Freshly deposited thirty six surface sediments from river Mingoa, main tributary to the Municipal lake of Yaounde in Cameroon, were sampled to determine the degree, sources and distribution of metals contamination. The concentrations of trace elements were measured by ICP-AES for the samples collected at different stations in January 2005. Generally, the concentration of metals (Si) in the sediments reflected an anthropogenic inputs. The sediments were characterized by a high amount of organic matter (LOI) with a mean value of 12.44%. Enrichment Factors (EF) and Geoaccumulation Index (Igeo) were calculated and the relative contamination levels were assessed at these sites. With the exception of Ni, the enrichment of toxic metals was high. Descriptive statistics and multivariate analysis (principal factor method) were used to assist the interpretation of elemental data. This allowed the determination of the correlations between the metals and LOI variability in the sediments, and the identification of four main factors loadings controlling by parent rocks, anthropogenic input, organic compounds and weathering of silicate minerals.

Concentrations of metals (As, Cr, Cd, Fe, Ni, Pb, Sb, and Zn) in soil samples from Kombo-Laka were investigated. The area under study is subjected to traditional gold mining and receives various wastes from miners and mining activities. Direct observations on the field displayed the destruction of soils by this activity. An assessment of pollution was performed using an Enrichment Factor (EF) and geoaccumulation index (I geo). Levels of As, Cr, Cd, Cu, Pb and Sb in soil samples were above average in the Upper Continental Crust (UCC). EF revealed anthropogenic sources for Cd, As and Sb in these soils. I geo indicates that Kombo-Laka soils are moderately to extremely polluted with As and Sb. There are high to very high positive correlations among the metals suggesting their possible common sources. This study reveals that traditional gold mining activities in the area are harmful to the environment.

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Metals are dangerous to aquatic organisms and they can bioaccumulate in the food chain and represent risk for humans. In order to appraise their levels in fish species, concentrations of various elements including Na, Mg, K, Ca, Al, Fe, Mn, Cr, Ni, Co, Cd, Cu, Pb, Zn, Ba, and Sr were determined in the muscles and gills of three fish species (Oreochromis niloticus, Sarotherodon galilaeus, and Clarias sp.) which are more fished and consumed in the Yaounde Municipal Lake, Cameroon. According to chemical results of the fish samples analyzed by ICP-AES, the concentrations of metals (mg kg(-1), wet tissues) in those fish tissues varied as follows for the muscle (and gill) Na 1480-3780 (4180-9310), Mg 897-1250 (843-1450), K 9600-18,500 (6020-10,400), Ca 430-3900 (22,200-62,400), Al 8.10-615 (113-951), Fe 12.0-725 (307-1160), Mn 1.61-30.1 (14.3-433), Cr 1.58-267 (0.31-35.4), Ni 0.16-1.85 (1.06-2.82), Co 0.10-0.47 (0.07-0.16), Cd 0.11-0.23 (0.10-0.22), Cu 0.59-5.13 (1.31-5.13), Pb 1.11-5.12 (2.56-5.74), Zn 15.4-47.2 (45.3-69.2), Ba 0.61-51.15 (0.35-83.2), and Sr 2.31-5.74 (2.09-5.75). The results revealed that Na, Ca, Zn, Fe, and Mn were higher concentrated in the gills than in the muscles, while K, Cr, Ni, Co, and Cd were more concentrated in the muscles of the species. In addition, all the elements were bioaccumulated in the fish species and the bioaccumulation factors (BAFs) were decreased in the following order: Cr > Ni > Zn > Al > Ca > Pb > Mn > Ba > K > Fe > Mg > Cu > Na > Sr > Co > Cd. Compared to international standards, Pb, Cd, Cr, Ni, and Zn were over the recommendations of the European Community, WHO, and Norwegian guidance values for human health. Therefore, fishes from the Yaounde Municipal Lake are not advised for human consumption as toxic elements might be taken above the recommended levels.

The main objective of this study was to assess the level of metal contamination of the soils used in the cultivation of onions in the city of Abéché. Thus, 04 plots were carried out and monitored for a period of five years (05 years). Two traditional plots were chosen in the Arkou site; and two control plots were carried out in the Bagarine site. Soil samples were taken annually (2016 to 2020) after harvesting on a thickness of 0 and 20 cm. In each plot, thirteen (13) samples were taken. After quartering, one (01) representative sample from each plot was retained. The samples were analyzed by optical emission spectrometry at the Food Quality Control Center Laboratory (FQCCL) in Ndjamena. The determination of heavy metal concentrations revealed relatively low levels for Ni, Zn, Cu, Cr and Fe. These levels are generally lower than the reference values ​​for all the plots. Geoaccumulation indices (Igeo) and Contamination factor (Cf) revealed pollution indices. Pb and Cd show contaminations in traditional plots. The correlations (P < 0.05) observed in our study area are positive and significant. This study shows that the use of chemical inputs are sources of soil contamination by heavy metals. Int. J. Appl. Sci. Biotechnol. Vol 11(1): 42-53.