Reviewing the demographic data showed that the average age and working experience in the exposure group are 31.81 years and 49.87 months, respectively; the average age and history of exposure to benzene in control group are 31.4 years and zero. Results obtained from the review of demographic data also revealed that age is normal (P value = 0.498) and the working experience is abnormal (P value = 0.043).
Investigating the normality of parameters of TD, TM, TL and %DNA showed that they have skewed distribution and the parameters of exposure to benzene and %TAC are normally distributed (Table 1).
Table 1
Results of the biomarkers normality TD, TM, TL, %DNA, %TAC, benzene
Variables
|
N
|
SD ± Mean
|
P-value*
|
benzene
|
21
|
16.28 ± 8.48
|
0.148
|
TL
|
64
|
68.90 ± 12.47
|
0.047
|
TD
|
64
|
42.05 ± 34.24
|
0.000
|
TM
|
64
|
29.87 ± 3.63
|
0.000
|
%DNA
|
64
|
6.80 ± 4.64
|
0.023
|
%TAC
|
64
|
20.95 ± 14.44
|
0.162
|
One-Sample Kolmogorov-Smirnov Test* |
The results showed that the average differences of TL, TD, TM, %DNA and %TAC parameters in both groups (with exposure and control) the statistically meaningful (P value < 0.05) (Table 2).
Table 2
Results of the average differences of DNA damage index factors among the participants
Variables
|
groups
|
Maximum
|
Minimum
|
SD ± Mean
|
P-value
|
TL
|
expose
|
70.47
|
43.07
|
4.44 ± 59.21
|
0.001*
|
control
|
92.72
|
61.02
|
10.13 ± 78.59
|
TD
|
expose
|
84.93
|
63.60
|
4.65 ± 75.74
|
0.001*
|
control
|
21.03
|
3.05
|
4.20 ± 8.35
|
TM
|
expose
|
68.34
|
41.85
|
4.28 ± 57.74
|
0.001*
|
control
|
5.12
|
0.14
|
1.16 ± 1.20
|
DNA%
|
expose
|
6.28
|
1.82
|
0.99 ± 3.56
|
0.001*
|
control
|
21.03
|
3.05
|
4.59 ± 10.05
|
TAC%
|
expose
|
41.45
|
3.63
|
10.53 ± 16.58
|
0.012**
|
control
|
69
|
1.8
|
16.61 ± 25.58
|
Mann-Whitney Test* |
Independent sample T-Test** |
The results also indicated that the interaction-based biomarkers are meaningfully correlated in pairs. The reverse correlation was observed between the %TAC marker and TM, TL and %DNA markers and also between the TL biomarker and TD and TM markers. DNA% was reversely correlated with TM and TD biomarkers (Table 3).
Table 3
Investigating the correlation between the biomarkers (TD, TM, TL, %DNA, %TAC) in the studied groups
parameters
|
variables
|
Correlation (r)
|
P-value
|
TM
|
TL
|
− 0.749*
|
0.001
|
TD
|
0.983*
|
0.001
|
%DNA
|
− 0.700*
|
0.001
|
%TAC
|
− 0.324**
|
0.009
|
TD
|
TL
|
− 0.787*
|
0.001
|
%DNA
|
-0.704*
|
0.001
|
%TAC
|
-0.298**
|
0.017
|
TL
|
%DNA
|
0.422*
|
0.001
|
%TAC
|
0.024**
|
0.085
|
%DNA
|
%TAC
|
− 0.353**
|
0.004
|
the correlation coefficient (Spearman), (significance level of 0.05)*the correlation coefficient (Pearson), (significance level of 0.05)** |
While reviewing, no correlation was seen between the respiratory exposure to benzene and age parameter, no correlation (p = 0.685, r = 0.094). A significant correlation was observed between the working experience and biomarkers (TD, TM, TL and %DNA) (P < 0.05). The working experience and TL were reversely correlated (r = 0.445), as it was the case for working experience and %DNA (r = 0.370) (Table 4).
