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Lead levels of certain consumer products in Nigeria: a case study of smoked fish foods from Abeokuta
Food and Chemical Toxicology 42 (2004) 1463–1468 www.elsevier.com/locate/foodchemtox
Lead levels of certain consumer products in Nigeria: a case study of smoked fish foods from Abeokuta I.M. Adekunle *, M.F. Akinyemi Department of Environmental Management and Toxicology, University of Agriculture, Abeokuta, Nigeria Received 7 April 2004; received in revised form 7 April 2004; accepted 14 April 2004
Abstract The total lead levels of 252 indigenously processed smoked fish foods exposed to the highways were determined via atomic absorption spectrometry. Metal content was monitored at various periods of the day. A fraction of the sample population was investigated for the effect of atmospheric exposure while the remaining portion was examined for the impact of processing technique on the fish metal levels. Quantitative evaluation of the vehicular traffic density per hour (VTD/h) of the near-by highway to each market was conducted. Data generated from both the VTD/h and the fish lead levels were subjected to Pearson correlations and regression analyses. Results indicate contamination of these fish foods by lead with mean values varying from 8.0 ± 0.8 to 12.5 ± 1.6 mg/kg The food processing technique accounted for up to seven times increase in fish lead levels. The average VTD/h ranged from 1510 ± 198 to 1752 ± 344. Results also indicate a certain degree of relationship between the vehicular traffic and the lead levels. Positive correlation coefficients (r) ranged from 0.336 to 0.867. The investigated systems conjoin to give fish lead contents of more than thirty folds above the stipulated safety standard for lead level in fish foods. The study provides additional data on lead pollution in Nigeria. This connotes a potential threat to the health, security and safety of such food items to the unsuspecting consumer. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Atmospheric exposure; Lead; Fish foods; Environment
1. Introduction Lead is a heavy metal found naturally in all parts of the world. It is found in many modern products such as pottery, batteries, stabilizers for plastics, pigment for inks, electrical accessories and plumbing pipes. Due to the manufacture, utilization and disposal of these products, fine lead particles are released into the environment. Lead particles can enter air, water, soil, dust and food. The best known products to have lead are paints and gasoline. In some parts of the world, unleaded gasoline are being used to fuel the automobiles but in many other nations leaded gasoline are yet to be completely phased out especially in Africa (Nriagu et al.,
* Corresponding author. Current Address: Engler-Bunte-Institute, Wasser Chemie Bereich, Universit€at Karlsruhe, D-76131 Karlsruhe, Germany. Tel.: +49-721-608-7060; fax: +49-721-608-4949. E-mail address: [email protected] (I.M. Adekunle).
0278-6915/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fct.2004.04.007
1996; Nriagu et al., 1997). The gasoline currently sold in Nigeria is estimated to have lead content of about 0.25 g/l. The national consumption of petrol is estimated as 25 million litres per day and a 75% emission rate of lead as particulate (Maduka, 2001; Enemari, 2001). It has been revealed that the highest level of lead in Nigeria occurs in Aviation, and Super grade gasoline. The presence of lead in diesel, kerosene and lubricating oil (products of crude oil refining) has also been reported (Osibanjo and Ajayi, 1989). The principal mode of transportation in Nigeria is mainly by road. Several studies showed that levels of lead deposits in the country in all cases were found to vary according to traffic volume, increasing with high-density areas (Osibanjo and Ajayi, 1980; Onianwa and Egunyomi, 1983; Ndiokwerre, 1984; Sridhar et al., 2000a,b). Lead poisoning is usually ranked as the most common environmental health hazard. Toxicity of lead is widely documented. Health hazards of lead include impairment of hearing ability, interference with the red blood cell
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I.M. Adekunle, M.F. Akinyemi / Food and Chemical Toxicology 42 (2004) 1463–1468
formation leading to anaemia, renal failure, increased frequency of miscarriages and still births. Others include reduced body immune system, low birth weights, premature births, reduced sperm counts and motility, (Goyer, 1991; ATSDR, 1998; Benowitz and Goldschlager, 1998). Elevated blood and urine lead levels have been reported in African nations including Nigeria (Adeniyi and Anetor, 1999; Anetor, 2001; Ademuyiwa et al., 2002). The same phenomenon has been observed in various parts of the globe (Sammut and SavonaVentur, 1996). Fine particles of lead emitted into the environment can travel a long distance, causing pollution far from the source. The most significant pathways of lead exposure is by ingestion of lead painted surfaces, inhalation from automobiles and consumption of lead contaminated foods. This study therefore investigates the lead level of fish foods sold in Nigerian markets, a case study of smoked fish from Abeokuta metropolitan city, southwest Nigeria. The contributory effects of the local food processing technique and the potential relationship between the fish lead levels and the vehicular traffic volume were also examined.
sixty minutes. This was carried out three times per day corresponding to 8 to 9 am in the morning (P1), 12 noon to 1 pm in the afternoon (P2) and 5 to 6 pm in the evening (P3). The exercise was conducted for a period of two weeks (fourteen consecutive days) at each station. 2.3. Sample collection and preservation In a given location and at a particular investigation period (Table 1) smoked fish samples were randomly collected and pooled together. Representative samples of the fish muscles were oven dried at 105 °C to constant weight. These were then ground to fine powder and stored in plastic wares. 2.4. Control samples An arrangement was made with some local smoked fish producers to collect fish samples before smoking (I) and immediately after smoking (II). Fish smoking is usually carried out in a courtyard of residential quarters before being conveyed to the outdoor market. Hence, at a particular investigation area, samples were collected for (I) and (II) at three replicates respectively.
