Occurrence of arsenic in core sediments and groundwater in the Chapai-Nawabganj District, northwestern Bangladesh

Groundwater and core sediments of two boreholes (to a depth of 50 m) from the Chapai-Nawabganj area in northwestern Bangladesh were collected for arsenic concentration and geochemical analysis. Groundwater arsenic concentrations in the uppermost aquifer (10-40 m of depth) range from 2.8 μg L⁻¹ to 462.3 μg L⁻¹. Groundwater geochemical conditions change from oxidized to successively more reduced, higher As concentration with depth. Higher sediment arsenic levels (55 mg kg⁻¹) were found within the upper 40 m of the drilled core samples. X-ray absorption near-edge structure spectroscopy was employed to elucidate the arsenic speciation of sediments collected from two boreholes. Environmental scanning electron microscopy and transmission X-ray microscopy were used to investigate the characteristics of FeOOH in sediments which adsorb arsenic. In addition, a pH-Eh diagram was drawn using the Geochemist's Workbench (GWB) software to elucidate the arsenic speciation in groundwater. The dominant groundwater type is Ca-HCO₃ with high concentrations of As, Fe and Mn but low levels of NO₃⁻ and SO₄²⁻. Sequential extraction analysis reveals that Mn and Fe hydroxides and organic matter are the major leachable solids carrying As. High levels of arsenic concentration in aquifers are associated with fine-grained sediments. Fluorescent intensities of humic substances indicate that both groundwater and sediments in this arsenic hotspot area contain less organic matter compared to other parts of Bengal basin. Statistical analysis clearly shows that As is closely associated with Fe and Mn in sediments while As is better correlated with Mn in groundwater. These correlations along with results of sequential leaching experiments suggest that reductive dissolution of MnOOH and FeOOH mediated by anaerobic bacteria represents an important mechanism for releasing arsenic into the groundwater.     

Controlling soluble iron and manganese in a water-supply reservoir using hypolimnetic oxygenation

Soluble metals such as iron (Fe) and manganese (Mn) often reach problematic levels in water-supply reservoirs during summer stratification following the onset of hypolimnetic hypoxia. The behavior of soluble and particulate Fe and Mn was studied following the installation of a hypolimnetic oxygenation system in Carvins Cove Reservoir, a water-supply impoundment managed by the Western Virginia Water Authority. During oxygenation, manganese concentrations were very low in the bulk hypolimnion (<0.05 mg l⁻¹), but high concentrations (>2.0 mg l⁻¹) were still observed in the benthic region close to the sediment, despite near-sediment dissolved oxygen concentrations in excess of 5.0 mg l⁻¹. Oxygenation appears to affect the location of the oxic/anoxic boundary sufficiently to restrict substantial transport of soluble Mn to the bulk water of the hypolimnion. However, the position of the oxic/anoxic boundary was not uniformly affected along the reservoir bottom, allowing horizontal transport of soluble Mn from higher elevations in contact with hypoxic sediments. During one summer, when the oxygen system was turned off for a month, the soluble Mn in the bulk hypolimnion increased substantially. Oxygen concentrations were quickly restored after the system was turned back on, but elevated levels of soluble Mn persisted until the sedimentation rate of detritus through the hypolimnion increased. When operated without interruption, the oxygenation system was able to reduce the bulk average hypolimnion soluble Mn concentration by up to 97%, indicating that source water control of soluble Mn and Fe can be accomplished with hypolimnetic oxygenation in water-supply reservoirs.     

Temporal variations in arsenic uptake by rice plants in Bangladesh: The role of iron plaque in paddy fields irrigated with groundwater

The transfer of arsenic to rice grains is a human health issue of growing relevance in regions of southern Asia where shallow groundwater used for irrigation of paddy fields is elevated in As. In the present study, As and Fe concentrations in soil water and in the roots of rice plants, primarily the Fe plaque surrounding the roots, were monitored during the 4-month growing season at two sites irrigated with groundwater containing ∼ 130 μg l^− 1 As and two control sites irrigated with water containing < 15 μg l^− 1 As. At both sites irrigated with contaminated water, As concentrations in soil water increased from < 10 μg l^− 1 to > 1000 μg l^− 1 during the first five weeks of the growth season and then gradually declined to < 10 μg l^− 1 during the last five weeks. At the two control sites, concentrations of As in soil water never exceeded 40 µg l^− 1. At both contaminated sites, the As content of roots and Fe plaque rose to 1000-1500 mg kg^− 1 towards the middle of the growth season. It then declined to ∼ 300 mg kg^− 1 towards the end, a level still well above As concentration of ∼ 100 mg kg^− 1 in roots and plaque measured throughout the growing season at the two control sites. These time series, combined with simple mass balance considerations, demonstrate that the formation of Fe plaque on the roots of rice plants by micro-aeration significantly limits the uptake of As by rice plants grown in paddy fields. Large variations in the As and Fe content of plant stems at two of the sites irrigated with contaminated water and one of the control sites were also recorded. The origin of these variations, particularly during the last month of the growth season, needs to be better understood because they are likely to influence the uptake of As in rice grains.     