Table 4
Investigating the correlation between the parameters of working experience, age and benzene and biomarkers (TD, TM, TL, %DNA, %TAC)
parameters
|
variables
|
Correlation (r)
|
P-value
|
Age
|
TL
|
− 0.051*
|
0.688
|
TD
|
− 0.011*
|
0.930
|
TM
|
0.070*
|
0.581
|
%DNA
|
− 0.063*
|
0.621
|
%TAC
|
0.034**
|
0.791
|
benzene
|
0.094**
|
0.685
|
benzene
|
TL
|
− 0.262*
|
0.252
|
TD
|
− 0.250*
|
0.274
|
TM
|
− 0.283*
|
0.214
|
%DNA
|
− 0.009*
|
0.969
|
%TAC
|
0.100**-
|
0.665
|
Working experience
|
TL
|
0.784*-
|
0.001
|
TD
|
0.778*
|
0.001
|
TM
|
0.785*
|
0.001
|
%DNA
|
0.666*-
|
0.001
|
%TAC
|
0.045**
|
0.001
|
The correlation coefficient (Spearman), (significance level of 0.05)*The correlation coefficient (Pearson), (significance level of 0.05)** |
Results obtained from investigating the average difference of biomarkers (TD, TM, TL, %DNA and %TAC) in the exposure group showed that there is no significant difference between the smoking and non-smoking people (P > 0.05). It was also found that the average difference of biomarkers (TD, TM, TL, %DNA and %TAC) in the exposure group is not meaningful among the smoking and non-smoking people (P > 0.05). But the average difference of TAC% biomarker in the control group among the smoking and non-smoking people was meaningful (P < 0.05) (Table 5).
Table 5
Comparing the average difference of biomarkers in both exposure and control groups among the smoking and non-smoking people
GROUP
|
variables
|
Tobacco use
|
workers
|
Mean
|
P-value
|
Exposed
|
TL
|
SMOKER
|
9
|
4.90 ± 60.15
|
0.329
|
NONSMOKER
|
23
|
4.30 ± 58.84
|
TD
|
SMOKER
|
9
|
5.11 ± 72.94
|
0.368
|
NONSMOKER
|
23
|
4.06 ± 76.84
|
TM
|
SMOKER
|
9
|
4.67 ± 58.45
|
0.430
|
NONSMOKER
|
23
|
4.19 ± 57.46
|
%DNA
|
SMOKER
|
9
|
0.98 ± 4.33
|
0.522
|
NONSMOKER
|
23
|
0.82 ± 3.25
|
%TAC
|
SMOKER
|
9
|
11.11 ± 19.17
|
0.698
|
NONSMOKER
|
23
|
10.37 ± 15.56
|
control
|
TL
|
SMOKER
|
5
|
13.36 ± 84.04
|
0.210
|
|
NONSMOKER
|
27
|
9.39 ± 77.58
|
TD
|
SMOKER
|
5
|
5.11 ± 72.94
|
0.314
|
|
NONSMOKER
|
27
|
4.46 ± 8.11
|
TM
|
SMOKER
|
5
|
0.92 ± 1.39
|
0.990
|
NONSMOKER
|
27
|
1.16 ± 1.21
|
%DNA
|
SMOKER
|
5
|
1.63 ± 8.19
|
0.104
|
NONSMOKER
|
27
|
4.89 ± 10.40
|
%TAC
|
SMOKER
|
5
|
6.90 ± 28.80
|
0.030
|
NONSMOKER
|
27
|
17.78 ± 24.98
|
Using Wilkes Lambda Multivariate test and concerning the results obtained for the parameters of smoking, age and working experience, one can say that smoking and age, as the risk factors, have no impact on the parameters of TL, TD, TM, %DNA and %TAC and benzene (P value > 0.05). But, the working experience in the exposure group affected significantly these parameters.
By making use of multivariate analysis of variance, the variables of age, working experience and smoking were evaluated as the dependent variables (risk factors) and parameters of TL, TD, TM, %DNA and %TAC as the independent variables (response). The effect of risk factors on the response parameters was also investigated. Results showed that smoking and age had no impact on the biomarkers (P > 0.05), but working experience affected significantly the biomarkers (P < 0.05). Smoking and age had no impact on TAC% (P > 0.05), while the working experience influenced significantly TAC% (P < 0.05) (Table 6).
Table 6. Impact of risk factors of smoking, age and working experience on the variables of biomarkers. Tests of Between-Subjects Effects
P-Value
|
Dependent variable
|
Risk factor
|
0.110
|
TL
|
smoking
|
0.300
|
TD
|
0.200
|
TM
|
0.320
|
%DNA
|
0.320
|
%TAC
|
0.360
|
benzene
|
0.430
|
TL
|
Age
|
0.270
|
TD
|
0.160
|
TM
|
0.300
|
%DNA
|
0.111
|
%TAC
|
0.220
|
benzene
|
0.001
|
TL
|
working experience
|
0.001
|
TD
|
0.001
|
TM
|
0.005
|
%DNA
|
0.001
|
%TAC
|
0.770
|
benzene
|