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Effects of dietary cadmium exposure on osmoregulation and urineconcentration mechanisms of the semi-desert rodent Meriones shawi

Sihem Mbarek,*a Tounes Saidi,a Javier M. Gonz�alez-Costas,b Elisa Gonz�alez-Romerob and Rafika BenChaouacha Chekira

Received 10th February 2012, Accepted 16th April 2012

DOI: 10.1039/c2em30121k

Contamination by cadmium in the environment is of great concern because of its toxicity and threats to

human and animal health. The current study was conducted to investigate the effects of a cadmium

contaminated diet on the osmoregulation and urine concentration mechanisms of the semi-desert

rodent Meriones shawi and eventual accumulation of this metal in vital organs such as the kidneys,

which are directly implicated in water regulation. Originally, we used Differential Pulse Anodic

Stripping Voltammetry (DPASV) to avoid the matrix interference due to the highly organic content in

the biological samples. Our results show that Meriones shawi successfully maintained a homeostasis

state and presented a special adaptation to regulate urine volume during cadmium exposure by

decreasing diuresis and increasing urinary osmolality. The plasma osmolality and hematocrit remained

constant throughout the experiment. The stripping signals of cadmium are linear up to 0.3–100 mg L�1

range, with a detection limit of 0.28 mg L�1. The DPASV technique was useful for easy, fast, selective

and sensitive determination of Cd, which permits working at cellular concentration. This gives us more

information about the chemical form in which Cd is introduced into the organ, as well as the

intracellular Cd quantities. This study has potential importance if this valuable novel animal model,

imitating human and animal environmental chronic exposure to Cd, could serve as an appropriate

terrestrial biomonitor for Cd contaminated sites. These results are encouraging in the context of

developing a low-cost and fast technology for the detection of pollutants and for studying the

impairment caused by their effects.

1. Introduction

For surviving in the continually changing environmental condi-

tions of the desert, behavioral patterns and interactions between

hormonal systems in rodents are important factors in the main-

tenance of homeostasis within a very narrow physiological range.

aLaboratory of Ecophysiology and Food Processes, Higher Institute ofBiotechnology at Sidi Thabet, University of Manouba, 2020 Ariana,Tunisia. E-mail: sihemmbarek@gmail.com; Tel: +216 22 594 677bAnalytical and Food Chemistry Dpt., University of Vigo, 36310 Vigo,Spain

Environmental impact

In Tunisia, cadmium pollution is mainly related to treatment with p

contamination, we targeted a semi-desert rodent as a bio-indicator o

detection and quantification of the metals ions in the biological sam

speciation between the various states of Cd ions and to judge their bi

in the context of developing a low-cost and fast technology for the

physiological disorders.

2212 | J. Environ. Monit., 2012, 14, 2212–2218

This is made possible by homeostatic mechanisms that concen-

trate urine as an indicator of the efficiency of water regulation as

well as an advantage for colonization and survival.1,2 Among

these small mammals,Meriones shawi (Muridae) has a particular

ability to support prolonged dehydration for several months by

obtaining preformed water from food and metabolic water.3,4

However, in the last decades, the continuous anthropogenic

pressure exerted on the environment has constituted a real

environmental problem and might have a negative impact on the

quality of human life.5,6 Therefore, environmental awareness has

grown dramatically and several nations are taking the lead in

implementing laws related to the environment. It is well

hosphate fertilizers across the country. To assess the level of this

f Cd land pollution. The use of electrochemical analysis for the

ples seem to be of particular importance. It allows us undertake

ological availability and toxicities. These results are encouraging

detection of heavy metals and determination of their effects on

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established that heavy metals have the potential to cause serious

