The present article study the case of an object exposed to pollution by diffusion mechanisms during a unitary time. After a certain resting period without any pollution exposures, we derive a universal upper-bound for the remaining concentration levels of pollution within that object. There are only 6 parameters involved: the saturated concentration levels of pollution within the considered object immediately after being exposed to pollution during an arbitrary long time, the diffusion coefficients of that pollution, the spatial dimensions of the considered object, the pollution exposure time, the resting time and the concentration levels of pollution within the considered object. A universal upper bound for the remaining concentration levels of pollution after backward diffusion can be found and can hold for any diffusion coefficients. This universal upper bound for the remaining concentration levels of pollution is particularly useful in the case of disinfection procedures with disinfecting toxic volatile fluids having unknown diffusion coefficients. Indeed, a too short duration of the disinfection procedures would not decontaminate well enough the considered object while a too long duration of the disinfection procedures would contaminate the considered object too much for a too long time. In addition, the toxicity of disinfecting volatile fluids is often not well known precisely and may vary under various circumstances. Therefore, this universal upper bound for the remaining concentration levels of pollution can be used to figure out the optimal duration for the disinfection procedures and the optimal resting time immediately after these disinfection procedures without needing to know the diffusion coefficients of the involved toxic disinfecting volatile fluids. For the convenience of calculations, we consider a unitary time for the pollution exposure time, we consider unitary dimensions for the considered object and we consider unitary saturated concentration levels of pollution. In the present article, the universal upper bound for the remaining pollution after backward diffusion and/or for the remaining pollution after re-suspension, are derived in the 1D case and in the 3D spherical case.