Mine-impacted Water Research Articles

Passive remediation of mine impacted water using selected treatment media containing-bioreactor

This study was carried out to develop a passive treatment method to treat contaminated water with heavy metals caused by mining activities using organic, industrial, quarry and mining waste itself. In particular, this study aims to evaluate the performance of selected treatment media in treating Acid Mine Drainage (AMD) (i.e. Spent mushroom compost (SMC), limestone (LS), steel slag (SS) and ochre). A series of tests were conducted to determine the effectiveness of the treatment media in single and mixed substrates treatment. For single substrate, both SMC and SS showed promising overall heavy metal removal efficiency of 94.6% and 96.7%, respectively. As for mixed substrates, R3 (composed of 40% SS, 30% SMC, 20% LS and 10% ochre) gave the best performance in overall heavy metal removal. This treatment ratio (4:3:2:1) was then used in column experiment where continuous flow of synthetic AMD water was supplied. After 30 days, results showed that heavy metals (i.e. Fe, Mn, Pb, Zn, and Al) were reduced significantly with 91–100% removal efficiencies except for Mn (61.15% efficiency). Therefore, this study has proven that the media chosen in passive treatment of AMD are efficient in the removal of selected heavy metals and in increasing the pH of AMD, which can be applied for real on-site treatment of such cases.

Regional isotopic investigation of evaporation and water-rock interaction in mine pit lakes in Nevada, USA

The isotopic geochemistry of mine-impacted waters may reveal water-budget relationships and geochemical mechanisms of water-rock interaction. In this study, stable isotopic analysis of water (δ2H and δ18OH2O) and sulfate (δ34S and δ18OSO4) were completed and cataloged in 15 mine pit lakes in Nevada, USA, representing the most spatially distributed and largest dataset related to the isotopic composition of pit lakes yet presented in the literature. The isotopic composition of groundwater and surface springs was also included at several sites to more fully characterize the connected groundwater-surface water systems. Results of δ2H and δ18OH2O analysis indicate that the pit lakes are highly evaporated (more so than natural lakes in the same region), although the strength of evaporative fractionation differs spatially. Pit lakes also vary in the degree to which they are enriched in heavy isotopes relative to influent groundwater, which gives insight into the basin-scale water budget for these areas. Isotopes of sulfate (δ34S and δ18OSO4) and water (δ18OH2O) were used to test several commonly-held models of sulfide oxidation, and results suggest that none of the applied models can fully explain the isotopic composition of pit-lake waters. Most sulfur isotope data suggest a mixed source of aqueous sulfate including the oxidation of pyrite and dissolution of sulfate salts.

Functionalised microwave sensors for real-time monitoring of copper and zinc concentration in mining-impacted water

Microwave spectroscopy has been identified as a novel and inexpensive method for the monitoring of water pollutants. Integrating microwave sensors with developed coatings is a novel strategy to make the sensing system more specific for a target contaminant. This study describes the determination of copper and zinc concentration in water in both laboratory-prepared and acquired mine water samples from two abandoned mining areas in Wales, UK. Uncoated sensors immersed in samples spiked with 1.25 mg/L concentrations of copper and zinc, using the standard addition method, were able to quantify the concentration at 0.44 GHz with a strong linear correlation (R2 = 0.99) for the reflection coefficient magnitude (|S11|). Functionalised microwave sensors with l-cysteine, chitosan and bismuth zinc cobalt oxide-based coatings have shown improvement in the sensing performance. Specifically, the linear correlation at 0.91–1.00 GHz between |S11| and a polluted water sample spiked with Cu showed a higher (R2 = 0.98), sensitivity (1.65 ΔdB/mg/L) and quality factor (135) compared with uncoated sensors (R2 = 0.88, sensitivity of 0.82 ΔdB/mg/L and Q-factor 30.7). A Lorentzian peak fitting function was applied for performing advanced multiple peak analysis and identifying the changes in the resonant frequency peaks which are related to the change in metal ion content. This novel sensor platform offers the possibility of in situ monitoring of toxic metal concentrations in mining-impacted water, and multiple peak features, such as area, full width half maximum, centre and height of the peaks, have the possibility to offer higher specificity for similar toxic metals, as between copper and zinc ions.

