Practice question

Intrinsic bioremediation operates as unassisted self-purification process driven solely by resident soil and groundwater microbiota that have evolved under chronic contaminant exposure, without any engineered addition of nutrients, oxygen-releasing compounds, or exogenous inocula. Native bacteria possessing catabolic plasmids like OCT encoding octane oxidation, NAH for naphthalene dioxygenase, or chromosomal pathways for monoaromatic degradation use industrial pollutants as carbon and electron donors, converting them through peripheral pathways to central intermediates catechol then to tricarboxylic acid cycle, releasing CO2 and water. Environmental conditions including temperature 15 to 25 Celsius, pH 6 to 8, moisture 60 percent field capacity and intrinsic oxygen flux from diffusion support basal activity. Rates remain slower than engineered biostimulation because growth limited by naturally available nitrogen and phosphorus, so doubling times longer and kinetics follow first-order decay with half-lives months to years. Evidence for adaptation includes increased copy numbers of nahAc and alkB genes via quantitative PCR over time due to natural selection. This concept underscores fundamental ecosystem resilience and capacity for self-restoration, forming baseline against which active remediation enhancements judged, and informs risk-based corrective action where natural processes acceptable.