Carcinogenesis Related Toxicity of Selected Heavy Metals in Tobacco Cigarette Smoking: The Bogus Claim *Osagie-Eweka, S. D. E.1, Ebhohon, S. O2., Aleogho, B. M. 1 and Agbi, F. O. 1, 1
Biochemistry Department, Faculty of Life Sciences, University of Benin, P.M.B. 1154, Benin City, Nigeria. 2 Department of Biochemistry, Michael Okpara University of Agriculture, Umudike, Abia State. Nigeria
*Presenting author email:
[email protected], KEY WORDS: Tobacco cigarette, Heavy metals, carcinogenesis INTRODUCTION The study was predicated on the basis of hues and cries of heavy metals in cigarette tobacco (smoke) vis-à-vis their implication in the onset of carcinogenesis. Tobacco is a product gotten by curing leaves of tobacco plant. It is an annual or bi-annual plant that grows to between 1-3 m tall with large sticky leaves that contains nicotine. It belongs to the genus Nicotiana and to the nightshade family Solanaceae (Geiss and Kotzias, 2007). Heavy metals are one of the asymptomatic but lethal pollutants and are toxic when their concentrations are exceeded. Some of these heavy metals are essential for enzymatic activities in living organisms but their accumulation in man, animal and plant’ tissues result in metal poisoning and toxicities (Boeck, 1986). There are a couple of toxic metals in cigarette smoke that carry an extra punch of danger for anyone breathing it in and most of which are radioactive (Akpoveta et al., 2011). Metals of carcinogenic interest reported to be toxic as classified by the working groups convened by the International Agency for Research on Cancer (IARC) are Arsenic (As), Cadmium (Cd), Nickel (Ni), Lead (Pb), Cobalt (Co). Other benign metals are Calcium (Ca), Magnesium (Mg), Potassium (K), Sodium (Na), and Strotium (St). Lead-210 (Pb-210) and Polonium-210 (Po-210) are poisonous radioactive heavy metals present in cigarette smoke commonly used in rat poison. A number of these heavy metals find their way into tobacco cigarette through some of the pesticides and chemical fertilizer used on tobacco farm lands (Cekic, 1998). According to the report of World Health Organization (2015), the statistics of prevalence of tobacco cigarette smoking in Nigeria of both male and female are 3.7 % for adults and 3.5 % for youths. The study sought to evaluate the concentration and heavy metal constituents of tobacco plants of cigarettes popularly consumed in Benin City metropolis with cognizance, the effects of wet or dry digestion procedures. MATERIALS AND METHOD Yes®, Oris®, Sterling®, Benson & Hedges®, Rothmans® and Pall Mall® tobacco cigarette brands, popularly smoked in Benin metropolis, Nigeria were obtained; twenty (20) sticks of cigarettes were sampled from five (5) packs of each cigarette brands in triplicate. Cigarette filter
and cellulose paper were removed and tobacco was weighed. Tobacco was ground to fine particles and stored in a sterile bottle, concentration and constituents of heavy metals were evaluated. The wet and dry digestion methods were used in the study according to the methods previously described by Noler (2006) and Adler and Wilcox (1985). The heavy metals of speculative carcinogenic interest were evaluated based on the principle of flame atomic absorption spectrophotometry. RESULTS Table 1: Essential information and weight (s) of Tobacco cigarette Cigarette Brand
Batch Number
Wt. of tobacco without paper and filter (g)*
State of Production