harm to the environment and human health if not identified.7For

living organisms, the chemical form, in which metal is introduced

into the environment, is crucial to the investigation as well as to

the quantification process.8,9 The availability and toxicity of

heavy metals in animals and humans are strongly influenced by

the physiological mechanisms of the organism. Thus, many

organisms have developed some elimination methods that help to

excrete even the assimilated quantities of these pollutants.10

Therefore, quantifying the transfer of heavy metals from foods to

mammalian target organs is key to estimate the health risk from

this exposure and will aim to deliver more effective enforcement

of food safety.11

Cadmium (Cd) is one of the most toxic metals present in soil,

water, air, food and cigarette smoke.12 Its flow in ecological

systems arises from industrial waste, phosphate fertilizers,

smelting, mining and fuel combustion. Cd poisoning includes

carcinogenicity,13 immunotoxicity, neurotoxicity and induces,

through the generation of oxygen radicals, oxidative stress.14–16A

large number of studies have reported that Cd exposure produces

marked neuroendocrine changes in animals17,18 and humans.19

Cd has been mentioned as toxic to all tissues such as liver and

kidneys,20 and reproductive organs including the placenta, testis,

and ovaries.21,22 It has been reported that kidneys, which play

a major role in hydro-mineral maintenance, are the critical target

organs with regard to environmental Cd exposure. Several

studies indicate that the main critical effect of cadmium exposure

is kidney dysfunction.23 Excretion of low molecular weight

proteins is characteristic of damage to the proximal tubules of

the kidney. The increased excretion of low-molecular weight

proteins in the urine is a result of proximal tubular cell damage.24

However, excretion of high molecular weight proteins such as

albumin, immunoglobulin G, and glycoproteins is characteristic

of damage to the glomeruli of the kidney.25 This raises the

possibility that water body homeostasis in animals could be

subtly disrupted. For this, we were interested in investigating the

effects of cadmium on osmoregulation and urine concentration

(diuresis) in Meriones shawi, a semi-desert rodent, which is

considered as a good animal model for both physiological

mechanisms studies.

Monitoring and quantifying of Cd accumulation in organs are

of great interest to early estimate its risk. Different analytical

methods are used for the determination of Cd in biological

samples include: spectrophotometry, atomic emission spec-

trometry, atomic absorption spectrometry, atomic fluorescence

spectrometry, inductively coupled plasma mass spectrometry

and electrochemistry.26 Direct spectrophotometric techniques, or

chromatographic separations combined with spectrophoto-

metric detection have been the most widely used in several types

of environmental samples: waters, effluent, soil extracts and

biological samples. However, most of these analytical measure-

ments dealt with the total content of metals in analyzed samples.

Few attempts have been made to evaluate the speciation of

metals in particulate forms. In addition, analyses of Cd, espe-

cially those in biological samples, are expensive, time consuming,

and complex, due to the high organic content causing matrix

interference. This leads to insufficient precision and may have

a negative impact on the measurement which can aggravate the

problem.27

This journal is ª The Royal Society of Chemistry 2012

The current study has two aims: the first one is to determine if

dietary Cd incorporated in food, would alter the physiological

adaptation of the semi desert rodent Meriones shawi (daily urine

volume, plasma and urine osmolalities). The second one is to

optimize the use of Differential Pulse Anodic Stripping Vol-

tammetry (DPASV)28 for easy and sensitive Cd analysis in bio-

logical samples such as Meriones kidney, which is directly

implicated in body water regulation.

Using fast, sensitive and reliable analysis, this study has

potential importance if this valuable novel animal model,

imitating human and animal environmental chronic exposure to

Cd could serve as an appropriate terrestrial biomonitor to be

used for Cd contaminated sites in Tunisia.

2. Materials and methods

2.1. Animals and housing conditions

All experiments were carried out on adult male of Muridae

Meriones shawi29 originating from the south of Tunisia. The

rodents were captured from non-polluted regions and kept in

captivity in our breeding facility for two generations (author-

isation no. 303; DGF/DCP). The animals were put in single cages

and housed in an air-conditioned room maintained at 25 � 1 �C,a relative humidity of 45� 10%, with a 12 h dark–light cycle. The

diet of the control group consisted of granular flour mixed with

distilled water. Cadmium contaminated diets of treated animals

consisted of granular flour mixed with a solution of cadmium

chloride (CdCl2; Sigma-Aldrich) at a dose of (1 g Cd per 1 L H2O

per 1.5 kg of granular flour, each animal takes about 2.6 mg Cd

per g of alimentation) The choice of concentration is available

from our previous studies and from bibliography data.30,31 Food

was given in the form of balls dried at 60 �C for 72 hours. Water

was supplied ad libitum.

