Vol.2, No.9, 1097-1100 (2010) Health
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Quantitative assessment of heavy metals in some tea
marketed in Nigeria
——Bioaccumulation of heavy metals in tea
Albert Cosmas Achudume, Dayo Owoeye
Institute of Ecology and Environmental Studies, Obafemi Awolowo University, Ile-Ife, Nigeria;
*Corresponding Author: aachudum@yahoo.com
Received 12 March 2010; revised 18 May 2010; accepted 4 June 2010.
Bioaccumulation of heavy metals in tea mar-
keted in Nigeria was investigated. Four major
and most consumed brand of tea were selected
for the present study. Both aqueous and dry
methods were used. Total contents of metal
were determined by digesting 1g of each brand
using a mixture (3:1) concentrated nitric acid
(NNO3) and hypochlorous acid (HCLO4). The
second method involved hot water extract of tea
samples. After boiling and filtration, the residue
was evaporated to near dryness and digested
with concentrated HNO3 and HCLO4 as de-
scribed above. Results indicate that Zn, Cd, Cu,
and Pb were present in lowest concentrations in
ascending order for which there were two sig-
nificant differences between the four sources of
samples. The general characteristics of heavy
metal concentrations in aqueous extract showed
high level of Fe and Mg in a descending order.
Going by the correlation study of our result in-
dicates that there is no significant relationship
between the two elements of Fe and Mg, though,
the numerical values of the two elements varied
widely among the samples. These differences
may have major impact on human health. How-
ever, the beneficial effects of tea are in a fairly
narrow concentration range between the essen-
tial and the toxic level. In conclusion, the varia-
tions in heavy metals content of tea brands may
be due to geographical, seasonal changes and
the chemical characteristics of the growing re-
Keywords: Bioaccumulation; Tea; Heavy Metals;
Human Health; Toxic Level
Exposure to various metal containing components of tea
varied widely and may have varying health implications
[1]. Depending on the origin of tea leaves, heavy metals
accumulation can be derived naturally by soil contami-
nation, use of pesticides and fertilizers [2]. Some trace
metals Cr, Fe, Co, Ni, and Zn are essential for growth of
organisms, while other heavy metals Pb, Cd, Hg and As
are not only biologically non essential, but toxic [3]. A
very important biological property of metals is their
tendency to bioaccumulations. Bioaccumulation is there-
fore essential in hazard evaluation strategies. For exam-
ple, calculation of percent available of Aluminum (Al)
and Zinc (Zn) in tea consumed by human showed that
tea can provide 37.2% of the daily dietary intake of Al,
the percent available for absorption in the intestine is
only 1.78% for overall mean concentration [4]. Similarly,
daily dietary intake of Zn was 2.13% while percentage
available for absorption in the intestine was 0.72% [5].
Thus chronic metal toxicity may often characterized by
tissue/organ damage resulting in mortalities which are
related to secondary physiological disturbances [5,6].
The extent of physiological disturbances depends upon
uptake and bioaccumulation of metals [3,7].
Considering that an estimated amount of 18 billion
teacups are consumed daily in the world [1,8,9] its eco-
nomic and social importance are unprecedented. In Ni-
geria, people drink tea by the bowl because of its thera-
peutic value. It is valuable in the treatment and preven-
tion of many diseases [8].
The presence of heavy metals in tea has become
world-wide study. For example, the concentrations of Fe
and Cu in Poland [10], Cu in India and US [9], Se in
Pakistan [11], As in Iran [2,12], Al in China [13] and in
Lithuania [14] have recently become the subject of wide
spread concern, since beyond the tolerable limits they
become toxic [15,16]. Determination of harmful and
toxic heavy metals in different tea marketed in Nigeria
A. C. Achudume et al. / HEALTH 2 (2010) 1097-1100
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
gives direct information on the significance of these
elements in tea beverages. Lack of basal data on the
contents of heavy metals in tea and the regulated on the
maximum allowable and safe concentration of metal in
tea are needed. This predicated the present study to de-
termine the quantitative assessment of heavy metal con-
taminants in some popular tea marketed in Nigeria.
Several samples of tea leaves which are commonly con-
sumed in Nigeria were procured from provisional stores.
Accordingly each sample tea was coded to conceal the
original source. The code is tagged by a letter designat-
ing the type of tea, that is black tea-Lip; green tea-Gin;
white tea-Tia and Top. Three replicate samples of each
tea were quantified using two different standard methods
of [11,17].
Total contents of metals were determined by having a
portion of one g of sample tea digested in 12 mL of a
mixture (3:1 v/v) concentrated HNO3 and HCLO4. The
mixture was heated until the solution turned white. The
digested sample was filtered and transferred to a 100ml
flask and the volume was adjusted to the mark with 5%
HNO3 acid. This digestion procedure was validated by
using the reference certified material of National Agency
for Food and Drug Administration and Control (NAF-
DAC) [18].