Heavy metals: confounding factors in the response of New Zealand freshwater fish assemblages to natural and anthropogenic acidity

Acidification of freshwaters is a global phenomenon, occurring both through natural leaching of organic acids and through human activities from industrial emissions and mining. The West Coast of the South Island, New Zealand, has both naturally acidic and acid mine drainage (AMD) streams enabling us to investigate the response of fish communities to a gradient of acidity in the presence and absence of additional stressors such as elevated concentrations of heavy metals. We surveyed a total of 42 streams ranging from highly acidic (pH 3.1) and high in heavy metals (10 mg L⁻¹ Fe; 38 mg L⁻¹ Al) to circum-neutral (pH 8.1) and low in metals (0.02 mg L⁻¹ Fe; 0.05 mg L⁻¹ Al). Marked differences in pH and metal tolerances were observed among the 15 species that we recorded. Five Galaxias species, Anguilla dieffenbachii and Anguillaaustralis were found in more acidic waters (pH< 5), while bluegill bullies (Gobiomorphus hubbsi) and torrentfish (Cheimarrichthys fosteri) were least tolerant of low pH (minimum pH 6.2 and 5.5, respectively). Surprisingly, the strongest physicochemical predictor of fish diversity, density and biomass was dissolved metal concentrations (Fe, Al, Zn, Mn and Ni) rather than pH. No fish were detected in streams with dissolved metal concentrations > 2.7 mg L⁻¹ and nine taxa were only found in streams with metal concentrations < 1 mg L⁻¹. The importance of heavy metals as critical drivers of fish communities has not been previously reported in New Zealand, although the mechanism of the metal effects warrants further study. Our findings indicate that any remediation of AMD streams which seeks to enable fish recolonisation should aim to improve water quality by raising pH above ≈ 4.5 and reducing concentrations of dissolved Al and Fe to < 1.0 mg L⁻¹.     

Assessment of arsenic exposure from groundwater and rice in Bengal Delta Region, West Bengal, India

Arsenic (As) induced identifiable health outcomes are now spreading across Indian subcontinent with continuous discovery of high As concentrations in groundwater. This study deals with groundwater hydrochemistry vis-à-vis As exposure assessment among rural population in Chakdaha block, West Bengal, India. The water quality survey reveals that 96% of the tubewells exceed WHO guideline value (10 μg/L of As). The groundwaters are generally anoxic (−283 to −22 mV) with circum-neutral pH (6.3 to 7.8). The hydrochemistry is dominated by HCO₃⁻ (208 to 440 mg/L), Ca²⁺ (79 to 178 mg/L) and Mg²⁺ (17 to 45 mg/L) ions along with high concentrations of As_T (As total, below detection limit to 0.29 mg/L), Fe_T (Fe total, 1.2 to 16 mg/L), and Fe(II) (0.74 to 16 mg/L). The result demonstrates that Fe(II)-Fe(III) cycling is the dominant process for the release of As from aquifer sediments to groundwater (and vice versa), which is mainly controlled by the local biogeochemical conditions. The exposure scenario reveals that the consumption of groundwater and rice are the major pathways of As accumulation in human body, which is explained by the dietary habit of the surveyed population. Finally, regular awareness campaign is essential as part of the management and prevention of health outcomes.     