YES®
600475000095
15.35 ± 0.04
Kaduna State, Nigeria
ORIS®
4260093460877
10.93 ± 0.02
Abuja, Nigeria
STERLING®
5010175819050
14.83 ± 0.02
Kwara State, Nigeria
PALL MALL®
6156000056302
13.81 ± 0.03
Oyo State, Nigeria
ROTHMANS®
6156000056364
14.18 ± 0.05
Oyo State, Nigeria
BENSON & HEDGES®
6156000056388
13.87 ± 0.02
Oyo State, Nigeria
*Results are reported as Mean ± SD
Table 2: Results of selected heavy metals in tobacco cigarette Metals
Wet Digest
Ash Digest
Wet Digest
Ash Digest
Wet Digest
YES® (µg/g)
YES® (µg/g)
ORIS® (µg/g)
ORIS® (µg/g)
STERLING® (µg/g)
Ash Digest STERLING® (µg/g)
Maximum allowable limits by W.H.O (mg/l)
Cd
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.0
Co
0.54 ± 0.16a
0.12 ± 0.02a
0.77 ± 0.06a
0.00 ± 0.00b
0.80 ± 0.01a
0.00 ± 0.00b
0.02
Ni
24.30 ± 0.62a
20.57 ± 0.79b
14.28 ± 0.55a
13.01 ± 0.01b
27.97 ± 0.63a
26.34 ± 0.51b
0.02
Pb
3.19 ± 0.11a
0.00 ± 0.00b
0.68 ± 0.02a
0.00 ± 0.00b
0.39 ± 0.01a
0.11 ± 0.01a
0.10
Results are reported as Mean ± SD
Table 3: Results of selected heavy metals in tobacco cigarette Wet Digest
Ash Digest
Wet Digest
Ash Digest
Wet Digest
Ash Digest
PALL MALL® (µg/g)
PALL MALL® (µg/g)
ROTHMANS® (µg/g)
ROTHMANS® (µg/g)
BENSON & HEDGES® (µg/g)
BENSON & HEDGES® (µg/g)
Cd
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.00 ± 0.00a
0.06
Co
0.29 ± 0.01a
0.00 ± 0.00a
0.43 ± 0.11a
0.00 ± 0.00a
0.67 ± 0.06a
0.00 ± 0.00a
0.02
Ni
12.72 ± 0.01a
12.67 ± 0.01a
16.27 ± 0.56a
15.56 ± 0.06b
23.99 ± 0.58a
23.41 ± 0.01a
0.02
Pb
2.47 ± 0.30a
0.00 ± 0.00b
3.81 ± 0.01a
0.00 ± 0.00b
4.26 ± 0.01a
0.00 ± 0.00b
0.10
Metals
Maximum allowable limits by W.H.O (mg/l)
Results are reported as Mean ± SD The results of selected heavy metal analyzed of six (6) tobacco cigarette brands are presented in tables 2 and 3. The resultant effects of wet or ash digestion procedures, particularly the incinerated tobacco on the heavy metal constituents of tobacco was evaluated. A reduction (for example, Nickel), in some cases, complete absence of these metals (cadmium, cobalt and lead) was observed of the ash digest samples of all tobacco cigarette brands considered compared to the wet digest samples. A reduction of Lead (Pb) was detected in the ash digest of Sterling® as against a complete absence as observed in the ash digests of other tobacco cigarette brands. At mass of one (1) gram, the concentration of heavy metals detected in the ash digests of all tobacco cigarette brands considered in the study did not exceed the World Health Organization (WHO) allowable limits except Nickel (Ni) in the ash digests of all tobacco cigarettes.
DISCUSSION Cadmium It is highly toxic to kidney, bone and the nervous, respiratory and circulatory systems and ocular tissues (Agency for Toxic Substances and Disease Registry, 2008 and Cekic, 1998). Cadmium was neither detected in the wet nor ash digest samples of all tobacco cigarette considered in the study. The findings in the study contrast the reports of Nnoromi et al., (2005) who reported the cadmium (Cd) concentration in approximately thirty (30) tobacco cigarettes in Nigeria; that includes some of the brands considered in this study ranged from 0.90-1.50 µg/g. The discrepancy observed could be attributed to increased campaign on ban of tobacco cigarette consumption and subsequent preventive steps by tobacco Company on abolition of chemical fertilizers or pesticides that convey cadmium to tobacco plants.
