Medical experts generally consider a lead of $30\mathrm{\mu g}$ Pb per (dL) of blood to pose a significant health risk (Pb = 208). Number of lead atoms per ${\mathrm{cm}}^3$ of blood is

$\begin{array}{l}1\mathrm{dL}=\frac{1}{10}\mathrm{L}=0.1\mathrm{L}=100{\mathrm{cm}}^3\\ 100{\mathrm{cm}}^3\mathrm{of}\mathrm{blood}\mathrm{has}=30\mathrm{mg}\mathrm{Pb}=30\times {10}^{-6}\mathrm{g}\mathrm{Pb}\\ =\frac{30\times {10}^{-6}}{208}\mathrm{mol}\mathrm{Pb}=\frac{30\times {10}^{-6}\times {\mathrm{N}}_0}{208}\mathrm{atoms}\mathrm{Pb}\\ =8.6827\times {10}^{16}\mathrm{atoms}\mathrm{Pb}\\ 1{\mathrm{cm}}^3\mathrm{of}\mathrm{blood}\mathrm{has}=8.627\times {10}^{+14}\mathrm{atoms}\mathrm{Pb}.\end{array}$