This study evaluates the contamination by heavy metals of the grounds taken in four of the public landfills in the districts of Brazzaville. Soil samples taken at a depth of 25 cm first underwent some physical treatment (drying, sieving and grinding) before undergoing physicochemical analyzes and determination of heavy metals by ICP-OES. Physicochemical analyzes showed that Landfill soils are heavily contaminated with heavy metals: lead (Pb), chromium (Cr), cobalt (Co), nickel (Ni), mercury (Hg) and zinc (Zn). The highest levels of these heavy metals are as follows: lead (220 mg/kg) in the soils of the Tsiémé landfill; chromium (13000 mg/kg), cobalt (160 mg/kg), nickel (7500 mg/kg) and zinc (12000 mg/kg) in the soils of the Diata landfill and mercury (0.66 mg/kg) in the soils of the Moukondo landfill. Mercury is also present in these four landfills but in small quantities.

One of the biggest problems with landfilling waste is the landfill leachate that is produced when water passes through the waste. The composition of the leachate obviously depends on the nature of the buried waste, the presence of fermentable organic matter and the climatic conditions combined with the mode of operation of the site. The objective of this study is to make a physicochemical characterization of leachate from two public landfills in Brazzaville. To carry out this characterization, we made a series of leachate sampling from December 2021 to February 2022. The potentiometric and colorimetric methods were used for the determination or different parameters. During this period, the physicochemical analyzes carried out on these samples revealed high levels of biodegradable organic matter, with nitrates, chlorides and phosphates levels below the WHO standard. For the metals, we note the total absence of Pb in the two landfills. The Fe, Zn, and Cu contents do not exceed the WHO standard, while the Cd content for tsiémé landfill exceeds the WHO standard. The average value of the ratio (BOD5/COD) is 0.34 for the two sites, which shows that it is the intermediate leachate.