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- 47 -
SAITM Research Symposium on Engineering Advancements 2014
(SAITM – RSEA 2014)
LEACHING OF ALUMINUM AND ITS INCORPORATION TO RICE DURING
COOKING UNDER DIFFERENT FLUORIDE CONCENTRATIONS IN WATER
A. A. G. D Amarasooriya1, H.A. Dharmagunawardhane2
1 Faculty of science, Uva wellassa University, Badulla. Sri Lanka. Email: gayanamarasooriya@gmail.com
2 Department of Geology, Faculty of Science, University of Peradeniya, Peradeniya. Sri Lanka
Email: dharmag@pdn.ac.lk
ABSTRACT
Majority of the people in Sri Lanka use aluminum cooking utensils for cooking rice and other types of
food. Aluminum is toxic to human if injected in excessive concentrations. Since fluoride in water has an
affinity to make complex ions with aluminum. Fluoride in cooking water can enhance attraction of
aluminum in to the cooking medium and hence to the cooked food. Under the present study natural
aluminum level and leaching of aluminum and its incorporation in to rice during cooking under different
fluoride stresses were studied.
Natural aluminum level of the raw rice (Oryza sativa) was significantly large. It was observed a
concentration of 0.2038 mg/g aluminum in rice. Rice cooked at the present of aluminum plate but
without fluoride water shows an addition of 0.0065 mg/g aluminum to rice. An addition of 0.1367 mg/g
aluminum was noted at a fluoride concentration of 6 mg/l in water which is comparative to highest
fluoride levels of Sri Lankan ground water. Total aluminum was found to be high in the rice cooked
under normal water as well as in the fluoride rich water. Aluminum in cooked rice increased with the
increasing fluoride concentration in the water. It was found that total aluminum level in cooked rice was
0.2135 mg/g when cooked in fluoride free water and it was 0.3438 mg/g at 6 mg/l fluoride in water. The
maximum allowed aluminum intake per normal person is 0.1428 mg/kg body weight per day. Based on
the assumption, one person who eat 250 g rice per day, the aluminum intake according to present
experiment is greater than 0.1428 mg/kg and hence risky.
Keywords: utensils, excessive
1. INTRODUCTION
The effects of aluminum intake for human have
been reported by several workers [2, 3] and the
indications are that it is neurotoxic under high
fluoride stress. Leaching of heavy metals such as
aluminum and lead, under high fluoride stress
represents a new way for the entry of toxic heavy
metals into the body and the formation of
complex fluorides provides a pathway for the
chemical amplification of toxins such as fluoride.
While fluoride alone may not affect the organs
like kidney, fluoride along with aluminum can
cause a detrimental effect on the kidneys of
healthy people [7].
The World Health Organization (WHO) reported
in 1989 that the Provisional Tolerance Weekly
Intake of aluminum (PTWI) is 7 mg/kg body
weight/week [6] .Therefore; the acceptable
dosage is not more than 50 mg/ day for a person
weighing 50 kg. In 2006, the Joint (Food and
Agriculture Organization/World Health
Organization) Expert committee on Food
Additives (JECFA) has re-evaluated the safety of
aluminum and recommended to lower the PTWI
by seven folds to 1 mg/kg body weight for
aluminum [9]. This was due to the potential to
affect the developing reproductive and nervous
system in experimental animals at doses lower
than those used in establishing the previous
PTWI.
2. METHODOLOGY
2.1. Procedure for Analysis
Previously used, Aluminum rice cooking utensil
was chosen. The pot was cut in to seven
rectangular specimens of dimension 2.54 cm
×2.54 cm. Two kg of raw rice (Oryza sativa) was
chosen from the local market. Ten g of rice was
cooked in a glass beaker with an aluminum plate
in it under different fluoride concentrated water.
Samples were then digested [1] and aluminum
was determined using a UV Spectrophotometer
by aluminum method [5] at 530 nm.
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SAITM Research Symposium on Engineering Advancements 2014
(SAITM – RSEA 2014)
2.2. Estimated aluminum intake for a person
The estimated aluminum intake for a person was
calculated based on the assumption that an
aluminum utensil of 20 cm diameter and 18 cm
height is used for a family of four person (weight
50 kg) to cook one kg raw rice. The area then
exposed to food during cooking is around 1440
cm2.
