What actually happens is quite the oppsite
As you of course know mold and fungus need a steady cool, dark, moist environment to grow, quite the opposite from happens with in the pervious concrete system. Because water is allowed to pass through the system and infiltrate into the ground, where it should go, the interior portions dry out quickly once the rain stops; no moisture, no mold.
In traditional concrete the base is highly compacted and impermeable, when it rains water is wicked into the space in between the bottom of the concrete slab and the base and because it has no place to go this area tends to stay wet for long periods of time: a perfect source of moisture for tree roots where they then grow and force the concrete up. Remember, roots only go where there is water. In a pervious concrete system ALL the water is allowed to soak deep into the ground, not only feeding the deep tree roots but replenishing the local aquifer.
Right now your local water way that receives the municipal storm water runoff IS a pollutant concentrator. Non-point source loads of pollutants (hydrocarbons, phosphates, nitrates, etc, etc) from local run-off is collected in a central drain system and dumped untreated in the local marine environment. All the major lakes, rivers and bays in the US are polluted due to contaminated storm water run-off. Pervious concrete systems as well as bio-swales and rain gardens have highly efficient and well documented bio-filtration/remediation functions.
Bottom line is that not only can a well designed and installed pervious concrete system satisfy municipal regulations to reduce or eliminate run-off, but we can also reverse a significant amount of environmental damage caused by our built environment. I like to say pervious concrete allows us to have our cake (hard surfaces) and eat it too.
David Liguori - Bay area pervious concrete