2. Materials and methods 2.5. Determination of lead in fish
2.1. Description of study area Abeokuta is a city in southwestern Nigeria and the capital of Ogun state (one of the 36 states of Nigeria). It is located within the Ogun river basin, about 74 km from Lagos. Abeokuta is inhabited largely by the Yoruba tribe and has an estimated population of over two million. Abeokuta has a good road network within the city. There are a lot of roadside (outdoor) markets, that is, open-markets which are situated very close to the highways, a phenomenon very common in the country. The markets selected for this study are as described in Table 1. 2.2. Evaluation of the vehicular traffic density The vehicular traffic density per hour (VTD/h) in Abeokuta metropolis was assessed by recording the number of automobiles plying the highways within
One thousand milligram portion of the pre-treated sample was subjected to wet digestion using 6 M trioxonitrate (v) acid (HNO3 ). The volume of the acid digest was minimally reduced by evaporation, filtered through Whatman No.1 paper and diluted to 100 ml using deionised water in a volumetric flask. Blank samples were also prepared. Total lead in the digest was analysed with the help of atomic absorption spectrometer (Buck Model 200). 2.6. Statistical analysis Data generated were subjected to 1-way analysis of variance (ANOVA) for statistical differences at P < 0:05. Pearson correlation and regression models were applied for possible relationships. Results are expressed as mean ± standard deviation.
Table 1 Study site description of Abeokuta markets Highway road
Market specification/code
Investigation period
Adatan Highway Ijaye Highway Itoku Highway Kuto Highway Lafenwa Highway Omida Highway
Adatan market (MKT-1-ADT) Ijaye market (MKT-2-IJA) Itoku market (MKT-3-ITK) Kuto market (MKT-4-KUT) Lafenwa market (MKT-5-LAF) Omida market (MKT-6-OMD)
8–9 8–9 8–9 8–9 8–9 8–9
am am am am am am
(P1); (P1); (P1); (P1); (P1); (P1);
12–1 12–1 12–1 12–1 12–1 12–1
pm pm pm pm pm pm
(P2); (P2); (P2); (P2); (P2); (P2);
5–6 5–6 5–6 5–6 5–6 5–6
pm pm pm pm pm pm
(P3) (P3) (P3) (P3) (P3) (P3)
I.M. Adekunle, M.F. Akinyemi / Food and Chemical Toxicology 42 (2004) 1463–1468
3. Results and discussion 3.1. Fish lead level The mean lead levels (unit in mg/kg) obtained in the investigated smoked fish products were MKT-1-ADT (9.5 ± 2.2, 10.0 ± 2.2, 9.6 ± 2.2); MKT-2-IJA (8.0 ± 0.8, 8.3 ± 0.9, 8.7 ± 0.6); MKT-3-ITK(12.1 ± 1.7, 11.7 ± 1.2, 12.5 ± 1.6); MKT-4-KUT (10.6 1.3, 9.7 ± 1.5, 8.9 ± 1.6); MKT-5-LAF (7.9 ± 0.8, 8.0 ± 0.8, 8.5 ± 0.6) and MKT-6OMD (9.8 ± 1.2, 11.1 ± 1.4, 11.4 ± 0.3) shown in Tables 2–7. The smoked fish lead levels were higher than the stipulated fish lead level of 0.2 mg/kg (EU, 2002), indicating pollution of these consumer products by the metal.
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Generally, low coefficient of variations (Cv), ranging from 3% to 25% were obtained, indicating a relative good reproducibility of data. Investigation at the morning period revealed that fresh products were not usually available at this time of the day. Results obtained immediately after smoking (before exposure at the outdoor markets) gave a mean value of 0.95 ± 0.01 mg/kg. A range of 8.3 ± 0.9 to 11.7 ± 1.2 mg/kg was obtained in the morning samples (Table 2). Fresh products are expected to give much lower lead values such as was obtained only once at MKT-3-ITK (1.0 mg/ kg; Table 2). Results suggest that fresh products were not usually sold until the previous stock was exhausted. The fish lead levels varied quantitatively at the various
Table 2 Fish lead levels obtained at the morning period (8–9 am) from the roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
9.5 2.2 23 5.6–12.6 14
8.0 0.8 10 6.7–9.3 14
12.1 1.7 14 1.0–14.0 14
10.6 1.3 12 8.6–11.9 14
7.9 0.8 10 6.8–9.1 14
9.8 1.2 12 7.9–11.9 14
Unit in mg/kg.
Table 3 Fish lead levels obtained at the afternoon period (12–1 pm) from the roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
10.0 2.2 22 5.6–12.6 14
8.3 0.9 11 6.7–9.3 14
11.7 1.2 10 9.9–14.1 14
9.7 1.5 15 7.2–11.8 14
8.0 0.8 10 7.2–9.1 14
11.1 1.4 13 8.1–12.0 14
Unit in mg/kg.
Table 4 Fish lead levels obtained at the evening period (5–6 pm) from the roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
9.6 2.2 23 6.6–12.8 14
8.7 0.6 7 7.9–9.4 14
12.5 1.6 13 9.9–14.1 14
8.9 1.6 18 7.1–12.1 14
8.5 0.6 7 6.9–9.1 14
11.4 0.3 3 10.6–12.1 14
Unit in mg/kg.
