A Survey of Levels of Some Heavy Metals in Scalp Hair of Urban Dwellers: A Case Study

MATERIALS AND METHODS

Sampling: Fourteen sampling locations were selected for this study. Twelve sampling locations were selected to cover the commercial centers of Benin City, where traffic wardens and small scale entrepreneurs were prevalent and well expose to motorized vehicle emissions and exhaust from industrial activities. Two locations were chosen to serve as control.

Samples of hair were taken with stainless steel clippers from fifty males made up of traffic wardens and small scale entrepreneurs (age 22 to 42 years) along motor ways in Benin City. The information supplied `by the donors showed that the scalp hair samples had not been dyed or bleached. The hair samples were stored in carefully labeled polyethylene bags and identified with the age of donors, sampling location and nature of business. Specimen of hair to serve as ‘control’ were similarly obtained from eight supposedly non-exposed male residents in the outskirt of Benin City, a rural village of about eighty kilometer from Benin City. This was to establish the normal level of these metals in the tissue. Difficulties were however, encountered in obtaining these samples because of the beliefs of people in this part of the World and are usually hesitant at given human tissue for non-clinical reason.

Pre-treatment of samples and analysis: Each hair sample was soaked in deionised water with stirring to remove any externally attached dust particles and other contaminants, which might also, contained trace metals. After each wash, the water was decanted and the sample was further boiled for few minutes, rinsed with deionised water and dried between filter papers. The samples were finally washed with carbon tetrachloride, CCl₄, by allowing a sufficient amount to cover the air. This was necessary to remove any oils or grease substances. The hair was thereafter rinsed with CCl₄ and air-dried.

The washing procedure was also necessary to ensure that salts of Na, K, Mg and Ca, which are normally accumulated by these tissues during growth, were quantitatively removed. This washing procedure is in agreement with the observations of Ndiokwere (1985) and Bate and Dyeer (1967), that the concentrations of some heavy metals in hair were essentially not affected by a similar washing procedure because of their tendency to complex with sulpurhydryl groups in the follicular proteins.

At the completion of the washing procedure, 1.0 g of the hair sample was accurately weighed and placed in a 250.0 mL polypropylene beaker and 10.0 mL of concentrated HNO₃ was added. The beaker was left over at room temperature and then heated to dryness. After cooling, 10.0 mL 30% hydrogen, H₂O₂, solution was added and heated again nearly to dryness. The residue was re-dissolved with 10.0 mL of 4.0 M HCl, warmed up and transferred to 500 mL volumetric flask. This was diluted with deionised water and made up to the mark. The solution was used for the elemental analysis.

For the analysis, the metal concentrations were determined in all standard solutions, samples and blank by atomic absorption spectroscopic method (AAS) using Buck Scientific Model 200A/210 atomic spectrophotometer with digital read out and appropriate Hollow cathode lamps as energy source for each element. Standard metal solutions were prepared from their pure metallic forms. All reagents were of BDH grade.

RESULTS AND DISCUSSION

The results of Pb, Ni, V, Cr, Cd and Zn levels measured in the hair of the 50 males of small scale business entrepreneurs (artisans and traders) along motor ways in Benin City are presented in Table 1. The Table also shows the ages of the donors and the location in Benin City. The Pb, Ni, V, Cr, Cd and Zn levels measured in the hair of 8 non-exposed donors resident in the outskirts of Benin City and a rural village (Usen and Idun) is also presented in Table 1. The mean levels of heavy metals in different donors and trades per sampling location are presented in Table 2 and 3, respectively.

Table 1:	Concentrations of heavy metal (μg g-1) in different donors

The reported levels of these elements represent the mean values of three replicated analyses of each sample. The levels of these elements measured in the hair of the small scale entrepreneurs along motor ways in Benin City are well above the concentration range measured for the control group. The high level of these elements in the hair of the small scale entrepreneurs can be interpreted to be largely due to their exposure to motorized vehicle emission (automobile exhaust) and industrial activities.

In recent times, there has been a tremendous increase in traffic volume in Benin City due to the increase in the level of industrialization (especially small scale industries) and commercial activities; Benin City is also a transitory town. As a transitory town, Benin City experiences daily heavy traffic flow from the western to the eastern and northern parts of the country.

Table 2:	Mean levels and ranges of heavy metal (μg g-1) in donors along motor ways in benin city

Table 3:	Mean levels of heavy metal (μg g-1) in different trades in the sampling locations

Table 4:	Inter-correlation coefficient matrix for the elements

The high level of Pb and Zn in the hair of these small scale entrepreneurs and traffic wardens is not unconnected with emissions from motor vehicle exhausts and from the wears and tears of brake pad and tyre to which they are exposed. Other factors responsible for the high levels of these elements in the hair of the small scale business entrepreneurs include road side dust, metal works and activities of other artisans.

