3.1 Arsenic exposure level
In the monitoring of arsenic levels in different environmental media, 150 water samples were tested in rural Y and 15 in rural D; 87 wheat samples were tested in rural Y and 10 in rural D. The mean values of arsenic in daily drinking water and cereals consumed by residents of rural Y were 29.979 μg/L and 0.237 mg/kg, respectively, while the mean values of arsenic in daily drinking water and cereals consumed by residents of rural D were 0.442 μg/L and 0.104 mg/kg, respectively. The arsenic content of drinking water in the rural Y samples significantly exceeded the standard limit value (10 μg/L), and the arsenic content of wheat was predominately within the standard limit value (0.5 mg/kg); the arsenic content in both types of samples in rural D was within the standard limit value. The distribution of arsenic levels in drinking water and wheat in rural Y and rural D conformed to a normal distribution, as shown in Figure 1. The results from the t-test showed (Table 1) that the differences in arsenic levels in water and wheat between rural Y and rural D were statistically significant (P<0.001).
Table 1. Arsenic concentration levels in different environmental media
Sample
|
Group
|
Mean±SD
|
T test
|
t
|
P
|
Water
|
Rural Y
|
29.979±15.752 μg/L
|
7.242
|
<0.001
|
Rural D
|
0.442±0.331 μg/L
|
Wheat
|
Rural Y
|
0.237±0.162 mg/kg
|
2.532
|
0.014
|
Rural D
|
0.104±0.073 mg/kg
|
3.2 Total arsenic in hair
A total of 99 hair samples from rural Y and 41 hair samples from rural D were tested in this study. From the test results, the average concentration of arsenic in the hair of the population in rural Y was 0.967 ± 0.878 mg/kg, ranging from 0.165 mg/kg to 4.463 mg/kg; the mean concentration of arsenic in the hair of the rural D population was 0.392 ± 0.215 mg/kg, ranging from 0.147 mg/kg to 0.977 mg/kg. For the concentration of arsenic in human hair investigated in 11 cities in China, the average concentration of arsenic was found to be 0.23 mg/kg (Zhou et al., 2016). In rural Y, 29.29% of the population had arsenic levels in hair above 1 mg/kg, while the population in rural D had arsenic levels in hair predominately within the range of 1 mg/kg, as shown in Figure 2.
Based on the K-S test for arsenic levels in hair, it was found that the distribution of arsenic levels in hair between rural Y and rural D did not conform to a normal distribution (P<0.05). The rank sum test for arsenic in hair (Table 2) revealed statistically significant differences in the levels of arsenic in the hair of the residents between rural Y and rural D (P<0.001).
Table 2 Levels of arsenic concentration in hair
Group
|
M(P25, P75)
|
K-S test
|
Wilcoxon's rank sum test
|
Z
|
P
|
Rural Y
|
0.633(0.437,1.100)
|
P<0.001
|
-5.335
|
< 0.001
|
Rural D
|
0.354(0.245, 0.483)
|
P=0.006
|
3.3 Demographics
The demographic information of the participants is shown in Table 3. A total of 140 study subjects were selected for this survey; 99 study subjects were included in rural Y; 41 study subjects were included in rural D. The mean age of the survey population in rural Y was 58.86 ± 13.39 years. The study area is a rural area, so the population living there is predominantly middle-aged and elderly, and the majority of the survey respondents are female, with 73.74% of the study area being female. Most of the local residents have lived in the area for a long time since birth or settled in the area due to marriage, and there are a few cases of middle-aged and elderly people moving out of the area. The weight of the residents in rural Y was predominately in the range of 50-70 kg, which is a normal weight standard for middle-aged and elderly people. The subjects in rural Y had a minority of chronic diseases, such as hypertension and hyperglycemia themselves. The results of the chi-squared test (Table S1) reveal no statistically significant differences (P>0.05) between the sex, age, and weight of the residents of rural Y and rural D.