Table 5 Vehicular traffic density per hour at the morning period (8–9 am) on the highways close to the investigated roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
1541 138 9 1331–1787 14
1510 198 13 1317–1963 14
1540 185 12 1294–1731 14
1567 141 9 1272–1738 14
1752 344 20 1214–2317 14
1509 75 4 1134–1681 14
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Table 6 Vehicular traffic density per hour at the afternoon period (12–1 pm) on the highways close to the investigated roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
1518 109 7 1311–1735 14
1529 172 11 1334–1809 14
1620 110 7 1425–1781 14
1543 167 11 1077–1730 14
1735 218 13 1307–1943 14
1627 154 9 1404-1979 14
Table 7 Vehicular traffic density at the evening period (5–6 pm) on the highways close to the investigated roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
1541 77 5 1414–1665 14
1549 90 6 1384–1675 14
1691 102 6 1561–1927 14
1509 159 11 1134–1681 14
1840 132 7 1575–1981 14
1721 122 7 1483–1965 14
periods of the day but were not statistically significant at P < 0:05. Previous works have reported high lead levels for other types of food sold at outdoor markets in Nigeria. These include 0–12.5 mg/kg in Elubo (Yam or cassava flour), 6.5 mg/kg in Suya (a type of meat preparation) and 0–15.1 mg/kg in dried meat (Okoye, 1994). A study on smoked fish in a certain part of the country about a decade ago gave lead level in the range of 0–9.7 mg/kg (Okoye, 1994). 3.2. Impact of the smoking method and atmospheric exposure on fish lead level The local food processing technique increased the fish lead level from 0.14 ± 0.02 mg/kg (I) to 0.95 ± 0.01 mg/ kg (II), from the difference, depositing up to 0.82 ± 0.01 mg/kg which is above the standard limit of 0.2 mg/kg (Fig. 1). This implies that before the local processing method was applied, the lead level was below the stipulated threshold. Results indicate that the smoking method contributes to the metal pollution in the fish food. The fuel sources employed in the smoking process
such as coal, charcoal and kerosene and even gasoline which have been reported to contain lead (Osibanjo and Ajayi, 1989) could have contributed to the multiple fold increase in the smoked fish lead level. The smoking method increased the fish lead by an approximate factor of seven. 3.3. Effect of atmospheric exposure on fish lead Calculation was made and the difference between the total fish lead after exposure and the lead in fish (0.95 ± 0.01 mg/kg) immediately after smoking, prior to exposure at the outdoor market gave the effect of atmospheric exposure on fish lead level. The effect varied from 7.0 to 11.2 mgPb/kg (Fig. 2). 3.4. Traffic density on the highways of Abeokuta The data of the traffic density per hour on the highway are presented in Tables 5–7. The smoked fish products are usually sold at a distance of 0–2 meters from the highways. The vehicular traffic density per 12
1 0.8 Before smoking After smoking
0.6
Pb deposited 0.4
Lead level in mg/kg
Lead level in mg/kg
1.2 10 8
Morning period Afternoon period Evening period
6 4 2 0
0.2
MKT-1- MKT-2- MKT-3- MKT-4- MKT-5- MKT-6ADT IJA ITK KUT LAF OMD
0 Fish-1 Fish-2 Fish-3 Fish-4 Fish-5 Fish-6
Location
Fish sample
Fig. 1. Effect of smoking method on fish lead level.
Fig. 2. Effect of atmospheric exposure on the fish lead levels in Abeokuta, Nigeria.
I.M. Adekunle, M.F. Akinyemi / Food and Chemical Toxicology 42 (2004) 1463–1468
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Table 8 Pearson correlations between vehicular traffic density per hour and fish lead levels in Abeokuta, Nigeria
Location
Investigation period
Study population (n)
MKT-1-ADT MKT-1-ADT MKT-1-ADT
P1 P2 P3
14 14 14
0.547 0.336 0.221
Y ¼ 0:0088x 4:0038 Y ¼ 0:0076x 1:5836 Y ¼ 0:0062x þ 0:1231
MKT-2-IJA MKT-2-IJA MKT-2-IJA
P1 P2 P3
14 14 14
0.677 0.801 0.474
Y ¼ 0:0027x þ 3:2748 Y ¼ 0:0041x þ 2:1279 Y ¼ 0:0030x þ 4:0069
MKT-3-ITK MKT-3-ITK MKT-3-ITK
P1 P2 P3
14 14 14
0.520 0.655 0.496
Y ¼ 0:0047x þ 4:9203 Y ¼ 0:0073x 0:2139 Y ¼ 0:0078x 1:6529
MKT-4-KUT MKT-4-KUT MKT-4-KUT
P1 P2 P3
14 14 14
0.613 0.744 0.688
Y ¼ 0:0054x þ 1:6019 Y ¼ 0:0066x 0:5087 Y ¼ 0:0070x 1:6529
MKT-5-LAF MKT-5-LAF MKT-5-LAF
P1 P2 P3
14 14 14
0.867 0.343 0.638
Y ¼ 0:0020x þ 4:3641 Y ¼ 0:0012x þ 5:9615 Y ¼ 0:0030x þ 2:9164
MKT-6-OMD MKT-6-OMD MKT-6-OMD
P1 P2 P3
14 14 14
and
Correlation coefficient
0.617 0.334 0.339
Regression equation
Y ¼ 0:0027x þ 5:2477 Y ¼ 0:0020x þ 14:2730 Y ¼ 0:0019x þ 8:1776
¼ levels significant at P < 0:05 and 0.01 respectively.
hour in Abeokuta varied from 1011 to 2317 with mean values as MKT-1-ADT (1541 ± 138, 1518 ± 109, 1541 ± 77), MKT-2-IJA (1510 ± 198, 1529 ± 172, 1549 ± 90), MKT-3-ITK (1540 ± 185, 1620 ± 110, 1691 ± 102), MKT-4-KUT (1567 ± 141, 1543 ± 167, 1519 ± 159), MKT-5-LAF (1752 ± 344, 1735 ± 218, 1840 ± 132) and MKT-6-OMD (1671 ± 75, 1627 ± 154, 1721 ± 122). There was no statistically significant variations in the number of vehicles plying the various highways close to the markets at P < 0:05 (ANOVA).
of the vehicular traffic per hour though positive correlation coefficients were obtained (Fig. 2, Tables 2–4). This implies that the cause of lead in the consumer product at the outdoor markets in Nigeria is multifactoral. Activities such as tyre burning, open-air waste combustion, hobbies and recreational activities that use lead could also account for the presence of lead in these products.