Rapid Colonization of Uranium Mining-Impacted Waters, the Biodiversity of Successful Lineages of Phytoplankton Extremophiles.

Anthropogenic extreme environments are emphasized as interesting sites for the study of evolutionary pathways, biodiversity, and extremophile bioprospection. Organisms that grow under these conditions are usually regarded as extremophiles; however, the extreme novelty of these environments may have favor adaptive radiations of facultative extremophiles. At the Iberian Peninsula, uranium mining operations have rendered highly polluted extreme environments in multiple locations. In this study, we examined the phytoplankton diversity, community structure, and possible determining factors in separate uranium mining-impacted waters. Some of these human-induced extreme environments may be able to sustain indigenous facultative extremophile phytoplankton species, as well as alleged obligate extremophiles. Therefore, we investigated the adaptation capacity of three laboratory strains, two Chlamydomonas reinhardtii and a Dictyosphaerium chlorelloides, to uranium-polluted waters. The biodiversity among the sampled waters was very low, and despite presenting unique taxonomic records, ecological patterns can be identified. The microalgae adaptation experiments indicated a gradient of ecological novelty and different phenomena of adaptation, from acclimation in some waters to non-adaptation in the harshest anthropogenic environment. Certainly, phytoplankton extremophiles might have been often overlooked, and the ability to flourish in extreme environments might be a functional feature in some neutrophilic species. Evolutionary biology and microbial biodiversity can benefit the study of recently evolved systems such as uranium-polluted waters. Moreover, anthropogenic extremophiles can be harnessed for industrial applications.

Geochemical behaviors of antimony in mining-affected water environment (Southwest China)

Antimony (Sb) is a harmful element, and Sb pollution is one of the typical environmental issues in China, meaning that understanding of the geochemical behaviors of Sb is the key to control the fate of environmental Sb pollution. Sb tends to migrate in soluble form in the water-sediment system, but the fate of dissolved Sb is poorly known. Duliujiang river basin, located in southwest China, provided us with a natural aqueous environment to study the transport of Sb because of its unique geological and geographical characteristics. Physicochemical properties (pH, EC, Eh, DO, Flux), trace elements (Sb, As, Sr) and main ions (Ca2+, Mg2+, SO42-) concentrations in mining-impacted waters were measured in order to determine their distribution and migration potential. There are three types of water samples; they are main stream waters (pH of 7.33-8.43), tributary waters (pH of 6.85-9.12) and adit waters with pH values ranging from 7.57 to 9.76, respectively. Results showed that adit waters contained elevated concentrations of Sb reaching up to 13350µgL-1 from the abandoned Sb mines, and mine wastes contained up to 8792mgkg-1 Sb from the historical mine dumps are the important sources of Sb pollution in the Duliujiang river basin. Dissolved Sb had strong migration ability in streams, while its attenuation mainly depended on the dilution of tributary water with large flow rate. In the exit section of the Duliujiang river basin, which had only 10µgL-1 of average Sb concentration. The simple deionized water extraction was designed to investigate the ability of Sb likely to dissolve from the mine wastes. The results indicated that a greater solubility of Sb in alkaline (pH of 7.11-8.16) than in acid (pH of 3.03-4.45) mine wastes, suggesting that mine wastes contained high Sb concentrations, could release Sb into solution in the natural river waters. Furthermore, the fate of Sb pollution depends on the comprehensive treatment of abandoned adit waters and mine wastes in the upper reaches of the drainage basin.

