In our present study, 209 university students completed the questionnaires validly and provided effective urine samples, which included 116 (55.50%) males and 93 (44.50%) females. The mean students' age was 19.94 ± 2.37 years, their mean BMI was 21.42 ± 3.01 kg/m2, and most participants (61.24%) were normal weight. There were 118 (56.46%) non-approaching graduation students and 91 (43.54%) approaching graduation students; 96 (45.93%) students came from rural areas and 113 (54.07%) students came from town (Table 1).
Table 1 Characteristics of 209 university students enrolled in the study
Variables
|
Mean ± SD or n (%)
|
General demographic characteristics
|
|
Age (y)
|
19.94 ±2.37
|
Gender
|
|
Male
|
116 (55.50)
|
Female
|
93 (44.50)
|
BMI (kg/m2)
|
21.42±3.01
|
Underweight (< 18.5)
|
39 (18.66)
|
Normal (18.5-23.9)
|
128 (61.24)
|
Overweight (≥ 24.0)
|
42 (20.10)
|
Grade
|
|
Non-Approaching graduation
|
118 (56.46)
|
Approaching graduation
|
91 (43.54)
|
Residence
|
|
Rural
|
96 (45.93)
|
Town
|
113 (54.07)
|
Eating habits
|
|
Daily food matching
|
|
More meat and less vegetables
|
37 (17.70)
|
Less meat and more vegetable
|
37 (17.70)
|
The meat and vegetables are even
|
132 (63.16)
|
Fruit frequency in the last week
|
|
1~3 days
|
144 (68.90)
|
4~6 days
|
52 (24.88)
|
Everyday
|
13 (6.22)
|
Daily water consumption in the
last week
|
|
< 1000 mL
|
98 (46.89)
|
1000~1500 mL
|
69 (33.01)
|
≥ 1500 mL
|
42 (20.10)
|
The distribution of iAs, MMA, DMA and TAs in urine were shown in Table 2. The detection rates of iAs (AsⅢ), MMA and DMA in urine among 209 university students were 100%, 96.65% and 72.73%, respectively. The concentration of DMA was the highest among all the measured As speciations and its median concentration was 12.17 µg/L, the median concentration of iAs was 1.22 µg/L, and the median concentration of MMA was 1.18 µg/L (Table 2). The proportion distribution of %iAs, %MMA, %DMA in urine was shown in Table 3. The %DMA was the highest, followed by %iAs and %MMA.
Table 2 Urine concentration distributions of As speciations among 209 university students
As speciation
|
Gender
|
> LOD (%)
|
Mean
(mg/L)
|
Min
(mg/L)
|
P5
(mg/L)
|
P25
(mg/L)
|
P50
(mg/L)
|
P75
(mg/L)
|
P95
(mg/L)
|
Max
(mg/L)
|
iAs
|
Total
|
96.65
|
1.59
|
< LOD
|
0.16
|
0.73
|
1.22
|
2.07
|
4.28
|
6.98
|
Males
|
95.69
|
1.83
|
< LOD
|
0.02
|
0.78
|
1.44
|
2.61
|
4.59
|
5.3
|
Females
|
97.85
|
1.3
|
< LOD
|
0.17
|
0.66
|
1.01
|
1.66
|
3.2
|
6.98
|
MMA
|
Total
|
72.73
|
1.19
|
< LOD
|
< LOD
|
< LOD
|
0.92
|
1.74
|
3.98
|
6.47
|
Males
|
80.17
|
1.45
|
< LOD
|
< LOD
|
0.41
|
1.18
|
2.1
|
4.41
|
6.47
|
Females
|
63.44
|
0.87
|
< LOD
|
< LOD
|
< LOD
|
0.63
|
1.24
|
3.36
|
5.09
|
DMA
|
Total
|
100
|
14.58
|
1.09
|
3.86
|
7.15
|
12.17
|
19.26
|
33.48
|
78.36
|
Males
|
100
|
16.13
|
1.7
|
3.51
|
7.32
|
14.57
|
21.14
|
42.09
|
78.36
|
Females
|
100
|
12.65
|
1.09
|
4.55
|
6.91
|
10.58
|
16.42
|
27.44
|
33.58
|
TAs
|
Total
|
100
|
17.37
|
1.09
|
4.37
|
8.36
|
15.02
|
23.17
|
39.31
|
86.94
|
Males
|
100
|
19.41
|
1.7
|
3.79
|
8.85
|
17.53
|
25
|
48.62
|
86.94
|
Females
|
100
|
14.82
|
1.09
|
5.11
|
8.2
|
12.44
|
18.91
|
31.96
|
40.12
|
Abbreviations: TAs, total urinary arsenic; iAs, inorganic arsenic (It mainly refers to the AsIII, since the AsV has not been detected in this population); MMA, monomethylarsonic acid; DMA, dimethylarsinic acid.
