et al., 2006; Fairweather-Tait
et al., 2010b). It is considered that only 50% of total selenium intake
spring
summer
exposed
autumn
winter
unexposed
Fig. 2. Distribution of selenium intake from beverages as estimated from the food
frequency questionnaire, stratified by season and exposure.
is assimilated (Mahapatra et al., 2001). This fact explains why
epidemiological studies rely increasingly on biologic markers of
selenium status (van den Brandt et al., 1993a). This type of data can
take into account multiple origin exposure, reflect previous exposure
and seems altogether to be a better measure than the others
(questionnaire or environmental samples) (Kroes et al., 2002). It is
worth noting that this study did not take into account the selenium
speciation. We know that selenium is mostly present in organic form
in food and inorganic form in drinking water but the toxicity assigned
to each form is not clear (Rayman et al., 2008). Vinceti et al. (2010a,
2010b) hypothesize that intake of selenium through drinking water
(b8 μg/L) might be associated with a risk factor for amyotrophic
lateral sclerosis (ALS). They suggest the need to further investigate
this issue.
5. Conclusions
This integrated exposure assessment survey showed that high
selenium concentrated drinking water increased selenium intakes
and toenail selenium concentrations. We also showed that selenium
toenail concentration could be used as a biomarker to reveal
negligible difference of selenium level. Whatever method used for
estimating selenium intake, the selenium level in this studied area
Table 3
Toenail selenium concentration (μg/kg) according to the characteristics of the 78
participants.
Toenail selenium concentration
Mean ± SD (n)
Non-exposed
Area of residence
532 ± 100 (36)
Educational level
Elementary
495 ± 117 (5)
College
550 ± 130 (12)
Secondary
526 ± 89 (8)
University or equivalent
564 ± 46 (6)
Household size
1 to 2 people
539 ± 107 (19)
≥3 people
523 ± 95 (17)
Tobacco
Non-smoker
558 ± 96 (27)
Smoker
453 ± 66 (9)
Alcohol consumption
At least twice a week
546 ± 115 (15)
Maximum once a week
631 ± 134 (18)
Physical activity
No activity
511 ± 69 (6)
At least one activity
596 ± 91 (9)
BMI (kg/m−2)
b20
594 ± 94 (2)
[20–24]
525 ± 82 (19)
[25–29]
518 ± 128 (13)
N29
627 ± 60 (4)
Consumption of locally produced food⁎
b2
532 ± 115 (9)
[2–3]
535 ± 91 (9)
[4–5]
511 ± 78 (6)
N5
539 ± 115 (12)
Exposed
p
613 ± 117 (36)
0.0030
625 ± 140 (12)
623 ± 95 (10)
568 ± 78 (9)
644 ± 166 (5)
0.0055
599 ± 120 (20)
631 ± 115 (16)
0.0036
626 ± 114 (31)
560 ± 146 (3)
0.0030
521 ± 90 (21)
596 ± 99 (18)
0.0039
536 ± 106 (30)
619 ± 126 (27)
0.0048
524 (1)
609 ± 131 (19)
619 ± 105 (15)
695 (1)
0.0035
567 ± 135 (4)
622 ± 126 (5)
577 ± 68 (9)
647 ± 130 (17)
0.0044
⁎ Corresponding to the sum of the frequency of consumption recorded for each
season (i.e. 0 = maximum once a week; 1 = maximum 3 times a week; 2 = maximum
every day).
160
B. Emmanuelle et al. / Environment International 40 (2012) 155–161
Table 4
Determinants of transformed toenail selenium concentration (μg/kg).
Adjusted geometric mean ± SD
Area of residence
Exposed
Non exposed
Tobacco
Smoker
Non smoker
β
95% CI
p
70
27; 110
0.0030
−111
− 201; −33
0.0054
2.753 ± 0.017
2.696 ± 0.014
2.679 ± 0.027
2.770 ± 0.010
* adjusted on educational level, household size, alcohol consumption, physical activity,
Body mass index, consumption of locally produced food, Duke score and Total selenium
intake estimated from food frequency questionnaire.
with high selenium concentrated drinking water is much lower than
in seleniferous areas. Therefore, these results could contribute to
discuss the maximum recommended limit (Barron et al., 2009).
Acknowledgements
We thank Pascale Pierre-Eugène for technical assistance, the
Direction Régionale des Affaires Sanitaires et Sociales de PoitouCharentes (J.C. Parnaudeau), the Conseil Général de la Vienne, the
towns of Montmorillon and Jouhet, the water boards of Leignes-surFontaine, Coussay-les-Bois and Vicq-sur-Gartempe for their financial
support, Marian Green and Astrid Harvard-de Hauteclocque for
providing the English translation.
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