Decrease In Metal Concentrations Research Articles

Highly Active Polymer‐Supported (Salen)Al Catalysts for the Enantioselective Addition of Cyanide to α,β‐Unsaturated Imides

AbstractIn this contribution, we describe polymer‐supported (R,R)‐(salen)AlCl complexes that were immobilized on poly(norbornene)s and display excellent activities and enantioselectivies as catalysts for the 1,4‐conjugate addition of cyanide to α,β‐unsaturated imides. These supported catalysts could be recycled up to 5 times without compromising catalyst activities or selectivities. Furthermore, the catalyst loadings could be reduced from 10–15 mol%, the common catalyst loadings for non‐supported (salen)Al catalysts, to 5 mol%, a decrease of metal content by 50–66%, without lowering product yields or enantioselectivities. Kinetic studies indicated that the polymer‐supported catalysts are significantly more active than their corresponding unsupported analogues, which makes this catalyst system key to a successful implementation of this catalytic transformation into the fine chemical and pharmaceutical industries.

Annual and Seasonal Variations of Trace Metals in Atmospheric Suspended Particulate Matter in Islamabad, Pakistan

Total Suspended particulate matter (TSP) in urban atmosphere of Islamabad was collected using a high volume sampling technique for a period of one year. The nitric acid–perchloric acid extraction method was used and the metal contents were estimated by atomic absorption spectrophotometer. The highest mean concentration was found for Ca at 4.531 µg/m3, followed by Na (3.905 µg/m3), Fe (2.464 µg/m3), Zn (2.311 µg/m3), K (2.086 µg/m3), Mg (0.962 µg/m3), Cu (0.306 µg/m3), Sb (0.157 µg/m3), Pb (0.144 µg/m3) and Sr (0.101 µg/m3). On an average basis, the decreasing metal concentration trend was: Ca > Na > Fe > Zn > K > Mg > Cu > Sb > Pb > Sr > Mn > Co > Ni > Cr > Li > Cd ≈ Ag. The TSP levels varied from a minimum of 41.8 to a maximum of 977 µg/m3, with a mean value of 164 µg/m3, which was found to be higher than WHO primary and secondary standards. The correlation study revealed very strong correlations (r > 0.71) between Fe–Mn, Sb–Co, Na–K, Mn–Mg, Pb–Cd and Sb–Sr. Among the meteorological parameters, temperature, wind speed and pan evaporation were found to be positively correlated with TSP, Ca, Fe, K, Mg, Mn and Ag, whereas, they exhibited negative relationships with relative humidity. On the other hand, Pb, Sb, Zn, Co, Cd and Li revealed significant positive correlations with relative humidity and negative with temperature, wind speed and pan evaporation. The major sources of airborne trace metals identified with the help of principle component analysis and cluster analysis were industrial emissions, automobile exhaust, biomass burning, oil combustion, fugitive emissions, resuspended soil dust and earth crust. The TSP and selected metals were also studied for seasonal variations, which showed that Na, K, Zn, Cu, Pb, Sb, Sr, Co and Cd peaked during the winter and remained lowest during the summer, while Ca, Fe, Mg and Mn were recorded highest during the spring.

Statistical source identification of metals in groundwater exposed to industrial contamination

Levels of selected metals Na, Ca, Mg, K, Fe, Mn, Cr, Co, Ni, Cd, Pb and Mn were estimated by flame atomic absorption spectrophotometry in groundwater samples from Kasur, a significant industrial city of Pakistan. Salient mean concentration levels were recorded for: Na (211 mg/l), Ca (187 mg/l), Mg (122 mg/l), K (87.7 mg/l), Fe (2.57 mg/l) and Cr (2.12 mg/l). Overall, the decreasing metal concentration order was: Na>Ca>Mg>K>Fe>Cr>Zn>Co>Pb>Mn>Ni>Cd. Significantly positive correlations were found between Na-Cr (r=0.553), Na-Mn (r=0.543), Mg-Fe (r=0.519), Mg-Cr (r=0.535), Pb-K (r=0.506) and Pb-Ni (r=0.611). Principal Component Analysis and Cluster Analysis identified tannery effluents as the main source of metal contamination of the groundwater. The present metal data showed that Cr, Pb and Fe levels were several times higher than those recommended for water quality by WHO, US-EPA, EU and Japan. The elevated levels of Cr, recorded as 21-42 fold higher compared with the recommended quality values, were believed to originate from the tanning industry of Kasur.