An initial study to assess the use of geological parent materials to predict the Se concentration in overlying soils and in five staple foodstuffs produced on them in Scotland

Evidence suggests that dietary-intakes of the essential element selenium have fallen in Scotland in recent years, due to changing sources of bread-making wheat. The Scottish environment is thought to be Se-poor due to the geology and climate. This initial study assessed whether geological parent-materials could be used to predict relatively high and low soil-Se areas in Scotland and whether differences in soil-Se were reflected in foodstuff-Se produced on them. Samples (n = 8 per farm) of wheat, calabrese (broccoli), potato, beef-steak, milk, cattle pasture (grass) and soil were collected from pairs of farms (one in each high/low predicted Se area (PSA)). Potatoes and soils were collected from a further 34 farms in high/low PSAs to assess a greater geographical zone. Total soil-Se ranged from 0.115 to 0.877 mg kg^-1 but most samples (90%) could be classed as Se-deficient (< 0.6 mg kg⁻¹), irrespective of PSA. Total soil-Se was significantly higher (p < 0.05) in the high than in the low PSAs as expected; however, the difference between the two was small (mean 0.48 and 0.37 mg kg⁻¹, respectively). Water-soluble soil-Se (6.69 to 26.78 μg kg⁻¹) concentrations were not significantly different between the two PSAs (p = 0.71). Soil loss-on-ignition (indicating organic matter content) correlated significantly with total and water-soluble soil-Se (p < 0.001) and exerted a greater control than parent-material on soil-Se. Significant differences between the PSAs for beef-Se (p < 0.001), wheat-Se (p < 0.001), calabrese-Se (p < 0.01) and beef-farm grass-Se (p < 0.05) indicated partial success of the parent-material soil-Se prediction. However, only wheat-Se (p < 0.001) and potato-Se (p < 0.001) correlated significantly with total soil-Se. The results suggest that soil-Se concentrations in the main agricultural areas of Scotland are generally low. Given the low Se concentrations also reported in the food commodities; further investigations may be warranted to fully characterise the Se-status of Scottish produce and dietary-Se intakes in Scotland.     

Groundwater quality in Scotland: major ion chemistry of the key groundwater bodies

Groundwater in Scotland is, for the most part, weakly to moderately mineralised and dominated by the Ca and HCO3 ions. The aquifer systems are almost entirely unconfined and most groundwater remains in contact with oxygen; some reducing groundwaters occur in deeper isolated cracks and joints within the many fractured bedrock aquifers such as Devonian sandstones. Groundwater depleted in oxygen is also common in the Coal Measures in the Midland Valley as a direct result of past coal and oil shale mining, when iron and other metals are taken into solution as the abandoned mine workings are allowed to flood. Low pH groundwaters are rare but do occur where calcite is absent in some basement rocks. Marine intrusion of coastal aquifers occurs locally in East Lothian and parts of Morayshire. Deeper circulating groundwaters are responsible for some of the more exotic spa waters, notably at Bridge of Earn near Perth. Nitrate contamination of groundwater is increasing in some areas, and is most prevalent in the south of Scotland. The Devonian aquifer in Fife and parts of the Permian sandstone aquifers of south-west Scotland are the worst affected.     

Nitrogen and phosphorus removal from an abattoir wastewater in a SBR with aerobic granular sludge

The formation and performance of granular sludge was studied in an 8 l sequencing batch reactor (SBR) treating an abattoir (slaughterhouse) wastewater. Influent concentrations averaged 1520 mg l⁻¹ volatile suspended solids (VSS), 7685 mg l⁻¹ Chemical oxygen demand (COD), 1057 mg l⁻¹ total kjeldahl nitrogen (TKN), 217 mg l⁻¹ total P. The COD loading was 2.6 kg m⁻³ d⁻¹. The SBR was seeded with flocculating sludge from a SBR with an 1 h settle time, but granules developed within 4 days by reducing the settle time to 2 min. The SBR cycle also had 120 min mixed (anaerobic) fill, 220 min aerated react, and 18 min draw/idle. The granules had a mean diameter of 1.7 mm, a specific gravity of 1.035, a density of 62 g VSS l⁻¹, a zone settling velocity (ZSV) of 51 m h⁻¹, and a sludge volume index (SVI) of 22 ml g⁻¹. Without optimizing process conditions, removal of COD and P were over 98%, and removal of N and VSS were over 97%. Nitrification and denitrification occurred simultaneously during react. The results indicate that conventional SBRs treating wastewaters with flocculating sludge can be converted to granular SBRs by reducing the settle time.     