4. Conclusion 3.5. Correlation between traffic density and fish lead Vehicles plying the highways include commercial, heavy duty and private automobiles. Lead levels in the exhausts of some automobiles in Nigeria were reported in the range of 0.043–11.40 (commercial automobiles), 0.096–18.00 (Heavy duty automobiles) and 0.038–11.20 (Private automobiles), units in mg/g (Sridhar et al., 2000a,b). Lead level in Super grade gasoline used in Nigeria was reported as 600–800 lg/ml (Osibanjo and Ajayi, 1989; Shy, 1990). Results indicate various degrees of relationships between the fish lead levels and the VTD/h. Positive correlations were calculated with correlation coefficients ranging from 0.339 to 0.867. Some of the correlations were statistically significant while the others were not (Table 8). A negative correlation was obtained at MKT6-OMD (r ¼ 0:334), an indication that there could be other sources of atmospheric lead pollution apart from the vehicular traffic on the highway. No consistent or definite trend was found between the quantitative values
The investigated consumer products (smoked fish) contain elevated lead levels. The cause of the lead pollution is multidimensional, including the food processing technique, highway pollution and other undisclosed factors. The part two of this study will examine the smoked fish lead level as a function of atmospheric exposure time.
Acknowledgements The Authors thank Dr. O. Oguntoke of the Department of Environmental Management and Toxicology, University of Agriculture, Abeokuta, Nigeria for assisting in the statistical analysis. References Ademuyiwa, O., Arowolo, T., Ojo, D.A., Odukoya, O.O., Yusuf, A.A., Akinhanmi, T.F., 2002. Lead levels in blood and urine of
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some residents of Abeokuta, Nigeria. Trace Elements and Electrolytes 19, 63–69. Adeniyi, F.A.A., Anetor, J.I., 1999. Lead––poisoning in two distant states of Nigeria: an indication of the real size of the problem. African Journal of Medicine and Medical Sciences 28, 107–112. Agency for Toxic Substances and Disease Registry, 1998. Toxicological profile for lead uptake. US Department of Health and Human Services, pp. 45–268. Anetor, J.I., 2001. High blood lead levels in general Nigerian population. In: Proceedings of Nigeria National Conference on Lead Phase-Out, Abuja, Nigeria. Organised by World Bank, 15–16 November. Benowitz, N.L., Goldschlager, N., 1998. Cardiac disturbances. In: Haddad, L.M., Shannon, M.W., Winchester, J.K. (Eds.), Clinical Management of Poisoning and Drugs Overdose, third ed. Saunders, Philadelphia. Enemari, E., 2001. Vehicular emission, environmental and health implication. In: Proceedings of Nigeria National Conference on Lead Phase-Out, Abuja, Nigeria. Organised by World Bank, 15–16 November. European Communities, 2002. Amending regulation, setting maximum levels of certain contaminants in foodstuffs. Official Journal of European Communities L37, 4–6. Goyer, R.A., 1991. Toxic effects of metals. In: Amdur, M.V, Douli, J., Klansmen, C.D. (Eds.), Caserrett and Doull’s Toxicology: The Basic Science of Poisons, fourth ed. Pergamon Press, New York, pp. 623–680. Maduka, J.O., 2001. Sources of environmental lead in Nigeria. In: Proceedings of Nigeria National Conference on lead phase-out, Abuja, Nigeria. Organised by World Bank, 15–16 November. Ndiokwerre, C.C., 1984. A study of heavy metal pollution from motor vehicle emissions and its effect on roadside soil, vegeta-
tion and crops in Nigeria. Environmental Pollution Series B 7, 35– 42. Nriagu, J.O., Blackson, M.I., Ocram, K., 1996. Childhood lead poisoning in Africa: a growing public health problem. Science of the Total Environment 181 (2), 93–101. Nriagu, J.O., Jirabhai, C.C., Naidoo, R., Coutsound, A., 1997. Science of the Total Environment 197, 1–11. Okoye, C.O.B., 1994. Lead and other metals in dried fish from Nigerian markets. Bulletin of Environmental Contamination and Toxicology 52, 825–832. Onianwa, P.C., Egunyomi, J.K., 1983. Trace metal levels in some Nigerian Mosses used as indictors of atmospheric pollution. Environmental Pollution Series B 5, 71–81. Osibanjo, O., Ajayi, S.O., 1980. Trace metal levels in tree barks as indicators of atmospheric pollution. Environmental International 4, 239–244. Osibanjo, O., Ajayi, S.O., 1989. Trace metal analysis of petroleum products by flame atomic absorption spectrometry. Nigerian Journal of Natural Sciences 4, 33–40. Sammut, M., Savona-Ventur, C., 1996. Petrol lead in a small Island environment. International Journal of Risk and Safety in Medicine 9, 33–40. Shy, C.M., 1990. Lead in petrol: the mistake of the xxth century. World Health Statistics Quarterly 43, 168–176. Sridhar, M.K.C., Adogame, L., Olawuyi, J., 2000a. Lead exposure in urban centres: a case study from Ibadan, Nigeria. Epidemiology, USA 10, 22, 227. Sridhar, M.K.C., Olawuyi, J., Adogame, L., Okekearu, A., Osajie, C.O., Linda, A., 2000. Lead in the Nigerian environment: problems and prospects. In: 11th Annual International Conference on Heavy Metals in the Environment. University of Michigan, School of Public Health, Ann Arbor, MI (CD-ROM).