The application of bioremediation: reduction of metal concentrations in river water and COD in distillery effluent

The major aim of this study was to evaluate and develop artificial bioremediation systems to reduce or remove metal pollutants from contaminated river water and to decrease the chemical oxygen demand (COD) in distillery effluent. Metals were extracted using the nitric acid digestion method, and the concentrations determined using inductively coupled plasma-atomic emission spectrometry. A decrease in metal concentrations was observed for most of the metals analysed in the river water after being pumped through the bioreactor system for approximately two weeks, e.g. Al concentration decreased from 0.75mg.l(-1) to 0.18mg.l(-) and for Ni, from 0.19mg.l(-1) to 0 mg.l(-l). In addition, the COD counts decreased from 2255 mg.l(-1) to a final value of < 150 mg.l(-1) in the distillery effluent. It could thus be concluded that the bioreactor system decreased the COD and metal concentrations in the distillery effluent as well as the river water, respectively. A bioreactor is being evaluated on-site at a wine cellar to reduce COD and will be constructed at a site along the Plankenbrug River.

Assessment of the historical trace metal contamination of sediments in the Elizabeth River, Virginia

Two sediment cores (Southern Branch, PC-1, and Western Branch, WB-2) were taken from the highly industrialized Elizabeth River, Virginia. The concentrations of trace metals cadmium, cobalt, chromium, copper, nickel, lead and zinc, major elements iron, manganese and aluminum, organic carbon content and the specific surface area of the sediments were determined in each of the cores. Down-core variations in metals varied significantly in each core with maximum contamination events occurring at different times in different portions of the river. In PC-1, maximum metal concentrations were seen after the appearance of 137Cs. In contrast, the highest levels in WB-2 occurred well before the appearance of 137Cs. Although stricter environmental regulations have caused a decrease in metal concentrations since the 1980s, the concentrations in the surface sediments of many trace metals were elevated to levels 2–5 times higher than the levels at the bottom of the cores in both the Southern and Western Branches of the river.

Crack growth resistance (R-curve) behaviour and thermo-physical properties of Al2O3 particle-reinforced AlN/Al matrix composites

Crack growth resistance behaviour and thermo-physical properties of Al2O3 particle-reinforced AlN/Al matrix composites have been studied as a function of AlN volume fraction as well as Al2O3 particle size. The fracture toughness of the composites decreased with increase in vol% AlN and decrease in Al2O3 particle size. All the composites exhibited R-curve behaviour which has been attributed to crack bridging by the intact metal ligaments behind the crack tip. The Young’s modulus of the composites increased with the vol% of AlN whereas the thermal diffusivity and coefficient of thermal expansion followed a reverse trend. The composites exhibited hysteresis in thermal expansion as a function of temperature and the hysteresis decreased with decrease in metal content of the composite.

Distribution of copper, lead, cadmium and zinc concentrations in soils around Kabwe town in Zambia

The extent of pollution of the environment as a result of mining activities in Kabwe, the provincial capital of Central province in Zambia has not yet been evaluated. Mining of lead and zinc were the core activities of Kabwe mine while cadmium and silver were produced as by-products. The smelting processes produced a significant amount of copper. The spatial distribution of four heavy metals in soils in the northern, eastern, southern and western directions of the mine was analyzed using atomic absorption spectrometry (AAS). Samples were collected up to 20 km in each direction from the mine. Results were consistent with the wind flow patterns in the town. Results ranged between 0.08 and 28 mg kg −1 (Cd); 0.20 and 0.61 mg kg −1 (Cu); 0.10 and 758 mg kg −1 (Pb) and 0.40 and 234 mg kg −1 (Zn) suggesting high precipitation of metals from the core mining activities. These concentrations were for only the fractions of metals extractable by 0.5 M nitric acid and that could be available for plant uptake in the environment. The distribution of metals indicated a decrease of metal concentrations with distance from the mine, which confirmed that precipitation due to mining activities was the main cause of soil contamination.

