John Poté

Four areas in the Kongo Central Province, western Democratic Republic of the Congo, with unexploited phosphate deposits were investigated to assess the composition of phosphatic materials and to evaluate pollution hazards, including radiological hazards arising from naturally occurring radionuclides. In those areas, phosphate rocks were sampled and analyzed for P₂O₅ content (by ED-XRF), and for the naturally occurring radionuclides ²³⁸U, ²²⁶Ra, ²³²Th, ⁴⁰K (by gamma-ray spectrometry). Phosphate rocks displayed P₂O₅ content ranging from 1.06 to 24.42% (dry weight) and exceptionally high ²³⁸U and ²²⁶Ra activity concentrations (up to 3069 and 2273 Bq kg⁻¹, respectively), significantly exceeding global averages in soils. Radiological hazard indices, including the radium equivalent (RaEq), annual effective dose and lifetime cancer risk, confirmed potential health risks associated with phosphate-rich rocks. With the upcoming development of phosphate deposits in DRC, such phosphate materials might become future sources of both geochemical contamination and radiological exposure, emphasizing the need for suitable radiation monitoring and waste management plans prior to and during mineral resource exploitation.

This study investigates the controls governing the spatial distribution of trace metals (TMs) in soils and coastal sediments of the Moanda-Banana sector within the Congo Coastal Basin. The objective is to discriminate the relative roles of near-surface sedimentary processes and deeper geogenic influences in the development of metal anomalies within an active Atlantic margin context. Eighteen samples were collected along an ~8 km coastal transect during the 2025 dry season and analyzed using ICP-MS and AMA-254. The geochemical dataset was evaluated through enrichment and contamination indices (EF, Igeo, CF, DC and PLI), ecological risk factors (Eri and RI), multivariate statistics, and residual Bouguer gravity data. Physico-chemical parameters show strong spatial contrasts between the estuarine domain of Moanda and the sandy environments of Banana. Fine estuarine sediments display high water contents (up to 76.9%) and total organic matter reaching 28.9%, whereas Banana soils are predominantly sandy (>80%). The highest metal concentrations occur at station M0S2, where Zn, Pb and Cu reach 412.6, 196.7 and 84.2 mg·kg⁻¹, respectively, indicating localized enrichment in fine-grained deposits. Zinc frequently exceeds the SQG guideline (123 mg·kg⁻¹) and locally approaches the PEL threshold (315 mg·kg⁻¹), while Pb surpasses the PEL value (91 mg·kg⁻¹) at stations M0S2 and M0S3. At the regional scale, geochemical indices indicate predominantly low-to-moderate contamination despite localized enrichments, particularly for Pb and Zn. Principal Component Analysis explains 88.91% of total variance (F1=74.73%; F2=14.19%) and reveals a coherent Cu-Zn-Pb association mainly controlled by surficial sedimentary conditions. The overall ecological risk remains limited, although Hg and Cd represent the main local contributors. Residual Bouguer anomalies (- 0.69 to +1.97 mGal) indicate basement heterogeneity and show partial spatial correspondence with surface geochemical patterns. This spatial relationship is compatible with a possible halokinetic structural influence but does not demonstrate direct deep metal transfer. Overall, trace metal distribution in the Moanda-Banana coastal zone is dominantly controlled by surficial sedimentary processes, while deep geogenic influences remain secondary and locally plausible.

In Morocco as well as in many countries located in semi-arid areas, irrigation with water from lake-reservoirs is a common agricultural practice and an important tool for farmers to improve crop yields. However, this kind of water can contain toxic bloom-forming cyanobacteria, and its use as a source for irrigation water can enable a transfer of cyanobacterial toxins (microcystins) into crop plant. When microcystins are accumulated in crop plants, they pose serious human health risk. The aim of this study is to explore the potential of selected rhizobacteria strains in inoculation with Vicia faba plants to mitigate microcystins-induced phytotoxicity and health risks. Irrigation with water containing 200 µg L ⁻¹ microcystins reduced plant growth, photosynthetic efficiency, and nitrogen assimilation. Inoculation with selected rhizobacteria strains alleviated these effects, enhancing root biomass, stomatal conductance, chlorophyll content, leaf quantum yield, and nitrogen content and slightly increasing GS activity. Among tested strains, Achromobacter marplatensis showed the strongest protection, reducing microcystin accumulation by approximately 36% compared to uninoculated plants. Estimated daily intake values derived from residual microcystins remained below World Health Organization safety thresholds, indicating a lowered potential risk. These findings demonstrate that soil-based inoculation with targeted rhizosphere bacteria can protect plants from microcystin-induced damage, providing a strain-specific, sustainable bioremediation strategy to maintain crop productivity and food safety in regions exposed to microcystin-contaminated irrigation water.

