Applied Geochemistry (v.18, #6)

The use of various methods for the study of metal pollution in marine sediments, the case of Euvoikos Gulf, Greece by M Dassenakis; H Andrianos; G Depiazi; A Konstantas; M Karabela; A Sakellari; M Scoullos (781-794).
This study presents the results on heavy metal (Mn, Fe, Cu, Zn) analyses of sediments taken from Euvoikos Gulf, Greece, which is a semi-enclosed system receiving pollution loads from several urban and industrial sources and is affected by a strong tidal current. A sequential extraction schema and two single-step methods were used for the determination of trace metals. The data of the 1997 period are compared with data from previous studies carried out in the authors' laboratory in the area (1980, 1993) using various analytical techniques, in an attempt to evaluate both the evolution of pollution in the area and the effectiveness of analytical methods. It has been confirmed that a significant part of the pollution load remains in coastal localities in the vicinity of the land based pollution sources, whereas there are also some more remote sites where small polluted particles are transported, deposited and accumulated. The sedimentology regime of the area affects the concentration of metals in a rather complex way depending also on its content of carbonates, organic C and clay minerals. The study of sediment cores has indicated elevated metal concentrations in recent surface sediments. On the other hand, some environmentally positive trends were also observed (i.e. the reduction of mobile metals). A systematic monitoring is needed in the marine environment coupled with some reduction in pollution inputs and integrated management on the coastal zone because the overall hydrological characteristics of the area favour its rapid self-restoration.

Simultaneous competitive adsorption of heavy metals by the mineral matrix of tropical soils by Maurı́cio Paulo F. Fontes; Paulo César Gomes (795-804).
Disposal of sewage sludge, composts and industrial wastes onto agricultural lands is commonly and increasingly used in Brazil, potentially adding multi-component heavy metal solutions. Soil organic matter was removed from representative Brazilian soils and the simultaneous competitive adsorption on the mineral matrix of Cr, Ni, Cu, Zn, Cd and Pb was determined. The competition affected the behavior of heavy metal cations in such a way that the soils adsorbed less Ni, Zn and Cd and more Cr, Cu and Pb with increasing total concentrations, regardless of the molar concentration applied. On the other hand, the occupancy of the adsorption complex by the heavy metals was proportional to the relative concentration applied. As the applied concentrations increased Cr, Cu and Pb adsorption increased, while Ni, Zn and Cd adsorption decreased. The maximum adsorption capacity for the heavy metal cations was calculated, with the soils differing markedly. Ultisol and Alfisol soils showed the highest maximum adsorption values, in the order of 50.76 and 64.52 mmol kg−1, whereas some Oxisols showed the lowest values, in the order of 23.92 and 30.86 mmol kg−1. The results suggest that the first two soil types are capable of receiving and holding higher heavy metal loadings compared to the Oxisols, which are more vulnerable to heavy metal contaminant inputs.

The geochemical processes taking place along an 800 km flow line in the non-carbonate Continental Intercalaire aquifer (CI) aquifer in North Africa are described using chemical (major and trace element) and isotopic indicators. The aquifer is hydraulically continuous from the Atlas Mountains in Algeria to the Chotts of Tunisia and the geochemical evidence corroborates this. The highest discharge temperature is 73 °C but silica geothermometry indicates a maximum temperature of 94 °C at depth. Chloride concentrations increase from 200 to 800 mg l−1 and the Br/Cl ratios confirm the dissolution of non-marine evaporites or interstitial waters as the main source of salinity. Fluoride concentrations are low and are likely to be derived from rainfall, recording oscillations in source. Radiocarbon ages, except near outcrop, are at or near detection limits and the δ18O and δ2H values indicate a cooler recharge regime with rainfall having lower primary evaporation than today. This is shown by the fact that mean isotope ratios of CI waters are around 3‰ lighter than the present-day weighted mean value for rain. Major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy, uniform evolution with continuous water-rock interaction takes place along the flow lines, which are only disturbed near the Tunisian Chotts by groundwater converging from additional flow lines. The ageing of the water can also be followed by the smooth increase in several indicator elements such as Li, K and Mn which are least affected by solubility controls. Similarly the influence of marine facies in the Tunisian sector may be recognised by the changing Mg/Ca and higher Br/Cl as well as trace element indicators. The groundwaters are oxidising up to 300 km from outcrop (dissolved O2 has persisted for at least 20 ka) and within this zone the concentrations of several elements forming oxy-anions, such as U and Cr, increase and NO3 remains conservative. Beyond 300 km from outcrop, the groundwaters are reducing and contain high Fe concentrations. The basin contains huge reserves of fresh/brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super-saturation caused during abstraction as well as high concentrations of some harmful elements such as Cr in the oxidising section.

