No. What people actually mean is fertilizer free. Most potting soil comes pre fertilized with chemicals which can be harmful to chameleons. People get "organic potting soil" which has none of the nasty chemicals.
People assume that fertilizer is harmful when in fact, whether it's synthetic fertilizer or organic sources, such as manure, it's all the same, on an elemental level. Plants REQUIRE nutrients to thrive and they only absorb and utilize a certain ration of nutrients, so fertilizer is not going to accumulate in the foliage and cause problems for the chameleons. What would be a problem is fertilizer sprayed on the foliage or eaten directly by the chameleon, but this is eliminated by washing the plant and covering the soil.
People feel more comfortable avoiding fertilizers and I understand the thinking behind it, but the science behind it says it's actually not a bad thing at all to have some slow release granules in your potted plants, with the soil covered to prevent ingestion. The "chemicals" are simple elements found in the air, in the feeders the chameleons are eating, and are the building blocks of life. They can and should be used properly in chameleon plantings and if people knew more about plant physiology and health, they'd have better luck with their plants in their cages and the chameleons would benifit. I never really understand why researching at least basic care for the particular plants people are growing isn't part of researching for their chameleon.....caring for one life successfully broadens the horizons for managing other life.
Soils will not have chemicals or toxic components in them, to the extent they are toxic for planting a plant inside the enclosure in. That said, soil mix is designed to be consumable, as it will carry organisms that could pose harm, components that could cause blockages, and yes, fertilizer that if directly consumed is harmful.
Cover the soil and use the best soil for the plants and the wet growing conditions, not the soil everyone else thinks it's best, because it has organic slapped in the label.
Perlite, charcoal, bark, all are organic, as is peat, compost, coir, and all components of a soil mix, save synthetic fertilizer, which is simply harvested, natural elements, concentrated for ease of use.