Mine Water as a Resource: Selective Removal and Recovery of Trace Antimony from Mine-Impacted Water

The objective of this study was to evaluate the feasibility of combined modular processes to selectively remove Sb from mine-impacted waters in an Arctic environment in order to fulfil local environmental criteria for discharged waters. Novel ion exchange, selective extraction and ultrafiltration, electrocoagulation, and dissolved air flotation technologies were investigated, individually or in combination, from the laboratory- to pilot-demonstration scale. Laboratory-scale testing using Fe2(SO4)3 precipitation, ion exchange resin, selective ion extraction and ultrafiltration, and electrocoagulation with or without subsequent dissolved air flotation indicated that any of the methods are potentially applicable to Sb removal from mine water. The observed differences between Sb and As removal efficiency by ion exchange resin illustrated the need for Sb-specific removal and recovery technologies. Techno-economic analyses showed that treatment of mine water using electrocoagulation-dissolved air flotation yields the lowest comparative life-cycle cost of examined technologies. Results demonstrated increased Sb attenuation efficiency using either electrocoagulation-dissolved air flotation or selective extraction and ultrafiltration, even when treating only 50% of the mine-impacted water, compared with conventional Fe2(SO4)3 precipitation from mine water. Additional investigation is necessary to characterize the long-term stability of the mineral phases in Sb-containing solid residues and to inform selection of Sb recovery methods and utilisation or final disposal options for the residual materials.

The Potential Role of Halothiobacillus spp. in Sulfur Oxidation and Acid Generation in Circum-Neutral Mine Tailings Reservoirs.

The biogeochemistry of acid mine drainage (AMD) derived from waste rock associated sulfide mineral oxidation is relatively well-characterized and linked to Acidithiobacillus spp.. However, little is understood about the microbial communities and sulfur cycling before AMD develops, a key component of its prevention. This study aimed to examine circum-neutral mining impacted water (MIW) communities and its laboratory enrichments for sulfur oxidizing bacteria (SoxBac). MIW in situ microbial communities differed in diversity, structure and relative abundance consistent with site specific variations in total aqueous sulfur concentrations (TotS; ~2–17 mM), pH (3.67–7.34), and oxygen (22–93% saturation). However, the sulfur oxidizer, Halothiobacillus spp. dominated seven of the nine total SoxBac enrichment communities (~76–100% relative abundance), spanning three of the four mines. The presence and relative abundance of the identified sixteen known and five unclassified Halothiobacillus spp. here, were the important clustering determinants across parent MIW and enrichment communities. Further, the presence of Halothiobacillus spp. was associated with driving the pH <4 in enrichment experiments, and the combination of specific Halothiobacillus spp. in the enrichments affected the observed acid to sulfate ratios indicating differential sulfur cycling. Halothiobacillus spp. also dominated the parent communities of the two acidic MIWs providing corroborating evidence for its active role in net acid generation within these waters. These results identify a putative indicator organism specific to mine tailings reservoirs and highlight the need for further study of tailings associated sulfur cycling for better mine management and environmental stewardship.

Chitin as a substrate for the biostimulation of sulfate-reducing bacteria in the treatment of mine-impacted water (MIW).

This study aims to know the basis of sulfate-reducing bacteria (SRB) and chitin source relationship for the development of a biotreatment system for mine-impacted water (MIW). The MIW consists of river water impacted by coal acid mine drainage (AMD), an extremely acid effluent, rich in sulfate and dissolved metal ions, with a high pollutant potential. Chitin was used as metal ion sorbent and biostimulant of SRB, whose anaerobic dissimilatory metabolism reduces sulfate to sulfide. Microcosms were built in an oxygen-free atmosphere using chitin from two different sources: commercial chitin and shrimp shell waste, which contains calcium carbonate, an acidity removal agent, in addition to chitin. The results indicate that the shrimp shell performs best in removing sulfate (99.75%), iron (99.04%), aluminum (98.47%), and manganese (100%) ions. The iron ion sorption kinetics of the sediments were also studied; pseudo-second order behavior was observed. High-throughput sequencing analysis revealed the present bacterial community and its abundance in the microcosms after 11 and 30 treatment days: SRB were detected but were not the majority. Thus, this research aims to contribute to the sustainable treatment MIW through the employment of an abundant and low-cost biomaterial.

