This article suggests an approach of sustainable development in Cuba based on the environmental impact assessment of mercurial sludge generated by a chlor-alkali Cuban plant. It consists of a study of mercury mobility and availability in the sludge samples using sequential extraction procedure. High values of total mercury content (2320 ± 40 mg/kg) in the sludge sample as well as in the toxicity characteristic leaching procedure (TCLP) extract (0.46 ± 0.02 mg/l) were obtained. The highest Hg concentration (52.2 ± 1.5%) was found in the mobile fraction (F1 + F2) indicating a high risk of Hg mobilisation by the presence of water-soluble and exchangeable mercury compounds such as HgCl2, HgSO4 and HgO. The water-soluble fraction (F1) accounts for the 13.7 ± 0.8% of total Hg representing a significant environmental risk due to its easy availability in environmental weathering conditions. The mercury fractionation analyses clearly demonstrate that the chlor-alkali Cuban plant does not represent a sustainable technology from environmental point of view. Furthermore, this study highlights the presence of a wide range of mercury compounds which represents a significant parameter for developing a sustainable technology to treat the mercurial sludge generated by the chlor-alkali Cuban plant.