Lead levels of certain consumer products in Nigeria: a case study of smoked fish foods from Abeokuta I.M. Adekunle *, M.F. Akinyemi Department of Environmental Management and Toxicology, University of Agriculture, Abeokuta, Nigeria Received 7 April 2004; received in revised form 7 April 2004; accepted 14 April 2004
Abstract The total lead levels of 252 indigenously processed smoked fish foods exposed to the highways were determined via atomic absorption spectrometry. Metal content was monitored at various periods of the day. A fraction of the sample population was investigated for the effect of atmospheric exposure while the remaining portion was examined for the impact of processing technique on the fish metal levels. Quantitative evaluation of the vehicular traffic density per hour (VTD/h) of the near-by highway to each market was conducted. Data generated from both the VTD/h and the fish lead levels were subjected to Pearson correlations and regression analyses. Results indicate contamination of these fish foods by lead with mean values varying from 8.0 ± 0.8 to 12.5 ± 1.6 mg/kg The food processing technique accounted for up to seven times increase in fish lead levels. The average VTD/h ranged from 1510 ± 198 to 1752 ± 344. Results also indicate a certain degree of relationship between the vehicular traffic and the lead levels. Positive correlation coefficients (r) ranged from 0.336 to 0.867. The investigated systems conjoin to give fish lead contents of more than thirty folds above the stipulated safety standard for lead level in fish foods. The study provides additional data on lead pollution in Nigeria. This connotes a potential threat to the health, security and safety of such food items to the unsuspecting consumer. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Atmospheric exposure; Lead; Fish foods; Environment
1. Introduction Lead is a heavy metal found naturally in all parts of the world. It is found in many modern products such as pottery, batteries, stabilizers for plastics, pigment for inks, electrical accessories and plumbing pipes. Due to the manufacture, utilization and disposal of these products, fine lead particles are released into the environment. Lead particles can enter air, water, soil, dust and food. The best known products to have lead are paints and gasoline. In some parts of the world, unleaded gasoline are being used to fuel the automobiles but in many other nations leaded gasoline are yet to be completely phased out especially in Africa (Nriagu et al.,
* Corresponding author. Current Address: Engler-Bunte-Institute, Wasser Chemie Bereich, Universit€at Karlsruhe, D-76131 Karlsruhe, Germany. Tel.: +49-721-608-7060; fax: +49-721-608-4949. E-mail address: [email protected] (I.M. Adekunle).
0278-6915/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fct.2004.04.007
1996; Nriagu et al., 1997). The gasoline currently sold in Nigeria is estimated to have lead content of about 0.25 g/l. The national consumption of petrol is estimated as 25 million litres per day and a 75% emission rate of lead as particulate (Maduka, 2001; Enemari, 2001). It has been revealed that the highest level of lead in Nigeria occurs in Aviation, and Super grade gasoline. The presence of lead in diesel, kerosene and lubricating oil (products of crude oil refining) has also been reported (Osibanjo and Ajayi, 1989). The principal mode of transportation in Nigeria is mainly by road. Several studies showed that levels of lead deposits in the country in all cases were found to vary according to traffic volume, increasing with high-density areas (Osibanjo and Ajayi, 1980; Onianwa and Egunyomi, 1983; Ndiokwerre, 1984; Sridhar et al., 2000a,b). Lead poisoning is usually ranked as the most common environmental health hazard. Toxicity of lead is widely documented. Health hazards of lead include impairment of hearing ability, interference with the red blood cell
1464
I.M. Adekunle, M.F. Akinyemi / Food and Chemical Toxicology 42 (2004) 1463–1468
formation leading to anaemia, renal failure, increased frequency of miscarriages and still births. Others include reduced body immune system, low birth weights, premature births, reduced sperm counts and motility, (Goyer, 1991; ATSDR, 1998; Benowitz and Goldschlager, 1998). Elevated blood and urine lead levels have been reported in African nations including Nigeria (Adeniyi and Anetor, 1999; Anetor, 2001; Ademuyiwa et al., 2002). The same phenomenon has been observed in various parts of the globe (Sammut and SavonaVentur, 1996). Fine particles of lead emitted into the environment can travel a long distance, causing pollution far from the source. The most significant pathways of lead exposure is by ingestion of lead painted surfaces, inhalation from automobiles and consumption of lead contaminated foods. This study therefore investigates the lead level of fish foods sold in Nigerian markets, a case study of smoked fish from Abeokuta metropolitan city, southwest Nigeria. The contributory effects of the local food processing technique and the potential relationship between the fish lead levels and the vehicular traffic volume were also examined.
sixty minutes. This was carried out three times per day corresponding to 8 to 9 am in the morning (P1), 12 noon to 1 pm in the afternoon (P2) and 5 to 6 pm in the evening (P3). The exercise was conducted for a period of two weeks (fourteen consecutive days) at each station. 2.3. Sample collection and preservation In a given location and at a particular investigation period (Table 1) smoked fish samples were randomly collected and pooled together. Representative samples of the fish muscles were oven dried at 105 °C to constant weight. These were then ground to fine powder and stored in plastic wares. 2.4. Control samples An arrangement was made with some local smoked fish producers to collect fish samples before smoking (I) and immediately after smoking (II). Fish smoking is usually carried out in a courtyard of residential quarters before being conveyed to the outdoor market. Hence, at a particular investigation area, samples were collected for (I) and (II) at three replicates respectively.
