High Metal Content Research Articles

Mineralogy, Geochemistry and Environmental Hazards of Different Types of Mining Waste from a Former Mediterranean Metal Mining Area

Mine waste constitutes one of the biggest environmental and management problems, both due to its quantity and its danger when they are rich in toxic elements. There is a wide variety of waste from the oxidation of ores in metal mining areas, both metal sulphide and other minerals. These residues may be enriched in potentially toxic elements that can spread and contaminate ecosystems, farmland and villages. This study has focused on the characterization and evaluation of residues derived from metal-bearing mining waste in abandoned mining areas. Mineralogy and geochemical characteristics were determined by XRD, WDXRF and TG-MS techniques. In addition, DIN 38414-S4 leaching tests were carried out to assess the risk and mobility of potentially toxic elements. Silicates and oxides were found as the main mineral groups, followed by sulphates. These tailings were particularly enriched in Zn, Pb, As, Sb and Cd, while their leachates had high or extreme metal content. Consequently, these mining wastes are considered toxic and hazardous, even for landfills. Sulphides, as the primary source, and sulphates from their oxidation, were the main sources of these pollutants. Sulphates, As, Zn, Cd and Cu determined the specific environmental impact of the different tailing types, which were grouped into different clusters according to their mineralogy and geochemistry. These results provided a better understanding of the environmental hazards associated with the different types of metal mining waste in the area studied.

Preparation of laminated Al/B4C composites with gradient structures and properties through centrifugal freezing and pressure infiltration

Lightweight Al/B4C composites with a gradient lamellar structure were fabricated through centrifugal freezing and pressure infiltration. Their ceramic volume fraction showed a continuous increase from the central region to the surface region, the increase being from approximately 23 vol% to 44 vol%, and the spatial variation of their composition and microstructure led to a gradient change in their mechanical properties. The bending strength and hardness increased with the B4C content, and they attained the highest values of 424 ± 16 MPa and 130.6 ± 4.2 HV0.3 at the surface region of the composite, respectively. By contrast, the work of fracture reached the maximum value (3763 ± 268 J/m2) at the central region of the composite because of the high metal content and the existence of multiple extrinsic toughening mechanisms. The proposed method is versatile and economical and is suitable for the preparation of composites with heterogeneous structures and gradient properties.

Transient tin mineralization from cooling of magmatic fluids in a long-lived system

AbstractFertility and longevity of hydrothermal systems are key parameters required to improve our ability in predicting new deposits and directly extracting metals from metalliferous fluids. Reconstructing evolutional trajectories of metalliferous fluids with high temporal resolution is critical for pushing our understanding forward, but this is inevitably challenging because traditional approaches for obtaining this information either have poor temporal resolution and/or bear considerable uncertainties. We present a novel approach (translating texture-controlled information to temporal patterns) to reconstruct the thermal and isotopic history of the Weilasituo vein-type tin deposit (Inner Mongolia, China) at the millennial scale. In situ oxygen isotope thermometry of paragenetically constrained quartz and cassiterite reveals that tin deposition was accompanied by gradual cooling of pure magmatic fluids from ~500 °C to ~390 °C at lithostatic conditions, while fluid mixing and/or water-rock interaction were not required. The system then transitioned to hydrostatic conditions and permitted penetration of meteoric water and further cooling. Aluminum diffusion in quartz chronometry yields time scales of ~50 k.y., ~5 k.y., and ~200 k.y. for pre-, syn-, and post-ore stages, respectively. Our results highlight that the magmatic-hydrothermal system did not form ore minerals for most of its lifetime, with mineralization occurring only briefly (i.e., <5% of its lifetime). Hence, the rates and efficiency of ore formation may need significant revision. For magmatic-hydrothermal systems with felsic magmas being stored at high crystallinity after extensive volatile exsolution, the efficiency of scavenging metals from melts to fluids critically controls their fertility. To directly extract metals from metalliferous fluids, the key is targeting systems with a high degree of magma crystallization (e.g., higher metal contents in fluids) in warm crust (e.g., able to sustain long-lived systems).

