Controls on microbial mercury transformations in contaminated sediments downstream of the Idrija mercury mine (West Slovenia) to the Gulf of Trieste (northern Adriatic)

Purpose

Concentrations and transformations of mercury were measured in river, estuarine, and marine sediments to determine factors affecting the fate of mercury entering the northern Adriatic Sea.

Materials and methods

Radiotracer methodology was used to compare rates of mercury methylation (²⁰³Hg), MeHg demethylation (¹⁴C), and sulfate reduction (³⁵S) in sediment depth profiles to concentrations of total and dissolved mercury species in the lower freshwater region of the Isonzo River, the coastal lagoons, and in the Gulf of Trieste, northern Adriatic Sea.

Results and discussion

Mercury was readily methylated and demethylated in all sediments, but the relative activity of these processes varied greatly with location. Methylation activity increased greatly from freshwater to the marine regions; however, demethylation was extremely high in the estuarine and lagoon sites. Ratios of methylation to demethylation were low in these coastal sites but increased further offshore in the gulf, which agreed with increased ratios of MeHg to total Hg (%MeHg) in gulf sediments. Comparisons of microbial activities indicated that sulfate reduction strongly controlled both methylation and demethylation. However, Hg methylation in coastal lagoon sediments was controlled by rapid demethylation and the bioavailability of Hg that was affected by Hg adsorption and precipitation. Methylation in offshore marine sites correlated with sulfate reduction but not the partitioning of Hg between pore water and solid phases. The decrease in sulfide production offshore exacerbated Hg methylation.

Conclusions

The freshwater to marine gradient in the Idrija/So?a/Isonzo/Adriatic region is dynamic, exhibiting horizontally variable rates of microbial activities and Hg transformations that create “hot spots” of MeHg accumulation that are controlled differently in each region.

     

Effects of humus on the environmental activity of mineral-bound Hg: influence on Hg plant uptake

Purpose  

Understanding the potential activation mechanisms and Hg transfer pathways is key to providing a basis for developing effective measures to prevent soil Hg from entering the food chain and dispersing into the environment. Besides acidification, the presence of natural complexing or chelating agents in the environment may also assist or intensify this process. The objective of this research is to understand the mechanisms behind the interaction of Hg with the complexity of humus material and other soil constituents with regards to plant uptake.     

The accumulation and transfer of arsenic and mercury in the soil under a long-term fertilization treatment

Purpose

The North China Plain (NCP) is a strategic grain production base in China with a wild distribution of fertile soils. During the past 20 years, high-input intensive agriculture with excess chemical fertilizer application has sustained high grain yields, but may have resulted in contamination of some elements in farmland. In this study, the accumulation and transfer of arsenic (As) and mercury (Hg) in typical Calcaric Fluvisols with long-term different fertilization practices were investigated.

Materials and methods

Field experiments with seven treatments were launched in 1989, and soil and plant samples were collected and analyzed periodically. The treatments include OM (organic manure), OM?+?NPK (50 % organic manure?+?50 % chemical fertilizer), NPK, NP, PK, NK, and CK (the control experiment with no fertilizer).

Results and discussion

With over 20 years (1989–2009) of cultivation, various extents of As and Hg accumulations were really observed in the soil. The higher As and Hg contents were found in P fertilizers than those in N, K, or OM fertilizers. As a result, the long-term P fertilization slightly promoted Hg accumulations with decreased soil Hg concentrations in the order of NPK?≈?NP?≈?PK?≈?OM?+?NPK?>?OM?>?NK?≈?CK, which was similar to the order of crop yields. At the tillage layer (0–20 cm), Hg accumulation in the soil was enhanced by crop production, due to the highly accumulated Hg in plant roots finally remained in the soil. However, no significant differences of soil As concentrations can be found between treatments with and without P fertilizers probably due to water leaching and plant uptake.

Conclusions

Soil As and Hg were mainly contributed by fertilizers, irrigation, and atmospheric deposition in recent years, but they did not exhibit in significant accumulations in the soil. The contents of As and Hg were not above the critical safe levels of soils for crop production (As, <30 mg kg^?1; Hg, <500 μg kg^?1). Arsenic and Hg tended to move downward in the soil profile and the movement was hindered by clay minerals.

