**4. Limiting factors for a successful biological remediation**

Bioremediation is influenced by abiotic factors such as temperature, humidity, pH, aeration, nutrient content, redox potential and soil type; however, interaction of biotic factors such as competition, predation and biological factors also play a major role in the success of this technique [20]. Some studies have shown that the microorganisms added for degrading contaminants at laboratory level were not able to mineralize, survive or compete with the native microorganisms when they were introduced into foreign environments, probably due to susceptibility to toxins or predators in the environment, due to the preferential use of easily assimilated organic compounds or due to slow motion throughout the inner porous soil that harbours the contaminant [21]. To facilitate the adaptation of microorganisms added to a soil, the following criteria must be considered: contaminant‐availability for microorganisms; microbial activity; survival of microorganisms in the foreign environment; and environmental conditions such as nutrient availability, water content and pore size of the aggregates [20]. On the other hand, when a population is introduced into a foreign site, it tends to decrease with time due to the abiotic and biotic factors mentioned above, and thus the treatment can be adjusted either by adding more specialized microorganisms or by using immobilized bacteria [22]. The introduction of a microorganism in an environment is complex and its permanence may be only temporarily, depending on the ability of the microorganism to adapt to environ‐ mental conditions. The strategy to isolate indigenous microorganisms and incorporate them into the environmental is a viable alternative; however, this technique does not always produce the expected results, suggesting that the above factors play an important role.