Ecotoxicological assessment of a polyelectrolyte flocculant

Flocculant blocks are commonly used as a component of (passive) water treatment systems to reduce suspended sediment loads in the water column. This study investigated the potential for aquatic biological impacts of a flocculant block formulation that contained an anionic polyacrylamide (PAM) active ingredient and a polyethylene glycol (PEG) based carrier. The toxicity of the whole flocculant block was assessed and the individual components of the block were also tested separately. Five Northern Australian tropical freshwater species (i.e. Chlorella sp. Lemna aequinoctialis, Hydra viridissima, Moinodaphnia macleayi and Mogurnda mogurnda) were exposed to a range of concentrations of the whole flocculant block, and of the individual PAM and PEG components. The concentration of Total Organic Carbon (TOC) in solution was used to provide a measure of the total amount of PAM and PEG present. An extremely wide range of toxic responses were found, with the flocculant blocks being essentially non-toxic to the duckweed, fish and algae (IC₅₀ > 1880 mg l⁻¹ C TOC, IC₁₀ > 460 mg l⁻¹ C TOC), slightly toxic to the hydra (IC₅₀ = 610-2180 mg l⁻¹ C TOC, IC₁₀ = 80-60 mg l⁻¹ C TOC) and significantly more toxic to the cladoceran (IC₅₀ = 10 mg l⁻¹ C TOC, IC₁₀ = 4 mg l⁻¹ C TOC). More detailed investigation of the two components indicated that the PAM was the primary “toxicant” in the flocculant blocks. Derived Protective Concentrations (PCs) for the flocculant blocks, expressed as equivalent TOC concentrations, were found to be lower than typically measured natural environmental concentrations of TOC. It will thus be possible to use TOC as measure of the concentration of PAM only in those situations where lower levels of ecosystem protection (i.e. higher PCs) are applicable.     

Environmental impact of mining activities in the Lousal area (Portugal): chemical and diatom characterization of metal-contaminated stream sediments and surface water of Corona stream

Lousal mine is a typical “abandoned mine” with all sorts of problems as consequence of the cessation of the mining activity and lack of infrastructure maintenance. The mine is closed at present, but the heavy metal enriched tailings remain at the surface in oxidizing conditions. Surface water and stream sediments revealed much higher concentrations than the local geochemical background values, which the “Contaminated Sediment Standing Team” classifies as very toxic. High concentrations of Cu, Pb, Zn, As, Cd and Hg occurred within the stream sediments downstream of the tailings sites (up to: 817 mg kg⁻¹ As, 6.7 mg kg⁻¹ Cd, 1568 mg kg⁻¹ Cu, 1059 mg kg⁻¹ Pb, 82.4 mg kg⁻¹ Sb, 4373 mg kg⁻¹ Zn). The AMD waters showed values of pH ranging from 1.9 to 2.9 and concentrations of 9249 to 20,700 mg L⁻¹ SO₄⁻², 959 to 4830 mg L⁻¹ Fe and 136 to 624 mg L⁻¹ Al. Meanwhile, the acid effluents and mixed stream waters also carried high contents of SO₄^2−, Fe, Al, Cu, Pb, Zn, Cd, and As, generally exceeding the Fresh Water Aquatic Life Acute Criteria. Negative impacts in the diatom communities growing at different sites along a strong metal pollution gradient were shown through Canonical Correspondence Analysis: in the sites influenced by Acid Mine Drainage (AMD), the dominant taxon was Achnanthidium minutissimum. However, Pinnularia acoricola was the dominant species when the environmental conditions were extremely adverse: very low pH and high metal concentrations (sites 2 and 3). Teratological forms of Achnanthidium minutissimum (Kützing) Czarnecki, Brachysira vitrea (Grunow) Ross in Hartley, Fragilaria rumpens (Kützing) G. W. F. Carlson and Nitzschia hantzschiana Rabenhorst were found. A morphometric study of B. vitrea showed that a decrease in size was evident at the most contaminated sites. These results are evidence of metal and acidic pollution.     