2. Materials and methods 2.5. Determination of lead in fish
2.1. Description of study area Abeokuta is a city in southwestern Nigeria and the capital of Ogun state (one of the 36 states of Nigeria). It is located within the Ogun river basin, about 74 km from Lagos. Abeokuta is inhabited largely by the Yoruba tribe and has an estimated population of over two million. Abeokuta has a good road network within the city. There are a lot of roadside (outdoor) markets, that is, open-markets which are situated very close to the highways, a phenomenon very common in the country. The markets selected for this study are as described in Table 1. 2.2. Evaluation of the vehicular traffic density The vehicular traffic density per hour (VTD/h) in Abeokuta metropolis was assessed by recording the number of automobiles plying the highways within
One thousand milligram portion of the pre-treated sample was subjected to wet digestion using 6 M trioxonitrate (v) acid (HNO3 ). The volume of the acid digest was minimally reduced by evaporation, filtered through Whatman No.1 paper and diluted to 100 ml using deionised water in a volumetric flask. Blank samples were also prepared. Total lead in the digest was analysed with the help of atomic absorption spectrometer (Buck Model 200). 2.6. Statistical analysis Data generated were subjected to 1-way analysis of variance (ANOVA) for statistical differences at P < 0:05. Pearson correlation and regression models were applied for possible relationships. Results are expressed as mean ± standard deviation.
Table 1 Study site description of Abeokuta markets Highway road
Market specification/code
Investigation period
Adatan Highway Ijaye Highway Itoku Highway Kuto Highway Lafenwa Highway Omida Highway
Adatan market (MKT-1-ADT) Ijaye market (MKT-2-IJA) Itoku market (MKT-3-ITK) Kuto market (MKT-4-KUT) Lafenwa market (MKT-5-LAF) Omida market (MKT-6-OMD)
8–9 8–9 8–9 8–9 8–9 8–9
am am am am am am
(P1); (P1); (P1); (P1); (P1); (P1);
12–1 12–1 12–1 12–1 12–1 12–1
pm pm pm pm pm pm
(P2); (P2); (P2); (P2); (P2); (P2);
5–6 5–6 5–6 5–6 5–6 5–6
pm pm pm pm pm pm
(P3) (P3) (P3) (P3) (P3) (P3)
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3. Results and discussion 3.1. Fish lead level The mean lead levels (unit in mg/kg) obtained in the investigated smoked fish products were MKT-1-ADT (9.5 ± 2.2, 10.0 ± 2.2, 9.6 ± 2.2); MKT-2-IJA (8.0 ± 0.8, 8.3 ± 0.9, 8.7 ± 0.6); MKT-3-ITK(12.1 ± 1.7, 11.7 ± 1.2, 12.5 ± 1.6); MKT-4-KUT (10.6 1.3, 9.7 ± 1.5, 8.9 ± 1.6); MKT-5-LAF (7.9 ± 0.8, 8.0 ± 0.8, 8.5 ± 0.6) and MKT-6OMD (9.8 ± 1.2, 11.1 ± 1.4, 11.4 ± 0.3) shown in Tables 2–7. The smoked fish lead levels were higher than the stipulated fish lead level of 0.2 mg/kg (EU, 2002), indicating pollution of these consumer products by the metal.
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Generally, low coefficient of variations (Cv), ranging from 3% to 25% were obtained, indicating a relative good reproducibility of data. Investigation at the morning period revealed that fresh products were not usually available at this time of the day. Results obtained immediately after smoking (before exposure at the outdoor markets) gave a mean value of 0.95 ± 0.01 mg/kg. A range of 8.3 ± 0.9 to 11.7 ± 1.2 mg/kg was obtained in the morning samples (Table 2). Fresh products are expected to give much lower lead values such as was obtained only once at MKT-3-ITK (1.0 mg/ kg; Table 2). Results suggest that fresh products were not usually sold until the previous stock was exhausted. The fish lead levels varied quantitatively at the various
Table 2 Fish lead levels obtained at the morning period (8–9 am) from the roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
9.5 2.2 23 5.6–12.6 14
8.0 0.8 10 6.7–9.3 14
12.1 1.7 14 1.0–14.0 14
10.6 1.3 12 8.6–11.9 14
7.9 0.8 10 6.8–9.1 14
9.8 1.2 12 7.9–11.9 14
Unit in mg/kg.
Table 3 Fish lead levels obtained at the afternoon period (12–1 pm) from the roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
10.0 2.2 22 5.6–12.6 14
8.3 0.9 11 6.7–9.3 14
11.7 1.2 10 9.9–14.1 14
9.7 1.5 15 7.2–11.8 14
8.0 0.8 10 7.2–9.1 14
11.1 1.4 13 8.1–12.0 14
Unit in mg/kg.
Table 4 Fish lead levels obtained at the evening period (5–6 pm) from the roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
9.6 2.2 23 6.6–12.8 14
8.7 0.6 7 7.9–9.4 14
12.5 1.6 13 9.9–14.1 14
8.9 1.6 18 7.1–12.1 14
8.5 0.6 7 6.9–9.1 14
11.4 0.3 3 10.6–12.1 14
Unit in mg/kg.