Metal contents in house geckos (Squamata: Gekkonidae) from industrial and urban areas of southern Tamaulipas, Mexico and western Andalucía, Spain, may reflect airborne metal pollution

ABSTRACT House geckos share living quarters with humans in the tropical and subtropical regions inhabited by these reptiles. Gecko behavior, biological traits, continuous exposure to suspended particulate matter 0 µm in diameter (PM10) and dust, as well as status as exotic species, motivated the choice of these species to examine environmental exposure to ambient air pollutants, in particular metals, and subsequent accumulation in these organisms. One part of the study was conducted in Tamaulipas (Mexico) where Hemydactylus frenatus is abundant in urban and industrial environments, the other part was conducted in Andalucia (Spain) where Tarentola mauritanica is found in similar environments. Adult geckos were collected on buildings in locations affected by various air pollution sources. For both species, higher metal contents were observed in whole-body (including digestive tracts) analysis and were markedly different between collection sites. Contents in tails, digestive tracts, and carcasses without digestive tracts were not correlated. Based on contamination factor values, bioaccumulation in H. frenatus tissues occurred for 12 of the 15 metals analyzed. Data suggest that H. frenatus might serve as a biomonitor for Cu, Ni, Pb, Cr, Li, and V, whereas T. mauritanica might be a biomonitor for Cu, Ni, Pb, and Cr. To our knowledge, metal contents for H. frenatus are reported here for the first time. House gecko data could be integrated into a highly representative monitoring system and health risk assessments related to air quality in residential areas.

Metal transportation mechanism by rainfall runoff as a contribution to the bioaccumulation in seafood.

Trace metal transport mechanism via rainfall runoff from soil to the water body in the context of the bioaccumulation in seafood was unprecedentedly investigated. Instead of a conventional simulation experiment at a laboratory, the twelve soil sampling sites were selected in the region (Windar Valley, Balochistan-Pakistan) reported with high trace metal content, and Threadfin Sea Catfish and Belanger's Croaker were caught from the adjacent coastal water body. The Pb, Cd, Ni, and Zn in soil samples were high in proportion; the average concentrations were 2793.8, 622.44, 331.33, and 440 in mg kg-1, respectively, as per expectations. Using ArcGIS, the soil sample results were extensively illustrated by the spatial distribution in the sampling regions. The Zn > Pb > Ni > Cd was found in pre- and post-rainfall fish flesh samples. Trace metals were higher in post-rain fish flesh samples than pre-rainfall samples, indicating that rainwater runoff could be the significant source for trace metal transport except for Zn. The Pb, Cd, Ni, and Zn elevated results were 0.80828 ± 0.17752, 0.12102 ± 0.03027, 0.71064 ± 0.24188, and 6.49223 ± 3.65094 in mg kg-1, respectively, in post-rainfall fish flesh samples. Appling chemometric tools revealed that Zn content depends on Zn-protein interaction, and Pb, Cd, and Ni contents significantly pertain to the rainwater runoff. Other probable transport routes for trace metals to the water body could be less responsible. The soil sampling region's NOAA HYSPLIT backward air trajectory showed that the air direction was mostly from ocean to land.

Primary study on the recovery of lead from waste flexible X/Gamma ray shielding materials using pyrolysis

Lead is typically utilized for X/gamma ray shielding and hazard dosage diminishing. The improper recycling of lead can cause serious hazards to the environment and human beings. In contrast, the recycling of lead from gamma-ray shielding materials with high metal content can be used as a secondary metal source, which contributes to the regulated accumulation and environment protection. Therefore, primary study on lead recovery from waste flexible Vinyl-Methyl-Silicone based gamma-ray shielding materials is conducted. The effects of pyrolysis temperature and heating rate on the lead recovery rates were analyzed. With the optimized pyrolysis conditions, 57.40 wt% lead was obtained at a pyrolysis temperature of 300 °C and duration of 15 min. The solid product is mainly a mixture of lead and lead oxides.

Fly ash treatment by desalination couples with solidification of heavy metals

Fly ash is the solid by-product of waste incineration. It contains high content of soluble salts and heavy metals, which causes difficulty in treatment. In this study, desalination coupled with heavy metal solidification is investigated for the treatment of fly ash from hazardous waste incineration. The distribution of salt and heavy metal and the leaching toxicity of heavy metal were detected. Sintering not only reduces the bulk density of fly ash but also can reduce heavy metal leaching toxicity. For instance, the soluble heavy metal was reduced by 95.4% after 700 °C sintering. The bulk density of fly ash increases from 0.295 g/cm3 to 1.046 g/cm3 after treatment, which significantly save the space of landfill. Meanwhile, the treated ash can meet the leaching limit of heavy metals for the flexible landfill in China. This research is meaningful for fly ash treatment industry and the sustainable development of waste incineration industry.