Animals were randomly selected and divided in two groups

with six animals per group. Each animal was put in a metabolic

cage for ten days, in order to collect 24 h urine each day at the

same time. The first group which received water and alimentation

ad libitum was used as a control (C). Meriones of the second

group received the Cd contaminated diet (Cd) in the form of

CdCl2 (Cd) at a dose of (1 g Cd per 1 L H2O per 1.5 kg of

granular flour). Water was given ad libitum. Urine samples were

collected on paraffin oil to prevent evaporation and measured in

mL per day. Daily consumption of drinking water and food of

each group were measured throughout the study. Animals were

put in metabolic cages one week before the experiment. All of the

protocols were carried out in accordance with French standard

ethical guidelines for laboratory animals (agreement 75-178,

5_16_2000).

2.2. Experimental

2.2.1. Analysis of organ elemental composition. The body

weight of each animal was determined throughout the experi-

ment. Blood samples were collected from the infra-orbital sinus

into heparinized hematocrit (Ht) capillary tubes at the end of the

experimental period. These samples were centrifuged at 1500g for

10 min in order to determine hematocrit (Ht) and plasma

osmolality. At the end of experimentation, rodents were sacri-

ficed by decapitation. Kidneys were immediately removed and

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weighed. The weight of organs (%) was calculated as g per 100 g

of body weight. Finally these organs were freeze–dried at 180 �Cwith a lyophilizer (Teslar lioalfa-6) and weighed for the deter-

mination of dry weight.

2.2.2. Digestion of samples. For analysis, the collected organs

were thawed naturally and after weighing they were dissolved in

10 mL nitric acid for wet digestion. For this purpose, we used

a microwave acid digestion (Mars Xtraction Technology Inside,

CEM corporation). We put 0.1 g of dry organ into 10 mL of

nitric acid. Then, it was wet digested at 170 �C, over 15 min, in

a long-necked 55 mL Teflon tube Xpress. The digested sample

which was clear and colorless was cooled to room temperature.

The same amount of acid was added to see if there is an

impurity peak when voltammograms were taken under the same

conditions. The voltammograms of the digested sample were

taken under various conditions and the trace elements in the

sample were determined by standard additions. The amount of

Cd in each organ was realized by DPASV that exploits the

electrochemistry of this metal.

2.2.3. Urinary and plasma osmolalities. The urinary osmo-

lality (UO) and plasma osmolality (PO) were measured with an

automatic microosmometer (Roebling; bioblock). They were

determined by depression of freezing point (Advanced Instru-

ments, Needham Heights, MA).

2.2.4. Diuresis. Each animal was put in a metabolic cage for

ten days in order to collect feces and 24 h urine each day at the

same time. Urine samples were collected on paraffin oil to

prevent evaporation and measured in mL per day.

2.2.5. Electrochemical measurements

2.2.5.1. Reagents. All solutions were prepared by dilution

using ultrapure water. Cadmium standard stock solution, diluted

as required and sodium acetate salt anhydrous (99%), acetic acid

glacial (99.7%), and nitric acid (65%) were purchased from

Panreac (Spain).

2.2.5.2. Apparatus. All electrochemical measurements were

performed with an Autolabsystem including PGSTAT 12

potentiostat/galvanostat (Eco Chemie) attached to an IME 663

autolab unit (Interface for mercury electrodes) used to connect

a Static Mercury Drop Electrode System (SMDE) and to control

the Metrohm 663 VA Stand (Swiss) and to a personal computer

for data acquisition and monitored by use of the software GPES

(General Purpose Electrochemical Systems) for Windows

version 4.6.