A Comparative Study Based on Gender and Age Dependence of Selected Metals in Scalp Hair

Levels of 10 metals (Ca, Mg, Fe, Zn, Cu, Mn, Cd, Co, Cr and Ni) in the scalp hair of male and female donors, with age groups between 3 and 100 years, were determined by ICP-AES. In total, 58 male and 30 female hair samples were analyzed in triplicate. The donors belonged to the rural area of district Chakwal, a well-known typical non-urban site in Pakistan. Calcium showed the highest concentration of 462 microg/g in the hair of males and 870 microg/g in those of females followed by Zn, at 208 and 251 microg/g for the two sexes. For male donors, Cd showed the lowest concentration (1.15 microg/g) while for female donors Co remained at minimum level (0.92 microg/g). The order of decreasing metal concentration in the hair of male donors was: Ca > Zn > Mg > Fe > Cu > Mn > Ni > Cr > Co > Cd while that for female donors it was: Ca > Zn > Mg > Fe > Cu > Mn > Cr > Ni > Cd > Co. The female group exhibited enhanced levels of all selected metals except Fe and Co in their hair as compared with the male counterparts. A strong bivariate positive correlation was found between Fe and Zn (r = 0.841) for the hair samples from male category while for the female category, strong positive correlations were observed between Ca-Mg (r = 0.617), Ca-Zn (r = 0.569), Ca-Mn (r = 0.565), Mg-Mn (r = 0.655), Cr-Cu (r = 0.655) and Cr-Ni (r = 0.685). The distribution of metals in the hair of donors with respect to different age groups was also investigated for both genders. The study showed that in case of males, the concentration of all selected metals decreased with increasing age except for Cu, Co and Cr. However, for females the hair metal levels increased with age, except for Co for which the concentration decreased with age. No appreciable change in the metal concentration was observed as a function of age for the combined sexes.

Anodic Dissolution of Cobalt Silicides in Alkaline Electrolytes

Anodic dissolution of cobalt silicides Co2Si, CiSi, CoSi2, CoSi2–Si (eutectic alloy), and also individual Co and Si in 0.1–5.0 N NaOH solutions is studied by using cyclic voltammetry (CVA). In alkaline electrolyte, despite the increasing activity of silicon, the electrode is passivated due to the formation of protective films of cobalt oxides and hydroxides. The anodic stability of cobalt increases with a decrease in metal content.

Biogeochemistry of the compost bioreactor components of a composite acid mine drainage passive remediation system

The compost bioreactor (“anaerobic cell”) components of three composite passive remediation systems constructed to treat acid mine drainage (AMD) at the former Wheal Jane tin mine, Cornwall, UK were studied over a period of 16 months. While there was some amelioration of the preprocessed AMD in each of the three compost bioreactors, as evidenced by pH increase and decrease in metal concentrations, only one of the cells showed effective removal of the two dominant heavy metals (iron and zinc) present. With two of the compost bioreactors, concentrations of soluble (ferrous) iron draining the cells were significantly greater than those entering the reactors, indicating that there was net mobilisation (by reductive dissolution) of colloidal and/or solid-phase ferric iron compounds within the cells. Soluble sulfide was also detected in waters draining all three compost bioreactors which was rapidly oxidised, in contrast to ferrous iron. Oxidation and hydrolysis of iron, together with sulfide oxidation, resulted in reacidification of processed AMD downstream of the compost bioreactors in two of the passive treatment systems. The dominant cultivatable microorganism in waters draining the compost bioreactors was identified, via analysis of its 16S rRNA gene, as a Thiomonas sp. and was capable of accelerating the dissimilatory oxidation of both ferrous iron and reduced sulfur compounds. Sulfate-reducing bacteria (SRB) were also detected, although only in the bioreactor that was performing well were these present in significant numbers. This particular compost bioreactor had been shut down for 10 months prior to the monitoring period due to operational problems. This unforeseen event appears to have allowed more successful development of AMD-tolerant and other microbial populations with critical roles in AMD bioremediation, including neutrophilic SRB (nSRB), in this compost bioreactor than in the other two, where the throughput of AMD was not interrupted. This study has revealed new insights into the operation of compost bioreactors used to remediate mine waters and has shown that, when operated under appropriate conditions, they can be highly efficient at generating alkalinity and removing metals from extremely acidic, metal-rich AMD.