Effect of COD/SO(4)(2-) ratio and sulfide on thermophilic (55 degrees C) sulfate reduction during the acidification of sucrose at pH 6

This study investigated the effect of the COD/SO₄²⁻ ratio (4 and 1) and the sulfide concentration on the performance of thermophilic (55 °C) acidifying (pH 6) upflow anaerobic sludge bed reactors fed with sucrose at an organic loading rate of 4.5 g COD l_reactor⁻¹ day⁻¹. Sulfate reduction efficiencies amounted to 65% and 25-35% for the COD/SO₄²⁻ ratios of 4 and 1, respectively. Acidification was complete at all the tested conditions and the electron flow was similar at the two COD/SO₄²⁻ ratios applied. The stepwise decrease of the sulfide concentrations in the reactors with a COD/SO₄²⁻ ratio of 1 by N₂ stripping caused an immediate stepwise increase in the sulfate reduction efficiencies, indicating a reversible inhibition by sulfide. The degree of reversibility was, however, affected by the growth conditions of the sludge. Acidifying sludge pre-grown at pH 6, at a COD/SO₄²⁻ ratio of 9 and exposed for 150 days to 115 mg l⁻¹ sulfide, showed a slower recovery from the sulfide inhibition than a freshly harvested sludge from a full scale treatment plant (pH 7 and COD/SO₄²⁻=9.5) exposed for a 70 days to 200 mg l⁻¹ sulfide. In the latter case, the decrease of the sulfide concentration from 200 to 45 mg l⁻¹ (35 mg l⁻¹ undissociated sulfide) by N₂ stripping caused an immediate increase of the sulfate reduction efficiency from 35% to 96%.     

Performance of a passive treatment system for net-acidic coal mine drainage over five years of operation

A full-scale passive treatment system (PTS) was commissioned in 2003 to treat two net-acidic coal mine water discharges in the Durham coalfield, UK. The principal aim of the PTS was to decrease concentrations of iron (< 177 mg L⁻¹) and aluminium (< 85 mg L⁻¹) and to increase pH (> 3.2) and alkalinity (≥ 0 mg L⁻¹ CaCO₃ eq). Secondary objectives were to decrease zinc (< 2.8 mg L⁻¹), manganese (< 20.5 mg L⁻¹) and sulfate (< 2120 mg L⁻¹). Upon treatment, water qualities were improved by 84% in the case of Fe, 87% Al, 83% acidity, 51% Zn, 23% Mn and 29% SO₄²⁻. Alkalinity (74%) and pH (95% as H⁺) were increased. Area adjusted removal rates (Fe = 1.49 ± 0.66 g d⁻¹ m⁻²; acidity = 6.7 ± 4.9 g d⁻¹ m⁻²) were low compared to design criteria, mainly due to load limitation. Disregarding seasonality effects, acidity removal and effluent pH were stable over time. A substantial temporal decrease in calcium and alkalinity generation suggests that limestone is increasingly armoured. Once pH is no longer buffered by the carbonate system, metals could be remobilized, putting treatment efficiency at risk.     

Changes in water quality of the River Frome (UK) from 1965 to 2009: is phosphorus mitigation finally working?

The water quality of the River Frome, Dorset, southern England, was monitored at weekly intervals from 1965 until 2009. Determinands included phosphorus, nitrogen, silicon, potassium, calcium, sodium, magnesium, pH, alkalinity and temperature. Nitrate-N concentrations increased from an annual average of 2.4 mg l^− 1 in the mid to late 1960s to 6.0 mg l^− 1 in 2008-2009, but the rate of increase was beginning to slow. Annual soluble reactive phosphorus (SRP) concentrations increased from 101 μg l^− 1 in the mid 1960s to a maximum of 190 μg l^− 1 in 1989. In 2002, there was a step reduction in SRP concentration (average = 88 μg l^− 1 in 2002-2005), with further improvement in 2007-2009 (average = 49 μg l^− 1), due to the introduction of phosphorus stripping at sewage treatment works. Phosphorus and nitrate concentrations showed clear annual cycles, related to the timing of inputs from the catchment, and within-stream bioaccumulation and release. Annual depressions in silicon concentration each spring (due to diatom proliferation) reached a maximum between 1980 and 1991, (the period of maximum SRP concentration) indicating that algal biomass had increased within the river. The timing of these silicon depressions was closely related to temperature. Excess carbon dioxide partial pressures (EpCO₂) of 60 times atmospheric CO₂ were also observed through the winter periods from 1980 to 1992, when phosphorus concentration was greatest, indicating very high respiration rates due to microbial decomposition of this enhanced biomass. Declining phosphorus concentrations since 2002 reduced productivity and algal biomass in the summer, and EpCO₂ through the winter, indicating that sewage treatment improvements had improved riverine ecology. Algal blooms were limited by phosphorus, rather than silicon concentration. The value of long-term water quality data sets is discussed. The data from this monitoring programme are made freely available to the wider science community through the CEH data portal (http://gateway.ceh.ac.uk/).     