Differential Pulse Anodic Stripping Voltammetry (DPASV)

experiments were carried out with a conventional three-electrode

system, comprising a mercury electrode, selected in SMDE mode

in the stand, a platinum auxiliary electrode and a Ag/AgCl/3.0 M

KCl reference electrode, all of them from Metrohm.

Unless otherwise indicated, the instrumental parameters for

polarographic experiments were a drop time of 1 s and a scan rate

of 0.0051 V s�1 for DPP, a deposition time of 240 s for DPP, and

a pulse amplitude of 0.04995 V and a modulation time of 0.5 s. A

total of 50 mL acetic/sodium acetate buffer solution, pH 4.8,

0.002 M, was de-aerated by a stream of nitrogen gas (99.999%)

2214 | J. Environ. Monit., 2012, 14, 2212–2218

for about 15 min. Polarograms were taken by scanning the

potential from �1.2 to �0.45 V. All measurements were made at

room temperature.

2.2.6. Statistical analysis. Data are shown as the standard

error of the mean (SEM). All results were compared with control

animals. For all our experiments, a one-way ANOVA was used

to analyze the differences between the two groups, followed by

Dunnett’s test with a threshold of significance of p < 0.05 and

p < 0.01 to detect specific differences, using a statistical package

(XLSTAT version 2009.1.1).

3. Results

3.1. Body weight, food and water consumption

The initial body weight of the Meriones in the two groups of

experimentation was the same, around 140.5� 3.66 g. At the end

of experimentation, body weight did not change in the control

group, whereas it decreased slightly by 5 � 0.62% in the Cd-

treated animals following ten days of exposure.

Mean food consumption expressed per 100 g of body weight in

the control reached around 4.5 g per day of food. Cd exposure

led to a significant (p < 0.01) decrease of food intake in the Cd-

treated group (2.7 g per day in comparison to controls).

However, no influence on water consumption (8 mL per day) was

determined (Table 1).

3.2. Hematocrit (Ht)

The Ht values were determined after ten days as shown in Table

1. No differences were observed among the Cd-exposed group

when compared with the control group.

3.3. Urinary and plasma osmolalities

The urinary osmolality (UO) in the control Meriones group was

around 1100 mOsm per kg H2O. Following 10 days of experi-

ment, urinary osmolality was increased significantly (p < 0.01) in

comparison to controls.

The plasma osmolality (PO) was around 270 mOsm per kg.

There was no difference between the two groups following 10

days of Cd exposure (Table 1).

3.4. Diuresis

The volume of excreted urine by the control Meriones group,

expressed per mL per 100 g per day of body weight, reached

around 2.26 � 0.58 mL per day per 100 g of body weight.

However throughout the experiment, the Cd exposure induced

a significant decrease (p < 0.05) on urine volume output from the

fourth day of experiment (2.04 � 0.65) in comparison to the

control group as shown in Table 2. This decrease became more

significant as the days of experimentation passed.

3.5. Stripping curves, calibration curves and performance of

method

Calibration data for the determination of Cd(II) in acetic/sodium

acetate buffer solution, 0.002 M at pH 4.8, were achieved by

DPASV under optimal conditions (deposition at �1.2 V for

This journal is ª The Royal Society of Chemistry 2012

Table 1 Effects of Cd exposure on different parameters (body weight, daily food consumption, daily drinking water, hematocrit, urinary osmolality,and plasma osmolality) in adultMeriones shawimale, following 10 days of exposure. Data are expressed as �SEM from 6 animals in each group. **p <0.01 significantly different from control

Different groups Body weight (g)Daily food consumption(g per day per 100 g of body weight)

Daily drinkingwater (mL) Hematocrit (%)

Urinary osmolality(mOsm per kg H2O)

Plasma osmolality(mOsm per kg H2O)

Control Meriones 140.16 � 6.41 4.34 � 0.56 8.10 � 3.61 46.5 � 0.2 1100 � 2 307.6 � 4.2Cd-treated Meriones 131.76 � 6.48 2.42 � 0.27 8.03 � 0.13 44.4 � 1.3 1560 � 1.9** 332 � 3

