Mercury in ground water, septage, leach-field effluent, and soils in residential areas, New Jersey coastal plain

New geochemical data for defining origin and distribution of mercury in groundwater of a coastal area in southern Tuscany (Italy)

A geochemical study was conducted in a coastal plain in the Orbetello Lagoon area in southern Tuscany (Italy), acquiring new data on groundwater, lagoon water, and stream sediment for insights into the origin, distribution, and behaviour of mercury in a Hg-enriched carbonate aquifer. The main hydrochemical features of the groundwater are ruled by the mixing of Ca-SO4 and Ca-Cl continental fresh waters of the carbonate aquifer and Na-Cl saline waters of the Tyrrhenian Sea and Lagoon of Orbetello. Groundwater had highly variable Hg concentrations (< 0.1-11 μg/L) that were not correlated with the percentage of saline water, depth in the aquifer, or distance from the lagoon. This excluded the possibility that saline water could be the direct source of Hg in groundwater and responsible for release of the element through interaction with the carbonate lithologies of the aquifer. The origin of Hg in groundwater could be ascribed to the Quaternary continental sediments overlying the carbonate aquifer because i) high Hg concentrations were found in the continental sediments of the coastal plain and in the contiguous lagoon sediments; ii) waters from the upper part of aquifer had the highest Hg concentrations; iii) Hg levels in groundwater increased with increasing thickness of the continental deposits. The high Hg content in the continental and lagoon sediments is geogenic due to regional and local Hg anomalies and to sedimentary and pedogenetic processes. It can be assumed that i) water circulating in these sediments dissolves the solid Hg-bearing constituents and mobilises this element mainly as chloride complexes; ii) Hg-enriched water moves from the upper part of the carbonate aquifer due to the cone of depression generated by intense pumping of groundwater by fish farms in the study area.

Geochemical modeling of mercury in coastal groundwater

The systematic analysis of groundwater in the Greek island of Skiathos revealed a seasonal increase of total mercury concentrations after the extensive groundwater abstraction during the busy and heavily touristic summer months. This contamination was accompanied by a corresponding increase of the chloride content of groundwater, attributed to seawater intrusion into the freshwater-depleted aquifer within mercury-rich bedrock. The effects of elevated concentrations of chloride anions in the mobilization of mercury and its speciation were addressed by geochemical equilibrium modeling, considering cinnabar (HgS) as the mineral source of mercury. Adsorption onto hydrous ferric oxide (Fe₂O₃·H₂O) was a necessary ingredient of the geochemical model for bringing the calculated concentrations in agreement with field measurements, after optimization of the cinnabar/adsorbent mass ratio to a value of 4.9 × 10^-8. The speciation of mercury was found to depend on the acidity and redox status as well as on the chloride content of groundwater. Mercury concentrations in the groundwater of Skiathos rise above the World Health Organization limit of 1 μg L^-1 for a seawater intrusion higher than 3 %, with HgCl₂ being the dominant species followed by HgClOH, HgCl₃^- and HgCl₄^2-. The assumed concentration of dissolved organic matter in groundwater had a negligible impact on the mercury speciation and its mobilization by chloride.

Iron Sulfide Minerals as Potential Active Capping Materials for Mercury-Contaminated Sediment Remediation: A Minireview

Several innovative approaches have been proposed in recent years to remediate contaminated sediment to reduce human health and environmental risk. One of the challenges of sediment remediation stems from its unfeasible high cost, especially when ex situ strategies are selected. Therefore, in situ methods such as active capping have been emerging as possible options for solving sediment problems. Active capping methods have been extensively tested in field-scale sediment remediation for organic pollutants (e.g., PCBs, PAHs, DDT) contamination with good sequestration efficiency; however, these methods have not been widely tested for control of heavy metal pollutants, such as mercury (Hg). In this review, the potentials of using iron sulfide minerals to sequestrate Hg were discussed. Iron sulfide minerals are common in the natural environment and have shown good effectiveness in sequestrating Hg by adsorption or precipitation. Iron sulfides can also be synthesized in a laboratory and modified to enhance their sequestration ability for Hg. Some of the potential advantages of iron sulfides are pointed out here. Additional tests to understand the possibility of applying iron sulfides as active caps to remediate complicated environment systems should be conducted.