The unmined Coles Hill U deposit of south central Virginia represents a natural setting where U is stabilized by phosphate mineral precipitation in an oxidizing bedrock aquifer. Drill cores from the shallow portion of the deposit preserve a sharp Fe redox front defined by Fe(III) oxide staining. This front is located near a discontinuity in U mineralogy with U(IV) assemblages (e.g. coffinite, uraninite) on the reducing side, and U(VI) assemblages on the oxidizing side. The discontinuity in U mineralogy does not, however, represent a major discontinuity in whole rock U concentrations, with sample groups from both oxidized and reduced sides of the front generally ranging from 500 to 1000 ppm. This observation suggests that the volume of shallow bedrock associated with the deposit has not lost significant amounts of U during the oxidation and incipient chemical weathering. The precipitation of Ba uranyl phosphate (Ba meta-autunite) is responsible for U retention within this zone. Ground waters sampled from the weathered bedrock aquifer associated with the deposit contain less than 15 μg l−1 dissolved U. This suggests that the low solubility of the Ba meta-autunite limits U concentrations to values lower than the US-EPA maximum contaminant level of 30 μg l−1. Ground water speciation and mineral saturation calculations show that, in addition to Eh and pH, the most important factor controlling this U fixation process is the activity ratio of dissolved phosphate to dissolved carbonate. Experimental results suggest that, at the Coles Hill site, the oxidation of U(IV) to U(VI) and subsequent precipitation of uranyl phosphate occurs rapidly (time scale of weeks) relative to ground water transport (e.g. 20 m/a). Furthermore, based on the rate of downward migration of the redox front, it is estimated that the oldest U(VI) phosphate assemblages associated with the Coles Hill U deposit have been stable for up to 150 ka. These observations have important implications for the design and long term performance assessment of phosphate-based stabilization and reactive barrier techniques.

Hydrothermal petroleum in the sediments of the Andaman Backarc Basin, Indian Ocean by M.I Venkatesan; E Ruth; P.S Rao; B.N Nath; B.R Rao (845-861).
Recent sediments of the Andaman Backarc Basin, Indian Ocean, between the Andaman Nicobar islands and the Malay Peninsula have been analyzed for biomarker lipids. Three cores were selected: one each from the fault zone in a deep basin (a graben between two fault systems), another from a location adjacent to the fault, and the third from the topographic high in the rift valley. The molecular composition of the lipid classes (n-alkanes, isoprenoids, alkylbenzenes, alkylcyclohexanes, hopanoids, polycyclic aromatic hydrocarbons, steranes, alcohols, sterols and fatty acids) was examined by gas chromatography (GC) and GC/mass spectrometry to understand the nature and source of the hydrocarbons present and the processes of maturation of organic matter. The data show that the hydrocarbons are of hydrothermal origin, derived from thermal alteration of sedimentary organic matter, consisting of a mixture predominantly of marine-derived components with some terrestrial inputs. Normal alcohols and fatty acids also corroborate the distribution of n-alkanes. The distribution profiles and various parameters computed from the concentration of the target compounds suggest that oxidative reactions and microbial degradation in this environment are insignificant. Triterpane and PAH compositions indicate that the thermal maturity of the bitumen in the samples is comparable to or lower than that found at other hydrothermal regions such as the Northern Juan de Fuca Ridge, Guaymas Basin and Escanaba Trough.

Natural and anthropogenic factors affecting groundwater quality of an active volcano (Mt. Etna, Italy) by A Aiuppa; S Bellomo; L Brusca; W D'Alessandro; C Federico (863-882).
New geochemical data on dissolved major and minor constituents in 276 groundwater samples from Etna aquifers reveal the main processes responsible for their geochemical evolution and mineralisation. This topic is of particular interest in the light of the progressive depletion of water resources and groundwater quality in the area. Multivariate statistical analysis reveal 3 sources of solutes: (a) the leaching of the host basalt, driven by the dissolution of magma-derived CO2; (b) mixing processes with saline brines rising from the sedimentary basement below Etna; (c) contamination from agricultural and urban wastewaters. The last process, highlighted by increased concentrations of SO4, NO3, Ca, F and PO4, is more pronounced on the lower slopes of the volcanic edifice, associated with areas of high population and intensive agriculture. However, this study demonstrates that natural processes (a) and (b) are also very effective in producing highly mineralised waters, which in turn results in many constituents (B, V, Mg) exceeding maximum admissible concentrations for drinking water.