Table 5 Vehicular traffic density per hour at the morning period (8–9 am) on the highways close to the investigated roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
1541 138 9 1331–1787 14
1510 198 13 1317–1963 14
1540 185 12 1294–1731 14
1567 141 9 1272–1738 14
1752 344 20 1214–2317 14
1509 75 4 1134–1681 14
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Table 6 Vehicular traffic density per hour at the afternoon period (12–1 pm) on the highways close to the investigated roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
1518 109 7 1311–1735 14
1529 172 11 1334–1809 14
1620 110 7 1425–1781 14
1543 167 11 1077–1730 14
1735 218 13 1307–1943 14
1627 154 9 1404-1979 14
Table 7 Vehicular traffic density at the evening period (5–6 pm) on the highways close to the investigated roadside markets of Abeokuta, Nigeria Location
MKT-1-ADT
MKT-2-IJA
MKT-3-ITK
MKT-4-KUT
MKT-5-LAF
MKT-6-OMD
Mean Standard deviation % Coefficient of variation Range Study population (n)
1541 77 5 1414–1665 14
1549 90 6 1384–1675 14
1691 102 6 1561–1927 14
1509 159 11 1134–1681 14
1840 132 7 1575–1981 14
1721 122 7 1483–1965 14
periods of the day but were not statistically significant at P < 0:05. Previous works have reported high lead levels for other types of food sold at outdoor markets in Nigeria. These include 0–12.5 mg/kg in Elubo (Yam or cassava flour), 6.5 mg/kg in Suya (a type of meat preparation) and 0–15.1 mg/kg in dried meat (Okoye, 1994). A study on smoked fish in a certain part of the country about a decade ago gave lead level in the range of 0–9.7 mg/kg (Okoye, 1994). 3.2. Impact of the smoking method and atmospheric exposure on fish lead level The local food processing technique increased the fish lead level from 0.14 ± 0.02 mg/kg (I) to 0.95 ± 0.01 mg/ kg (II), from the difference, depositing up to 0.82 ± 0.01 mg/kg which is above the standard limit of 0.2 mg/kg (Fig. 1). This implies that before the local processing method was applied, the lead level was below the stipulated threshold. Results indicate that the smoking method contributes to the metal pollution in the fish food. The fuel sources employed in the smoking process
such as coal, charcoal and kerosene and even gasoline which have been reported to contain lead (Osibanjo and Ajayi, 1989) could have contributed to the multiple fold increase in the smoked fish lead level. The smoking method increased the fish lead by an approximate factor of seven. 3.3. Effect of atmospheric exposure on fish lead Calculation was made and the difference between the total fish lead after exposure and the lead in fish (0.95 ± 0.01 mg/kg) immediately after smoking, prior to exposure at the outdoor market gave the effect of atmospheric exposure on fish lead level. The effect varied from 7.0 to 11.2 mgPb/kg (Fig. 2). 3.4. Traffic density on the highways of Abeokuta The data of the traffic density per hour on the highway are presented in Tables 5–7. The smoked fish products are usually sold at a distance of 0–2 meters from the highways. The vehicular traffic density per 12
1 0.8 Before smoking After smoking
0.6
Pb deposited 0.4
Lead level in mg/kg
Lead level in mg/kg
1.2 10 8
Morning period Afternoon period Evening period
6 4 2 0
0.2
MKT-1- MKT-2- MKT-3- MKT-4- MKT-5- MKT-6ADT IJA ITK KUT LAF OMD
0 Fish-1 Fish-2 Fish-3 Fish-4 Fish-5 Fish-6
Location
Fish sample
Fig. 1. Effect of smoking method on fish lead level.
Fig. 2. Effect of atmospheric exposure on the fish lead levels in Abeokuta, Nigeria.
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Table 8 Pearson correlations between vehicular traffic density per hour and fish lead levels in Abeokuta, Nigeria
Location
Investigation period
Study population (n)
MKT-1-ADT MKT-1-ADT MKT-1-ADT
P1 P2 P3
14 14 14
0.547 0.336 0.221
Y ¼ 0:0088x 4:0038 Y ¼ 0:0076x 1:5836 Y ¼ 0:0062x þ 0:1231
MKT-2-IJA MKT-2-IJA MKT-2-IJA
P1 P2 P3
14 14 14
0.677 0.801 0.474
Y ¼ 0:0027x þ 3:2748 Y ¼ 0:0041x þ 2:1279 Y ¼ 0:0030x þ 4:0069
MKT-3-ITK MKT-3-ITK MKT-3-ITK
P1 P2 P3
14 14 14
0.520 0.655 0.496
Y ¼ 0:0047x þ 4:9203 Y ¼ 0:0073x 0:2139 Y ¼ 0:0078x 1:6529
MKT-4-KUT MKT-4-KUT MKT-4-KUT
P1 P2 P3
14 14 14
0.613 0.744 0.688
Y ¼ 0:0054x þ 1:6019 Y ¼ 0:0066x 0:5087 Y ¼ 0:0070x 1:6529
MKT-5-LAF MKT-5-LAF MKT-5-LAF
P1 P2 P3
14 14 14
0.867 0.343 0.638
Y ¼ 0:0020x þ 4:3641 Y ¼ 0:0012x þ 5:9615 Y ¼ 0:0030x þ 2:9164
MKT-6-OMD MKT-6-OMD MKT-6-OMD
P1 P2 P3
14 14 14
and
Correlation coefficient
0.617 0.334 0.339
Regression equation
Y ¼ 0:0027x þ 5:2477 Y ¼ 0:0020x þ 14:2730 Y ¼ 0:0019x þ 8:1776
¼ levels significant at P < 0:05 and 0.01 respectively.
hour in Abeokuta varied from 1011 to 2317 with mean values as MKT-1-ADT (1541 ± 138, 1518 ± 109, 1541 ± 77), MKT-2-IJA (1510 ± 198, 1529 ± 172, 1549 ± 90), MKT-3-ITK (1540 ± 185, 1620 ± 110, 1691 ± 102), MKT-4-KUT (1567 ± 141, 1543 ± 167, 1519 ± 159), MKT-5-LAF (1752 ± 344, 1735 ± 218, 1840 ± 132) and MKT-6-OMD (1671 ± 75, 1627 ± 154, 1721 ± 122). There was no statistically significant variations in the number of vehicles plying the various highways close to the markets at P < 0:05 (ANOVA).
of the vehicular traffic per hour though positive correlation coefficients were obtained (Fig. 2, Tables 2–4). This implies that the cause of lead in the consumer product at the outdoor markets in Nigeria is multifactoral. Activities such as tyre burning, open-air waste combustion, hobbies and recreational activities that use lead could also account for the presence of lead in these products.
