Mercury is a metal whose physical, chemical and toxicological characteristics make it one of the most monitored metals in the world today. The Republic of Benin is certainly not industrialized; however, it presents risks of contamination of its ecosystems by mercury. This publication, as a prelude to research work on the mercury pollution of rivers in the Republic of Benin, takes stock of existing work relating to the said pollution of the waters of the southern Benin basin. It highlights some scientific work on mercury pollution in surface water, as well as plausible sources of contamination. It is apparent from publications that have addressed the issue that mercury pollution of soils and waters, with their sources, has reached disturbing limits. In fact, the use of pesticides in the cotton basin of Benin has caused mercurial pollution of the soil from 22.3 to 33 ppb. As for surface water, a mercury pollution of the order of 181.2 to 616.9 1μg / L, was obtained against 6μg / L recommended by WHO.

A proliferation of hotels in major cities in developing countries such as Benin leads to more waste water production. The present work aims to evaluate the efficiency of the wastewater treatment methods of Cotonou hotels. But after investigation, most hotels do not have a wastewater treatment plant. During the investigation, wastewater samples were collected and analyzed. The measurement of the field parameters was made with a pH meter, a conductivity meter and a turbidimeter. BOD5 was measured by respirometry and COD by colorimetry. A molecular absorption spectrophotometer was used to measure: suspended matter, total nitrogen and total phosphorus content. Microbiological parameters were determined by the incorporation technique. These analyzes show that the effluents at the entrance of the stations are heavily loaded with pollutants. However, significant declines are observed on site n°4 (activated sludge) with non-standard values only for phosphorus and Escherichia coli. The adoption of a disinfection and phosphorus removal treatment would make it possible to obtain water of acceptable quality for reuse of these waters in irrigation.