Cobalt Although it’s required nutritionally at trace concentrations, Cobalt has also been reported to induce immunological sensitization including epidermal and oral allergic contact sensitization, contact dermatitis, pulmonary inflammation, pneumoconiosis and asthma amongst many others (Rüegger, 1995). There was
a reduction in the concentration of Cobalt (YES® tobacco cigarette) and complete absence of Cobalt in the ash digests samples of all other tobacco cigarettes compared to the wet digests. The complete absence of Cobalt in ash digests of tobacco cigarettes is absolutely attributed to the temperature (≥ 600ºC) at which the tobacco were incinerated. Although, the method of digestion reported in the study is similar to the digestion method reported in the study conducted by Yebpella et al., (2011), while Cobalt was detected in the ash digests tobacco of the former study, Cobalt was completely absent in the ash digests tobacco cigarettes of the present study. The disparity in the findings is hypothetical ascribed to the different temperatures. The higher the temperature at which tobacco plants are incinerated, the more volatile the metals. Nickel Nickel is an essential micronutrient but toxic at high concentration and can be deleterious. Scientific reports have revealed that tobacco plants accumulate nickel and other heavy metals. Humans may be exposed to nickel by breathing air, drinking water, eating food or smoking cigarettes; studies have shown that smokers have a higher nickel uptake through their lung (Underwood, 1997). Tobacco plants are reported to accumulate high Nickel (Abdulkadir et al., 2013). The results obtained in the present study is consistent with the studies of Iwuoha et al., (2013), Yebpella et al., 2011), and Asubiojo et al., (2009) who reported 4.67 and 3.43 µg/g (Benson and Hedges and Rothmans), 1.33 μg/g and 16.92 μg/g respectively. Although, the present study revealed higher mean concentrations of Nickel in all the tobacco cigarettes considered, there was however a significant reduction in Nickel of ash digests samples related to the wet digests. The mean values of Nickel in the study substantiate numerous hypotheses of possible exposure of smokers to Nickel, irrespective of volatility of metals at temperatures (≥ 900ºC) at tobacco cigarette are incinerated (Baker, 1981). Lead Lead is a toxic metal, at exceeded concentration, it is neurotoxic, and at low levels of exposure, it may interfere development and growth. In adults, blood lead concentrations considered to be acceptably low (< 10 μg/dl) have been associated with raised systemic blood pressure and reduced glomerular filtration rate (Xiao et al., 2004). Lead accumulates in tissue; over a lifetime, in bone. The results of the present study reveals the presence of Lead (Pb) in the wet digests of all tobacco cigarette considered; compares favorably with the report of Iwuoha et al., (2013), however, the complete absence of Lead in the ash digests of all tobacco cigarettes (with an insignificant exception to the ash digest of STERLING® tobacco brand) contrast the studies conducted by Iwuoha et al., (2013); obviously attributed to the difference in temperature at which the tobacco were incinerated. While the present study incinerated tobacco at ≥ 650ºC, Iwuoha and partners (2013) incinerated at 105ºC.
CONCLUSION In as much as the study revealed the presence of heavy metals of carcinogenic interests as convened by IARC, in tobacco cigarettes popularly consumed in Benin metropolis; supports the claim that exposure to heavy metals contributes a great deal to oxidative stress of organs or tissues (Cekic, 1998, Nnoromi et al., 2005, and Eriyamremu et al., 2008), outcome of analyzed tobacco digests incinerated at ≥ 650ºC revealed significant absence of claimed carcinogenic heavy metals considered in the study. The findings in the study is further validated by the study reported by Denissenko et al., (1996), wherein it was reported that Benzo(a)pyrene, a potent carcinogenic polyhydrocarbon compound present in tobacco cigarette can bind to the Guanine present in the P53 gene of the lungs. This action results to mutation that causes a permanent damage which leads to lung cancer. Currently, studies have reported the strongly dangers of exposure to toxic metals, however, none has demonstrated their mechanisms of carcinogenesis. Therefore, the claim by IARC that these metals are carcinogenic should be dismissed as they are non-radioactive. SELECTED REFERENCES Abdulkadir, L., Yavuz, Y and Cengiz, D (2013). Determination of Trace Metal and Mineral Levels in the Tobacco and Cigarette Samples by FAAS. Journal of Chemical Society of Pakistan 35(2): 257-261. Akpoveta, V., Osakwe, S., Egharevba, F., Osaro, I., Akpoveta, A., Osazuwa, J., Okoh, B., Okwagi, P., Aweatefe, K., Odighere, M. and Weltime, M (2011). A comparative evaluation and toxicity assessment of heavy metals in commonly smoked cigarette brands and local tobacco snuff purchased and consumed in Nigeria. Research Journal of Environmental Toxicology 5: 359–368. Alireza, P. and Pourkhabbaz, H (2012). Investigation of toxic metals in the tobacco of different Iranian cigarette brands and related health issues. Iranian Journal of Basic Medical Sciences. 15(1):636–644. Eriyamremu, G. E., Ojimogho, S. E., Asagba, S. O and Osagie, V. E (2008). Palm oil induced changes in ocular tissue lipid peroxidation, antioxidant enzymes and ATPases of rabbits in cadmium toxicity. Food and Chemistry Toxicology 46(9): 3155-3158. IARC (2006).Summaries & evaluations: Inorganic and organic lead compounds Lyon, International Agency for Research on Cancer (IARC Monographs for the Evaluation of Carcinogenic Risks to Humans, 87. Iwuoha, G. N., Oghu, E. I and Onwuachu, U. I (2013). Levels of Selected Heavy Metals in Some Brands of Cigarettes Marketed in University of Port Harcourt, Rivers State. Journal of Applied Sciences and Environmental Management 7(4): 561-564.
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