     

Estimation of dynamic load of mercury in a river with BASINS-HSPF model

Purpose  

Mercury (Hg) is a naturally occurring element and a pervasive toxic pollutant. This study investigated the dynamic loads of Hg from the Cedar–Ortega Rivers watershed into the Lower St. Johns River (LSJR), Florida, USA, using the better assessment science integrating point and nonpoint sources (BASINS)-hydrologic simulation program—FORTRAN (HSPF) model.     

Formation and distribution of methylmercury in sediments at a mariculture site: a mesocosm study

Purpose

The aim of the present study was to investigate the differences of methylmercury (MeHg) formation and distribution between mariculture (aquaculture) sediments (MS) and reference sediments (RS) collected from a site in Hong Kong.

Materials and methods

The MS and RS samples were split into four batches, three of which were spiked with HgCl₂ aqueous solution to a concentration of 0.8, ,2 and 8 mg k g^?1 in sediment samples SP1, SP2, and SP3, respectively, while the rest served as a control batch (referred to as C).

Results and discussion

The results showed that the highly Hg-polluted sediment produced greater amounts of MeHg. During the culture period, MeHg concentrations in sediments decreased over time. The decreasing percentage increased in the order of SP3?<?SP2?<?SP1, which might be due to the inhibition of MeHg degradation by high Hg concentrations. The mean value of MeHg concentrations and %MeHg of the total Hg (THg) in MS was significantly lower than those in RS, possibly due to the complexation of Hg with organic ligands, leading to lower Hg bioavailability for methylation bacteria. The distribution coefficient of THg (K_dT) was relatively high in MS compared to RS, indicating that the former had a greater number of binding sites for Hg adsorption.

Conclusions

Methylmercury formation was inhibited in MS, probably due to increased complexation of Hg²⁺ with organic matter and adsorption of Hg to MS. Furthermore, the mean value of K_dT in MS was relatively high when compared to RS, which illustrates that MS sediments have more binding sites than RS for adsorption of Hg.     

Accumulation,transfer, and environmental risk of soil mercury in a rapidly industrializing region of the Yangtze River Delta,China

Purpose  

Mercury (Hg) accumulation and transfer in soil ecosystems has been altered on local, regional, and even global scales, and their environmental risk has increasingly been a concern to the public and the scientific community.     

Mercury content in volcanic soils across Europe and its relationship with soil properties

Purpose  

Volcanoes are a natural source of Hg, whose deposition can occur in neighbouring soils. This study examines the role of soil compounds in the geochemical behaviour of total Hg (Hg _T ) in volcanic soils. An estimation of Hg from lithological origin is also assessed to ascertain the relevance of other sources in Hg _T accumulated in volcanic soils.     

Greenhouse gas emissions from Silphium perfoliatum and silage maize cropping on Stagnosols

Background

The sustainability of bioenergy is strongly affected by direct field-derived greenhouse gas (GHG) emissions and indirect emissions form land-use change. Marginal land in low mountain ranges is suitable for feedstock production due to small impact on indirect land-use change. However, these sites are vulnerable to high N₂O emissions because of their fine soil texture and hydrology.

Aims

The perennial cup plant (Silphium perfoliatum L.) might outperform silage maize (Zea mays L.) on cold, wet low mountain ranges sites regarding yield and ecosystem services. The aim of this study was to assess whether the cultivation of cup plant also provides GHG mitigation potential compared to the cultivation of maize.

Methods

A t-year field experiment was conducted in a low mountain range region in western Germany to compare area and yield-scaled GHG emissions from cup plant and maize fields. GHG emissions were quantified using the closed chamber method.

Results

Cup plant fields emitted an average of 3.6 ± 4.3 kg N₂O-N ha^–1 year^–1 (–85%) less than maize fields. This corresponded to 74.0 ± 94.1 g CO_2-eq kWh^–1 (–78%) less emissions per produced electrical power. However, cup plant had a significantly lower productivity per hectare (–34%) and per unit of applied nitrogen (–32%) than maize.

Conclusion

Cup plant as a feedstock reduces direct field-derived GHG emissions compared to maize but, due to lower yields cup plant, likely increases emissions associated with land-use changes. Therefore, the increased sustainability of bioenergy from biogas by replacing maize with cup plant is heavily dependent on the performance of maize at these sites and on the ecosystem services of cup plant in addition to GHG savings.     

Impact of global climate change and fire on the occurrence and function of understorey legumes in forest ecosystems

Introduction  

The objective of this review was to provide a better understanding of how global climate change and fire influence the occurrence of understorey legumes and thereby biological nitrogen (N) fixation rates in forest ecosystems. Legumes are interesting models since they represent an interface between the soil, plant, and microbial compartments, and are directly linked to nutrient cycles through their ability to fix N. As such, they are likely to be affected by environmental changes.     