Mercury in the unconfined aquifer of the Isonzo/Soča River alluvial plain downstream from the Idrija mining area

This work aims at evaluating mercury (Hg) occurrence, spatial distribution and speciation in groundwater of the Isonzo/Soča River upper alluvial plain downstream from the Idrija Hg mine (Western Slovenia). Several wells and piezometers were sampled both in static and dynamic mode. Total (THg) and filtered (FHg) concentrations were generally higher in static (THg, 1.87-855 ng L^-1; FHg, 0.20-13.61 ng L^-1) than in dynamic mode (THg, 0.08-78.77 ng L^-1; FHg, 0.28-6.65 ng L^-1). The estimated background value accounts for 2-3 ng L^-1. On the basis of hydrochemistry and isotopic composition, the main sources of groundwater were established. Hg concentrations in the Slovenian sector, supplied by local rainfall, are comparable to values measured close to the Isonzo River. Possible further Hg local sources have been suggested. Stability field analysis for the aqueous Hg species revealed that in the presence of chloride Hg solubility may be increased by the formation of chlorocomplexes. Mercury that rarely enters reduced surrounding conditions can be bound to sulphur to form polysulphide species depending on the pH of water. Since Hg-contaminated alluvial sediments of the Isonzo River may act as a secondary Hg source in groundwater, a borehole was dug down to the water table. Mercury content and speciation revealed that cinnabar (HgS) is the prevalent form followed by the matrix-bound Hg (Hg_bound). Variations of the physico-chemical boundary conditions, as well as the raising/lowering of the water table, may be locally responsible for the slight variability of Hg concentrations in the aquifer.

Calcium (II) - and dipicolinic acid mediated-biostimulation of oil-bioremediation under multiple stresses by heat, oil and heavy metals

The oil-producing Arabian Gulf states have hot summer seasons of about 7-month in length. Therefore, environmental oil spills should be bioremediated by the activity of indigenous, hydrocarbonoclastic (hydrocarbon-degrading) microorganisms with optimum growth at about 50 °C. Soils in such arid countries harbor thermophilic bacteria, whose oil-consumption potential is enhanced by calcium (II) - and dipicolinic acid (DPA)-supplement. Those organisms are, however, subjected to additional stresses including toxic effects of heavy metals that may be associated with the spilled oil. Our study highlighted the resistance of indigenous, thermophilic isolates to the heavy metals, mercury (II), cadmium (II), arsenic (II) and lead (II) at 50 °C. We also detected the uptake of heavy metals by 15 isolates at 50 °C, and identified the merA genes coding for Hg²⁺-resistance in 4 of the studied Hg²⁺-resistant isolates. Hg²⁺ was the most toxic metal and the metal toxicity was commonly higher in the presence of oil. The addition of Ca²⁺ and DPA enhanced the Hg²⁺-resistance among most of the isolates at 50 °C. Crude oil consumption at 50 °C by 4 selected isolates was inhibited by the tested heavy metals. However, Ca²⁺ and DPA limited this inhibition and enhanced oil-consumption, which exceeded by far the values in the control cultures.

Biogeochemical transformations of mercury in solid waste landfills and pathways for release

