Compartment

N
_{O}

P

N_{E}

RDI

X^{2}

Fraction of total X^{2} [%]


Conductive airway (lumen)

5

150

61.86

0.08

52.26

2.76

Alveolus (lumen)

527

1125

463.94

1.14

8.57

0.45

Macrophages

50

3

1.24

48.76

1781.45

94.22

Epithelial cell

12

38

15.67

0.77

0.86

0.05

Interstitium

13

34

14.02

0.93

0.07

0.004

Endothelial cell

12

38

15.67

0.77

0.86

0.05

Residual

0

113

46.6

0

46.6

2.46

Total

619

1501

619

1

1890.67

100

 Note. With 6 degrees of freedom (71 compartments × 21 groups) and a total chisquared value 1890.67 the nullhypothesis of random particle distribution has to be rejected with p < 0.001. The alveolar macrophages are the only compartment that fulfils the criteria for preferential particle localization: RDI > 1 and the partial chisquared contributes substantially (more than 10%) to the nonrandomness of the distribution, i.e. the total chisquared [34, 103]. However, although the nanoparticles are preferentially located in the macrophages it is interesting to note that they deposit mainly in the alveolar region and are not found in the lumen of the blood vessels which are contained in the compartment residual. Abbreviations: N_{O} = Number of observed particles; N_{E} = Number of expected particles; P = Number of observed points; RDI = Relative deposition index; X^{2} = Chi squared values.