Initial screening studies on potential of high phenolic-linked plant clonal systems for nitrate removal in cold latitudes

Purpose  

Nitrate removal is a major challenge in drinking water systems and is more acute in colder latitudes due to low metabolic conversion rates of biological systems. To achieve rapid nitrate removal, designed plant systems in greenhouse microenvironments has potential. In such localized controlled microenvironments, higher temperatures can be managed for plant growth in an appropriate growth medium through which nitrate-contaminated water is fed for denitrification.     

Phytoremediation of a multi contaminated soil: mercury and arsenic phytoextraction assisted by mobilizing agent and plant growth promoting bacteria

Purpose

The possibility of using chemical and microbial additives to enhance the phytoextraction of mercury (Hg) and arsenic (As) from a multi-contaminated soil could be very effective, leading to a significant saving in terms of time and costs of the reclamation. The aim of this study was to evaluate the efficacy of the addition of (i) thiosulfate and (ii) metal-tolerant bacteria isolated from the polluted soil having plant growth promotion (PGP) potential to perform As and Hg phytoextraction by Brassica juncea and Lupinus albus.

Materials and methods

A collection of 13 bacterial isolates able to tolerate As and Hg was obtained from the contaminated soil, identified by partial 16S rRNA gene sequencing and tested in vitro for PGP activities. The most promising strains were further tested in vivo for the evaluation of plant growth ability and rhizocompetence on model plants. Pot experiments were conducted in microcosms, with polluted soil vegetated with B. juncea and L. albus. Ammonium thiosulfate and potassium dihydrogen phosphate were used as mobilizing agents, together with a bacterial consortium composed by the most promising PGP isolates.

Results and discussion

Thirteen indigenous metal-tolerant bacterial strains were isolated, and their in vitro characterization highlighted their great potential in assisting the phytoremediation process; most of them tolerated both trace elements and showed, at the same time, multiple PGP traits. The results were confirmed in vivo on model plants and lead to the selection of the most promising PGP strains to be applied in microcosm-scale phytoextraction experiments. Thiosulfate addition significantly increased the mobilization of both elements, promoting bioavailability and phytoextraction. When a selected bacterial consortium was supplemented in addition to thiosulfate, the efficacy of the phytoaccumulation was increased up to 85 % for As and up to 45 % for Hg.

Conclusions

The use of the common fertilizer thiosulfate appeared to have great potential in phytoextraction practices since it was able to facilitate the uptake by plants of both Hg and As. Moreover, the application of a consortium of indigenous PGP bacteria (PGPB) produced a further positive effect on the plant biomass, supporting and enhancing the phytoextraction strategy, thus demonstrating their potential in a microbe-assisted phytoremediation intervention.

     

Historical sedimentary trends of mercury and other trace elements from two saltmarshes of the Marano and Grado lagoon (northern Adriatic Sea)

Purpose

Previous research conducted in the Marano and Grado lagoon (northern Adriatic Sea) has shown that this environment has been affected by trace metal contamination, especially by mercury (Hg), from both industrial (the chlor-alkali plant) and mining activities (Idrija mine, Slovenia). Sediment cores were collected from two different saltmarshes of this lagoon environment to evaluate the degree of the anthropogenic enrichments and the geochronology of Hg accumulation.

Materials and methods

Core subsampling was performed by cutting 1-cm thick slices at discrete intervals. Mercury determination was done differently from the other parameters in that the two long cores were subsampled at 1-cm intervals to obtain continuous concentration profiles. Samples were completely decomposed, using a mixture of mineral acids in a closed microwave system before being analysed for trace metal content using ICP-OES. Total Hg content in the solid phase was determined by DMA-80. ¹³⁷Cs was measured via gamma spectrometry. ²¹⁰Pb activity was measured via alpha-counting of its daughter, ²¹⁰Po, assuming secular equilibrium between the two isotopes.

Results and discussion

In saltmarsh sediments, Fe, Co, Li, Sc and V show no enrichment at both sites thus suggesting that they are essentially lithogenic elements. Conversely, enrichments are minimal (EF = <2) for As, Cd, Cr, Ni, Pb and Zn and moderate (EF = 2–5) for Cu and Mn and also for Pb and Zn but only in some levels of the sedimentary sequences. An exception is Hg, as expected due to the long-term input proceeding from the historical mining activity which has especially affected the eastern sector of the lagoon.