Sources and controls for the mobility of arsenic in oxidizing groundwaters from loess-type sediments in arid/semi-arid dry climates - evidence from the Chaco-Pampean plain (Argentina)

In oxidizing aquifers, arsenic (As) mobilization from sediments into groundwater is controlled by pH-dependent As desorption from and dissolution of mineral phases. If climate is dry, then the process of evaporative concentration contributes further to the total concentration of dissolved As. In this paper the principal As mobility controls under these conditions have been demonstrated for Salí River alluvial basin in NW Argentina (Tucumán Province; 7000 km²), which is representative for other basins or areas of the predominantly semi-arid Chaco-Pampean plain (1,000,000 km²) which is one of the world’s largest regions affected by high As concentrations in groundwater. Detailed hydrogeochemical studies have been performed in the Salí River basin where 85 groundwater samples from shallow aquifers (42 samples), deep samples (26 samples) and artesian aquifers (17 samples) have been collected. Arsenic concentrations range from 11.4 to 1660 μg L⁻¹ leaving 100% of the investigated waters above the provisional WHO guideline value of 10 μg L⁻¹. A strong positive correlation among As, F, and V in shallow groundwaters was found. The correlations among those trace elements and U, B and Mo have less significance. High pH (up to 9.2) and high bicarbonate (HCO₃) concentrations favour leaching from pyroclastic materials, including volcanic glass which is present to 20-25% in the loess-type aquifer sediments and yield higher trace element concentrations in groundwater from shallow aquifers compared to deep and artesian aquifers. The significant increase in minor and trace element concentrations and salinity in shallow aquifers is related to strong evaporation under semi-arid climatic conditions. Sorption of As and associated minor and trace elements (F, U, B, Mo and V) onto the surface of Fe-, Al- and Mn-oxides and oxi-hydroxides, restricts the mobilization of these elements into groundwater. Nevertheless, this does not hold in the case of the shallow unconfined groundwaters with high pH and high concentrations of potential competitors for adsorption sites (HCO₃, V, P, etc.). Under these geochemical conditions, desorption of the above mentioned anions and oxyanions occurs as a key process for As mobilization, resulting in an increase of minor and trace element concentrations. These geochemical processes that control the concentrations of dissolved As and other trace elements and which determine the groundwater quality especially in the shallow aquifers, are comparable to other areas with high As concentrations in groundwater of oxidizing aquifers and semi-arid or arid climate, which are found in many parts of the world, such as the western sectors of the USA, Mexico, northern Chile, Turkey, Mongolia, central and northern China, and central and northwestern Argentina.     

Significance and interspecific variability of accumulated trace metal concentrations in Antarctic benthic polychaetes

Trace metals were analysed in polychaetes collected on Polarstern cruise ANT XXI/2 (2003/04) to the Weddell Sea. Pb concentrations were largely less than 1.3 mg kg⁻¹ DW in all samples analysed. Statistical results indicate that the accumulated Cd, Cu and Zn concentrations are related to the feeding guild to which the animals are belonging. Relatively low Cd and Cu concentrations are found in macrophagous carnivores and relatively high concentrations in microphagous detritus feeders. The relationship between Zn concentrations and the feeding guilds of polychaetes is reverse. Cd concentrations range from (median values and interquantile ranges in brackets) 2.6 (1.5-3.2) mg kg⁻¹ DW in the carnivorous Trypanosyllis gigantea to 133 (37-176) mg kg⁻¹ in the microphagous detritus feeder Lanicides bilobata; Cu concentrations from 16 (11-19) mg kg⁻¹ in the carnivorous Antarctinoe spicoides to 40 (23-68) mg kg⁻¹ in the microphagous detritus feeder Phyllocomus crocea and Zn from 89 (69-97) mg kg⁻¹ in the microphagous detritus feeder Isocirrus yungi to 396 (372-404) mg kg⁻¹ in the carnivorous Aglaophamus trissophyllus. Ni is ranging from 3.7 (1.8-6.0) mg kg⁻¹ in Polyeunoa laevis to 34 (20-41) mg kg⁻¹ in A. spicoides, but no significant differences are obvious regarding the feeding guilds. Since information on metals in Antarctic polychaetes is almost completely lacking, our results suggest further studies to clarify the role of feeding in the bioaccumulation of metals in this ecologically important taxonomic group.     

