Quantitative biokinetics over a 28 day period of freshly generated, pristine, 20 nm titanium dioxide nanoparticle aerosols in healthy adult rats after a single two-hour inhalation exposure

Table 4 Fractional contribution of [⁴⁸V]TiO₂-NP absorbed in the GIT to the retention in secondary organs and tissues

	GIT-absorbed NP fraction after NP gavage [23]		Estimated NP fraction of GIT-absorption cleared from lungs		Ratio: GIT-absorb. NP over measured fractions after NP inhalation
2nd organs	24 h	7d	24 h	7d	24 h	7d
liver	1.27E-04	2.26E-05	1.21E-07	4.62E-08	4.53E-03	5.67E-03
spleen	3.19E-05	1.16E-05	1.68E-09	2.37E-09	2.50E-04	5.65E-04
kidneys	3.82E-05	2.30E-05	2.74E-08	3.19E-08	3.42E-03	3.86E-03
heart	7.96E-05	4.89E-06	2.78E-09	2.24E-10	1.66E-04	1.27E-04
brain	1.01E-05	2.38E-05	7.66E-11	1.12E-09	3.59E-05	1.31E-04
uterus	2.44E-05	4.37E-05	1.43E-09	3.61E-09	2.77E-04	2.29E-04
carcass	8.07E-04	2.88E-04	5.82E-06	4.51E-06	3.42E-02	4.34E-02
skeleton	4.39E-04	8.96E-04	1.87E-06	7.09E-06	2.02E-02	2.20E-02
soft tissue	4.58E-04	5.00E-06	1.40E-06	3.86E-08	1.45E-02	2.15E-02

Mean values of GIT-absorbed fractions after [⁴⁸V]TiO₂-NP gavage in the left two columns at 24 h or 7 days were taken from [23]. Estimated contribution of GIT-absorption of [⁴⁸V]TiO₂-NP cleared from lungs were calculated by multiplying the mean values of [⁴⁸V]TiO₂-NP cleared after 24 h by MCC into the GIT and the sum of all [⁴⁸V]TiO₂-NP which had entered the GIT within the first 7 days p.e. (Table 2) and the fraction in the according left column of the Table 4. These are shown in the middle columns of Table 4. The ratios of GIT-absorbed [⁴⁸V]TiO₂-NP at 24 h or 7 days divided by the mean values of the measured organ or tissue fractions of Table 3 after [⁴⁸V]TiO₂-NP inhalation are presented in the right columns of Table 4. These ratios confirm the rather low contribution of GIT-absorbed [⁴⁸V]TiO₂-NP to the measured accumulation of each secondary organ or tissue in Table 3

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