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As shown in Figure 1, Figure 2, and Figure 3, the diameter of PM in the ME was less than 1 μm. The peak value occurred at a diameter less than 100 nm for the diluted ME; whereas, the non-dilution ME had a diameter larger than 100 nm.
Figure 1. Motorcycle exhausts particle size distribution with respect to number concentration in different diluted ME. The x-axis is the particle size of the particulate matter (nm). The y-axis is the number concentration in all diameters of PM in the ME: (A) Clean air; (B) 1:20 diluted ME; (C) 1:10 diluted ME; (D) 1:5 diluted ME; (E) 1:2 diluted ME; and (F) Non-diluted ME.
Figure 2. Motorcycle exhausts particle size distribution with respect to surface area concentration in different dilution ME. The x-axis is the particle size of the particulate matter (nm). The y-axis is the surface area concentration in all diameters of PM in the ME: (A) Clean air; (B) 1:20 diluted ME; (C) 1:10 diluted ME; (D) 1:5 diluted ME; (E) 1:2 diluted ME; and (F) Non-diluted ME.
Figure 3. Motorcycle exhausts particle size distribution with respect to mass concentration in different dilution ME. The x-axis is the particle size of the particulate matter (nm). The y-axis is the mass concentration in all diameters of PM in the ME: (A) Clean air; (B) 1:20 diluted ME; (C) 1:10 diluted ME; (D) 1:5 diluted ME; (E) 1:2 diluted ME; and (F) Non-diluted ME.
The number, surface area, and MC of PM in the ME are shown in Table 1. There was a favorable decreased linear relationship between the NC of MEPs and dilution ratio. The same relationship was also observed between the SAC and MC of the MEPs (all P ≤ 0.001). Compared with the clean air group, the NC in the 1:20, 1:10, 1:5, and 1:2 diluted ME groups as well as in the non-diluted ME group were 13.8, 19.1, 22.4, 286.0, and 1237.0 times higher than that of the clean air group, respectively. The SAC in the 1:2 diluted ME and non-diluted ME groups were higher than those in the clean air group and 1:20, 1:10, and 1:5 diluted groups (P < 0.05). For MC, the 1:20 and 1:2 diluted and non-diluted ME groups were significantly higher when compared with the clean air group and the non-diluted ME group was also higher than those in the 1:20, 1:10, 1:5, and 1:2 diluted ME group (P < 0.001). Therefore, the number, surface area, and MC of PM in the ME were gradually reduced with increase in the dilution.
Groups Number concentration
(#/cm3)Surface area concentration
(× 107nm2/cm3)Mass concentration
(μg/m3)Clean air 27 ± 8 0.74 ± 0.60 0.07 ± 0.06 1:20 diluted ME 373 ± 60* 1.01 ± 0.10 0.28 ± 0.07* 1:10 diluted ME 517 ± 47* 1.81 ± 0.66 0.88 ± 0.96 1:5 diluted ME 606 ± 15*# 2.23 ± 0.65 1.72 ± 0.95 1:2 diluted ME 7,723 ± 48*#△▲ 16.57 ± 0.22*#△▲ 2.78 ± 0.16*# non-diluted ME 33,400 ± 883*#△▲□ 462.75 ± 13.12*#△▲□ 192.32 ± 6.27*#△▲□ Linear-by-Linear Association x2 = 13.438 x2 = 10.412 x2 = 10.130 P-value < 0.001 0.001 0.001 Note. The particle size of scanning ranges from 18.1–947.5 nm; Data represent Mean ± SD, n = 5/group.
*P < 0.05, as compared with the clean air group. #P < 0.05, as compared with the 1:20 diluted ME. △P < 0.001, as compared with the 1:10 diluted ME. ▲P < 0.001, as compared with the 1:5 diluted ME. □P < 0.001, as compared with the 1:2 diluted ME.Table 1. Number, surface area, and mass concentrations characterization of motorcycle exhausts particle in different diluted ME groups
To investigate the concentration of the MEPs with diameter ≤ 100 nm and > 100 nm, we selected NC as a variable and analyzed the NC of MEPs with diameter ≤ 100 nm or > 100 nm in different diluted ME groups. Results show that most of the PMs were smaller than 0.1 μm according to NC in the diluted groups (Table 2). The NC of MEPs with diameter ≤ 100 nm were 3.7, 3.1, 5.5, and 5.2 times higher than those with diameter > 100 nm in 1:20, 1:10, 1:5, and 1:2 diluted ME groups, respectively. But for the non-diluted ME, NC of the PM with diameter ≤ 100 nm was less than that with diameter > 100 nm (Table 2). These results indicate that dilution will greatly affect the particle size.
