Mold is a foul-smelling and potentially dangerous fungus most commonly associated with porous materials like wood, plaster, grout and fabrics. Under the right conditions, though, mold can also grow on semi-porous and nonporous materials like glass, metal and also plastic. The speed at which mold grows on plastic depends on multiple factors.
Amount of Moisture
For mold to grow, moisture must present itself on the plastic surface. Since some plastics, like shower curtains, are semi-porous; while others, like food containers, are nonporous; not all plastics can grow mold as efficiently or as quickly. Because a semi-porous surface can trap moisture for long periods of time, while a nonporous surface cannot trap moisture, mold can grow much more easily with the former. For a nonporous surface to grow mold, it must have a consistent source of moisture, like a puddle of water left for an extended period of time.
Amount of Nutrients
Mold will also not grow on plastic unless it has a nutrient source. Since plastic does not provide natural nutrients, like cellulose, for mold spores, mold must rely on old food particles, dirt or soil to provide ample nutrients. For instance, it might grow inside a plastic container where a residue of rotting food remains, or inside a used plastic water bottle that has not been rinsed clean. The more soil and organic residue present, the faster mold can grow.
Other factors also determine the speed at which mold can grow on plastic. For instance, if the environment has poor air circulation, as can be the case with a bath mat in a windowless bathroom, or high humidity, like a plastic gardening tool left lying in a humid yard, mold can germinate more quickly than if the plastic object is located outdoors in the clear and near rays of sunlight. The cleanliness of the overall environment also plays a role, because dirt and dust in the air can settle on the plastic, providing additional soil and possibly additional mold spores. Temperature plays a role, since mold grows more slowly at low temperatures.
Specific Growth Speed
If all of the necessary conditions exist, including the existence of dirt and excessive moisture on the surface of the plastic, as well as a porous construction in the plastic, mold may begin to grow in as little as 24 to 48 hours. Since plastic once again does not provide the ideal growth conditions, mold will usually not colonize, multiplying to cover a large surface area, but it can still germinate and produce fumes and even toxins. As a result, you should keep all plastic objects clean and dry to avoid mold growth.