The interaction of arsenic (III) onto the tetrahedral Au20 cluster was studied computationally in order to get insights about the interaction of arsenic traces (presented in polluted waters) onto embedded electrodes with gold nanostructures. Pollutant interactions onto the vertex, edge or inner gold atoms of Au20 were observed to have a covalent character by forming metal-arsenic or metal-oxygen bonding, with adsorption energies ranging from 0.5-0.8 eV, even with a stable physisorption. However, in aqueous media, the Au-vertex-pollutant interaction was found to be disadvantageous. The substituent effect of a platinum atom onto the Au20 cluster was evaluated to get insights about the changes in the adsorption and electronic properties of the adsorbent-adsorbate systems due to chemical doping. It was found that the dopant atom increases both the metal-pollutant adsorption energy and stability onto the support in a water media for all the interaction modes; adsorption energies were found to be in a range of 0.6-1.8 eV. All the interactions were determined to be accompanied by electron transfer, as well as changes in the local reactivity that determines the amount of transferred charge, and a decrease of the HOMO-LUMO energy gap respect to the isolated substrates.