Located on the Congolese (DRC) side of the Lemba depression, our study area is the part that was returned by "ex-Zaïrep", just east of the concession currently operated by Perenco rep. Open to oil and mining exploration, we brought back phosphate rock samples from the field, which were analyzed by the Commissariat Général à l'Energie Atomique (CGEA) using the ED- XRF Xepos III spectrometer. These analyses were used to characterize the geochemistry of the Kanzi and Mvuangu phosphates. The results of the Chemical Analyses (Oxides) and Chemical Elements are as follows: (1) Major oxides (%:) Al2O3 (21,21 – 17,24); SiO2 (14,85 – 30,40); P2O5 (19,48 -13,34 %) finally Fe2O3 (8,544 – 10,74 %), and other oxides with concentrations in mg/kg (MnO, ZnO, Rb2O, SrO, ZrO2, Nb2O5, Sb2O5, Ta2O5); (2) Major Chemical Elements (%): Aluminum (11.22- 9.124); Silicon (6.939-14.21); Phosphate (8.5-5.823 %) and several trace metallic elements that will be exposed in another soil and sediment matrix to assess the state of the environment prior to mining and petroleum activities. The origin of these metallic elements, including heavy metals, rare earths and radionuclides, is phosphate. Phosphate rocks, such as apatite, may contain heavy metals, rare earths and radionuclides in their mineral structure. The gravity anomaly map of the Lemba sub-basin, where the phosphate sites are located, clearly shows that the phosphates of Kanzi in the south and Mvuangu in the north are not located in the central deposits, but in the upper parts of the sub-basin. These areas are potentially anticlines, which are geological structures capable of containing hydrocarbons. This study is a contribution to our knowledge of the phosphate resource in Kanzi and Mvuangu, and contribute to understanding the geological structures capable of containing hydrocarbons. It is also an important contribution in the field of geochemistry and gravimetry.

A wastewater treatment plant (WWTP) prototype coupled with Moringa oleifera seeds (MOSs) was developed to evaluate its effectiveness to reduce metallic trace elements (MTEs) in domestic wastewater. The WWTP is composed of a septic tank (F0) where wastewater is treated by biological processes under anaerobic conditions, followed by a bacterial filter (F1) where wastewater is filtered under aerobic conditions, followed by an infiltration well (F2), which provides additional filtration of wastewater before discharge into the soil. MTEs present in waters can bind with humic substances contained in colloid particles and then be eliminated by coagulation–flocculation with a cationic polyelectrolyte. MOSs contain positively charged cationic polymers that can neutralize the colloids contained in waters, which are negatively charged. Based on this observation, 300 mg·L⁻¹ of MOS was added into F0, 50 mg·L⁻¹ into F1, and 50 mg·L⁻¹ into F2 mg·L⁻¹. MOS activation in samples was performed by stirring rapidly for 1.5 min, followed by 5 min of gentle stirring and 3 h of settling. The data analysis shows that wastewater samples had significant concentrations of MTEs, particularly for Cu, Ni, Sr, and Ti, and sediment samples had high amounts of Cr, Cu, Ni, Sr, Ti, and V. The addition of MOS to F0, F1, and F2 samples resulted in reductions in MTE concentration of up to 36%, 71%, 71%, 29%, 93%, 81%, 13%, 52%, and 67% for Co, Cr, Cu, Ni, Pb, Se, Sr, Ti, and V, respectively. The quantified MTEs (As, Co, Cr, Cu, Ni, Pb, Se and V) in treated samples were reported to be lower than UN-EP standards for a safe reuse for irrigation and MOS proved to be as effective as chemical coagulants such as lime and ferric iron for the removal of MTEs contained in wastewater. These results highlight the potential of MOSs as natural coagulants for reducing MTE content in domestic wastewater. This study could be the first to evaluate the effectiveness of MOS in reducing 10 MTEs, including As, Co, Se, Sr, Ti, and V, which are currently understudied. It could also provide a better understanding of the origin of MTEs found in domestic wastewaters and how an effective treatment process can result in high-quality treated wastewaters that can be reused for irrigation without posing health or environmental risks. However, more research on MOSs is needed to determine the type and composition of the coagulant substance found in the seeds, as well as the many mechanisms involved in the decrease in MTEs by MOSs, which is currently understudied. A better understanding of MOS structure is required to determine the optimum alternative for ensuring the optimal effect of MOS paired with WWTP in removing MTEs from domestic wastewaters.

Dimba Cave is a large array of natural galleries in limestone mountains of the Democratic Republic of the Congo that contains highly valued pre-historic archaeological artifacts. The cave attracts a high number of tourists every year and is used by local populations as a water supply source. The main objective of the research undertaken in Dimba Cave consisted of assessing the quality of water and sediments from Dimba Cave ponds through evaluating contamination by heavy metals (15 elements analyzed, including As, Cd, Pb, and Hg) and by microbial populations (including Escherichia coli and total coliforms) in order to estimate the ecotoxicological risk to humans and to non-human biota. All water samples collected in the cave ponds showed very high metal concentrations exceeding the internationally recommended limits for drinking water, particularly for Cr, Mn, As, Pb, and Hg. Most sediment samples from cave ponds also displayed high heavy metal concentrations. The calculated pollution parameters, such as the enrichment factor (EF), and ecological risk parameters, such as the ecological risk index (Eri), indicated that the sediment may be toxic to aquatic biota. Furthermore, the microbiological analysis of pond waters indicated a widespread contamination with bacteria such as Escherichia coli, Enterococcus spp., total coliforms, and Pseudomonas spp., probably from anthropogenic and/or animal sources. Therefore, the consumption of Dimba Cave water as a drinking water represents a threat to public health. Urgent management measures should be enforced to protect public health and the cave ecosystem.