2.3. Corrosion rate
The corrosion rates presented in tables are
calculated by using below eq. (01).
Corrosion rate = WL/AT (mg/cm2.h) (01)
WL- is the weight loss [mg],
A - Surface area of the test specimen [cm2]
T - Immersion time [hours].
3. RESULTS
3.1. Total aluminum in the cooked rice
samples
According to the results it shows that there is a
significant amount of aluminum present in the
studied samples. It is important to note that
aluminum presence even in the blank rice sample
cooked without the aluminum plate.
The blank rice sample shows mean 0.2038 mg/g
which is the lowest aluminum concentration. The
highest level was detected in the sample cooked
with water containing highest fluoride
concentration (0.3385 mg/l).
Figure 1: Total aluminum in the cooked rice sample
Table 1:Total aluminum in the cooked rice samples
According to USDA food standard database
aluminum is not mentioned as present in rice. But
the raw rice sample which was taken from the Sri
Lankan local market shows 0.2038 mg/g of
According to USDA food standard database [8]
aluminum is not mentioned as present in rice. But
the raw rice sample which was taken from the Sri
Lankan local market shows significant 0.2038
mg/g of aluminum level. Therefore aluminum in
local raw rice should be further investigated.
A number of reasons could probably cause
presence of aluminum in rice. It could be due to
rice processing method, irrigation water
aluminum level, aluminum level in the soil etc.
Aluminum toxicity is the major constraint to crop
productivity on acid soils, which comprise over
50% of the world’s arable land Under highly
acidic soil conditions [4] (pH less than 5.0),
Aluminum is entered in to the soil solution as
Al3+, which is highly phytotoxic, causing a rapid
inhibition of root growth that leads to a reduced
and stunted root system, thus having a direct
effect on the ability of a plant to acquire both
water and nutrients. Acid rain ensures that more
aluminum is available for plant uptake, which
often occurs and is concentrated in root tissue.
3.2. Total diet exposure of aluminum
The estimated aluminum intake for a person
when fluoride water is used to cook rice is shown
in figure 2
Sample
Number
Numbe
r of
samples
taken
for the
analysis
Mean value of
aluminum
present in the
1g of rice
samples
(mg/g)
Fluoride
concentr
ation in
water
( mg/l )
Blank(0)
3
0.2038
0
Sample(1)
3
0.2103
0
Sample(2)
3
0.2462
1
Sample(3)
3
0.2615
2
Sample(4)
3
0.2885
3
Sample(5)
3
0.3077
4
Sample(6)
3
0.3167
5
Sample(7)
3
0.3385
6
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SAITM Research Symposium on Engineering Advancements 2014
(SAITM – RSEA 2014)
1.019 1.065
1.334 1.448
1.648 1.791 1.858
2.021
0
0.5
1
1.5
2
2.5
Blank( 0) F
0 mg/l Sampl e(1)
F 0 mg/ l Sample(2)
F 1mg /l Sampl e(3)
F 2 mg/ l Sample(4)
F 3 mg/ l Sample(5)
F 4 mg/ l Sample(6)
F 5 mg/ l Sample(7)
F 6 mg/ l
Aluminu m intake mg/kg body weight
Sample number
Figure 2:-Aluminum intake for 1 kg body weight
(mg/kg)
This calculation is based on the assumption that
an aluminum utensil of 20 cm diameter and 18
cm height is used for a family of four person
(weight 50 kg) to cook one kg raw rice. The area
then exposed to food during cooking is around
1440 cm2.
When compared to (2006) JECFA safety
aluminum level [9] of 0.1428 mg/kg of body
weight, calculated values for all the samples were
greater than that. Presence and absence of fluoride
incorporate aluminum by leaching. In addition,
rice may alone have a significant amount of
aluminum. According to Department of Census
and Statistics Ministry of Finance and Planning
Sri Lanka 2010/09 survey daily “kakulu” rice
consumption exceeds 250 g/ day. Therefore
people in Sri Lanka are under risk of excessive
aluminum intake, especially in areas where
fluoride rich in ground water.