4. Conclusion 3.5. Correlation between traffic density and fish lead Vehicles plying the highways include commercial, heavy duty and private automobiles. Lead levels in the exhausts of some automobiles in Nigeria were reported in the range of 0.043–11.40 (commercial automobiles), 0.096–18.00 (Heavy duty automobiles) and 0.038–11.20 (Private automobiles), units in mg/g (Sridhar et al., 2000a,b). Lead level in Super grade gasoline used in Nigeria was reported as 600–800 lg/ml (Osibanjo and Ajayi, 1989; Shy, 1990). Results indicate various degrees of relationships between the fish lead levels and the VTD/h. Positive correlations were calculated with correlation coefficients ranging from 0.339 to 0.867. Some of the correlations were statistically significant while the others were not (Table 8). A negative correlation was obtained at MKT6-OMD (r ¼ 0:334), an indication that there could be other sources of atmospheric lead pollution apart from the vehicular traffic on the highway. No consistent or definite trend was found between the quantitative values
The investigated consumer products (smoked fish) contain elevated lead levels. The cause of the lead pollution is multidimensional, including the food processing technique, highway pollution and other undisclosed factors. The part two of this study will examine the smoked fish lead level as a function of atmospheric exposure time.
Acknowledgements The Authors thank Dr. O. Oguntoke of the Department of Environmental Management and Toxicology, University of Agriculture, Abeokuta, Nigeria for assisting in the statistical analysis. References Ademuyiwa, O., Arowolo, T., Ojo, D.A., Odukoya, O.O., Yusuf, A.A., Akinhanmi, T.F., 2002. Lead levels in blood and urine of
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some residents of Abeokuta, Nigeria. Trace Elements and Electrolytes 19, 63–69. Adeniyi, F.A.A., Anetor, J.I., 1999. Lead––poisoning in two distant states of Nigeria: an indication of the real size of the problem. African Journal of Medicine and Medical Sciences 28, 107–112. Agency for Toxic Substances and Disease Registry, 1998. Toxicological profile for lead uptake. US Department of Health and Human Services, pp. 45–268. Anetor, J.I., 2001. High blood lead levels in general Nigerian population. In: Proceedings of Nigeria National Conference on Lead Phase-Out, Abuja, Nigeria. Organised by World Bank, 15–16 November. Benowitz, N.L., Goldschlager, N., 1998. Cardiac disturbances. In: Haddad, L.M., Shannon, M.W., Winchester, J.K. (Eds.), Clinical Management of Poisoning and Drugs Overdose, third ed. Saunders, Philadelphia. Enemari, E., 2001. Vehicular emission, environmental and health implication. In: Proceedings of Nigeria National Conference on Lead Phase-Out, Abuja, Nigeria. Organised by World Bank, 15–16 November. European Communities, 2002. Amending regulation, setting maximum levels of certain contaminants in foodstuffs. Official Journal of European Communities L37, 4–6. Goyer, R.A., 1991. Toxic effects of metals. In: Amdur, M.V, Douli, J., Klansmen, C.D. (Eds.), Caserrett and Doull’s Toxicology: The Basic Science of Poisons, fourth ed. Pergamon Press, New York, pp. 623–680. Maduka, J.O., 2001. Sources of environmental lead in Nigeria. In: Proceedings of Nigeria National Conference on lead phase-out, Abuja, Nigeria. Organised by World Bank, 15–16 November. Ndiokwerre, C.C., 1984. A study of heavy metal pollution from motor vehicle emissions and its effect on roadside soil, vegeta-
tion and crops in Nigeria. Environmental Pollution Series B 7, 35– 42. Nriagu, J.O., Blackson, M.I., Ocram, K., 1996. Childhood lead poisoning in Africa: a growing public health problem. Science of the Total Environment 181 (2), 93–101. Nriagu, J.O., Jirabhai, C.C., Naidoo, R., Coutsound, A., 1997. Science of the Total Environment 197, 1–11. Okoye, C.O.B., 1994. Lead and other metals in dried fish from Nigerian markets. Bulletin of Environmental Contamination and Toxicology 52, 825–832. Onianwa, P.C., Egunyomi, J.K., 1983. Trace metal levels in some Nigerian Mosses used as indictors of atmospheric pollution. Environmental Pollution Series B 5, 71–81. Osibanjo, O., Ajayi, S.O., 1980. Trace metal levels in tree barks as indicators of atmospheric pollution. Environmental International 4, 239–244. Osibanjo, O., Ajayi, S.O., 1989. Trace metal analysis of petroleum products by flame atomic absorption spectrometry. Nigerian Journal of Natural Sciences 4, 33–40. Sammut, M., Savona-Ventur, C., 1996. Petrol lead in a small Island environment. International Journal of Risk and Safety in Medicine 9, 33–40. Shy, C.M., 1990. Lead in petrol: the mistake of the xxth century. World Health Statistics Quarterly 43, 168–176. Sridhar, M.K.C., Adogame, L., Olawuyi, J., 2000a. Lead exposure in urban centres: a case study from Ibadan, Nigeria. Epidemiology, USA 10, 22, 227. Sridhar, M.K.C., Olawuyi, J., Adogame, L., Okekearu, A., Osajie, C.O., Linda, A., 2000. Lead in the Nigerian environment: problems and prospects. In: 11th Annual International Conference on Heavy Metals in the Environment. University of Michigan, School of Public Health, Ann Arbor, MI (CD-ROM).