Heavy Metal Contamination and Ecological Risk Assessment in Soils of the Pawara Gold Mining Area, Eastern Cameroon

Abstract

Pawara area is a mining district in the eastern region of Cameroon. Mining in the area is generally artisanal and semi-mechanized, practiced by the local miners and immigrants from neighboring African countries and China. The lack of strict regulations and control of mining activities permits the miners to use illegal substances, especially Hg in gold separation. These expose the area to toxic and heavy metals pollution. This study highlights the source of heavy metals concentration in the Pawara soils and the potential adverse effects of Hg on gold separation to the environment and health. Three mining sites and one control site were investigated, namely Site A, Site B and Site C. The control Site 0 (background) is an area where no mining and agricultural activities have taken place. Soil samples were collected at depth of 20 cm, with six from each site (24 samples). Samples were analyzed for Al, Cd, Cr, Cu, Fe, Hg, Pb, Cd and Zn content using atomic absorption spectrophotometry in a graphite furnace. The metals, except for Fe, show high values for all three sites exceeding the background levels in the soils. Hg shows the highest concentration on Site A with a value of 1590 mg kg−1. Pb is highest on Site B with a concentration of 12,274 mg kg−1. The contamination degree was assessed with the help of contamination indices (Igeo—index of geo-accumulation; PLI—pollution load index; RI—potential ecological risk; Eri—ecological risk; Pi—single pollution index; CF—contamination factor) and all parameters show a high degree of contamination on all three sites compared to the control site. Hg, Pb, Cd, Cr and Cu as single pollutants show the highest ecological risk on Site A and Site B where intense mining is taking place. The absence of industrial and large-scale agricultural activities in the Pawara area, the nonexistence of contaminants on the control site and the presence of contaminants on Site C where farming is high and mining is low jointly show that the discharge of mine wastes onto the soils and stream channels are the main source of contaminants and potential pollutants of the Pawara ecological environment.

Ecological risk assessment and mobility of arsenic and heavy metals in soils and mine tailings from the Carmina mine site (Asturias, NW Spain)

“…In general terms, Igeo classi cation is in agreement with the EF classi cation for heavy metals as occur in other studies(Fodoué et al 2022). However, unlike EF study, Igeo emphasizes the As pollution in the studied soils which is clearly in accordance with sequential fractionation results…”

“…The results of EF indicated that the soils of the study area were highly enriched with Pb which was observed to show an extremely high enrichment (EF = 200). Observed mean value is even higher than that recently found for sul de mine wastes at a mine site of Ghana (Akoto and Anning 2021) and are in the same order of levels found in mine tailings rich in galena from the Pawara gold mining area, Eastern Cameroon or the San Quintín mining group in Spain(Fodoué et al 2022;Martín-Crespo et al 2015). This high value clearly indicates that the Pb enrichment in this case comes from mine waste through the process of weathering and leaching, which is in agreement with the high mobility found for Pb in the studied soils.…”

Source Distribution and Ecological Risk Assessments of Heavy Metals from the Soils of Riruwai Mining Area, North-Western Nigeria

“…Ecological risk assessment quantitatively evaluates the potential detrimental effects of single and multiple HMs on the external environment (Fodoué et al, 2022). To assess the accumulative In the present study, the IPERI values of HMs varied from 115.90 to 1462.64, with the highest value recorded in the active mining site, whereas the lowest value was obtained in the control site (Figure 4).…”

Assessment of the ecological risk and mobility of arsenic and heavy metals in soils and mine tailings from the Carmina mine site (Asturias, NW Spain)

“…Mineralization appears in the contact zone between a thick level of white and hard quartzites locally known as the Los Cabos Series and the black slates of the Luarca Formation, both of Middle Ordovician age and N–S trending, constituting the western flank of the San Martin de Oscos anticline. The paragenetic sequence of the deposit is complex: primary sulfide associations that include pyrite, pyrrhotite, cubanite, sphalerite, galena, fahlore, boulangerite and marcasite (García-Iglesias & Loredo, 1979 ). In terms of supergene phases, only covellite and anglesite have been found.…”

“…The presence of these amphibolite layers has led some authors (García-Iglesias et al, 1985 ) to propose a volcano-sedimentary origin for this deposit. Mineralization is related to Hercynian fractures by filling open spaces (Garcia-Iglesias & Loredo, 1979 ).…”