The radioactivity associated with artisanal and small-scale gold mining activities (ASM) carried out along the Ulindi River, in the eastern Democratic Republic of the Congo, was evaluated by gamma-ray spectrometry and inductively coupled plasma–mass spectrometry of soil and sediment samples. The results revealed that activity concentrations of ²³⁸U (up to 3127 ± 98 Bq kg⁻¹), ²²⁶Ra (up to 2710 ± 89 Bq kg⁻¹) and ²³²Th (up to 2142 ± 162 Bq kg⁻¹) were 71- to 89-fold higher than the worldwide average concentrations reported by UNSCEAR in soils. Primordial radionuclides are, thus, present in high concentrations in deposits of gold in that region and the average ambient effective radiation dose rate was determined at 8.4 mSv y⁻¹ (range 0.5 to 40 mSv y⁻¹). This area may be classified as a natural high background radiation area (HBRA). The radiation risk for artisanal miners and population members manipulating those geological materials were assessed through radiological parameters. such as the radium equivalent activity index (Ra_Eq), outdoor gamma absorbed dose rate (ODRA), annual effective dose equivalent (AEDE), and excess lifetime cancer risk (ELCR). The mean values of these parameters were significantly elevated in comparison to the world average levels and indicated the existence of significant radiation risks for gold miners and members of the local population. A radiation safety policy seems needed to protect workers and the local population in this region.

Surface sediments collected in several areas along the N’djili River, in the Kinshasa Province, Democratic Republic of the Congo, were analyzed for persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), organochlorine, polycyclic aromatic hydrocarbons (PAHs), and also organophosphorus and pyrethroid (PYR) pesticides. High values of POPs were determined in the DIGUE area of the river reaching 710 µg kg⁻¹ for ∑₁₂ PCBs, 397 µg kg⁻¹ for ∑₆ DDTs, 1138 µg kg⁻¹ for ∑₁₆ PAHs, and 23 µg kg⁻¹ for ∑₆ PBDEs. Regarding toxic effects on aquatic biota, the Total PCBs (∑_{7 × 4.3}) were above the Threshold Effect Level (TEL) value of 34.1 μg kg⁻¹ and above the Probable Effect Level (PEL) value of 277 μg kg⁻¹ in most sampling sites. ∑₁₆ PAHs values were, in general, below the TEL value of 610 μg kg⁻¹, but with exceptions for several sampling sites where values exceeded the TEL value. The ∑₆ DDTs in all sampling sites were higher than both TEL and PEL values of 6.15 and 20.03 μg kg⁻¹, respectively. These values above TEL and PEL indicate potential adverse effects on benthic organisms. In general, the ratio values of (DDD + DDE)/DDT were higher than 0.5 reflecting past DDT use mostly, and Fluo/(Fluo + Pyr), IDP/(IDP + BghiP) and BaA/(BaA + Chry) ratios indicated several PAHs origins including petrogenic and pyrolytic sources, petroleum, grass, wood and coal combustion. Globally, the results of this research showed high contamination of N´djili River sediments by a plethora of organic pollutants and at toxic levels to the aquatic biota. Furthermore, the river water quality might be not suitable for human consumption.

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.