Facile Preparation of Metallic Sites Anchored Nanocarbon Materials for Electrocatalysis

AbstractHerein, a novel method, heat mechanochemical synthesis (HMCS), is reported for facile and scalable preparation of electrocatalysts with metallic sites anchored on carbon materials. The method simultaneously provides mechanical energy and heat to drive reaction, by which target metal atoms are efficiently trapped in N‐doped and defect‐rich carbon that prepared in advance (NC). The advantages of this method are: (1) high contents of metals at the outermost surface; (2) unique metal sites formed under collisions with mechanical energy; and (3) not annealed at high temperatures, which would retain some unique active sites on the materials. A series of unitary transition metal (Cr, Mn, Fe, Co, Ni, Cu, or Zn) superficially anchored carbons are obtained via the HMCS. More than this, it is quite convenient to prepare multiple metals, such as combinations among these metals, highly dispersed and anchored on the carbon materials in one time. As a representative, the as‐prepared Fe‐NC (denoted as FeNCHM in context) is investigated in detail as catalyst for ORR and Zn‐air battery applications. The authors envision that the method of HMCS provides a good support of surface engineering for preparation of metals sites containing carbon at large scale.

Gemological and Mineralogical Characteristics of Emerald from Ethiopia

Ethiopia has been gaining attention in recent years as an emerging source of high-quality emerald. Ethiopian emerald samples with different colors ranging from dark green to light green were selected to study the gemological properties, chemical composition, and spectral characteristics. The Ethiopian emeralds were examined using conventional gemological instruments, including X-ray fluorescence spectrometry, LA-ICP-MS, UV/Vis/NIR, infrared spectrometry, and Raman spectrometry, providing a wealth of data and research information related to Ethiopian emeralds. The EDXRF results show that the chemical composition of Ethiopian emeralds is distinctly regional compared to emeralds of Colombian origin, being low in Cr, low in V, and high in Fe. LA-ICP-MS results demonstrate consistent results for Cr (734.34 to 1644.3 ppmw), V (89.61 to 106.61 ppmw), and Fe (4468.04 to 5022.3 ppmw) based on the chemical composition analysis by EDXRF. In addition, the LA-ICP-MS assay revealed that the combination of alkali metals (Li, Na, K, Rb, and Cs) and some trace elements (Sc, V, Cr, and Fe) could distinguish the Ethiopian emeralds from those from other regions. The Ethiopian emerald had absorption of Fe2+, Cr3+, V3+, and Fe3+, and the typical absorption intensity of Fe2+ (around 850 nm) was higher than that of Fe3+ (around 371 nm) in the UV/Vis/NIR spectra. The infrared spectrum of samples indicated that the absorption of type II H2O was higher than type I H2O in the emeralds from Ethiopia, which is consistent with the high content of alkali metals detected by LA-ICP-MS that would lead to an increase in the content of type II H2O. The Raman spectra showed absorption at 410 cm−1, 569 cm−1, 687 cm−1, 995 cm−1, and 1067 cm−1, with an emerald species recognition pattern. The gas–liquid two-phase inclusions of the emerald in this area were mainly CO2 and H2O, and the samples contained typical dark inclusions of magnesium-rich biotite sheets that revealed the tectonic-magmatic-related geological environment in this region.

Recovery of Valuable Metals by Roasting of Jarosite in Cement Kiln

The jarosite residue is a harmful byproduct of the zinc hydrometallurgical process and has been classified as hazardous waste due to its high content of heavy metals and poor stability. In this work, the recovery of valuable metals by synergistic disposal of jarosite residue with cement kiln has been investigated. A series of investigations were undertaken to assess the effect of amount of jarosite residue, roasting time, and the addition of CaCl2 on phase transformation and migration of valuable elements in the cement clinker. When 25% of jarosite residue was added to the raw cement materials and roasted at 1400 °C for 30 min, the silicate content in the cement clinker reached 54.4%. In the presence of CaCl2 as the mineralizer, the volatilization rates of Pb and Zn were 93% and 75%, respectively. The results indicated that jarosite residue can be used as the cement additive and valuable metals of Pb and Zn can be recovered simultaneously during the roasting process.