Table 3 Demographics and concentration of arsenic in hair
Variables
|
n(%)
|
M
|
Min
|
Max
|
H
|
P
|
Gender
|
|
|
|
|
10.066
|
0.002
|
|
Female
|
73(73.74)
|
0.604
|
0.170
|
3.470
|
|
|
|
Male
|
26(26.26)
|
0.956
|
0.360
|
4.460
|
|
|
Age
|
|
|
|
|
16.272
|
0.006
|
|
20~30
|
3(3.03)
|
0.261
|
0.240
|
0.600
|
|
|
|
30~40
|
8(8.08)
|
0.522
|
0.250
|
2.880
|
|
|
|
40~50
|
14(14.14)
|
0.494
|
0.170
|
1.200
|
|
|
|
50~60
|
29(29.29)
|
0.571
|
0.200
|
1.750
|
|
|
|
60~70
|
25(25.25)
|
0.788
|
0.230
|
4.140
|
|
|
|
70~
|
20(18.18)
|
0.950
|
0.240
|
4.460
|
|
|
Residence time
|
|
|
|
|
8.544
|
0.036
|
|
~20
|
14(14.14)
|
0.533
|
0.237
|
1.201
|
|
|
|
20~40
|
34(34.34)
|
0.574
|
0.165
|
3.467
|
|
|
|
40~60
|
23(23.23)
|
0.788
|
0.196
|
2.914
|
|
|
|
60~
|
28(28.28)
|
1.197
|
0.233
|
4.463
|
|
|
Wight(kg)
|
|
|
|
|
6.457
|
0.264
|
|
30~40
|
2(2.02)
|
0.725
|
0.500
|
0.950
|
|
|
|
40~50
|
6(6.06)
|
0.825
|
0.240
|
2.910
|
|
|
|
50~60
|
40(40.40)
|
0.575
|
0.230
|
4.140
|
|
|
|
60~70
|
43(43.43)
|
0.630
|
0.170
|
3.490
|
|
|
|
70~80
|
6(6.06)
|
1.160
|
0.570
|
4.460
|
|
|
|
80~
|
2(2.02)
|
1.670
|
0.460
|
2.880
|
|
|
Chronic diseases
|
|
|
|
5.887
|
0.015
|
|
No
|
82(82.83)
|
0.606
|
0.165
|
4.463
|
|
|
|
Yes
|
17(17.17)
|
1.061
|
0.344
|
3.338
|
|
|
3.4 Behavioral characteristics
Information on the behavioral characteristics of the study population regarding drinking, eating, and bathing habits is presented in Table 4. In rural Y, 66.67% of the population used tap water as a drinking method, 17.17% used buckets or water purifiers as a drinking method, and 16.16% used tap water and buckets or water purifiers as a drinking method. Of these, 59.60% of the study population had an average daily water intake within the range of 1000 mL/d, and 40.4% of the study population had an average daily water intake above 1000 mL/d. In rural Y, 37.37% of the population consumed pasta products in the range of 100 g/d per day, 38.38% consumed pasta products in the range of 100-200 g/d per day, and 24.24% consumed more than 200 g/d per day. Based on the estimated average bathing time throughout the year, 47.47% of the rural Y population was controlled within the range of 0.12 to 0.14 h/d. The percentages of the surveyed population with smoking habits and drinking habits were both small in rural Y, with 12.12% having smoking habits and 8.08% having drinking habits. According to the results of the chi-squared test of the population in rural Y and rural D (Table S2), there were no statistically significant differences (P>0.05) between the population in the two areas in terms of drinking patterns, water consumption, diet, and behavioral habits of smoking and alcohol consumption. The difference in mean bathing time between residents of rural Y and rural D was statistically significant, with c2 being 20.561, P-value < 0.001.
Table 4 Behavioral characterization and information on concentration of arsenic in hair
Variables
|
n(%)
|
M
|
Min
|
Max
|
H
|
P
|
Drinking water method
|
|
|
|
|
2.778
|
0.249
|
|
Tap water
|
66(66.67)
|
0.695
|
0.170
|
4.460
|
|
|
|
Barrel water/water purifier
|
17(17.17)
|
0.763
|
0.250
|
2.880
|
|
|
|
Both
|
16(16.16)
|
0.507
|
0.250
|
1.760
|
|
|
Drinking water intake(mL/d)
|
|
|
|
|
4.414
|
0.110
|
|
~1000
|
59(59.60)
|
0.788
|
0.196
|
4.463
|
|
|
|
1000~2000
|
35(35.35)
|
0.566
|
0.165
|
4.139
|
|
|
|
2000~3000
|
5(5.05)
|
0.620
|
0.467
|
0.746
|
|
|
Dietary intake(g/d)
|
|
|
|
|
11.016
|
0.026
|
|
~100
|
37(37.37)
|
0.599
|
0.196
|
2.914
|
|
|
|
100~200
|
38(38.38)
|
0.609
|
0.165
|
3.491
|
|
|
|
200~300
|
6(6.06)
|
0.596
|
0.276
|
2.659
|
|
|
|
300~400
|
10(10.10)
|
1.287
|
0.584
|
4.463
|
|
|
|
400 ~
|
8(8.08)
|
1.243
|
0.263
|
3.467
|
|
|
Bathing time(h/d)
|
|
|
|
|
5.981
|
0.113
|
|
~0.1
|
4(4.04)
|
0.914
|
0.522
|
1.884
|
|
|
|
0.1~0.12
|
8(8.08)
|
0.537
|
0.233
|
2.046
|
|
|
|
0.12~0.14
|
47(47.47)
|
0.746
|
0.237
|
4.463
|
|
|
|
0.14~
|
40(40.40)
|
0.557
|
0.165
|
3.338
|
|
|
Smoking
|
|
|
|
|
3.934