Conclusions

The core collected from the saltmarsh in the eastern lagoon (Grado) displays a better time resolution during the last century although the Hg background level has not been reached. Conversely, the core collected in the western sector (Marano) has recorded a longer and more complete history of Hg contamination, from the beginning of the peak of Hg extraction activity at the Idrija mine (1850). Both saltmarshes still receive Hg inputs and the sediment accumulation rates in the upper section appear to have increased over the last 10–20 years (from 0.30 to 0.45 cm year^?1 at Marano and from 0.30 to 0.74 cm year^?1 at Grado). Many of these morphological structures suffer erosive processes thus representing a potential source of contaminants associated with sediments, in particular Hg. Conservation and monitoring of saltmarshes should be taken into consideration also from this environmental point of view.

     

Temporal dynamics of iron-rich, tropical soil organic carbon pools after land-use change from forest to sugarcane

Background, aim, and scope  

Land-use change can significantly influence carbon (C) storage and fluxes in terrestrial ecosystems. Soil–plant systems can act as sinks or sources of atmospheric CO₂ depending on formation and decomposition rates of soil organic matter. Therefore, changes in tropical soil C pools could have significant impacts on the global C cycle. This study aims to evaluate the impacts of long-term sugarcane cultivation on soil aggregation and organic matter, and to quantify temporal dynamics of soil organic matter in cultivated sugarcane plantation soils previously under a tropical natural secondary forest.     

A comparison of measured catchment sediment yields with measured and predicted hillslope erosion rates in Europe

Purpose  

This study aims to understand better the relationship between measured soil loss rates due to sheet and rill erosion (SL), predicted SL rates and measured catchment sediment yields (SY) in Europe.     

Heavy metal pollution of the world largest antimony mine-affected agricultural soils in Hunan province (China)

Purpose  

The present work concerns the distribution of ten heavy metals (Sb, As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, and Zn) in the surrounding agricultural soils of the world largest antimony (Sb) mine in China. The objective is to explore the degree and spatial distribution of heavy metal pollution of the Sb mine-affected agricultural soils. The presented data were compared with metal concentrations in soils from mining and smelting sites in China and other countries.     

Specific rates of net methylmercury production in lake sediments

Specific rates of Hg (²⁰³HgCl₂) methylation and McHg (¹⁴CH₃HgI) demethylation in aerobic and anaerobic conditions were determined in samples of surface sediments (0 to 2 cm) taken from five small headwater lakes in Southern Finland. The highest rates of methylation were measured in anaerobic conditions. However, the importance of aerobic methylation increased with increasing Fe and Mn content in sediment. There was little difference between aerobic and anaerobic demethylation. The results demonstrate that the net McHg production in lake sediments depends on the individual characteristics of the lake, particularly pH and and sediment properties. These characteristics seem to affect demethylation in anaerobic conditions and methylation in aerobic conditions.     

Comparison of soil phosphorus extraction methods regarding their suitability for organic farming systems

Background

Organic farmers frequently report sufficient yield levels despite low or even very low soil phosphorous (P) contents questioning the applicability of widely used laboratory methods for soil P testing for organic farming.

Aims

The aim of this study was to compare the validity of a broad range of different soil extraction methods on soils under organic management from South West Germany and to test the correlation of the measured soil P concentration with plant offtake.

Methods

Twenty-two soil samples of eight different organic farms were extracted with different solutions: (1) water, (2) CAL, (3) Olsen, (4) Mehlich 3, (5) Bray P1, (6) Bray P2, (7) NaOH+Na₂EDTA, and (8) total P. The results were then correlated with above ground plant P.

Results

Spearman's rank correlation coefficient (r_s) of correlations between above ground plant P and extractable soil P (Water-P, CAL-P, and Olsen-P [+active charcoal {+AC}]) determined with ICP-OES were strong (0.94, 0.90, and 0.93, respectively). Among the tested methods, above ground plant P showed a strong correlation with CAL-P as detected by ICP-OES (r_s = 0.90) and colorimetry (r_s = 0.91). The comparison of CAL-P data provided by farmers and CAL-P analyzed during this research showed discrepancies between the results.

