The proliferation of chronic kidney disease of unknown etiology (CKDu) in Sri Lanka may be attributed to exposure to trace elements of both natural and human origin in the environment, which has been extensively explored and widely debated within the scientific community. This research aims to investigate the fluctuation of soil quality in paddy fields concerning depth and to evaluate the corresponding groundwater parameters in a region identified as a high-risk area for CKDu in the North Central region via determining different parameters including trace metals in both paddy soils and groundwater. The slightly alkaline paddy soils in the study area displayed elevated electrical conductivity values in the uppermost soil layer compared to the subsoil layer. Although hazardous metals, including lead (Pb), chromium (Cr), arsenic (As), and cadmium (Cd), were detected in the paddy soil, they did not surpass the critical toxic concentrations. A statistically remarkable robust positive correlation was discovered between the concentration of Pb in the soil and its depth. Additionally, the levels of toxic metals, such as lead, arsenic, cadmium, and chromium, in the study area’s groundwater were substantially lower than the safety standards set by the World Health Organization. However, some groundwater samples were found to contain anionic species, including fluoride, in concentrations that exceeded the established permissible limits. The gradual accretion of trace elements within the paddy soil presents a potential hazard for the translocation of such elements into the rice plants, thus constituting a possible threat to human health.

The kinetics of plasma nitriding of CoCr alloy below temperatures of nitrides formation and mechanisms of nitrogen penetration are analyzed by proposed kinetic modeling in this article. Proposed nitrogen diffusion model is based on the trapping – detrapping (TD) model and developed taking into account the effect of the concentration dependent diffusivity of nitrogen, nitrogen adsorption on the surface of alloy and surface swelling process. The model indicates the influence of chromium atoms to nitrogen atoms diffusivity. The model consists of time and depth dependent diffusion, which is described by a partial differential equation, and it is solved by using Crank – Nicolson finite difference method. By fitting of experimental nitrogen depth profiles, it is shown that nitrogen diffusion coefficient varies with nitrogen concentration according to Einstein-Smoluchowski relation. Nitrogen depth profiles in plasma nitrided medical grade CoCr alloy (ISO 5831 – 12) at T = 400 °C for 1, 4 and 20 hours calculated on the basis of this model are in good agreement with experimental nitrogen profiles. Furthermore, the swelling process is showed and analysed, derived the dependency of swelling rate on nitriding duration – the swelling rate is inversely proportional to the square root of nitriding duration. The obtained diffusion coefficient value and the swelling process rates satisfy the experimental data form Ref. The derived model explains physical processes during plasma nitriding and allows obtaining nitrogen depth profiles for any requisite nitriding duration.