|
0.047
|
|
Yes
|
12(12.12)
|
0.956
|
0.456
|
3.338
|
|
|
|
No
|
87(87.88)
|
0.615
|
0.165
|
4.463
|
|
|
Drinking
|
|
|
|
1.732
|
0.188
|
|
Yes
|
8(8.08)
|
0.847
|
0.467
|
3.338
|
|
|
|
No
|
91(91.92)
|
0.618
|
0.165
|
4.463
|
|
|
3.5 Factors associated with arsenic accumulation in hair
Univariate analysis of demographic factors is shown in Table 3. Differences in arsenic content in hair by sex were statistically significant (P<0.05). The arsenic content of the hair was 0.956 mg/kg and 0.604 mg/kg for males and females, respectively, and the arsenic content in the hair of male residents was higher than that of females. There was a significant difference (P<0.05) in the arsenic content in hair among the different age groups. The two comparisons adjusted for Bonferroni correction revealed a statistically significant difference in arsenic levels in hair between those over 70 years of age and those between 40 and 50 years of age, with higher levels of arsenic in hair in those over 70 years of age (0.95 mg/kg>0.494 mg/kg). The differences in arsenic levels in hair were statistically significant among people with different years of residence, and the results of the two-by-two comparison showed statistically significant differences in arsenic levels in hair between people with more than 60 years of residence and people with 20 years of residence and in the range of 20 to 40 years, with a high level of arsenic in hair (1.197 mg/kg) among people with more than 60 years of residence. The presence or absence of disease in the population had a statistically significant effect on the content of arsenic in hair, and residents with chronic diseases had significantly higher levels of arsenic in their hair (1.061 mg/kg>0.606 mg/kg). There was no statistically significant difference found in arsenic content in hair among different weight groups (P>0.05).
A univariate analysis of the behavioral characteristics factors is shown in Table 4. The difference in arsenic levels in hair was statistically significant (P<0.05) for people with different pasta intakes. The two comparisons revealed statistically significant differences in arsenic levels in hair between the population with average daily intake of pasta products in the range of 300-400 g/d and the population with average daily intake of 100 g/d or less, 100-200 g/d, or 200-300 g/d. Among them, those with an average daily intake of wheat manufactured products in the range of 300-400 g/d had high levels of arsenic levels in their hair (1.286 mg/kg). There was also a statistically significant effect on content of arsenic in hair in relation to whether or not the population smoked, with a high level of arsenic in hair (0.956 mg/kg) in the population with smoking habits.
For the multiple linear regression analysis of demographic information factors, the gender and age of the population were found to be significantly associated with the level of arsenic in hair (P<0.01). Also, the results of multiple linear regression of behavioral factors indicated that the intake of wheat-based foods by the population was also correlated with levels of arsenic in hair (P<0.05). The multiple linear regression analysis of the influencing factors is shown in Table 5.
Table 5 Hair arsenic levels and multifactorial regression analysis
Variables
|
B
|
95% CI
|
t
|
P
|
VIF
|
Sociodemographic factors
|
|
|
|
|
|
Age
|
0.019
|
0.007~0.031
|
3.039
|
0.003
|
1.142
|
Gender
|
0.708
|
0.322~1.093
|
3.646
|
0.000
|
1.200
|
Chronic diseases
|
0.183
|
-0.250~0.616
|
0.840
|
0.403
|
1.111
|
Wight
|
0.003
|
-0.017~0.022
|
0.275
|
0.784
|
1.208
|
Behavioral characteristics factors
|
|
|
|
|
|
Dietary intake
|
0.001
|
0.000~0.001
|
2.148
|
0.034
|
1.215
|
Drinking water intake
|
0.000
|
-0.001~0.000
|
-1.732
|
0.087
|
1.262
|
Bathing time
|
-0.828
|
-5.984~4.327
|
-0.319
|
0.750
|
1.010
|
Smoking
|
0.486
|
-0.167~1.139
|
1.479
|
0.143
|
1.617
|
Drinking
|
0.037
|
-0.743~0.817
|
0.093
|
0.926
|
1.611
|