Influence of soil properties on trace element availability and plant accumulation in a Mediterranean salt marsh polluted by mining wastes: implications for phytomanagement

The aims of this study were to determine the factors which control metal and As phytoavailability in the different microenvironments (Sand Dunes, Salt Flat, Dry River and Shrubs) present at a Mediterranean salt marsh polluted by mining wastes. We performed a field study following a plot sampling survey. The analyses of soil parameters (pH, electrical conductivity (EC), organic carbon contents, etc.), total metal and As concentrations and their phytoavailability assessed with EDTA were related to each microenvironment and the corresponding plant species uptake. The averages of pH and EC were slightly alkaline (pH ≈ 7.5) and saline (≈ 2.2 to 17.1 dS m⁻¹) respectively. The soil samples from the Salt Flat subzone showed the highest metal concentrations (e.g. 51 mg kg⁻¹ Cd, 11,600 mg kg⁻¹ Pb) while for As, the highest concentrations occurred in the Dry River (380 mg kg⁻¹ As). The total metal and EDTA-extractable concentrations occurred as it follows: Salt Flat > Dry River > Degraded Dunes > Shrubs. In relation to plant metal and As accumulation, the highest root concentrations were obtained in the species from the Salt Flat subzone: ~ 17 mg kg⁻¹ As, ~ 620 mg kg⁻¹ Pb, for both, Juncus maritimus and Arthrocnemum macrostachyum. However the highest metal and As shoot concentrations occurred in species from the Sand Dunes: ~ 23 mg kg⁻¹ As ~ 270 mg kg⁻¹ Pb for Dittrichia viscosa; ~ 23 mg kg⁻¹ As, ~ 390 mg kg⁻¹ Zn for Crucianella maritima. The occurrence of edaphic gradients including salinity and texture determined the vegetation distribution. However, it cannot be concluded that there was a disturbance due to metal(loid)s soil concentrations in terms of vegetation composition except in the Degraded Dunes and Dry River. The higher EDTA-extractable concentrations were coincidental with the most saline soils but this did not result in higher metal(loid)s plant accumulation.     

The intake of lead and associated metals by sheep grazing mining-contaminated floodplain pastures in mid-Wales, UK: II. Metal concentrations in blood and wool

Sheep grazing metal-contaminated floodplain pastures across mid-Wales ingest high concentrations of lead (Pb) in vegetation and directly in the form of soil. Sheep whole blood analysis indicated that Pb concentrations can be significantly elevated for animals grazing contaminated sites: in winter/spring, a median blood concentration of 147 µg Pb l^− 1 was found at the location with the highest soil enrichment of this metal compared to only 26 µg Pb l^− 1 for the control flock. There was within-flock variability in blood-Pb concentration, and overlap between blood-Pb ranges in animals grazing control and contaminated sites, although use of the Kruskal-Wallis H test established a number of significant (P < 0.05) differences between the blood-Pb content of flocks grazing the various study locations. Despite total daily intakes of up to 723 mg Pb d^− 1, only one individual sheep showed a blood-Pb content above the ‘normal safe’ concentration of 250 µg l^− 1. Blood and wool analyses were found to have limited value for the diagnosis of environmental exposure to Pb, and further consideration of metal accumulation in offal, bone and muscle tissue is recommended.     

Mineralogical and geochemical controls of arsenic speciation and mobility under different redox conditions in soil, sediment and water at the Mokrsko-West gold deposit, Czech Republic

Naturally contaminated soil, sediment and water at the Mokrsko-West gold deposit, Central Bohemia, have been studied in order to determine the processes that lead to release of As into water and to control its speciation under various redox conditions. In soils, As is bonded mainly to secondary arseniosiderite, pharmacosiderite and Fe oxyhydroxides and, rarely, to scorodite; in sediments, As is bonded mainly to Fe oxyhydroxides and rarely to arsenate minerals.The highest concentrations of dissolved As were found in groundwater (up to 1141 μg L^− 1), which mostly represented a redox transition zone where neither sulphide minerals nor Fe oxyhydroxide are stable. The main processes releasing dissolved As in this zone are attributed to the reductive dissolution of Fe oxyhydroxides and arsenate minerals, resulting in a substantial decrease in their amounts below the groundwater level. Some shallow subsurface environments with high organic matter contents were characterized by reducing conditions that indicated a relatively high amount of S^− 2,0 in the solid phase and a lower dissolved As concentration (70-80 μg L^− 1) in the pore water. These findings are attributed to the formation of Fe(II) sulphides with the sorbed As. Under oxidizing conditions, surface waters were undersaturated with respect to arsenate minerals and this promoted the dissolution of secondary arsenates and increased the As concentrations in the water to characteristic values from 300 to 450 μg L^− 1 in the stream and fishpond waters. The levels of dissolved As(III) often predominate over As(V) levels, both in groundwaters and in surface waters. The As(III)/As(V) ratio is closely related to the DOC concentration and this could support the assumption of a key role of microbial processes in transformations of aqueous As species as well as in the mobility of As.     