Mercury (Hg) is present in a variety of solid wastes including industrial wastes, household products, consumer electronics, and medical wastes, some of which can be disposed in conventional landfills. The presence of this neurotoxic metal in landfills is a concern due to the potential for it to leach or volatilize from the landfill and impact local ecosystems. The objective of this review is to describe general practices for the disposal of mercury-bearing solid wastes, summarize previous studies on the release of mercury from landfills, and delineate the expected transformations of Hg within landfill environments that would influence transport of Hg via landfill gas and leachate. A few studies have documented the emissions of Hg as landfill gas, primarily as gaseous elemental Hg(0) and smaller amounts as methylated Hg species. Much less is known regarding the release of Hg in leachate. Landfill conditions are unique from other subsurface environments in that they can contain water with very high conductivity and organic carbon concentration. Landfills also experience large changes in redox potential (and the associated microbial community) that greatly influence Hg speciation, transformations, and mobilization potential. Generally, Hg is not likely to persist in large quantities as dissolved species, since Hg(0) tends to evolve in the gas phase and divalent Hg(ii) sorbs strongly to particulate phases including organic carbon and sulfides. However, Hg(ii) has the potential to associate with or form colloidal particles that can be mobilized in porous media under high organic carbon conditions. Moreover, the anaerobic conditions within landfills can foster the growth of microorganisms that produced monomethyl- and dimethyl-Hg species, the forms of mercury with high potential for bioaccumulation. Much advancement has recently been made in the mercury biogeochemistry research field, and this study seeks to incorporate these findings for landfill settings.

Quality modeling of drinking groundwater using GIS in rural communities, northwest of Iran

Given the importance of groundwater resources in water supply, this work aimed to study quality of drinking groundwater in rural areas in Tabriz county, northwest of Iran. Thirty two groundwater samples from different areas were collected and analyzed in terms of general parameters along with 20 heavy metals (e.g. As, Hg and …). The data of the analyses were applied as an attribute database for preparing thematic maps and showing water quality parameters. Multivariate statistical techniques, including principal component analysis (PCA) and hierarchical cluster analysis (CA) were used to compare and evaluate water quality. The findings showed that hydrochemical faces of the groundwater were of calcium-bicarbonate type. EC values were from 110 to 1750 μs/cm, in which concentration of salts was high in the east and a zone in north of the studied area. Hardness was from 52 to 476 mg/l and CaCO3 with average value of 185.88 ± 106.56 mg/L indicated hard water. Dominant cations and anions were Ca(2+) > Na(+) > Mg(2+) > K(+) and HCO3 (-) > Cl(-) > SO4 (2-) > NO3 (2), respectively. In the western areas, arsenic contamination was observed as high as 69 μg/L. Moreover, mercury was above the standard level in one of the villages. Eskandar and Olakandi villages had the lowest quality of drinking water. In terms of CA, sampling sites were classified into four clusters of similar water quality and PCA demonstrated that 3 components could cover 84.3% of the parameters. For investigating arsenic anomaly, conducting a comprehensive study in the western part of studied area is strongly recommended.

Mercury speciation and mobilization in a wastewater-contaminated groundwater plume

We measured the concentration and speciation of mercury (Hg) in groundwater down-gradient from the site of wastewater infiltration beds operated by the Massachusetts Military Reservation, western Cape Cod, Massachusetts. Total mercury concentrations in oxic, mildly acidic, uncontaminated groundwater are 0.5-1 pM, and aquifer sediments have 0.5-1 ppb mercury. The plume of impacted groundwater created by the wastewater disposal is still evident, although inputs ceased in 1995, as indicated by anoxia extending at least 3 km down-gradient from the disposal site. Solutes indicative of a progression of anaerobic metabolisms are observed vertically and horizontally within the plume, with elevated nitrate concentrations and nitrate reduction surrounding a region with elevated iron concentrations indicating iron reduction. Mercury concentrations up to 800 pM were observed in shallow groundwater directly under the former infiltration beds, but concentrations decreased with depth and with distance down-gradient. Mercury speciation showed significant connections to the redox and metabolic state of the groundwater, with relatively little methylated Hg within the iron reducing sector of the plume, and dominance of this form within the higher nitrate/ammonium zone. Furthermore, substantial reduction of Hg(II) to Hg(0) within the core of the anoxic zone was observed when iron reduction was evident. These trends not only provide insight into the biogeochemical factors controlling the interplay of Hg species in natural waters, but also support hypotheses that anoxia and eutrophication in groundwater facilitate the mobilization of natural and anthropogenic Hg from watersheds/aquifers, which can be transported down-gradient to freshwaters and the coastal zone.

