Air pollutants generated from traffic and
industrial plants are believed to be one of the major causes of DNA damage in
living species. As a result of rapid urbanization, air pollution and
environmental quality deterioration have been affecting our daily lives as well
as the nature.
Several experimental
studies have reported that lead has a moderate genotoxic potential.
In a study conducted by
Valverde and colleagues ,(26) a lead inhalation model in mice was used to
detect the induction of genotoxic damage as single-strand breaks and
alkali-labile sites in several mouse organs (nasal epithelial cells, lung,
whole blood, liver, kidney, bone marrow, brain, and testes), assessed by the
comet assay. Following single and subsequent inhalations, differences were
found among the organs studied. A positive induction of DNA damage in the liver
and the lung after a single inhalation was observed. The response was positive
in all organs, except the testicle, in subsequent inhalations. DNA damage
induction over time varied for each organ. The brain and bone marrow showed the
highest damage induced. Differences in DNA damage occurred in organs when lead
was administered acutely or sub-chronically.
Our study
revealed a significant
increase in the
blood lead level of
study group and controls ( p value 0.000). The mean pb in
our study was 18.76±8.8 and controls
mean pb was 12±3.5 as compared to study in Islamabad that was carried out in
2005 in which blood lead levels of wardens were 27.27 ±4.04 and a similar study
on traffic wardens in Karachi indicated
a value of lead in wardens of 47.7±15.8.micrograms
/dl.Another study in Alexandrria Eygpt reported that their traffic constables had a higher blood lead
level than our study (27).
Blood lead levels were
analyzed in Nigerian traffic wardens, comprising sixty from Lagos , thirteen
from the sparsely populated university town of Ile-Ife and a control group of
twenty-four subjects . The mean lead level in Lagos wardens was 18.1 ± 6.4 ?g/dl,
which was significantly higher than the level of 10.2 ± 2.7 ?g/dl in Ife
wardens and 12.9 ± 7.0 ?g/dl obtained in the controls (P <
0.001). However, there was no significant difference between the levels of
blood lead in Ife traffic wardens and normal controls (28)
Nigeria wardens
had almost similar values as our study
but their study was conducted 17 years ago and since that time urbanization and
population has increased tremendously. Alexandria and Karachi both are
populated cities and have more traffic congestion that is why their lead levels
were high as compared to our study. Also after 2005 when the law of using unleaded petroleum was introduced no study had been conducted
since then on this occupationally exposed group. Our study indicated
that law had actually been implemented that has reduced lead from the
atmosphere and from this exposed group.
The mean age in cases in
our study was from 24-39 years and in controls was 25-35 years. There was no
difference statistically in the mean age of cases and controls in our study (p
value 0.241). The mean age of wardens in the study of Islamabad and Karachi had
a mean value of 21-45 years and 20-52
years respectively, not comparable with our study .
The various parameters
of comet assay that is Mean tail moment ,% DNA in tail and Mean tail length in
our study had values of 0.0583 ±1.960 (p
valve 0.04),4.101 ±5.87 (p value 0.136) and7.156 ±12.56 (p value 0.003)
respectively in cases and 0.045±0.108
,2.055 ±2.481 and 1.50±2.12 respectively in controls. There was a significant
correlation of lead with TM , but no statistically significant correlation of
lead with tail length in cases. The mean % DNA in tail in cases gave a mild
positive correlation with lead.
The other parameters
given in our study were % DNA in head with a difference in the mean value of
cases and controls with a (p value 0.16). The % DNA in head gave a mild
negative correlation with lead in cases (p value 0.03 and rho -0.380). Comet
length in our study had a difference in the means of two groups having a p
value 0.005 that was statistically significant but it gave no significant correlation
with lead in cases.
A study
of DNA damage by comet assay in Traffic wardens in China (29)
showed that occupational exposure to
traffic exhaust significantly increased tail length 4.20µm , (3.98 - 4.42) µm in outside ones vs. 3.23 µm, (2.82 - 3.7) µm in office work policemen, P < 0.001. The p value
of mean tail length is 0.003 in our cases and controls that is statistically
significant and comparable to their study however our study did not give a
significant correlation of lead with
tail length in cases.
The results confirm that
inhaling lead induces systemic DNA damage, but certain organs, such as the lung
and the liver, are special targets of this metal, partly depending on the
duration of exposure.