Effects of lanthanum and lanthanum-modified clay on growth, survival and reproduction of Daphnia magna

The novel lanthanum-modified clay water treatment technology (Phoslock^®) seems very promising in remediation of eutrophied waters. Phoslock^® is highly efficient in stripping dissolved phosphorous from the water column and in intercepting phosphorous released from the sediments. The active phosphorous-sorbent in Phoslock^® is the Rare Earth Element lanthanum. A leachate experiment revealed that lanthanum could be released from the clay, but only in minute quantities of 0.13-2.13 μg l⁻¹ for a worst-case Phoslock^® dosage of 250 mg l⁻¹. A life-history experiment with the zooplankton grazer Daphnia magna revealed that lanthanum, up to the 1000 μg l⁻¹ tested, had no toxic effect on the animals, but only in medium without phosphorous. In the presence of phosphorous, rhabdophane (LaPO₄ · nH₂O) formation resulted in significant precipitation of the food algae and consequently affected life-history traits. With increasing amounts of lanthanum, in the presence of phosphate, animals remained smaller, matured later, and reproduced less, resulting in lower population growth rates. Growth rates were not affected at 33 μg La l⁻¹, but were 6% and 7% lower at 100 and 330 μg l⁻¹, respectively, and 20% lower at 1000 μg l⁻¹. A juvenile growth assay with Phoslock^® tested in the range 0-5000 mg l⁻¹, yielded EC₅₀ (NOEC) values of 871 (100) and 1557 (500) mg Phoslock^® l⁻¹ for weight and length based growth rates, respectively. The results of this study show that no major detrimental effects on Daphnia are to be expected from Phoslock^® or its active ingredient lanthanum when applied in eutrophication control.     

Spatial and temporal trends in nitrate concentrations in the River Derwent, North Yorkshire, and its need for NVZ status

Long-term spatial and temporal variations in nitrate-N concentrations along the River Derwent have been examined using Environment Agency data to investigate the relative importance of impacts of atmospheric N deposition, land use, and changes in management. Where moorland and rough grazing dominate upstream of Forge Valley and Malton, over the 20 years since 1988 mean nitrate-N concentrations were initially increasing significantly, but are now levelling off, with peaks at ca. 4.5 mg N l⁻¹. As expected in a catchment in a nitrate vulnerable zone (NVZ), more agricultural land use increases mean nitrate concentrations and the occurrence of distinct winter maxima, though the latter have become markedly less pronounced since 2001. It is suggested that this improvement is a combined effect of imposition of NVZ designation in the lower reaches in 2002, animal number declines associated with the Foot & Mouth outbreak in the region in 2001, and the impact of farmers' responses to increasing fertilizer prices and to beneficial pollutant mineral N inputs from the atmosphere. Minima in nitrate-N concentrations in summer have become much less pronounced over the past decade and are typically ca. 60% higher in concentration than a decade earlier. This probably is attributable to the effects of pollutant-N leaching to depths in soil below the rooting zone when near surface biotic uptake is low in winter. The resultant N mineralization in summer enhances summer nitrate leaching. The Derwent is a relatively clean river; however, its entire catchment was designated justifiably as a NVZ in January 2009, apparently based upon a projected 95 percentile nitrate-N concentration > 11.29 mg l^− 1 for 2010 based upon forward projection of data from 1990 to 2004 for Derwent Bridge. A survey of water quality in March 2009 showed that some agricultural areas are still making a significant contribution to the total nitrate level well downstream, at the point responsible for implementation of NVZ status. At 3 of the 29 sites sampled, nitrate concentration exceeded 60 mg l^− 1.