Transport and interactions of kaolinite and mercury in saturated sand media

To evaluate the potential of Hg release and co-transport by colloids, it is important to understand how Hg, colloids and Hg-loaded colloids migrate in soils. Hg sorption by kaolinite and sand were nonlinear and fit the Langmuir model, with the maximum Hg sorption capacity being 1.2mg/g kaolinite and 0.11 mg/g sand. Co-transport of Hg and kaolinite was evaluated using: (1) 1 or 100 mg/L Hg or 100mg/L kaolinite, (2) 1 or 100 mg/L Hg mixed with 100mg/L kaolinite, (3) 1 or 100 mg/L Hg presorbed onto kaolinite, and (4) 25 0mg/L kaolinite in Hg-loaded sand columns. The presence of kaolinite (100 mg/L) reduced Hg's mobility through sand column by increasing deposition rate of Hg-loaded kaolinite. At 100 mg/L Hg, soluble Hg dominated Hg transport; but at 1 mg/L Hg, colloidal Hg (Hg sorbed on kaolinite) affected Hg transport. Preloading 100 mg/L Hg onto kaolinite (0.43 mg/g) reduced kaolinite's mobility with low recovery rate (78%), with Hg retardation (R=1) in Hg-loaded kaolinite being lower than Hg retardation at 100 mg/L Hg (R=1.287). The Hg recovery rate (93%) from Hg-loaded kaolinite at 1mg/L Hg was higher compared to 22% from 1 mg/L Hg. Kaolinite can serve as a carrier to enhance Hg transport in porous media, with 250 mg/L kaolinite mobilizing ~2.4% Hg presorbed onto sand media. Correlation analysis revealed that desorbed Hg was significantly correlated with kaolinite (r=0.81, P<0.0001). Hence kaolinite enhanced Hg transport in the sand media serving both as a carrier (Hg was loaded before transport) and as mobile colloids stripping Hg off the sand media (Hg was loaded during transport).

Indigenous soil bacteria with the combined potential for hydrocarbon consumption and heavy metal resistance

INTRODUCTION

Transconjugant bacteria with combined potential for hydrocarbon utilization and heavy metal resistance were suggested by earlier investigators for bioremediation of soils co-contaminated with hydrocarbons and heavy metals. The purpose of this study was to offer evidence that such microorganisms are already part of the indigenous soil microflora.

METHODS

Microorganisms in pristine and oily soils were counted on nutrient agar and a mineral medium with oil as a sole carbon source, in the absence and presence of either sodium arsenate (As V), sodium arsenite (As III) or cadmium sulfate, and characterized via 16S rRNA gene sequencing. The hydrocarbon-consumption potential of individual strains in the presence and absence of heavy metal salts was measured.

RESULTS

Pristine and oil-contaminated soil samples harbored indigenous bacteria with the combined potential for hydrocarbon utilization and As and Cd resistance in numbers up to 4 × 10⁵ CFU g⁻¹. Unicellular bacteria were affiliated to the following species arranged in decreasing order of predominance: Bacillus subtilis, Corynebacterium pseudotuberculosis, Brevibacterium linens, Alcaligenes faecalis, Enterobacter aerogenes, and Chromobacterium orangum. Filamentous forms were affiliated to Nocardia corallina, Streptomyces flavovirens, Micromonospora chalcea, and Nocardia paraffinea. All these isolates could grow on a wide range of pure aliphatic and aromatic hydrocarbons, as sole sources of carbon and energy, and could consume oil and pure hydrocarbons in batch cultures. Low As concentrations, and to a lesser extent Cd concentrations, enhanced the hydrocarbon-consumption potential by the individual isolates.

CONCLUSION

There is no need for molecularly designing microorganisms with the combined potential for hydrocarbon utilization and heavy metal resistance, because they are already a part of the indigenous soil microflora.