Influence of Organic Carbon Sources on Metal Removal from Mine Impacted Water Using Sulfate-Reducing Bacteria Bioreactors in Cold Climates

Acid mine drainage (AMD) is a major environmental challenge for the mining industry in northern climates. Laboratory-scale experiments were conducted to test various simple and complex carbon sources available in the Yukon as electron donors for sulfate reduction to allow the subsequent removal of Cd and Zn from a Yukon AMD. The 1 L capacity bioreactors were monitored biweekly at 5 °C. After 162 days, a diminution of both total organic carbon and sulfate concentrations was observed in all bioreactors. A long adaptation period was necessary before consumption of the carbon source started, which might be due to the cold temperature. Simple organic sources of carbon (methanol and ethylene glycol) and complex organic sources of carbon (potato oil, brewery residue, peat, and straw) were used to support SRB growth. Methanol and ethylene glycol led to a diminution of sulfate concentrations of 71.2 and 36.9%, respectively, while the decrease of sulfate concentrations was limited to 13.8 and 5.3% when using peat and straw, respectively.

South Africa’s options for mineimpacted water re-use: A review

South Africa’s options for mineimpacted water re-use: A review

Performance of a sulfidogenic bioreactor inoculated with indigenous acidic communities for treating an extremely acidic mine water

Mining contributes to water pollution through the generation and uncontrolled release of sulfuric acid and metalliferous drainage (AMD). While sulfate reducing bacteria have been used for the bioremediation of AMD, one of the main limitations to using sulfate-reducing bioreactors is that most species are highly sensitive to acidity; therefore it is necessary to avoid direct contact between acidic mine waters and the bacteria, which is normally achieved by using “off-line” systems. There have been few successful applications using acidophilic, sulfate-reducing bacterial populations, which tolerate low pH and high metal concentrations and allow direct metal sulfide precipitation to occur within a single bioreactor unit. Here, we describe the performance of a low pH sulfidogenic bioreactor inoculated with an indigenous microbial community to treat mine-impacted water. The inoculum was obtained from anaerobic sediments collected from an acidic river located in northern Chile. The sulfidogenic bioreactor system (2.3 L) was operated as a continuous flow mode unit for 99 days at 30 °C and fed with synthetic water based on the chemical composition of the acidic river, characterized by extremely low pH (2.1) and, zinc and iron as main transition metals (0.5 and 2 mM, respectively). The bioreactor pH was set to 4.5 initially and was increased in stages to pH 6.0 during the experiment. The results show that zinc concentrations in liquors draining the bioreactor were below the detection level in most of the samples analyzed. In addition, by progressively increasing the glycerol concentration, it was possible to increase the removal of iron (70% of the total present), though more acetic acid (from 1 to 5 mM) was generated. Analysis of the microbial populations showed that they changed with varying operation parameters, and a known acetogenic sulfidogen (Desulfoporosinus acididurans) became more dominant over time. The modular unit used for treating mine-impacted water demonstrated robust activity with low complexity engineering.

Remediation of manganese in mine impacted water by clay/manganese oxide hybrid adsorbent: equilibrium, kinetics and thermodynamic studies

The present study investigated the potential of clay/manganese oxide (CMnO) hybrid adsorbent for the removal of manganese (Mn2+) from mine impacted water (MIW). The adsorbent was characterised by X-ray diffraction, Fourier transform infra-red (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmet–Teller and X-ray photoelectron spectroscopy (XPS) techniques. The equilibrium sorption capacity was depended on solution pH, MnO content of the clay, concentration and temperature. Isothermal adsorption highly inclined towards Freundlich isotherm model while thermodynamic parameters directed that the adsorption process was spontaneous and endothermic in nature. The adsorption kinetics of Mn2+ onto CMnO fitted well with the pseudo-second-order model and the value of activation energy of adsorption (Ea) was 32 kJ/mol, inferring that the adsorption proceeded by activated chemisorption process. Both intra-particle and film diffusion mechanisms were found to be the sorption rate-controlling steps. Experiments with real MIW water revealed that CMnO exhibited high Mn2+ removal efficiency in the presence of interfering ions but anions removal posed a great challenge. The XPS, FT-IR and pH analyses suggested that oxidation, complexation and ion-exchange mechanisms were responsible for Mn2+ removal by CMnO. These findings demonstrate that CMnO could serve as an inexpensive adsorbent for polishing Mn2+ polluted water.