Atomic absorption spectrophotometric determination of Pb, Cd, Cu, Mn, Cr, Ni and Fe levels in human hair. Influence of age, hair colour and smoking habit

Pb, Cd, Cr, Mn, Fe, Ni and Cu levels in human hair of 629 healthy subjects exposed to these metals were determined by Atomic Absorption Spectrophotometry in relation to age, hair colour and smoking habit. Decrease in metal concentrations were observed in higher age group. Ni, Fe and Cr levels were significantly high at P < 0.05 in black hair with respect to white hair. Pb, Cd, Cr and Ni concentrations were significant at P < 0.05 in smokers.

Distribution of Mn, Al, Cu and Zn in a constructed wetland receiving municipal sewage

A constructed wetland at Nucice near Prague, Czech Republic, has been in operation since 1996 and the system is designed to treat sewage from 650 PE together with stormwater. The total area of the beds planted with Phalaris arundinacea and Phragmites australia is 3,224 m2 (two beds 62 x 26 m each). Pea gravel (8/16 mm) is used as a filtration material. During the period 1998-1999, removal of Mn, Al, Cu and Zn from wastewater and distribution of the metals in sediments and plants were studied. Metals were measured in three vertical profiles of the filtration bed (0-15, 15-30 and 30-60 cm) and at four locations along the longitudinal profile of the bed (5, 16, 32, 48 m from the inlet). Metal concentrations in plant tissues (roots, stems, leaves) of Phalaris arundinacea were measured along the longitudinal profile of the bed at the same locations as for sediments. The results showed that the retention of metals is high (up to 98%) with the major decrease in metal concentrations within the first 5 metres of the bed. The major decrease in metal concentration in the filtration material was observed in the inlet zone between 5 and 16 metres. In Phalaris tissue, metal concentrations decreased in the order roots > stems > leaves but statistically significant differences varied among the studied metals.

Natural variation of copper, zinc, cadmium and selenium concentrations in Bembicium nanum and their potential use as a biomonitor of trace metals

Copper, zinc, cadmium and selenium were measured in the gastropod mollusc Bembicium nanum at two uncontaminated locations, Jervis Bay and Rosedale, NSW, to determine natural variability of metals associated with gender, mass, shore position and temporal variability. Trace metals were also measured in B. nanum at three industrialised locations to determine the accumulation of trace metals in contaminated environments. Copper, zinc, cadmium and selenium concentrations were not significantly different between male and female B. nanum. No significant relationships were found between zinc, cadmium and selenium concentrations and mass. There was a significant relationship between copper concentration and mass but only 19% of the variation was explained by mass. Generally inherent variability within samples had a greater influence than gender or variations in mass on trace metal concentrations. No trend was found in cadmium and selenium concentrations with variation in shoreline position. Copper and zinc concentrations increased further away from the low tide mark, with a decrease in metal concentrations at the furthest site from the water. Variability in metal concentrations is attributable to variations in food source, food availability and different immersion times. Copper, zinc, cadmium and selenium concentrations varied over a 12-month period. Copper, cadmium and selenium were taken up and lost over time, as metal body burden followed the same trend as metal concentrations. Zinc concentrations were influenced by mass. Copper and cadmium concentrations fluctuated throughout the 12-month period but with no clear seasonal trends. Selenium concentrations peaked in spring (October), with concentrations remaining uniform over the other months. These differences in mean concentrations between months were most likely due to inherent trace metal variability associated with differences in food availability and changes in metabolic rates associated with changes in temperature during the study period. Measurement of trace metals in B. nanum at contaminated sites showed that B. nanum accumulates metals in response to contamination. B. nanum meets most of the requirements to be a biomonitor of trace metal contamination as they are abundant, sedentary, easy to identify, provide sufficient tissue for analysis, tolerate high concentrations of pollutants and they accumulate trace metals in response to contamination. However, as trace metal concentration can vary with mass, shoreline position and temporally, care must be taken to collect individual organisms with similar mass from similar shoreline positions and times.

