Sources of water pollution by mercury in large urbanized deltas of Africa and Asia

Urbanization of large river deltas strengthens anthropogenic pressure on water objects, which are of utmost importance for sustainability of aquatic landscapes and freshwater provision. The aim of the present work was to synthesize the scientific information about sources of water pollution by mercury in large urbanized deltas of Asia and Africa. The materials for this study were collected with an international bibliographical database via standardized search, with subsequent “manual” filtration and data extraction. The analytical procedures included the data systematization and evaluation of data certainty, as well as typization of the pollution sources. It was established that the evidence of elevated concentrations of mercury in water is available from six deltas, from which the most polluted are those of the Nile, the Mekong, and the Niger. The pollution sources are diverse and related, particularly, to mining and petroleum extraction, agriculture, and discharge of wastewater and solid waste. Some sources are not linked to urbanization or located far from deltas. The information about the pollution sources is often uncertain. The practical importance of the findings is determined by the indication of the possible factors of sustainability disturbance in urbanized deltas. Prospects for further research are associated, first of all, with expanding the geographical focus and improving approaches to collecting and critically evaluating scientific information on various aspects of anthropogenic pressure on unique natural landscapes.