Hot water extract of metals were determined by hav-
ing a portion of one g of each brand boiled in 50 ml of
distilled water for 10min in a porcelain cup and filtered.
The residue was evaporated to near dryness and digested
with concentrated HNO3 as described earlier. The final
volume of the solution was made up to 100 ml. Follow-
ing digestion, ten drops of H2O2 were added and centri-
fuged. The acid digested sediments were filtered and
A Perkin Elmer Analyst 300 flame atomic absorption
spectrometer (AAS) (Central Science laboratory, Obafemi
Awolowo University, Ile-Ife) was used to quantify the
heavy metal concentrations [19]. Calibration standard
curves provided the basis for quantifying metal contents
for both sediments and plant tissues after the initial ash-
ing digestion. Correlation coefficients for metals in plant
tissues and sediments were found to be 99.59% and
99.54% respectively. Calibration curves, developed us-
ing standards, provided the basis for quantifying metals
concentrations for analysis of plants tissues and sedi-
ments using both the dry and wet analysis techniques.
The data were statistically analyzed and the least sig-
nificant differences (SD) at the 5% level used to separate
means. The relationship between the different variables
was elevated by a simple correlation and regression ana-
lysis [20].
Results of the present study show the actual concentra-
tion of heavy metals in tea samples after digestion (Ta-
ble 1). The metals present in lowest concentration (<
1.00 mg/kg) were Zn, Cd, Cu, and Pb in ascending order
respectively, for which there were two significant dif-
ferences between the four sources of samples. The
sources differ with regard to Se and Fe contents, but
similar with respect to Cu, Pb, and Zn and more substan-
tially with respect to Fe and Mg with total metal content
in Gin samples about double the other samples.
Table 2 shows the general characteristics of metal
concentrations transferred to hot water extracts from
brand of teas. The metals present in greatest concentra-
tion were Fe (442-1344 mg/kg), followed closely by Mg
(123-239 mg/kg) and highly toxic element Cu (2-7
mg/kg). Except for Pb, all these metals are release very
slowly from tea leaves because they are complexed by
porphyrins [21]. The mean SD values of all determined
heavy metals for the group of tea are indicated in the
Tables. Going by the performed t-test the concentrations
of heavy metals were not significantly different (P >
0.05). The numerical values of heavy metals concentra-
tions of Fe and Mg contents varied widely among the
samples. From the regression plot, it can be inferred that
since the significant value is 0.414 which is far higher
than 0.05 and the R and R square values are 0.586 and
0.344 respectively, that there is no significant relation-
ship between the two elements (Figure 1). According to
correlation study between heavy metals Fe-Mg, and Cd-
Cu showed no significant relationship in all the tea sam-
ples, otherwise, the differences can have major impact
on staying healthy. The excessive heat in tea boiling for
example can alter the natural chemical nature of these
The result of total contents of the studied heavy met-
als (As, Se, Zn, Fe, Mg, Cd,, Cu, Pb ) in these teas com-
pared to tea grown in other countries showed accumula-
tion of different heavy metals, for example, studies have
shown that Cu in Iranian, Lithuanian and Chinese tea
[12-14] respectively, K in Pakistanis [1] and Pb in Tuni-
sian tea [22] bioaccumulations. It goes to show the abil-
ity of these plants in accumulating metals. Other studies
showed accumulation of Al [23] and Fe [10] in tea
leaves. However, in the present study, Fe and Mg com-
plexes are higher than other metals in tea marketed in
Nigeria and may be due to high metal levels in the geo-
graphical locations and more to preferential absorption
of these metals. The percent solubility of Fe and Mg
revealed these are in form of least water soluble com-
From all indications, differentiation of metal contents
A. C. Achudume et al. / HEALTH 2 (2010) 1097-1100
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Table 1. Total (mean ± SD) contents of heavy metals in tea samples.
Samples metal ions
As Cd Cu Fe Mg Pb Se Zn
Lip 1.48 ± 0.01 0.01 ± 0.00 0.12 ± 0.02 2.39 ± 0.22 5.22 ± 2.54 0.03 ± 0.00 0.52 ± 0.01 0.02 ± 0.01
Tia 2.73 ± 0.01 0.31 ± 0.01 0.31 ± 0.04 0.99 ± 0.10 4.06 ± 2.16 0.13 ± 0.01 1.53 ± 0.01 0.01 ± 0.01
Top 1.48 ± 0.01 0.02 ± 0.02 0.12 ± 0.02 2.23 ± 0.21 2.31 ± 1.47 0.33 ± 0.02 3.21 ± 0.01 0.01 ± 0.00
Gin 3.17 ± 0.01 0.39 ± 0.01 0.34 ± 0.05 0.99 ± 0.10 2.96 ± 1.75 0.27 ± 0.02 3.26 ± 0.09 0.02 ± 0.01
Mean ± SD 2.22 ± 0.01 0.12 ± 0.01 0.22 ± 0.03 1.65 ± 0.16 3.64 ± 1.98 0.19 ± 0.02 2.13 ± 0.03 0.02 ± 0.01
All the values are in mg/L
Table 2. Mean (± SD) heavy metals contents in tea aqueous extract.