The concentrations observed in the hair tissues have no correlation with the age of the donors but mainly dependent on anthropogenic sources.

Inter elemental relations: The correlation coefficient matrixes for the elements and the sampling locations are presented in Table 4 and 5. Correlation coefficient of 0.5 was taken as significant.

From Table 4, all the elements (parameters) determined are strongly correlated except V which is moderately correlated with Pb. In the same vein Cd is moderately correlated with Zn. This might be attributed to the same source as earlier refer to in the text. It might also be due to refuse incineration and other industrial processes. The sampling locations are also correlated as seen in Table 5 except Idun and Usen.

Source identification: One of the objectives of this study is to identify source contributing heavy metals in the areas under study. Therefore, the results were subjected to Factor Analysis (FA) and Cluster Analysis (CA). The results of factor analysis for the elements and sampling locations are presented in Table 6 and 7, respectively.

Two factors were identified for both the elements and sampling locations. Factors with variances ≥ 1 are significant. In this case there are two significant variances greater than unity and that explains the 80.52 and 10.67% for the elements (Table 6 and 7a-c). Those of the sampling locations are 98.47 and 1.40%. This signature represents a common source for all the elements and the sampling locations as seen from the positive correlation of all the elements and the sampling locations except Idun and Usen.

From Table 6, factor 1 has high loadings in Pb and Zn. This might probably represent vehicular emission/auto exhaust and industrial activities while factor 2 with high loadings in Ni, Cr, V and Cd might be due to road side dust, variety of metal processing industries and artisans. Table 7a which represents the factor analysis for the sampling locations have high loading for all the sampling locations except for the ‘control’ sites. All the sampling locations are moderately loaded in factor 2 and this is in agreement with the results of the correlation coefficient matrix (Table 5). The distinctive behaviour of Pb and Zn in Factor 1 also manifested itself in the result of varimax rotations for the elements (Table 7b and c). Pb and Zn were less significant in the first factor as compared to other metals and then significantly appear in Factor 2 in a less association with other metals. This indicates that roadside dust, varieties of metal processing industries and artisans are responsible for the levels of these elements found in the hair samples collected for analysis. The results of factor analysis for the sampling stations (Table 7b) showed that seven sampling stations participated to a lesser extent in Factor 1 while the remaining stations participated actively in Factor 2. This was in agreement with that of the varimax rotations.

The mean levels of these metals were highest for the traffic wardens, vulcanizers and battery chargers and lowest for the control sites when the various occupations/trades were compared (Table 8). This implies that these trades’ men will be prone to the deleterious effect of these metals which will likely manifest itself health wise in the near possible future.

Table 5:	Correlation coefficient matrix for the sampling locations

Table 6:	Principal factor (Component) analysis for the elements

Table 7a:	Principal factor analysis for the sampling locations

Table 7b:	Varimax rotation for the elements

Table 7c:	Varimax rotation for the sampling location

Cluster analysis: The results were also subjected to cluster analysis with the aid of cluster package using Euclidean Distance and complete linkage furthest neighbour as a measure of correlation. The results obtained for the elements and the sampling locations are shown in Fig. 1 and 2. These results are in agreement with the results of factor analysis. Two major clusters were identified for the elements and the locations, respectively. There was a significant clustering of Pb, Zn and Ni, V, Cr, Cd. That observed for the sampling stations are RR, IK, UR, NB, SI, TX, TH, SA and AG, UG, US, EK, UN, ID.

V/Ni ratio: Vanadium is found in petroleum in relatively high levels. It is associated with crude oil in two forms, as organo-metallic complexes of high molecular weight (Porphyrins) and as asphaltenic component of crude oil (Okuo and Ndiokwere, 2006). Hence vanadium is released into the atmosphere as a result of residual oil combustion. The ratio of vanadium to nickel in crude oil is about 2. This ratio has been used to identify residual oil as contributing to ambient fall out particles. The vanadium/nickel ratio obtained in this study is approximately 1.05. The reduction in the V/Ni ratio might result from the various stages which the crude oil had undergone before it is put into final use.

Table 8:	Comparison of mean levels of heavy metal concentration in hair of donors of the various occupations/trades

Fig. 1:	Cluster analysis/dendrogram of the elements

Fig. 2:	Dendrogram of the locations