Assessment of Heavy Metal Pollution of Agricultural Soil, Irrigation Water, and Vegetables in and Nearby the Cupriferous City of Lubumbashi, (Democratic Republic of the Congo)

Lubumbashi (DR Congo)—the capital of copper mining—has been considered as one of the richest mining regions of the world for more than a decade. These riches have brought along multiple mining companies responsible for soil, river water and vegetable pollution, as in many African cities. The aim of the present study was to quantify and evaluate the pollution levels and the potential sources of soil, irrigation water and vegetable contamination by the metals As, Cd, Cr, Cu, Pb, Co and Zn in the urban gardens of Lubumbashi (DR Congo). The contamination, pollution and enrichment levels of the gardens were determined based on different indices in order to rank the soils. The results show that soils, waters and vegetables present contamination levels that represent a serious concern for human health. All soils presented contamination indices ranging from low (72% of the soils) to very high (3.4% of the soils) metal (copper, lead, zinc) contamination. The Cu and Cd contents varied between 1355 mg/kg et 236 mg/kg, much higher than the World Health Organisation (WHO) thresholds (100 mg/kg for Cu and 2 mg/kg for Cd). Moreover, the water used for crop and garden irrigation presented high Pb (57% of the waters), Fe (52%), Cu (19%) and Cd (10%) contamination levels, above the Association Française de Normalisation (AFNOR) U4441 toxicity thresholds (2 mg/kg for Cu; 0.1 mg/kg for Fe and 0.01 mg/kg for Pb) for crop irrigation. Finally, the vegetables produced in these gardens and sold in the local markets had very high metal content (47% contained Cu; 100% contained copper and cobalt) above the WHO standard (10 mg/kg for Cu, 2 mg/kg for Cd and 1 mg/kg for Co) for human consumption. In the face of these issues, it would be preferable to consider cheaper, more sustainable techniques that reduce soil-to-plant metal transfer.

Enhancing the dechlorination of CuCl residue using a microwave sulfation-roasting method: Process optimization and mechanism investigation

Spent CuCl residue produced from zinc hydrometallurgy is a typical toxic and hazardous solid waste as well as a secondary resource owing to its high contents of chlorine and valuable metals (Pb, Cu, Zn). The removal of chlorine from the CuCl residue and recycling of valuable metals are critical issues for the copper slag resource treatment process. In this study, a novel method of microwave sulfation-roasting under an oxygen atmosphere is used to improve the dechlorination process, and various parameters, such as roasting temperature, duration, sulfuric acid concentration, and liquid/solid ratio, are optimized. First, according to thermodynamic calculations, the addition of H2SO4 can significantly decrease both the roasting temperature and time needed for microwave oxidation-roasting. The dechlorination experimental results reveal that the dechlorination rate of the CuCl residue is as high as 91.91% under a temperature of 250 °C, holding time of 120 min, sulfuric acid concentration of 70%, and liquid-solid ratio of 1.42. The microstructure, chemical composition, and phase changes of the CuCl residue before and after roasting are characterized using scanning electron microscopy coupled with energy-dispersive spectroscopy, X-ray fluorescence and X-ray diffraction; further, the mass contents of the main elements in the roasting product and tail gas absorption solution are determined by chemical analysis, Evidently, the selective heating property of microwaves produces more holes and cracks in the copper slag, which can provide a new reaction channel for H2SO4 and CuCl slag reactions, and almost all CuCl in the copper slag is completely removed by transformation into CuO, CuSO4 and Cu2O(SO4). Simultaneously, a large number of gas by-products produced in the dechlorination process, such as SO2 and Cl2, can be absorbed by the NaOH solution. Therefore, no pollution is generated in the environment. These findings illustrate that microwave sulfation-roasting is an effective method for promoting the treatment and recycling of CuCl waste residues.

