metal / metal-organic ligand complexes / important chemical elements / soil/groundwater systems / neutral systems / chemical equilibrium / typical soil solution / primer to modelers and site / chemical composition / soil systems / groundwater systems / surface metal cation / metal-organic complexes / e- = / chemical interactions / conceptual device / metal chemistry / e- does / neutral pH aquatic systems / metal cation / amino / bivalent metal cation / metal sulfides / chemical reaction / aqueous systems / important processes affecting metal / chemical / natural systems / e- + / possible chemical forms / chemical species / metal-like radionuclides / metal-ligand complexes / aqueous solution / chemical heterogeneity / carbonate systems / chemical elements / metal cations / chemical nonequilibium / e- / / /