Samples As Cd Cu Fe Mg Pb Se Zn
Lip 1.65 ± 1.60 0.37 ± 0.01 4.15 ± 0.091716.6 ± 186.15*244.56 ± 10.0700 ± 0.07 0.00 ± 0.32 0.80 ± 0.4
Tia 2.3 ± 0.20 7.92 ± 0.73 5.69 ± 0.09442.95 ± 8.25 123.54 ± 10.920.06 ± 0.08 0.00 ± 0.95 0.03 ± 0.04
Top 1.20 ± 0.00 0.31 ± 0.01 2.33 ± 0.711551.20 ± 159.15*221.59 ± 10.360.11 ± 0 10.39 ± 0.16 0.12 ± 0.01
Gin 0.30 ± 0 2.41 ± 0.02 3.95 ± 0.54591.95 ± 27.1541.10 ± 0.7200 ± 0.02 11.09 ± 0.29 0.12 ± 0.01
Mean ± SD 1.36 ± 0.83 2.75 ± 0.19 4.03 ± 0.36975.68 ± 95.16157.77 ± 8.100.09 ± 0.57 10.74 ± 0.43 0.28 ± 0.23
*Significantly different from the rest tea p < 0.001; All the values are in mg/L
Figure 1. Showing regression table of Mg as constant and Fe
as dependent variable.
in variety of tea brand may be due to their geographical
origin [21], due in part to leachate characteristic of soil.
Long-term plantation of tea can cause soil acidification
and elevated concentrations of bioavailable heavy metals
in the soil, therefore, enhance the risk of heavy metals
accumulation in tea leaves. The variations in the present
study might be due to different agro-climatic origins of
the imported tea. Although toxic effects of heavy metals
have sufficiently being described by WHO 1998a [24],
however, the beneficial effects of tea is in a fairly narrow
concentration range between the essential and the toxic
level [12]. The tea aqueous extracts have considerable
amounts of metals ions that could contribute towards
daily intake, but these values are lower than the daily
requirements of human being (WHO 1998b) [25]. The
determination of these elements in beverages, water,
food, plant and soil is thus of outermost important tasks.
One of the major food sources of these metals is green
leafy vegetable [26]. It is equally recommended that
aqueous extracts be routinely consumed for the essential
nutrients. Routine check and frequent analysis of tea in
Nigeria and elsewhere is required to avoid the risk of
exceeding the daily in-take beyond the tolerance limits
In conclusion, the geographical variations in heavy
metal concentrations among the tea samples were evi-
dent in all the brands. At the same time, we found sig-
nificant differences in the percent solubility of Fe and
Mg in all water soluble complexes. Some authors have
noted some differences between the metal concentrations
in other tea brands. The wide variations of metal con-
centrations observed could be due to seasonal changes
and to the chemical-physical characteristics of the grow-
ing regions.
The authors herewith state that there are no conflicts
of interest and the present study was not funded nor re-
ceive any grant from funding agency.
A. C. Achudume et al. / HEALTH 2 (2010) 1097-1100
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
[1] Soomro, M.T., Zahir, E., Mohiuddin, A., Khan, N. and
Naqui, I.I. (2007) Quantitative assessment of metals in
local brands of tea in Pakistan. Pakistan Journal of Bio-
logical Sciences, 1(2), 1-5.
[2] Ebadi, A.G., Zare, S., Mahdavi, M. and Babaee, M. (2005)
Study and measurement of Pb, Cd, Cr, and Zn in green
leaf of tea cultivated in Gillan province of Iran. Pakistan
Journal of Nutrition, 4(4), 270-272.
[3] Shukla, V., Dhankhar, M., Prakash, J. and Sastry, K.V.
(2007) Bioaccumulation of Zn, Cu and Cd in Channa
punctatus. Journal of Environmental Biology, 28(2), 395-
[4] Atta, M.B. (1995) Aluminum content in dust black tea
leaves and its beverages. Menofiya Journal of Agricultural
Research, 20(4), 137-150.