Exploring a new approach for assessing the fate and behavior of the tailings released by the Brumadinho dam collapse (Minas Gerais, Brazil)

In 2019, the Brumadinho dam rupture released a massive amount of iron ore mining tailings into the Paraopeba River. Up to now, it remains a public health issue for the local and downstream populations. The present study aims to assess the behavior and fate of metal contamination following the disaster. Using new sampling strategies and up-to-date geochemistry tools, we show that the dissolved metal concentrations (< 0.22 µm cutoff filtration) remained low in the Paraopeba River. Although the tailings present high metal concentrations (Fe, Mn, Cd, and As), the high local background contents of metals and other previous anthropogenic contamination hamper tracing the sediment source based only on the geochemical signature. The Pb isotopic composition coupled with the metals enrichment factor of sediments and Suspended Particulate Matter (SPM) constitutes accurate proxies that trace the fate and dispersion of tailing particles downstream of the dam collapse. This approach shows that 1) The influence of the released tailing was restricted to the Paraopeba River and the Retiro Baixo reservoir, located upstream of the São Francisco River; 2) The tailings' contribution to particulate load ranged from 17 % to 88 % in the Paraopeba River; 3) Other regional anthropogenic activities also contribute to water and sediment contamination of the Paraopeba river.

Metal-oxo Cluster Mediated Atomic Rh with High Accessibility for Efficient Hydrogen Evolution.

Achieving single-atom catalysts (SACs) with high metal content and outstanding performance as well as robust stability is critically needed for clean and sustainable energy. However, most of the synthesized SACs are undesired on the loading content of the metal due to the anchored metals and the supports as well as the synthesizing methods. Herein, a Rh-SAC with high accessibility by loading it on the metal nodes of metal-porphyrin-based PCN MOFs (PCN-224) as supporting material is reported. Significantly, the PCN-Rh15.9 /KB catalyst with a high Rh content of 15.9wt% exhibits excellent hydrogen evolution activity with a low overpotential of 25mV at a current density of 10mAcm-2 and a mass activity of 7.7Amg-1 Rh at overpotential of 150mV, which is much better than that of the commercial Rh/C. Various characterizations reveal the Rh species is stabilized by the metal nodes bearing -O/OHx in MOFs, which is of importance for the high loading amount and the good activity. This work establishes an efficient approach to synthesize high content SACs on the nodes of MOFs for wide catalyst design.

Modeling the effects of cultivar and harvest on the decomposition kinetics of potato crop residues

Thermogravimetry and kinetic analysis is carried out of the decomposition of potato crop residues, integrated by model compound measurements. Compared with other herbaceous by-products, conversion takes place at lower temperatures, gives rise to higher char amounts and, apart from the usual well evident absolute peak, the rate curves generally exhibit two additional local maxima, at low and high temperatures. Multiple integral and differential data modeling requires six parallel reactions (one, two, one and two steps for the pseudo- extractives, pectin-hemicellulose, cellulose-starch, and lignin-protein, in the order). Residue variability (five samples of different cultivar and harvest year) can be associated with increasing average plant ageing, essentially resulting into variable product yields and, in a few cases, activation energies, describing variations in macro-component contents and properties, respectively. With ageing, the activation energies (180–206 kJ/mol) and volatile yields (19–27 wt%) of the pseudo-cellulose-starch progressively increase (higher cellulose content and crystallinity). Moreover, although the decomposition of pseudo-pectin-hemicellulose gives approximately constant volatile yields (17–19 wt%), the decrease in the activation energy (163–127 kJ/mol) of the first reaction indicates progressively lower contributions of pectin (and extractives). Also, volatile yields from pseudo-lignin-protein decomposition decrease (21–14 wt%), owing to successively lower contents of the second component. Peculiar features of the six-step scheme are originated from pectin, starch and protein components and very high alkali metal contents.