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240 s, window potentials set from �1.2 V to �0.45 V, and scan

rate 0.0051 V s�1) using a SMDE mercury electrode system. The

resulting calibration plots are linear over the range from 0.3–

100 mg L�1 and deposition time was around 240 s. Fig. 1a shows

Cd voltammograms. The peak of Cd appears at

approximately �0.58 V. The height peak of Cd increased

following the addition of increasing volumes of the standard

solutions Fig. 1b. A second peak in the buffer solution was also

observed at �1.1 V. This peak is from zinc (Zn) amounting to

around 41 ppb (data not shown). We suggest that Zn comes from

the solutions used for buffer preparation. We chose to start

from�1.2 V to detect simultaneous metals (data not shown). The

Relative Standard Deviation (RSD) was around 1.28%. The

detection limit (LOD), based on a signal noise ratio equal to 3 : 1

was around 0.28 � 0.03 mg L�1. The blank of the procedure is

evaluated from five repetitive measurements in 0.1 M acetic/

sodium acetate buffer solution, pH 4.8. The limit of quantifica-

tion (LOQ), amounting to 0.95 � 0.08 mg L�1, was calculated

based on a signal noise ratio equal to 10 : 1. All analytical

measurements are presented in Table 3.

The stripping curves for Cd in kidneys from Cd-treated

rodents and controls are plotted in Fig. 2a. The presence of Cd

was confirmed by standard additions (10, 20 and 30 ppb)

(Fig. 2b). Analysis of Cd was determined in kidney samples after

acid digestion. A good linearity was obtained during analysis of

samples. All analytical measurements of the analysis are pre-

sented in Table 4.

3.6. Intracellular Cd content in real biological sample: kidney

Cd concentrations were measured in kidneys, tissues that typi-

cally retain Cd following administration in the organism and

which play a crucial role in water regulation. Cd concentration

was around 9.148 � 1.87 mg L�1 in the kidney. Considering this

amount, the factor dilution realized during the mineralization

step and the dry weight of the kidney, the Cd content was around

914.8 � 4.41 mg g�1 of dry weight organ. Our data indicated

a significant accumulation of Cd (p < 0.01) in the kidney of

treatedMerioneswith 1 g Cd per 1 LH2O per kg of diet during 10

days. No Cd was detected in the kidneys of the control group.

Table 2 Effects of 10 days Cd exposure on daily urine excretion (diuresis) inanimals in each group. *p < 0.05; **p < 0.01 significantly different from con

Day 1 Day 2 Day 3 Day 4 Day 5

Control Meriones (C) 2.25 �1.8

2.85 �1.3

2.77 �0.98

2.46 � 0.41 2.34 � 1

Cd-exposed Meriones(Cd)

2.65 �2.3

2.85 �1.3

2.08 �0.12

1.98 �0.74*

1.83 �2.30**

This journal is ª The Royal Society of Chemistry 2012

4. Discussion

The importance of conservation and improvement of the envi-

ronment from harmful heavy metals is critical and urgent. It is

well-known that heavy metal ions occur in the environment in

different oxidation states and forms and the toxicity of these

metals in animals and humans is strongly influenced by the

physiological mechanisms.11 On the perception that the health of

the system is measured by the living organisms, we were inter-

ested first in elucidating whether Cd exposure could alter the

homeostatic state of a semi-desert rodent, which survives dry and

wet seasons by stimulating anti-diuretic and diuretic systems

alternately. For this, water conserving abilities of this species

were assessed through measurements of daily urine volume, and

plasma osmolalities. The plasma volume was evaluated by

hematocrit (Ht). We also aimed to use a cheap, fast and reliable

method by the use of (DPASV) for the monitoring and the

prevention against chemical contaminants accumulated in bio-

logical samples: kidneys.

Our results showed that diuresis had decreased significantly

since the fourth day of experiment. The plasma osmolality

remained constant following Cd exposure. However, the urinary

osmolality increased as Cd exposure went on. Volume constancy

of plasma was evaluated by hematocrit and remained constant.