Effect of pore-water velocity on chemical nonequilibrium transport of Cd, Zn, and Pb in alluvial gravel columns

This paper investigates the effects of pore-water velocity on chemical nonequilibrium during transport of Cd, Zn, and Pb through alluvial gravel columns. Three pore-water velocities ranging from 3 to 60 m/day were applied to triplicate columns for each metal. Model results for the symmetric breakthrough curves (BTCs) of tritium ( 3H 2O) data suggest that physical nonequilibrium components were absent in the uniformly packed columns used in these studies. As a result, values of pore-water velocity and dispersion coefficient were estimated from fitting 3H 2O BTCs to an equilibrium model. The BTCs of metals display long tailing, indicating presence of chemical nonequilibrium in the system, which was further supported by the decreased metal concentrations during flow interruption. The BTCs of the metals were analysed using a two-site model, and transport parameters were derived using the CXTFIT curve-fitting program. The model results indicate that the partitioning coefficient ( β), forward rate ( k 1), and backward rate ( k 2) are positively correlated with pore-water velocity ( V); while the retardation factor ( R), mass transfer coefficient ( ω), and ratio of k 1/ k 2 are inversely correlated with V. There is no apparent relationship between the fraction of exchange sites at equilibrium ( f) and V. The influence of V on k 2 is much greater than on R, β, ω, and k 1. A one-order-of-magnitude change in V would cause a two-order-of-magnitude change in k 2 while resulting in only a one order-of-magnitude change in R, β, ω, and k 1. The forward rates for the metals are found to be two to three orders-of-magnitude greater than the corresponding backward rate. However, the difference between the two rates reduces with increasing pore-water velocity. Model results also suggest that Cd and Zn behave similarly, while Pb is much more strongly sorbed. At input concentrations of about 4 mg/l and pore-water velocities of 3–60 m/day in the groundwater within alluvial gravel, this study suggests retardation factors of 26–289 for Cd, 24–255 for Zn, and 322–6377 for Pb.

Geochemical consequences of acid mine drainage into a natural reservoir: inorganic precipitation and effects on plankton activity

