Determination of Heavy Metal Levels in Edible Salt
author: Ali Heshmati, Department of Biochemistry and Nutrition, Faculty
of Medicine, Hamadan University of Medical Sciences, Hamadan, IR Iran.
Tel: +98- 8118380572, Fax: +98-8118380208, Email: email@example.com
salt is the most commonly used food additive worldwide. Therefore, any
contamination of table salt could be a health hazard.
Objectives: The present study aimed to determine the levels of heavy metals in table and bakery refined salts.
Materials and Methods: Eighty-one
table refined salt samples and the same number of bakery refined salt
samples were purchased from retail market in the province of Hamadan,
Iran. The levels of lead (Pb), cadmium (Cd), mercury (Hg), copper (Cu),
and iron (Fe) were determined using atomic absorption spectroscopy
levels (mean ± SD, μg/g) of Pb, Cd, Hg, Cu, Fe in table refined salt
samples were 0.852 ± 0.277, 0.229 ± 0.012, 0.054 ± 0.040, 1.25 ± 0.245
and 0.689 ± 1.58, respectively. The results for the same metals in
bakery refined salt samples were as follows (mean ± SD, μg/g): 22 ±
0.320 for Pb, 0.240 ± 0.018 for Cd, 0.058 ± 0.007 for Hg, 1.89 ± 0.218
for Cu, and 8.75 ± 2.10 for Fe. Heavy metal concentrations were
generally higher in bakery refined salt.
results obtained in the present study were compared with the literature
and legal limits. All values for these metals in the table and bakery
refined salts were lower than the permitted consumption level defined by
Codex (2 µg/g of Pb, 0.5 µg/g of Cd, 0.1 µg/g of Hg, and 2 µg/g of Cu).
Keywords: Cadmium; Lead; Heavy Metals; Mercury; Sodium Chloride
Trace elements or heavy
metals are widely present in the earth’s crust, air, water and food.
Heavy metal contamination of food is a great concern for human health
because of their toxicity and even at relatively low concentrations can
cause harmful effects. Although these effects have been known for a long
time, exposure to heavy metals exists and is even increasing in some
countries (1, 2).
To limit the possibility of food poisoning by trace elements, the highest allowable concentrations of them are determined (3).
Human may expose to heavy metals through inhalation and dermal contact;
however, contaminated food and drink are the major exposure path in
most people (4).
Edible salt is biologically necessary because it provides two important
macro elements of sodium and chlorine for human body. Furthermore, it
improves food taste, could serve as a preservative, and elongates shelf
life. Generally, salt is the most additive used in food industry (2).
might be contaminated by various chemical substances in different
amounts and forms that may harm the consumers’ health. Some studies
showed that heavy metals are found in edible salt (2, 5-9).Therefore, the concentration of heavy metals in table salt should be rigorously controlled.
refined salt (fortified by iodine and used for home cooking), and
bakery refined salt (used in production of bread and is free of iodine)
are two types of edible salt supplied in Iran.
The aim of this study was
to determine lead (Pb), cadmium (Cd), mercury (Hg), copper (Cu) and
iron (Fe) content of table and bakery refined salt samples consumed in
the province of Hamadan, Iran and to compare their values with the
standards established for human health. According to Iran standard, the
maximum permitted levels of heavy metals in salt are 1 µg/g of Pb, 0.2
µg/g of Cd, 0.05 µg/g of Hg, 2 µg/g of Cu, and 10 µg/g of Fe (10).
3. Materials and Methods
Eighty-one table and 81 bakery refined salt samples from 26
commercial brand (three samples from each brand) were purchased from
retail market in the province of Hamadan, Iran. Twenty-five gram of each
sample was used for analysis.
3.2. Reagents and Solutions
All materials of the study were obtained from Merck, Darmstadt,
Germany. Solutions were prepared with double-deionized water. The
calibration curve was established using standard solutions prepared in 1
mol HNO3 by dilution from 1000 mg/L stock solutions. The calibration
standards were not submitted to the preconcentration procedure.
Approximately, 0.1% solution of Dy2O3 was prepared freshly by dissolving
dysprosium (III) oxide (Merck, Suprapur grade) in small amounts of
nitric acid and diluted to 50 mL with double distilled water. Nitric
acid (65%) (Used for preparing of diluted acid solution) was Suprapure
grade from Merck.
3.3. Analysis of Table and Bakery Refined Salts
Graphite furnace atomic absorption spectroscopy (model AA240 G,
Varian, Inc.) was used for measuring heavy metals (Pb, Cd, Cu, and Fe)
in edible salt samples. The procedure applied by Soylak et al. (2008)
and Peker et al. (2007) was used to determine heavy metals in all salt
samples (8, 11).
brief, 2.0 g of salt sample was dissolved in 20 mL of distilled water.