Semi-passive in-situ pilot scale bioreactor successfully removed sulfate and metals from mine impacted water under subarctic climatic conditions

Mine drainage contaminated with metals is a major environmental threat since it is a source of water pollution with devastating effects on aquatic ecosystems. Conventional active treatment technologies are prohibitively expensive and so there is increasing demand to develop reliable, cost-effective and sustainable passive or semi-passive treatment. These are promising alternatives since they leverage the metabolism of microorganisms native to the disturbed site at in situ or close to in situ conditions. Since this is a biological approach, it is not clear if semi-passive treatment would be effective in remote locations with extremely cold weather such as at mines in the subarctic. In this study we tested the hypothesis that sulfate-reducing bacteria, which are microorganisms that promote metal precipitation, exist in subarctic mine environments and their activity can be stimulated by adding a readily available carbon source. An experiment was setup at a closed mine in the Yukon Territory, Canada, where leaching of Zn and Cd occurs. To test if semi-passive treatment could precipitate these metals and prevent further leaching from waste rock, molasses as a carbon source was added to anaerobic bioreactors mimicking the belowground in-situ conditions. Microbial community analysis confirmed that sulfate-reducing bacteria became enriched in the bioreactors upon addition of molasses. The population composition remained fairly stable over the 14 month operating period despite temperature shifts from 17 to 5 °C. Sulfate reduction functionality was confirmed by quantification of the gene for dissimilatory sulfite reductase. Metals were removed from underground mine drainage fed into the bioreactors with Zn removal efficiency varying between 20.9% in winter and 89.3% in summer, and Cd removal efficiency between 39% in winter and 90.5% in summer. This study demonstrated that stimulation of native SRB in MIW was possible and that in situ semi-passive treatment can be effective in removing metals despite the cold climate.

Hydrogeochemical assessment of mine-impacted water and sediment of iron ore mining

This study was carried out to evaluate the hydrogeochemical behaviour of mine-impacted water and sediment of a former iron ore mining area. Sampling of mine water and sediment were carried out at selected locations within the mine including the former mining ponds, mine tailings and the nearby stream. The water samples were analysed for their hydrochemical facies, major and trace elements including heavy metals. The water in the mining ponds and the mine tailings was characterised as highly acidic (pH 2.54-3.07), but has near-neutral pH in the nearby stream. Results indicated that Fe and Mn in water have exceeded the recommended guidelines values and was also supported by the results of geochemical modelling. The results also indicated that sediments in the mining area were contaminated with Cd and As as shown by the potential ecological risk index values. The total risk index of heavy metals in the sediment were ranked in the order of Cd>As>Pb>Cu>Zn>Cr. Overall, the extent of potential ecological risks of the mining area were categorised as having low to moderate ecological risk.

Combined hydrochemical, isotopic, and multivariate statistics techniques to assess the effects of discharges from a uranium mine on water quality in neighboring streams

The Caldas Uranium Mine (CUM), located on the Pocos de Caldas Plateau in the southeastern region of Brazil, is presently undergoing a decommissioning process. The aim of the present investigation is to identify and characterize the effects of acid mine drainage (AMD) originating from the CUM on surface water quality. To achieve these aims, sampling stations were located at two AMD sources: the retention pond at the foot of waste rock pile#4 (WRP#4) and the settling pond that receives effluents from the tailings dam (TD). Ten additional sampling stations were located along watercourses in the vicinity, both downstream and upstream of the mine. Sampling was performed during the rainy and dry seasons in 2010 and 2011. The water analysis detected significant changes in pH, electrical conductivity, F−, Cd, U, Zn, Al, Mn, As, Ca, SO4 2−, Pb, 238U, 226Ra, 210Pb, 232Th, 228Ra, and Mo in waters downstream of both pond discharge sites. It was demonstrated that the disequilibrium between 226Ra and 238U can be used to trace the extent of AMD impacts in nearby streams. Variations in 18O and 2H enabled the flow of mining-impacted water to be traced from the ponds to nearby streams. Multivariate analysis yielded a three-factor model: Factor 1 was interpreted as being associated with AMD (from WRP#4) and Factor 2 with a Ca–Mo relationship associated with the chemical constitution of the ore and with the treatment of tailings wastes in the area (from TD); Factor 3 was interpreted as being associated with the natural influence of geogenic processes on water quality in the area. The results of this study provide a scientific basis for recommending appropriate remedial actions during mine decommissioning.