Results of a field experiment demonstrating the response of a reservoir (Ob reservoir) to the inflow of a restricted portion of an acid mine drainage solution (AMD) derived from the Berikul sulfide tailings is presented. Drainage water samples from Berikul tailings are acidic (pH 2.0–2.4), with high levels of Fe (up to 30 mg/l), As (up to 4.5 mg/l) and other metals (e.g. Pb, Zn, Cu, Cd). High metal concentration and low pH of these solutions are the result of the intensive interaction of rainwater and soluble efflorescent phases on the Berikul tailings surface. The experiment was carried out in 3 mesocosms (bounded water volume), located in the small gulf of the Ob reservoir without any industrial activity. The discharge of an AMD solution to the mesocosms caused the development of an abundant reddish suspension. The latter relates to the neutralization of the acid solution and formation of gypsum, jarosite and Fe-oxides. The uptake of dissolved metals resulted in fast mortality of phytoplankton due to the strong toxic effect. Compared with background phytoplankton numbers, the population decreased with a factor 2–5. pH values decreased sharply both due to acidification by drainage fluids and the effect on plankton activity. A decrease in zooplankton quantity took place after two days as a consequence of a loss in food. The subsequent decrease in metal concentrations in the reservoir is the result of both co-precipitation with new-forming mineral phases and the adsorption by phytoplankton. Fe and As occurred dominantly in the suspended phase, while Zn and Cd remained in dissolution. Two mechanisms of metal precipitation have been traced, namely precipitation as sorbed ions onto surfaces of newly formed Fe compounds and bioaccumulation, whereby physico-chemical reactions played the dominant role during the first 40 h. The latter are very effective (with settling rate is about 0.5 cm/s) but single factor of metal removal. Biotic mechanism became detectable from the 40th hour, till the end of the experiment (i.e. 234th hour). Metal settling occurred rather slow (rate is ∼0.01 cm/s), but it is a continuous cyclic process, owing to renascent of new phytoplankton cells. The restoration of original reservoir conditions is attained after 10 days.

Lake Süßer See as a natural sink for heavy metals from copper mining

Lake Süßer See, west of Halle, Germany, is a natural sink for heavy metals, which are abundant in the streams crossing the Mansfeld copper shale mining and smelting district in Central Germany. The lake and its environment serve as a recreational area for the local residents. We investigated the vertical distribution of key metals such as Cu, Pb and Zn in the lake sediments. To estimate the future stability of the heavy metals in the lake sediments, speciation analysis of the metals was carried out on selected samples using several analytical methods, including X-ray diffraction, synchrotron-based X-ray fluorescence imaging, microprobe X-ray absorption near-edge structure spectroscopy and scanning electron microscopy. The lake sediments contain up to 5% Zn, 5000 ppm Pb, 4500 ppm Cu and 2000 ppm As. These maximum values are reached within the upper 60 cm of the sediment. There is a general trend of decreasing metal concentrations with depth. Several potential metal sources of geogenic and anthropogenic pollutants have to be taken into account. Pollutants of geogenic origin are mainly heavy metals from the outcropping copper shale at the periphery of the Mansfeld geosyncline. Man-made pollutants are dominated by seepage from the mine tailings and smelting products of copper shale mining (in particular scrubber dust, ‘Theisen-sludge’). Trace elements and their ratios in the lake sediments can serve as geochemical tracers. These tracers could help to identify the main sources of pollution. The data show that scrubber dust is the main carrier of the heavy metal contamination in the lake sediments.

Estimating the kinetic parameters of heavy metal uptake by aquatic plants in batch culture

A simple and effective least-squares procedure for the estimation of the kinetic parameters of a heavy metal uptake model by aquatic plants in batch culture experiments was developed, using only the data of the decreasing metal concentration in the substrate. The basic approach was the transformation of the parameter estimation problem to a mathematical model that contains a single decision variable. The resulting model was then solved by an efficient one-dimensional search algorithm, based on the estimation of the maximal concentration of metal in the plant (EP,∞). The model can be adapted for any microcomputer or advanced programmable calculator. The procedure was tested on Fe2+ uptake kinetics in Apium nodiflorum aquatic plant and the estimated parameters were compared with those estimated elsewhere using a continuous culture system.

An assessment of the impact of motorway runoff on a pond, wetland and stream

The impact of soil filtered runoff from a section of the M25 outer London motorway (constructed in 1981) on a pond, wetland and stream in a nature reserve was investigated by monitoring water, sediment. The tissues of the emergent plants Typha latifolia and Glyceria maxima collected from the pond were analysed for the heavy metals, Cd, Pb, Cu and Zn. Macroinvertebrates were monitored in the stream and biotic indices applied to the data. The plant tissue concentrations for Typha and Glyceria show decreasing metal concentrations from root to rhizome to leaf. This trend has previously been reported for Typha exposed to runoff although the tissue concentrations are lower in this study with the exception of Cd in root tissue. The Biological Monitoring Working Party (BMWP) score and Average Score Per Taxon (ASPT) for the stream at sites above and below the pond outlet are lower than the scores recorded by the Environment Agency for England and Wales at an upstream site above the Pond/Wetland. The sites have an Overall Quality Index of ‘moderate water quality’, and there is no evidence of a deterioration of biologically assessed water quality between them. The results of the study show the long-term impact on sediment of filtered road runoff discharges to a natural wetland and pond located in a nature reserve. The use of natural wetlands for the discharge of road runoff is inadvisable. Constructed wetlands in combination with other structures including settlement trenches and ponds should be considered as an alternative treatment option.

