Validation of an analytical method is a necessary step in controlling the quality of quantitative analysis. Method validation is an established process, which is the provision of documentary evidence that a system fulfils its pre-defined specification or the process of providing that an analytical method is acceptable for its intended purpose. To implement a validated method for the analysis of 22000 soil samples stemming from 2009 LUCAS Soil Survey as well as from sewage sludge and treated biowaste samples from to FATE-Programme, a validation study was conducted with the following objectives: (i) to validate these methods for the determination of heavy metals by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and Could Vapour-Atomic Adsorption Spectrometry (CV-AAS) techniques, respectively, according to the ISO 17025 requirement and (ii) to implement these methods for the determination of heavy metals in soil, sludge and compost samples on a routine basis. The two methods were validated using Certified Reference Materials (CRMs): BCR 141R `Calcareous Loam Soil?, BCR 142 `Light Sandy Soil?, ?San Joaquin Soil? SRM 2709 and LCG 6181 `sewage sludge?. The calibration curves, detection and quantification limits, trueness as well as repeatability were determined. The budget uncertainty was also estimated (including a full uncertainty budget and Ishikawa-diagram). The observed expanded uncertainty were establish for Ag (4.0%, Al (6.1%), As(7.6% ), Ba (5.3%), Cd (4.5%), Co(7.4%), Cr (5.8%), Cu (3.5%), Fe (5.4%), Mg (6.5%), Mn (4.1%), Mo (2.5%), Ni (5.4%), Pb (7.0%), Sb (6.8%), Se (3.1%), Ti (8.3%), V (4.3%), Zn (5.9%), P (14.2%), K (20.0%).