All these data show that Meriones shawi maintained a homeo-

stasis state and presented a special adaptation to regulate urine

volume during Cd exposure. This work is the first investigation

of the cadmium effect on the osmoregulation mechanism of

Meriones shawi. This adaptation process has been well developed

and studied under water stress but few attempts have been

reported to study the effects of the accumulation of pollutants on

this adaptation process. A similar response was observed when

Meriones shawi was submitted to water stress and the activation

of the maintenance of body fluids was made by homeostatic

mechanisms that concentrate urine as an indicator of the effi-

ciency of water regulation.1,2

This is in agreement with our previous work31 showing that

Meriones shawi presented a body water content compatible with

survival (water influx ¼ water efflux) even under Cd exposure.

The involvement of the hypothalamo-vasopressinergic system

adult Meriones shawi male. Data are expressed as mean �SEM from 6trol

Day 6 Day 7 Day 8 Day 9 Day 10

.93 2.93 � 1.9 2.44 � 1.8 2.02 � 1.2 2.02 � 1.5 2.44 � 0.75

1.77 �0.45**

1.04 �0.66**

1.3 �0.7**

1.26 �0.42**

1.26 �0.42**

J. Environ. Monit., 2012, 14, 2212–2218 | 2215

Fig. 1 Stripping voltammograms for increasing levels of Cd in the range of 0 to 100 ppb. (a) Calibration curve of Cd; analyses are done in an electrolyte,

acetic/sodium acetate buffer solution 0.002 M at pH 4.8; deposition at �1.2 V for 240 s, window potentials set from �1.2 V to �0.45 V; scan rate

0.0051 V s�1.

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plays a fundamental role in this protective reaction of the

organism during Cd exposure in Meriones shawi by secreting

AVP, which acts as an antidiuretic hormone.31–33 It is well

established that modifications of serum osmolality during

depletion are detected via osmoreceptors by magnocellular

neurons mainly located in the hypothalamic supraoptic and

paraventricular nucleus in the brain.34,35 These neurons increase

their electrophysiological activity during water privation. Thus it

leads to an increase of vasopressin (AVP) synthesis and release in

order to facilitate sustained antidiuresis.36,37 The synthesis of

AVP is induced in response to a variety of physiological stimuli,

including osmotic and nonosmotic stimuli.35

The determination of Cd in biological samples by DPASV has

been successfully applied in vital organs (kidneys). The accuracy

of the results attained are satisfactory and allows us to make

a speciation between the various Cd oxidation states and to judge

the biological availability and the toxicity of Cd by DPASV. Our

findings are in agreement with G€uell and co-workers,38 which

indicate that the use of DPASV voltammetric techniques has

proved equally effective owing to the dependence of the signals

on the metal species and to the sensitivity.28 We showed

a significant accumulation of Cd(II) (p < 0.01) in the kidney of

Meriones shawi following Cd exposure.

Several studies established that Cd is widely distributed in the

body after uptake from the lung or the gastrointestinal tract with

Table 3 Analytical performance of the measurements performed by DPASbuffer solution 0.002 M at pH 4.8, deposition at �1.2 V for 240 s, window p

MetalWorking range(mg L�1) a � SEMa slope b � SEMb

Cd 0.3–100 0.66 � 0.02 2.10 � 0.04

a a: slope; b: intercept; R2: correlation coefficient; RSD: relative standard dev

2216 | J. Environ. Monit., 2012, 14, 2212–2218

the major portion of the body burden located in the liver and

kidney. Initially, cadmium is transported in blood plasma

initially bound to albumin. Then, the cadmium–albumin

complex is preferentially taken up by the liver. Then cadmium

induces the synthesis of metallothionein (MT) and a complex

Cd–MT is formed and then moved to the kidney.39 Huang and

co-workers.40 believe that Cd-induced MT binds Zn ions

important for enzyme stability and thus depletes cellular Zn,

which in turn modifies enzyme folding and changes its activity.