Groups Number concentration (#/cm3) P-value* Diameter ≤ 100 nm Diameter > 100 nm Clean air 14 ± 8 13 ± 5 0.944 1:20 diluted ME 294 ± 61 79 ± 13 0.007 1:10 diluted ME 392 ± 28 125 ± 20 < 0.001 1:5 diluted ME 513 ± 19 93 ± 13 < 0.001 1:2 diluted ME 6,490 ± 36 1,232 ± 39 < 0.001 non- diluted ME 1,877 ± 56 31,550 ± 858 < 0.001 Note. Data represent Mean ± SD, n = 5/group. *Compared between MEPs with diameter ≤ 100 nm and MEPs with diameter > 100 nm. Table 2. Number concentration of the MEPs with the diameter ≤ 100 nm and > 100 nm
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CRV% of the clean air group and 1:20 diluted ME group were higher than 90%; while CRV% of 1:10, 1:5, 1:2 diluted ME group and non-diluted ME group were reduced by about 14%, 23%, 42%, and 40% compared to that of 1:20 group, respectively (P < 0.001) (Figure 4). Compared to 1:10 and 1:5 diluted ME groups, both the 1:2 diluted and non-diluted ME group had a decreased CRV (P < 0.001). When comparing the CRV% between 1:2 diluted and non-diluted ME groups, there was no significant reduction (P > 0.05; Figure 4). These results indicate that the low concentration of ME exposure had a good dilution-dependent decrease of CRV in the BEAS-2B cells, with CRV more than 60%. However, at high concentration (1:2 diluted and non-diluted ME), CRV was less than 60%.
Figure 4. Dose-dependent cytotoxicity of BEAS-2B cells induced by ME using CCK-8 assay. Data represent Mean ± SD, n = 3/group. ***P < 0.001, as compared with group exposed to clean air; ∆∆∆P < 0.001, as compared with 1:20 diluted ME; ▪▪▪P < 0.001, as compared with 1:10 diluted ME; ▫▫▫P < 0.001, as compared with 1:5 diluted ME.
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Based on the four models (including Hill, Linear, Polynomial and Power in the BMDS), the AIC, P-value, BMD, and BMDL (the 95% CI limit of BMD) were calculated automatically and presented in Table 3. According to the P-value (> 0.05) and minimal AIC, the best-fitting models for the NC, SAC and MC were Hill, Hill, and Polynomial models, respectively. The BMD of NC, SAC, and MC that induced the decrease of CRV were 450.6#/cm3, 1.449 × 107 nm2/cm3, and 0.369 μg/m3, respectively. The best-fitting model showed that BMDL of particulates in ME for the CRV of BEAS-2B cell via ALI exposure were as follows: 364.2#/cm3 for NC; 0.662 × 107 nm2/cm3 for SAC; and 0.278 μg/m3 for MC; respectively (Table 3).
Model name BMD BMDL AIC P-value Number concentration (#/cm3) Hill 450.6 364.2 87.88 0.5031 Linear 14339.8 9314.5 115.35 < 0.0001 Polynomial 1605.6 1130.1 102.39 0.0005 Power 14339.8 9314.5 115.35 < 0.0001 Surface area concentration (× 107 nm2/cm3) Hill 1.449 0.662 87.41 0.6348 Linear 278.125 164.574 119.21 < 0.0001 Polynomial 3.694 2.654 101.31 0.0008 Power 278.125 164.574 119.21 < 0.0001 Mass concentration (μg/m3) Hill 0.709 0.397 92.67 0.0458 Linear 119.907 70.14 119.53 < 0.0001 Polynomial 0.369 0.278 86.91 0.4914 Power 119.907 70.14 119.53 < 0.0001 Note. AIC: Akaike information coefficient. Table 3. BMD and BMDL for the decrease of CRV in BEAS-2B cells in terms of number, surface area and mass concentration calculated by different models
Assessment of Benchmark Dose in BEAS-2B Cells by Evaluating the Cell Relative Viability with Particulates in Motorcycle Exhaust via the Air-liquid Interface Exposure
doi: 10.3967/bes2021.036
- Received Date: 2020-02-15
- Accepted Date: 2020-11-03
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Key words:
- Motorcycle exhaust particulates /
- Air–liquid interface /
- Bronchial epithelial cells /
- Cell relative viability /
- Dose-dependent effect
Abstract:
Citation: | YU Tao, ZHANG Xue Yan, LI Shu Fei, ZHOU Yu Mei, LI Bin, WANG Zhong Xu, DAI Yu Fei, ADAMSON Sherleen Xue-Fu, ZHENG Yu Xin, BIN Ping. Assessment of Benchmark Dose in BEAS-2B Cells by Evaluating the Cell Relative Viability with Particulates in Motorcycle Exhaust via the Air-liquid Interface Exposure[J]. Biomedical and Environmental Sciences, 2021, 34(4): 272-281. doi: 10.3967/bes2021.036 |