MicroDegrade aims to reveal bottlenecks of degradation, and to identify superior bioremediation strategies for a most notorious environmental pollution of our time: chemical micropollutants at low (sub-ug/L) concentrations. Finding out why micropollutants occur in ground and surface water despite the presence of bacterial degraders has become an elusive goal for microbiologists, environmental scientists and geochemists. Competing paradigms claim that either (i) mass transfer limitations (bioavailability, cell uptake) or (ii) physiological limitations (enzyme down-regulation) prevent complete biodegradation at contaminant threshold concentrations. To design strategies for remediation, insight is warranted which bottlenecks of degradation prevail. "Do molecules - once inside an organism - get out into solution again? Or is mass transfer so limiting that organisms are desperate for supply?" Pillaring on our recent advances with compound-specific isotope analysis at sub-ug/L concentrations, MicroDegrade will be able to provide a revolutionary angle on this dilemma. Isotope fractionation will give the first direct answers to these questions for degradation of two prominent pollutants at low bacterial growth and low concentrations - 2,6-dichlorobenzamide (BAM), a highly recalcitrant, ubiquitous pesticide metabolite with Aminbacter MSH1; and toluene, an abundant groundwater pollutant with Geobacter metallireducens. The approach pillars on three consecutive aims: (1) investigate if, and at what concentrations mass transfer becomes limiting in chemostat cultures; (2) understand analogous limitations in concentrations gradients of an aquifer model; (3) derive superior bioremediation strategies. The objectives of MicroDegrade have the potential to change our view on drivers behind thresholds values and bottlenecks of degradation, to offer a new angle on competitive strategies of microorganisms at low concentrations, and to identify superior future bioremediation strategies.