Mercury Bioaccumulation in Crayfish in Acid Mine-Impaired Appalachian Streams

We tested the hypothesis that mercury (Hg) bioaccumulation in crayfish inhabiting acid mine-impacted streams increases with the severity of acidification. Sixty-four sites in southeast Ohio were ranked for severity of acid mine impact using an index of six water chemistry parameters (Fe, Mn, Al, sulfate, acidity, and pH) characteristic of acid mine drainage. Macroinvertebrate communities along the acid mine drainage (AMD) gradient were sampled by kick and dip net, and the abundances of different functional feeding groups characterized to evaluate differences in dietary prey availability to crayfish inhabiting AMD-impaired streams. Mercury in crayfish (Orconectes sanbornii) was measured at 19 sites. Composite samples (N = 10) of tail tissue from these sites were analyzed for mercury, along with sediment from six sites. Sediment methyl mercury (MeHg) ranged from 0.03 to 0.479 ng/g, typical of background (uncontaminated by Hg or AMD) levels for lakes and streams in this region. MeHg concentrations in crayfish tail tissue ranged from 26.7 to 122 ng/g. Contrary to our hypothesis, total Hg and MeHg in crayfish tissue were negatively correlated with acid mine impairment (r = −0.479, p = 0.036; r = −0.049, p = 0.0293, respectively), suggesting that crayfish bioaccumulate Hg more slowly in acid mine-impaired streams. This pattern is opposite of trends for increased bioaccumulation rates in food webs of lakes acidified by atmospheric deposition. Total macroinvertebrate (prey) abundance at study sites declined with increasing AMD impact. The reduced Hg accumulation in acid mine-impacted waters may be related to a change in diet, greater reliance on detritus-based food items, and/or lower trophic status of crayfish in acidified streams.

Dissolved Selenium(VI) Removal by Zero-Valent Iron under Oxic Conditions: Influence of Sulfate and Nitrate.

Dissolved Se(VI) removal by three commercially available zero-valent irons (ZVIs) was examined in oxic batch experiments under circumneutral pH conditions in the presence and absence of NO3– and SO42–. Environmentally relevant Se(VI) (1 mg L–1), NO3– ([NO3—N] = 15 mg L–1), and SO42– (1800 mg L–1) were employed to simulate mining-impacted waters. Ninety percent of Se(VI) removal was achieved within 4–8 h in the absence of SO42– and NO3–. A similar Se(VI) removal rate was observed after 10–32 h in the presence of NO3–. Dissolved Se(VI) removal rates exhibited the highest decrease in the presence of SO42–; 90% of Se(VI) removal was measured after 50–191 h for SO42– and after 150–194 h for SO42– plus NO3– depending on the ZVI tested. Despite differences in removal rates among batches and ZVI materials, Se(VI) removal consistently followed first-order reaction kinetics. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analyses of reacted solids showed that Fe(0) present in ZVI undergoes oxidation to magnetite [Fe3O4], wüstite [FeO], lepidocrocite [γ-FeOOH], and goethite [α-FeOOH] over time. X-ray absorption near-edge structure spectroscopy indicated that Se(VI) was reduced to Se(IV) and Se(0) during removal. These results demonstrate that ZVI can be effectively used to control Se(VI) concentrations in mining-impacted waters.