3.3. Diet exposure of aluminum from utensils
According to the observations there is a
significant amount of aluminum present in
natural raw rice sample. By subtracting the
amount of aluminum occurring in raw rice
exposures due to leaching of aluminum utensils
can be re calculated as shown in the figure: 3.
Figure 3:-Aluminum intake due to leaching of
aluminum from utensil
3.4. Corrosion rate
Corrosion rate of the aluminum depends on the
surface area of aluminum plate, rice itself,
fluoride concentration and length of cooking
time. The table 6.4 presents corrosion rate for
different fluoride stresses. The maximum and
lowest rate of corrosion is 0.3129 (mg/cm2) and
0.0143 (mg/cm2) respectively for 20 minute
cooking time. The maximum rate of corrosion is
observed when cooked with 6 mg/l fluoride water
and the lowest rate of corrosion in cooking where
fluoride free water. There is an increment of
corrosion rate with respect to the fluoride
concentration. Also result shows rice alone may
leach aluminum.
Table2: Corrosion rate of the aluminum due to
presence of the fluoride and rice
Fluoride
concentration of
water used to
cook rice for 20
minutes
(mg/l)
Weight loss
of the
aluminum
specimen
Corrosion
rate
(mg/.cm2.
hr)×10-2
0
0.0641
1.43
08
1
0.4231
9.83
66
2
0.5769
13.4
135
3
0.8462
19.6
731
4
1.0385
24.1
443
5
1.1282
26.2
010
6
1.3462
31.2
981
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SAITM Research Symposium on Engineering Advancements 2014
(SAITM – RSEA 2014)
4. CONCLUSION
The present study indicated that use of
aluminium utensils in the presence of
fluoride rich water for cooking pose a threat
to the rice consumer with increased
aluminium intake.
Raw rice appear to contain significant
amount of aluminium
Aluminium leaching from aluminium
utensils increase with the increasing fluoride
content in cooking water.
Combined aluminum contribution from rice,
cooking utensils, and other food such as
curries cooked in aluminium utensils
particularly in acidic medium could be
higher than the acceptable levels and hence
pose a threat to consumer especially in the
areas of fluoride rich ground water.
5. REFERENCES
[1] AOAC (1995). “Official Methods of Analysis
of AOAC International”, 16th ed. The Association
of Official Analytical Chemists, Arlington. pp.
1011.
[2] D. Shore & J. R. Wyatt, (1982). Research
design issues: “Ant aluminum drug studies in
Alzheimer disease”.Clinical neuropharmacology,
5, 337-45.
[3] H. M. Wisniewski, J. A. Sturman, J. W.
Shek (1982). “Chronic model of neurofibrillary
changes induced in mature rabbits by
metallic aluminum”. Neurobiol. Aging, 3, 11-
22.
[4] H.R. Von Uexku, E. Mutert (1995), “Global
extent, development and economic impact of acid
soils”. In: R. A Date, N.J Grundon, G.E Raymet.
M.E. Probert (eds.) “Plant-Soil Interactions at
Low pH: Principles and Management.
[5] HSU, P. HO, 1963. “Effect of initial pH,
phos-phate and silicate on the determination of
alu-minum with aluminon”, Soil Sci. 96: 230-
238.
[6] J.A.T Pennington, J.W. Jones, (1989).
”Dietary intake of aluminium. Aluminium and
Health – A critical review”. Gitelman, p. 67-70.
[7] O.A. Ileperuma, H.A. Dharmagunawardhane
,K.P.R.P. Herath (2009). “Dissolution of
aluminium from sub-standard utensils under high
fluoride stress: a possible risk factor for chronic
renal failure in the north-Central Province”,
J.Natn. Sci. Foundation Sri Lanka 37 ,219-222
[8] USDA, National Nutrient Database for
Standard, (2003) ”Food and Agriculture
Organization of the United Nations” Vol.197.
Pp. 332-341.
[9] WHO. (2007). “Evaluation of certain food
additives and contaminants: sixty-seventh report
of the Joint FAO/WHO Expert Committee on
Food Additives”. WHO Technical Report Series
940. Geneva.