The molecular mechanism of Cd-induced damage is still under

investigation. Some studies have shown that Cd depletes gluta-

thione and protein-bound sulfhydryls, induces lipid perox-

idation, alters DNA structure and the activity of antioxidant

enzymes, and changes the structure and function of cell

membranes, which can result in oxidative stress and oxidative

tissue damage.41,42

Oxidative stress is a condition of overproduction of reactive

oxygen species and/or disturbances of the antioxidant defense

system and/or inability of the system to remove induced

damage.43,44 Other authors have suggested that Cd indirectly

inactivates the enzyme by enhancing production of free radicals,

which leads to protein fragmentation.40

The ability of Cd to imitate essential metals such as Zn and

calcium in many biological pathways and processes is a very

probable explanation for its toxicity.45 Cd may interact with

V for Cd analysis. Measurement cell: electrolyte, acetic/sodium acetateotentials set from �1.2 V to �0.4 V and scan rate 0.0051 V s�1a

R2 RSD (%) LOD (mg L�1) LOQ (mg L�1)

0.9987 1.28 0.28 � 0.03 0.95 � 0.08

iation; LOD: limit of detection; LOQ: limit of quantification.

This journal is ª The Royal Society of Chemistry 2012

Fig. 2 Determination of Cd in adult Cd-treated Meriones kidney by

DPASV following 10 days of experiment. (a) Stripping voltammograms

for increasing levels of Cd (10, 20 and 30 ppb) in Cd-treated Meriones

kidney. (b) Additions of standard solutions of Cd (10, 20 and 30 ppb). Cd

analysis was undertaken in electrolyte, acetic/sodium acetate buffer

solution 0.002 M at pH 4.8, deposition at �1.2 V for 240 s, window

potentials set from �1.2 V to �0.45 V and scan rate 0.0051 V s�1.

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membrane transporters involved in the uptake of Zn. Interac-

tions between Zn and Cd might result from their physical and

chemical similarities through the mechanism of ionic and

molecular mimicry and can influence metal accumulation and

toxicity in living organisms.46

5. Conclusion

On the basis of the current study, we show that Cd was

bioavailable to Meriones shawi and readily accumulated in the

liver and kidney. Cd increases the urine osmolality, without

directly affecting water metabolism in Meriones shawi.

Moreover, the enhancement of urine osmolality suggests

a protection role against Cd intoxication. Taken together, our

present study and other works conducted on Meriones shawi

demonstrate that this rodent represents an ideal model to

study physiological adaptations restraints and a suitable

Table 4 Analytical performance of Cd determination by DPASV in real samMeasurement cell: electrolyte, acetic/sodium acetate buffer solution 0.002M atto �0.45 V and scan rate 0.0051 V s�1. **p < 0.01 significantly different from

Different groups a � SEMa b � SEMb E

Control Meriones kidney 0.375 � 0.002 �0.306 � 0.03 �Cd-treated Meriones kidney 0.705 � 0.003 6.45 � 0.012 �a a: slope; b: intercept; E: potential; R2: correlation coefficient; [Cd]: Cd concenorgan.

This journal is ª The Royal Society of Chemistry 2012

terrestrial biomonitor for Cd-contaminated sites in Tunisia.

The use of electrochemical analyses for the detection and the

quantification of the ions of metals in the biological samples

seem to be of particular importance. It allows us to make

a speciation between the various states of oxidation of Cd

ions and to judge the biological availability and the toxicity of

heavy metals. These results are encouraging in the context of

developing a low-cost and fast technology for the detection of

pollutants.

Acknowledgements

The authors gratefully thank Dr Slaheddine khilifi, for his

precious help in English revision. This work has been supported

by AECID-PCI-Mediterranean (A/028138/09 and A/031592/10)

and grant from Ministry of Higher Education, Scientific

Research and Technology of Tunisia. Rodents were captured

with authorisation from Ministry of Agriculture and Water

Resources; General management of forests, no. 303/DGF/DCP.

Tunisia.

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/V R2 [Cd] (mg L�1) [Cd] (mg g�1 of d. w. organ)

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