We investigated the chemical composition of {rho} Pup using high-resolution spectral observations taken from the Very Large Telescope and the IUE archives and also spectra obtained at the 1.8m telescope of the Bohyunsan observatory in Korea. The abundances of 56 chemical elements and the upper limits of Li and Be abundances were determined. The abundance pattern of {rho} Pup was found to be similar to that of Am-type stars. The possibility of the influence of the accretion of interstellar gas and dust on the abundance patterns of B--F-type stars is discussed. The plots of the relative abundances of chemical elements in the atmospheres of {rho} Pup and {delta} Sct versus the second ionization potentials of these elements show the correlations. The discontinuities at 13.6 and 24.6eV--the ionization potentials of hydrogen and helium, respectively, are also exhibited in these plots. These discontinuities can be explained by interaction of the atoms of interstellar gas, mainly hydrogen and helium atoms, with the atoms of stellar photospheres (so-called charge-exchange reactions). Note that only the jumps near 13.6 and 24.6eV were pointed out in previous investigations of relative abundances versus the second ionization potentials for Am-type stars. The dependencies of the relative abundances of chemical elements on the second ionization potentials of these elements were investigated using the published abundance patterns of B-F-type stars. The correlations of relative and absolute abundances of chemical elements, second ionization potentials, and projected rotational velocities are clearly detected for stars with effective temperatures between 7000 and 12000K. If the correlation of relative abundances and second ionization potentials can be explained by the accretion of interstellar gas on the stellar surfaces, the investigation of these correlations can provide valuable information on the density and velocities of interstellar gas in different regions of the Galaxy and also on the influence of this phenomenon on stellar evolution. The dependencies of the relative abundances of chemical elements on the condensation temperatures of these elements were also found in the atmospheres of {rho} Pup, {delta} Sct, and other B--F-type stars. Ten possible {lambda} Boo-type stars were detected. The effective temperatures of these objects are between 10900 and 14000K.