[5] Moghaddam, M.A., Mahvi, A.H., Asgari, A.R., Yonesian,
M., Jahed, G.H. and Nazmara, S.H. (2007) Determination
of aluminum and zinc in Iranian consumed tea. Envi-
ronmental Monitoring and Assessment ISSN 0167-6369,
[6] Rachh, P.P., Rachh, M.R., Soniwala, M.M., Joshi, V.D.
and Suthar, A.P. (2010) Effect of Gymnema leaf extract
on UV-induced damage on Salmonella typhi. Asian
Journal of Biological Science, 3(1), 28-33.
[7] Seenivasan, S., Manikandan, N., Muraleedharan, N.N.
and Selvasundandan, R. (2007) Heavy metal content of
black teas from South India. http//www.elsevier.com/lo-
[8] Fernandez-Caceres, P., Martini, M.J., Pablos, M. and
Gonzalez, A.G. (2001) Differention of tea (Camellia
sinensis) varieties and their metal content. Journal of Ag-
ricultural and Food Chemistry, 49(5), 4775-4779.
[9] Kumar, A., Nair, A.G.C., Reddy, A.V.R. and Garg, A.N.
(2005) Availability of essential elements in India and US
tea brands. Food Chemistry, 89(2), 441-448.
[10] Gramza, A., Wojciak, R.W., Korezak, J., Hes, M., Wis-
niewska, J. and Krejpcio, Z. (2005) Influence of the Fe
and Cu presence in tea extracts on antioxidant activity.
Food Science and Technology, 8(4), 30. http://www.ejpau.
[11] Saud Al-oud, S. (2003) Heavy metal contents in tea and
leaves. Pakistan Journal of Biological Sciences, 6(4),
[12] Ansari, F., Norbaksh, R. and Daneshmandirani, K. (2007)
Determination of heavy metals in Iranian and imported
black tea. Iranian Journal of Environmental Health, Sci-
ence and Engineering, 4(4), 243-248.
[13] Jin, C.W., Du, S.T., Zhang, K. and Lin, X.Y. (2008) Fac-
tors determining copper concentration in tea leaves pro-
duced at Yuyao County, China. Food Chemistry and
Toxicology, 20(6), 1-5.
[14] Tautkus, S., Kazlauskas, R. and Kareiva, A. (2004) De-
termination of copper in tea leaves by flame atomic ab-
sorption spectrometry. CHEIJA, 15(4), 49-52.
[15] Koller, K., Brown, T., Spurgeon, A. and Levy, L. (2004)
Recent development in low level exposure and intellec-
tual impairment in children. Environmental Health,
112(9), 987-994.
[16] Han, W.Y., Shi, Y.Z., Ma, L.F. and Ruan, J.Y. (2005)
Arsenic, cadium, chromium, cobalt, and copper in dif-
ferent types of Chinese tea. Bulletin of Environmental
Contamination and Toxicology, 75(2), 272-277.
[17] Aziz-Al-Rehman, A.M. (1985) Estimation of copper in
tea by using two different methods of solution prepara-
tion for FAAS. International Journal of Environmental
Analytical Chemistry, 22(3), 25.
[18] National Agency for Food and Drug Administration and
Control (NAFDAC) (2003) Detention and Estimation of
Food Additives, 2(2), 55-59.
[19] Sperling, M.B. and Welz, B. (1999) Atomic absorption
spectrophotometer. Wiley-VCH, Weinheim.
[20] Neter, J., Wasserman, W., Kutner, M.H. and Nachtsheim,
C.J. (1996) Applied linear statistical models. 4th Edition,
McGraw-Hill, Chicago.
[21] Wedepohl, K.H. (2000) The composition of the upper
earth’s crust and the natural cycles of selected metals.
Metals in raw materials. Natural resources. In: Merian, E.,
Ed., Metals and their Compounds in the Environment,
Part 1, John Wiley and Sons, New York, 3-19.
[22] Hamdaoui, M., Chahed, A., Ellouze-Chabchoud, S., Ma-
rouani, N., Abid, Z.B. and HAdhili, A. (2005) Effect of
green tea decoction on long-term iron, zinc and selenium
status of rats. Annals of Nutrition and Metabolism 49(2),
[23] Zhang, M, Zhou, C. and Huang, C. (2006) Relationship
between extractable metals in acid soils and metals taken
up by tea plants. http://cat.inist.fr/?a modele=afiche N&
[24] WHO (1998a) Guidelines for drinking water quality. 2nd
Edition, Health Criteria and Other Supporting Informa-
tion, World Health Organization, Geneva.
[25] WHO (1998b) Guidelines for drinking water quality. 2nd
Edition, Health Criteria and Other Supporting Informa-
tion. World Health Organization, Geneva.
[26] MacLaren, D.S., Burman, D. and Belton, N.R. (1991)
Textbook of paediatric nutrition. 3rd Edition, Churchill
Livingstone Co., London.