Volunteer Tomato Plant?

A tomato plant, with many nice sized tomatoes sprang up spontaneouslly from a crack in the pavement on our property. While I know that tomato seeds spread and this is not uncommon, my question is about how safe are the tomotoes to eat? The reason I ask, is that it grew out of concrete, not soil, and more concerning, it is located about 50 cm-1 meter above the underground sewage pipe. Considering that this all happend in a period, when there was no rain, do we assume that it fed on (ugh) sewage? Or do these plants not need much water and it is not strange that it came out of concrete? The tomatoes are more robust than any plant I ever cultivated, they are almost the size of tangerines!