Table 3 Urine As speciations percentages among 209 university students
As speciation percentages
|
Gender
|
Mean
(%)
|
Min
(%)
|
P5
(%)
|
P25
(%)
|
P50
(%)
|
P75
(%)
|
P95
(%)
|
Max
(%)
|
%iAs
|
Total
|
9.25
|
0
|
2.16
|
6.26
|
8.76
|
11.77
|
17.32
|
46.12
|
Males
|
9.54
|
0
|
0.46
|
6.2
|
8.98
|
12.04
|
18.93
|
24.49
|
Females
|
8.88
|
0
|
2.23
|
6.28
|
8.3
|
10.64
|
16.66
|
46.12
|
%MMA
|
Total
|
6.23
|
0
|
0
|
0
|
6.13
|
10.1
|
15.08
|
21.09
|
Males
|
6.23
|
0
|
0
|
0
|
6.13
|
10.1
|
15.08
|
21.09
|
Females
|
5.15
|
0
|
0
|
0
|
4.58
|
8.94
|
14.32
|
20.34
|
%DMA
|
Total
|
84.52
|
43.01
|
71.21
|
79.45
|
84.84
|
90.33
|
96.6
|
100
|
Males
|
83.36
|
64.53
|
70.69
|
78.07
|
82.91
|
89
|
99.54
|
100
|
Females
|
85.97
|
43.01
|
72.92
|
81.86
|
87.54
|
91.91
|
95.28
|
100
|
The association of demographic features, eating habits with As speciations in urine among 209 university students were shown in Table 4. The lnTAs concentration in urine of students over 20 years old was 0.31 µg/L lower than that of students under 20 years old (p < 0.01). Similar to the age, the urine lnTAs concentration of approaching graduation students was 0.34 µg/L lower than that of non-approaching graduation students (p < 0.01). Compared with the males, ln%MMA in urine of females was lower while ln%DMA and lnSMI was higher, and the difference was statistically significant. Dietary habits were only correlated with the urine lnTAs. The lnTAs level of students with balanced diet was higher than that of students with unbalanced diet, but the difference was only statistically significant when compared to those with less meat and more vegetables (p < 0.01). There was also a significant correlation between fruit consumption and urinary lnTAs level, so were water consumption. The more frequent fruit consumption, the lower lnTAs concentration, and the more water consumption, the lower lnSMI.
Table 4
The analyses about influencing factors of As speciations in urine and TAs by linear regression models
|
ln%iAs
|
ln%MMA
|
ln%DMA
|
lnTAs
|
lnPMI
|
lnSMI
|
Age
|
|
|
|
|
|
|
< 20 y
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
≥ 20 y
|
-0.11 (-0.25, 0.03)
|
0.16 (-0.07, 0.39)
|
0.01 (-0.02, 0.03)
|
-0.31 (-0.50, -0.13)**
|
0.01 (-0.01, 0.03)
|
-0.01 (-0.02, 0.01)
|
Gender
|
|
|
|
|
|
|
Male
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Female
|
0.10 (-0.24, 0.04)
|
-0.38 (-0.60, -0.15)**
|
0.03 (0.003, 0.06)*
|
-0.19 (-0.38, 0.004)
|
0.01 (-0.01, 0.03)
|
0.02 (0.01, 0.04)*
|
BMI
|
|
|
|
|
|
|
Underweight
|
0.07 (-0.12, 0.27)
|
-0.08 (-0.38, 0.22)
|
0.004 (-0.03, 0.04)
|
0.03 (-0.23, 0.29)
|
0.004 (-0.02, 0.03)
|
0.001 (-0.02, 0.02)
|
Normal
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Overweight
|
0.02 (-0.07, 0.12)
|
-0.01 (-0.16, 0.13)
|
-0.003 (-0.02, 0.02)
|
-0.02 (-0.15, 0.10)
|
0.00001 (-0.01, 0.01)
|
-0.003 (-0.01, 0.01)
|
Residence
|
|
|
|
|
|
|
Urban
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Rural
|
0.07 (-0.07, 0.21)
|
0.07 (-0.16, 0.30)
|
-0.02 (-0.05, 0.004)
|
0.10 (-0.09, 0.29)
|
-0.01 (-0.03, 0.004)
|
-0.01 (-0.03, 0.01)
|
Grade
|
|
|
|
|
|
|
Non-Approaching graduation
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Approaching graduation
|
-0.11 (-0.25, 0.03)
|
0.17 (-0.06, 0.40)
|
0.003 (-0.03, 0.03)
|
-0.34 (-0.53, -0.16)**
|
0.01 (-0.01, 0.03)
|
-0.01 (-0.02, 0.01)
|
Eating habits
|
|
|
|
|
|
|
Daily food matching
|
|
|
|
|
|
|
More meat and less vegetables
|
-0.07 (-0.26, 0.11)
|
-0.03 (-0.34, 0.28)
|
0.01 (-0.03, 0.04)
|
-0.04 (-0.29, 0.20)
|
0.01 (-0.02, 0.03)
|
-0.002 (-0.02, 0.02)
|
Less meat and more vegetable
|
-0.02 (-0.11, 0.08)
|
0.05 (-0.11, 0.20)
|
0.01 (-0.01, 0.03)
|
-0.26 (-0.40, -0.13)**
|
0.01 (-0.01, 0.02)
|
-0.002 (-0.01, 0.01)
|
The meat and vegetables are even
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Fruit frequency in the last week
|
|
|
|
|
|
|
1 ~ 3 days
|
0.004 (-0.31, 0.32)
|
-0.48 (-0.96, 0.01)
|
0.01 (-0.05, 0.07)
|
0.43 (0.03, 0.84)*
|
-0.01 (-0.05, 0.03)
|
0.03 (-0.01, 0.06)
|
4 ~ 6 days
|
0.02 (-0.12, 0.16)
|
-0.15 (-0.38, 0.08)
|
-0.003 (-0.03, 0.02)