Passive Biological Treatment of Mine Water to Reduce Conductivity: Potential Designs, Challenges, and Research Needs

The remediation of mine water to preserve receiving water quality has advanced substantially over the past half century, but prospective regulations to limit the conductivity of mining-impacted waters pose a significant new challenge. Conventional approaches to reduce high levels of conductivity in these mine waters are often costly, requiring high levels of maintenance and significant inputs of energy and refined chemicals. In contrast, passive biological treatment (PBT) systems are a relatively low-cost, low-maintenance treatment technology for mine waters that have been used for over three decades. However, their practical ability to reduce conductivity is unclear, given previous research reports focused on the removal of metals, acidity, and solids. A systematic literature review to identify previous reports of PBT systems at the laboratory or field scale that include evaluations of changes in conductivity suggests that decreases in conductivity of 30 to 40% are achievable. Substantial variability in performance is common, however, and conductivity increased markedly in some systems. This variation may be associated with the dissolution of limestone, which is a key treatment material in some systems. Although the development of PBT to serve as pre-, post-, or stand-alone treatment systems targeting conductivity may reduce overall treatment cost in some settings, optimization of these designs requires an increase in the number of published conductivity datasets from similar systems, detailed reports on the key ions contributing to elevated conductivity region to region, and further investigation of the underlying biochemical processes responsible for conductivity reductions.

Acute toxicity of arsenic to larvae of four New Zealand freshwater insect taxa

ABSTRACTArsenic, often found in gold deposits, can enter aquatic systems. The toxicity of arsenate (As(V)), the most common valence state of arsenic in freshwater, was assessed on the larvae of four freshwater insect taxa from naturally acidic (pH 5.9) and circumneutral (pH 7.4) New Zealand streams. Insects from the acidic stream were more sensitive to arsenate-spiked water than those from the circumneutral stream. Early instars (<3 mm) of the mayfly Deleatidium spp. (Leptophlebiidae) were the most sensitive compared to later instars (3–6 mm) (4-d LC50 1.5 and 3.5 mg/L, respectively) or to the stonefly Zelandobius spp. (Gripopterygidae) (4-d LC50 2.5 mg/L). The cased caddisflies Pycnocentria spp. (Conoesucidae) and Helicopsyche spp. (Helicopsychidae) from circumneutral stream were the most tolerant (4-d LC50 45.4 and 113 mg/L, respectively). The 14-day arsenic LC10 and LC50 for Deleatidium spp. late instars exposed to mining-impacted water were 0.12 and 0.36 mg/L, respectively.

The occurrence and potential ecological risk assessment of bauxite mine-impacted water and sediments in Kuantan, Pahang,Malaysia

Recent bauxite mining activities in the vicinity of Kuantan, Pahang, have been associated with apparent environmental quality degradation and have raised environmental concerns among the public. This study was carried out to evaluate the overall ecological impacts on water and sediment quality from the bauxite mining activities. Water and sediment samples were collected at seven sampling locations within the bauxite mining areas between June and December 2015. The water samples were analyzed for water quality index (WQI) and distribution of major and trace element geochemistry. Sediment samples were evaluated based on geochemical indices, i.e., the enrichment factor (EF) and geoaccumulation index (I geo). Potential ecological risk index was estimated to assess the degree to which sediments of the mine-impacted areas have been contaminated with heavy metals. The results showed that WQIs of some locations were classified as slightly polluted and contained metal contents exceeding the recommended guideline values. The EFs indicated minimal to moderate enrichment of metals (Pb, Cu, Zn, Mn, As, Cd, Cr, Ni, Co, and Sr) in the sediments. I geo showed slightly to partially polluted sediments with respect to As at some locations. The potential ecological risk index (RI) showed that As posed the highest potential ecological risk with RI of 52.35-60.92 at two locations, while other locations indicated low risk. The findings from this study have demonstrated the impact of recent bauxite mining activities, which might be of importance to the local communities and relevant authorities to initiate immediate rehabilitation phase of the impacted area.