Water washing and acid washing of gasification fly ash from municipal solid waste: Heavy metal behavior and characterization of residues

Gasification fly ash (GFA) is a hazardous solid residue generated in the slagging-gasification of municipal solid waste (MSW). GFA contains higher amounts of heavy metals such as Pb and Zn than incineration fly ash (IFA), which increases the difficulty of heavy metal immobilization but simultaneously makes it a potential feedstock for metal recovery. Water washing and acid washing are conventional and economic methods to treat wastes with high heavy metal and chloride contents. However, the research on the effects of such methods in treating GFA is still blank. Hence, in this study, water washing and acid washing of GFA were investigated in detail. Heavy metal behaviors at different time points during the washing processes were studied in a wide pH range and comprehensive characterizations of washed GFAs were also conducted. The results show that different re-precipitates could be identified in washed GFAs depending on different pH conditions. After water washing for 24 h, more than 60% of Zn in GFA would dissolve and re-precipitate into calcium zincate. It is also revealed that the precipitation effect could in turn influence the pH during the washing process. After acid washing with a low-concentration acid, heavy metal leachabilities were found reduced due to the pH and precipitation effect. High-concentration acid washing could effectively extract Zn and Cd with extraction ratios exceeding 90%. Applying 1.2 M-HCl washing, a short washing period of 15 min could realize a Pb extraction ratio of 81.2%, much higher than 53.2% when extending the washing period to 24 h.

Heavy Metal Determination by ICP-MS in Fenugreek and Spinach Vegetables

Lead, Chromium, Cadmium, and Nickel levels in cultivated spinach and fenugreek were the focus of this study. Inductively Coupled Plasma Mass Spectrometry was used to analyse all of the samples (ICP-MS). The transfer factor of HMs from soil to examined vegetables and exposure to examined heavy metals was computed. Vegetable roots, stems, and leaves have higher percentage quantities of the heavy metals Ni, Pb, Cr, and Cd than has considered acceptable. Due to their high metal content, in our study may endanger human health.

Metal-Organic Frameworks as Electrocatalysts.

Transition metal complexes are well-known homogeneous electrocatalysts. In this regard, metal-organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF-derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Metal–Organic Frameworks as Electrocatalysts

AbstractTransition metal complexes are well‐known homogeneous electrocatalysts. In this regard, metal–organic frameworks (MOFs) can be considered as an ensemble of transition metal complexes ordered in a periodic arrangement. In addition, MOFs have several additional positive structural features that make them suitable for electrocatalysis, including large surface area, high porosity, and high content of accessible transition metal with exchangeable coordination positions. The present review describes the current state in the use of MOFs as electrocatalysts, both as host of electroactive guests and their direct electrocatalytic activity, particularly in the case of bimetallic MOFs. The field of MOF‐derived materials is purposely not covered, focusing on the direct use of MOFs or its composites as electrocatalysts. Special attention has been paid to present strategies to overcome their poor electrical conductivity and limited stability.

Using machine learning models to assess the population dynamic of the freshwater invasive snail Physa acuta Draparnaud, 1805 (Gastropoda: Physidae) in a tropical urban polluted streams-system

The poor understanding of the spread conditions and the geographical patterns of the exotic freshwater snail Physa acuta in sub-Saharan Africa urban streams makes it difficult to design and implement sustainable management tools, especially in deteriorating global and local environments. This study aimed to determine the ecological preferences and the major environmental variables associated with P. acuta abundance, occurrence and distribution in Douala urban streams-system using modelling approaches based on discriminant factor analysis, canonical Spearman correlation and random forest tree models. We inductively define four clusters for snail’s distribution along a geographical and upstream–downstream pollution gradient. Snail’s specimens were collected monthly over a 13-month period in two forest and ten urban sites using a long-handled net (30x30cm side, 400-µm mesh). Meanwhile, measurements of the physicochemical properties of water and streambed sediment were taken. In addition, ten metal contents were determined in P. acuta tissues to assess its ability of bioaccumulation of heavy metals. Results revealed that urban streams of Douala are adversely impaired, especially downstream of industrial effluents. Discriminant factor analysis and random forest regression trees model showed that dissolved oxygen, biochemical oxygen demand, alkalinity, salinity, pH, water depth, wetted width, zinc, iron, cadmium, encumbrance rate of the sediment and sediment types (high sandy mud, sandy mud and muddy sand) were the major environmental variables responsible for structuring P. acuta distribution. Abundances decline drastically following pollution gradient, with great decrease observed in juvenile size classes. High contents of metals were detected in P. acuta tissues, especially downstream of industrial effluents. This study highlights that P. acuta spread in Douala urban-streams system is structured by key environmental variables related to an upstream–downstream pollution gradient. Therefore management plans should emphasize on proper disposal ways of industrial wastes, and stakeholders should take responsible actions in water pollution control and implement the polluter-payer principle.