|
0.20 (-0.01, 0.41)
|
-0.01 (-0.03, 0.02)
|
0.01 (-0.01, 0.02)
|
Everyday
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Daily water consumption in the
last week
|
|
|
|
|
|
|
< 1000 mL
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
Ref
|
1000 ~ 1500 mL
|
-0.10 (-0.26, 0.05)
|
0.42 (0.16, 0.69)
|
-0.03 (-0.05, 0.003)
|
-0.002 (-0.22, 0.22)
|
-0.001 (-0.02, 0.02)
|
-0.02 (-0.04, -0.01)*
|
≥ 1500 mL
|
-0.44 (-0.13, 0.04)
|
0.13 (-0.03, 0.29)
|
-0.01 (-0.03, 0.10)
|
-0.04 (-0.16, 0.09)
|
-0.004 (-0.02, 0.01)
|
-0.01 (-0.02, 0.01)
|
The univariate linear regression models analysis was conducted. |
*, P value < 0.05; **, P value < 0.01; Ref, reference group; TAs, total urinary arsenic; iAs, inorganic arsenic (It mainly refers to the AsIII, since the AsV has not been detected in this population); MMA, monomethylarsonic acid; DMA, dimethylarsinic acid; PMI, the Primary Methylation Index; SMI, the Secondary Methylation Index; ln, the natural logarithm transformed. |
The estimated joint effect of lnTAs and lniAs on As methylation indices (ln%MMA, ln%DMA, lnPMI, lnSMI) are shown in Fig. 1–4. We firstly displayed some numerical summaries of their overall effect, which was identified as the change in As methylation indices (ln%MMA, ln%DMA, lnPMI, lnSMI) associated with a simultaneous change in lnTAs and lniAs from a particular percentile as compared to when lnTAs and lniAs were at their median values (50th percentile) (Fig. 1A, Fig. 2A, Fig. 3A, Fig. 4A). As can be seen from Fig. 1A, combined exposure was not associated with ln%MMA. When both lnTAs and lniAs levels are above the 60th percentile, the lnTAs and lniAs were significantly negatively correlated with ln%DMA; on the contrary, when both lnTAs and lniAs levels are below the 55th percentile, a significantly positive correlation was observed when compared to the 50th percentile, and the similar result was also found about lnSMI. While compared with the 50th percentile, the lnTAs and lniAs were positively correlated with lnPMI only at 35th, 40th and 55th percentile. The variation in the association of lnTAs or lniAs when it increased from 25th to 75th percentile accompanied by another factor was set at 25th, 50th or 75th percentile with As methylation indices (ln%MMA, ln%DMA, lnPMI, lnSMI), respectively was shown in Fig. 1B, Fig. 2B, Fig. 3B and Fig. 4B. LnTAs displayed a significantly positive association with ln%DMA and lnPMI levels when lniAs was set at the 25th, 50th, and 75th percentiles. And lniAs displayed a significantly negative association with ln%DMA, lnPMI, and lnSMI levels when lnTAs is set at the 25th, 50th, and 75th percentiles, and displayed a significantly positive association with ln%MMA. Finally, we also examined the potential nonlinear exposure-response relationship when another factor was held at the corresponding median concentration by BKMR analysis. We found that lnTAs was positively correlated with ln%DMA, lnPMI and lnSMI. However, lniAs was negatively correlated with these three indices (Fig. 1C, Fig. 2C, Fig. 3C and Fig. 4C).
Considering the study participants are university students and environment As exposure level is not very serious in Anhui province (Zhong and Zhang et al. 2019), we thought that their urinary As are mainly source from food and drinking water. Therefore, we measured the TAs content in the food and drinking water from the canteen. The results showed that the TAs content in cereals was the highest among all the our purchased foods, with an average of 90.340 µg/kg, while TAs in fruits, vegetables and meats were similar to be lower. The mean concentration of TAs in drinking water was 0.284 µg/L (Table 5).
Table 5
Average levels of total arsenic in some foods.
Food group
|
Levels of total arsenic
(mean ± SD, µg/kg or µg/L)
|
Cereals
(polished rice, flour)
|
90.340 ± 41.834
|
Fruits
(banana, cantaloupe, dragon fruit)
|
17.507 ± 8.540
|
Vegetables
(potato, tomato, cabbage, bean sprout, carrot)
|
7.338 ± 1.844
|
Meats
(pork, chicken, beef, fish, shrimp)
|
7.369 ± 11.086
|
Drinking water
|
0.284 ± 0.324
|