First phase of macroinvertebrate repopulation of Lake Orta (Buccione Basin) after liming

The research described here was performed during 1993 and 1994 in the context of studies on the recovery of Lake Orta from acidification after the liming conducted from May 1989 to June 1990. The causes of the pollution were due to the oxidation of ammonium sulphate discharged from a factory producing rayon by a cupro-ammoniacal method and to the loads of heavy metals (Cu, Cr, Ni, Zn) derived from plating factories. One year after liming, an increase in pH and a marked decrease in metal concentrations were observed, and as a consequence some qualitative and quantitative changes were observed in 1992-93 in the planctonic communities and in the littoral macrobenthic fauna. This paper presents qualitative and quantitative data on macrobenthos collected along a transect between the littoral and the maximal depth in the Buccione Basin, which was directly affected by the effluents of the rayon factory. The data revealed some quantitative repopulation of this community, especially along the littoral. Qualitatively, however, the macrobenthos was still quite poor, consisting essentially of Oligochaeta and Diptera Chironomidae. The former were rare and mainly represented by Naididae between 15 and 22 m, while the Tubificidae were well represented in the littoral and the profundal zones. As regards the Chironomidae, the genera Procladius and Chironomus gr. thummi extended as far as the maximum depth, while others, such as Ablabesmyia, Parakiefferiella bathophila and Dicrotendipes gr. nervosus were mostly distributed in the littoral layers. Among the other taxonomic groups only the Trichoptera and the Diptera Ceratopogonidae were quantitatively significant. However, many systematic entities typical of the less polluted Italian subalpine lakes are still absent. In fact, the colonisation of Lake Orta by macrobenthic organisms is still influenced by the increased concentrations of heavy metals in the sediment precipitated from the water column. The research included analysis of lake water and sediments chemistry to obtain information on the trophic level of the environment.

Alkalinity generation and metals retention in a successive alkalinity producing system

Alkalinity generation and metals retention were evaluated during the initial year of operation of a treatment wetland, consisting of four 185 m2 inseries cells comprised of alternating vertical-flow anaerobic substrate wetlands (VFs) and surface-flow aerobic settling ponds (SFs). The substrate in the VFs consists of spent mushroom substrate (SMS) and limestone gravel, supplemented with hydrated fly ash in a 20∶10∶1 ratio by volume. Approximately 15±4 L/min of acid mine drainage (AMD) from an abandoned underground coal mine in southeastern Oklahoma, USA, was directed to the system in October 1998 (mean influent water quality: 660 mg L−1 net acidity as CaCO3 eq., pH 3.4, 215 mg L−1 total Fe, 36 mg L−1 Al, 14 mg L−1 Mn, and 1000 mg L−1 SO4 −2). Flow through the first VF resulted in substantial increases in alkalinity, decreased metal concentrations and circumneutral pH. 258±84 mg L−1 of alkalinity was produced in the first VF by a combination of processes. Final discharge waters were net alkaline on all sampling dates (mean net alkalinity=136 mg L−1). Total Fe and Al concentrations decreased significantly from 216±45 to 44±28 mg L−1 and 36±6.9 to 1.29±4.4 mg L−1, respectively. Manganese concentrations did not change significantly in the first two cells, but decreased significantly in the second two cells. Mean acidity removal rates in the first VF (51 g m−2 day−1) were similar to those previously reported.