Plant growth-promoting rhizobacteria (PGPR) play an important role in the biodegradation of natural and xenobiotic organic compounds in soil. They can also alter heavy metal bioavailability and contribute to phytoremediation in the presence or absence of synthetic metal chelating agents. In this study, the inhibitory effect of Cd 2+ and Ni 2+ at different concentrations of Ca 2+ and Mg 2+ , and the influence of the widely used chelator EDTA on growth of the PGPR Pseudomonas brassicacearum in a mineral salt medium with a mixture of four main plant exudates (glucose, fructose, citrate, succinate) was investigated. Therefore, the bacteriostatic effect of Cd 2+ , Ni 2+ and EDTA on the maximum specific growth rate and the determination of EC50 values was used to quantify inhibitory impact. At high concentrations of Ca 2+ (800 μmol L -1 ) and Mg 2+ (1,250 μmol L -1 ), only a small inhibitory effect of Cd 2+ and Ni 2+ on growth of P. brassicacearum was observed (EC50 Cd 2+ , 18,849 ± 80 μmol L − 1 ; EC50 Ni 2 + , 3,578 ± 1,002 μmol L −1 ). The inhibition was much greater at low concentrations of Ca 2+ (25 μmol L −1 ) and Mg 2+ (100 μmol L −1 ) (EC50 Cd 2+ , 85±0.5 μmol L −1 and EC Ni 2+ , 62±1.8 μmol L −1 ). For the chosen model system, a competitive effect of the ions Cd 2+ and Ca 2+ on the one hand and Ni 2+ and Mg 2+ on the other hand can be deduced. However, the toxicity of both, Cd 2+ and Ni 2+ , could be significantly reduced by addition of EDTA, but if this chelating agent was added in stoichiometric excess to the cations, it also exhibited an inhibitory effect on growth of P. brassicacearum.

In this study, a 3D urban groundwater model is presented which serves for calculation of multispecies contaminant transport in the subsurface on the regional scale. The total model consists of two submodels, the groundwater flow and reactive transport model, and is validated against field data. The model equations are solved applying finite element method. A sensitivity analysis is carried out to perform parameter identification of flow, transport and reaction processes. Coming from the latter, stochastic variation of flow, transport, and reaction input parameters and Monte Carlo simulation are used in calculating probabilities of pollutant occurrence in the domain. These probabilities could be part of determining future spots of contamination and their measure of damages. Application and validation is exemplarily shown for a contaminated site in Braunschweig (Germany), where a vast plume of chlorinated ethenes pollutes the groundwater. With respect to field application, the methods used for modelling reveal feasible and helpful tools to assess natural attenuation (MNA) and the risk that might be reduced by remediation actions.