After adding 1.0 mg of dysprosium, precipitates of dysprosium hydroxide
were formed and ammonia was used to adjust the pH of the solution (pH =
11). The tube is slowly and carefully shaken for several seconds and
then allowed to stand for 10 minutes. The precipitate is centrifuged at
3000 rpm for 10 minutes and the supernatant is discarded. A small
precipitate adheres to the bottom of the tube. Then, 1 mL of 1 M HNO3 is
added to dissolve the precipitate. The final volume was completed to
2.0 mL with distilled water. An aliquot of 100 μL of the solution was
introduced into graphite furnace atomic absorption spectroscopy for
measurement of Pb, Cd, Fe and Cu. Hg was measured by using cold vapor
atomic absorption spectrophotometry (12).
3.4. Statistical Analysis
All data were analyzed using SPSS version 17.1. One-sample t test
was used for determination of the difference between levels of heavy
metals in refined or unrefined salt samples and maximum limits levels
permitted in codex standard. Difference between mean of heavy metals in
table and bakery refined salt samples was compared by independent
t-test. P < 0.05 was considered as a significant difference.
shows the heavy metal contents obtained from analysis of table refined
salt samples based on dry weight. Contents of Pb, Cd, Hg, Cu, and Fe in
table refined salt were lower than that of in bakery refined salt,
however, there were no significant differences between the two salt
groups in Cd and Hg. Concentrations of Pb, Cu and Fe were significantly
higher in bakery refined salt (P < 0.05).
Contents of Pb, Cd, Hg, Cu and Fe in Table and Bakery Refined Salts a
Several researchers reported the presence of trace elements in the salt (2, 5-9).
Lead is one of the most toxic heavy metals that accumulates in the body
and data published in literature indicates that its excessive intake
harm different systems and organs such as central and peripheral nervous
system, gastrointestinal tract, muscles, kidneys, and hematopoietic
system (13). The maximum permitted level of lead in food-grade salt is 2.0 μg/g according to the Codex legislation (14) and 1.0 μg/g according to the Iranian food standards (10).
In our study, Pb content of table and bakery refined salt samples were
0.852 μg/g and 1.22 μg/g respectively, which is between Codex and the
Iranian code. In another report from Iran, Pb concentration was 2.728
μg/g (range 0.01-5.8 μg/g) and in salt samples from Tehran, lead content
was 0.87 μg/g (4) and 0.438 μg/g (2). Pourgheysari et al. (2007) in Isfahan reported lead content to be 0.57 μg/g in refined salt and 0.61 μg/g in unrefined salt (7).
In the literature, it was reported in the range of 0.5-1.64 μg/g in
refined and unrefined table salt samples from Turkey, Egypt and Greece,
and 0.03 μg/g from Brazil (8).
our study, mean Cd concentrations found in table and bakery refined
salts were 0.229 and 0.240 µg/g, respectively. These values are
comparable with the values reported in other studies. In Turkey, Cd
content found in refined and unrefined salt was < 0.14-0.3 µg/g and
0.14-0.21 µg/g, respectively. In other countries such as Brazil, Egypt,
and Greece, Cd concentration in table salts were reported in a range of
0.01-0.03 µg/g, 0.18-0.22 µg/g and 0.18-0.19 µg/g, respectively (8).
Other researchers in Iran have shown that Cd amount in salt was more
than our results. In a survey in Tehran, Cd content in bakery and table
salt were 0.91 and 0.65 µg/g, respectively (6).
At low concentration, copper and iron are essential for human health; however, high levels of these elements are toxic (15, 16).
Despite the positive eﬀects of optimal levels of copper, harmful eﬀects
may occur if the threshold level is exceeded. Wilson’s disease
(hepatolenticular degeneration) is one of the diseases linked to the
excess copper in the body. It results from dysfunction of the copper
transmission, which occurs due to the lack of suitable enzyme to
catalyze the process of copper deletion from detached bonds with
albumins and binding to ceruloplasmin. The condition leads to neuron
degradation, liver cirrhosis, and occurrence of colorful rings on the
cornea (17, 18).
results are consistent with the previous studies on the content of
toxic and essential metals in recrystallized and washed table salt in
Shiraz, Iran (5).
In conclusion, all values for toxic metals were significantly lower
than the permitted values set by Codex and Iran standards. Lead was
generally at higher concentration in all analyzed samples whereas
mercury was at thelowest level. In comparison, analyzed heavy metal
contents of table refined salt were generally higher than that of bakery
The authors would like to thank the Vice-Chancellor
of Research and Technology of Hamadan University of Medical Sciences and
Health for financial support.
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