Conclusions

The results of this study indicate that the CAL method can be used in organic farming despite a low extraction of organic P (P_org). Furthermore, it is recommended for farmers to take soil samples for analyses regularly and interpret changes in P in the long-term instead of interpreting individual samples.     

Measurement of Hg methylation in sediments using high specific-activity203Hg and ambient incubation

Two methods were developed for estimating the rate ofin situ methylmercury (MeHg) formation in sediments. One method is based on incubation of intact sediment cores without added Hg over a period of days. The second method uses²⁰³HgCl₂ with a specific activity high enough to be used as a tracer (relative to bulk Hg). Use of high-specific activity²⁰³HgCl₂ allowed measurement of methylation rate in hours at ambient total Hg concentrations.²⁰³HgCl₂ was pre-equilibrated with pore water before injection into intact cores, to allow complexation with dissolved ligands. Methylation rates were measured with²⁰³HgCl₂ additions as low as 0.02 μCi and 1.2 ng Hg per g wet weight sediment. These methods were tested in epilimnetic and littoral sediments of two pristine seepage lakes in Northern Wisconsin, and found to compare well.In situ methylation rates in Pallette and Little Rock Lake sediments ranged from 0.1 to 0.4 ug/m² d. Use of²⁰³Hg gave lower errors with shorter incubation times than the ambient incubation method. A method for extraction of Me²⁰³Hg from bulk sediments is given.     

Determination of mercury methylation rates using A 203-HG radiotracer technique

A radiotracer method for the determination of mercury (Hg) methylation rates in bulk water and water overlying intact sediment cores has been developed. A sediment core with overlying water is collected in a core tube, the overlying water is spiked with high specific activity 203-Hg radiotracer, and the core is incubated at ambient temperature. Aliquots of the overlying water are removed, the Hg is extracted from the sample, and the activity in the extract is measured. A 10–25 fold sample preconcentration is achieved using a dithizone-chloroform extraction technique and a sodium nitrite back extraction step to separate inorganic Hg(II) from monomethylmercury (MMHg). The use of this technique, in conjunction with high specific activity 203-Hg, has allowed for spiking concentrations in the overlying water of approximately 1 ng Hg/L. This spiking level is about the same concentration as the ambient water overlying the core, thus not significantly perturbing the system. Our technique is a significant improvement over previous methodologies which used 203-Hg spike additions of 1 μg Hg/L or higher. The technique was used to measure Hg methylation rates at the Experimental Lakes Area (ELA) in Ontario, Canada during August of 1993 and at an extensively studied estuarine site in Gulf Breeze, Florida, USA during September, 1993 and June, 1994. Multiple cores were collected and spiked with a range of 1 to 11,800 ng Hg (as 203-Hg) into the overlying water. MMHg production at the ELA site indicated rates of 0.25 to 3.7 pg/cm²/day (0.08 to 2.5 % methylation/day). Results from Gulf Breeze were significantly higher at 1.5 to 425 pg/cm²/day or 0.06 to 18 % methylation/day. These rates are one to three orders of magnitude greater than previously measured “specific rates” in bulk water samples and sediments. A direct comparison of rates with previous sediment methylation assay techniques is not possible, however, because of the significant differences between our methodology and previous assay protocols.     

Effects of phosphate on trace element accumulation in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.): a 5-year phosphate application study

Purpose

Phosphate (P) fertilizers are being widely used to increase crop yield, especially in P-deficient soils. However, repeated applications of P could influence trace element bioaccumulation in crops. The effects of 5-year P enrichment on trace element (Cu, Zn, Cd, Pb, As, and Hg) accumulation in Oryza sativa L. were thus examined.

Materials and methods

Two paddy soils with different initial P availabilities were amended with and without P fertilizer from 2009 to 2013. Trace elements and P levels in rice and soils were analyzed.

Results and discussion

In soil initially with limited P, P amendment enhanced grain Pb, As, and Hg concentrations by 1.8, 1.5, and 1.4-fold, respectively, but tended to decrease the grain Cd level by 0.73-fold, as compared to the control. However, in soil initially with sufficient P, P amendment tended to reduce accumulation of all examined elements in rice grain.

Conclusions

Phosphate amendment in initially P-limited and P-sufficient soils had different effects on trace element availability in soil (as reflected by extractable element) and plant physiology (growth and metal translocation), resulting in contrasting patterns of trace element accumulation in rice between the two types of soils. Our study emphasized the necessity to consider the promoting effects of P on Pb, As, and Hg accumulation in grain in initial P-deprived soil.