Effective accretion rate of refractory materials onto grains (here for carbonaceous grains) as a function of the turbulent Mach number for two different mean density $\overline{n}=1$ and 100 H cm⁻³ (respectively in solid blue and in dashed blue). The various colors stand for different density cut-offs n_max = 10³ and 100⁴ H cm⁻³ (respectively in dark and light blue). For comparison we show the free-fall time corresponding to the quoted gas density $\overline{n}$ in black, and the SN time delay in red dot-dashed.