methods are disclosed for preparing novel biodegradable nanoparticles based on complexation of poly - gamma - glutamic acid or its cross - linked derivatives with bivalent lead ions . the final products are stable in aqueous media at low ph , neutral and mild alkaline conditions . the size of the complexes depends on the ph , concentrations and the ratios of γ - pga and lead ions the γ - pga nanoparticles made from biodegradable biopolymers with high flocculating and heavy metal binding activity of the present invention may be used for various water treatment applications in aqueous media .