Redistribution of trace metals in a mineralized spodosol due to weathering, Liikavaara, northern Sweden by Björn Öhlander; Jonas Thunberg; Magnus Land; Lars Olof Höglund; Han Quishang (883-899).
The till east of the Liikavaara Östra ore deposit in northern Sweden is in some parts rich in Cu and other sulphide-associated metals. Groundwater flowing in this till has higher concentrations of Cu than groundwater in a reference area where the till has low concentrations of Cu and other metals. To understand the processes that release metals from the mineralized till at Liikavaara into the groundwater, the authors performed a detailed study of the <2 mm fraction of a till profile where the highest metal concentrations in the Liikavaara area occur. The geochemistry and mineralogy of the till were determined, and the soil water was sampled by tension lysimeters. The importance of local diffusion of Cu-bearing airborne dust from the adjacent Aitik mine tailings impoundment was quantified and solid speciation of metals in airborne material was performed by sequential extraction. The results from Liikavaara were compared to results from the reference area. Glacial ice picked up sulphide-rich material from the Liikavaara Östra Cu ore during its flow. This material was deposited in the till east of the ore body when the ice melted. The sulphides have been dissolved in the <2 mm fraction during 8.7 ka of weathering since the glacial ice retreated. After dissolution of the sulphides, Cu was redistributed and secondarily retained in association with Fe-oxyhydroxides and altered biotite. Other sulphide-associated elements such as Co, Ni and Zn show the same pattern in the till profile as Cu, though the concentrations are much lower. Uptake of Cu2+ in the biotite through ion exchange with K+ may be an important mechanism for Cu-enrichment in biotite at Liikavaara. The airborne dust is not the source of Cu in the till. Although the soil water at Liikavaara has higher concentrations of Cu and other metals than the soil water at the reference area, the Cu-concentration is too low for infiltrating soil water to explain the high Cu-concentrations observed in groundwater. The high metal concentrations in the till, of Cu in particular, cause the increased concentrations in the local groundwater. A fluctuating groundwater table washes out Cu and other metals from the till. It is possible that increased Cu concentration in the local groundwater is caused by dissolved organic complexes, or by colloids (<0.45 μm) rich in organic matter and/or Fe-oxyhydroxides.

The Tessier sequential extraction procedure was applied to discrete layers from 9 sediment cores from Dulas Bay, Anglesey. Results provide data on the chemical association of heavy metals (Fe, Mn, Cu, Zn, Cd, and As with major) sedimentary phases, and provide information on changes in metal partitioning associated with the changing physico-chemical conditions encountered during burial. Extremely high concentrations of heavy metals were recorded (e.g. Zn 3000 μg g−1, Cu 2000 μg g−1) and resulting depth profiles clearly indicate the differential behaviour of metals during diagenesis where, with increasing depth, Fe, Mn and Cu become increasingly associated with sulphide phases. Substantial changes in porewater concentrations indicate zones of preferential mobilisation due to sharp alterations in physicochemical conditions. All metals are involved in processes of post depositional diagenetic cycling driven by organic matter degradation and O2 utilisation in thermodynamically favoured sequence, Fe and Mn oxide and oxyhydroxide dissolution act as controlling variables leading to zones of solid phase metal enrichment. Phase equilibria have been calculated to elucidate observed solid phase partitioning at the redox boundary and processes of subsurface sulphide mineral formation.

In this paper, two small but practical case studies are presented that demonstrate the utility of detailed petroleum fingerprinting in investigating known or suspected pipeline releases. The two cases involve: (1) a known release of automotive gasoline from a product pipeline, which was accompanied by an intense fire, which prompted an investigation to determine the source of a peculiar, non-aqueous phase liquid (NAPL) discovered beneath the affected area during the accident’s clean-up and (2) a former trunk line pipeline from an oil field that was suspected as the source of a recently discovered NAPL. The known facts, analytical strategy, petroleum fingerprinting data and results for each case study are presented. Respectively, these cases highlight the utility of detailed petroleum fingerprinting of the diagnostic (1) volatile hydrocarbons comprising gasoline(s) and (2) non-volatile hydrocarbons, including petroleum biomarkers and an extended suite of parent and alkylated polycyclic aromatic hydrocarbons, found in crude oil(s) (and other heavy petroleum products).

The formation of incrustations seriously affects the performance of wells, piezometers and drains. Their economic relevance must not be underestimated. Oxides of Fe(III) represent the most common incrustation type. Their formation via oxidation of dissolved Fe(II) is enhanced at zones of elevated flow velocities. The first, “amorphous” precipitates (ferrihydrite) are thermodynamically unstable and re-crystallise with time to form stable phases, mainly goethite (“ageing”). This transformation involves a decrease of surface area and a simultaneous decrease in reactivity and explains why older incrustations are harder to remove by chemical treatment. During formation, Fe oxide incrustations take up large amounts of trace elements from groundwater. Anions such as phosphate and arsenate dominate over cations. Anions are surface-bound and are mostly expelled with the decrease of surface area during ageing. Cations are probably bound in the crystal structure rather than as sorbed surface species. Only those with large ionic radius are mostly not expelled during ageing. Trace element concentrations influence the rate of transformation and the solubility of Fe oxide incrustations.

The formation of Fe oxide and Mn incrustations seriously affects the performance of wells, piezometers and drains. Chemical dissolution can be a valuable tool for their removal. Standardized dissolution experiments were performed to study the efficiency of different chemicals on synthetic Fe oxides. They showed that buffered Na-dithionite and oxalic acid are the most effective agents, followed by ascorbic, malonic and sulfamic acid. Citric acid and especially NaOH proved to be ineffective. As expected, a strong dependency of the dissolution rates on the surface area of the individual Fe oxides was observed, goethite being far less soluble than ferrihydrite. In many cases linear, zeroeth order rate laws were sufficient to model the measured dissolution curves. In other cases more advanced model approaches had to be applied. Sometimes different models were equally well suited to describe a dissolution process.