Phytoremediation of mercury in pristine and crude oil contaminated soils: Contributions of rhizobacteria and their host plants to mercury removal

The rhizospheric soils of three tested legume crops: broad beans (Vicia faba), beans (Phaseolus vulgaris) and pea (Pisum sativum), and two nonlegume crops: cucumber (Cucumis sativus) and tomato, (Lycopersicon esculentum) contained considerable numbers (the magnitude of 10(5)g(-1) soil) of bacteria with the combined potential for hydrocarbon-utilization and mercury-resistance. Sequencing of the 16S rRNA coding genes of rhizobacteria associated with broad beans revealed that they were affiliated to Citrobacter freundii, Enterobacter aerogenes, Exiquobacterium aurantiacum, Pseudomonas veronii, Micrococcus luteus, Brevibacillus brevis, Arthrobacter sp. and Flavobacterium psychrophilum. These rhizobacteria were also diazotrophic, i.e. capable of N(2) fixation, which makes them self-sufficient regarding their nitrogen nutrition and thus suitable remediation agents in nitrogen-poor soils, such as the oily desert soil. The crude oil attenuation potential of the individual rhizobacteria was inhibited by HgCl(2), but about 50% or more of this potential was still maintained in the presence of up to 40 mgl(-1) HgCl(2). Rhizobacteria-free plants removed amounts of mercury from the surrounding media almost equivalent to those removed by the rhizospheric bacterial consortia in the absence of the plants. It was concluded that both the collector plants and their rhizospheric bacterial consortia contributed equivalently to mercury removal from soil.

Fate of effluent-borne contaminants beneath septic tank drainfields overlying a Karst aquifer

Groundwater quality effects from septic tanks were investigated in the Woodville Karst Plain, an area that contains numerous sinkholes and a thin veneer of sands and clays overlying the Upper Floridan aquifer (UFA). Concerns have emerged about elevated nitrate concentrations in the UFA, which is the source of water supply in this area of northern Florida. At three sites during dry and wet periods in 2007-2008, water samples were collected from the septic tank, shallow and deep lysimeters, and drainfield and background wells in the UFA and analyzed for multiple chemical indicators including nutrients, nitrate isotopes, organic wastewater compounds (OWCs), pharmaceutical compounds, and microbiological indicators (bacteria and viruses). Median NO3-N concentration in groundwater beneath the septic tank drainfields was 20 mg L(-1) (8.0-26 mg L(-1)). After adjusting for dilution, about 25 to 40% N loss (from denitrification, ammonium sorption, and ammonia volatilization) occurs as septic tank effluent moves through the unsaturated zone to the water table. Nitrogen loading rates to groundwater were highly variable at each site (3.9-12 kg N yr(-1)), as were N and chloride depth profiles in the unsaturated zone. Most OWCs and pharmaceutical compounds were highly attenuated beneath the drainfields; however, five Cs (caffeine, 1,7-dimethylxanthine, phenol, galaxolide, and tris(dichloroisotopropyl)phosphate) and two pharmaceutical compounds (acetaminophen and sulfamethoxazole) were detected in groundwater samples. Indicator bacteria and human enteric viruses were detected in septic tank effluent samples but only intermittently in soil water and groundwater. Contaminant movement to groundwater beneath each septic tank system also was related to water use and differences in lithology at each site.

Environmental fate of Ra in cation-exchange regeneration brine waste disposed to septic tanks, New Jersey Coastal Plain, USA: migration to the water table

Fate of radium (Ra) in liquid regeneration brine wastes from water softeners disposed to septic tanks in the New Jersey Coastal Plain was studied. Before treatment, combined Ra ((226)Ra plus (228)Ra) concentrations (maximum, 1.54 Bq L(-1)) exceeded the 0.185 Bq L(-1) Maximum Contaminant Level in 4 of 10 studied domestic-well waters (median pH, 4.90). At the water table downgradient from leachfields, combined Ra concentrations were low (commonly < or =0.019 Bq L(-1)) when pH was >5.3, indicating sequestration; when pH was < or =5.3 (acidic), concentrations were elevated (maximum, 0.985 Bq L(-1) - greater than concentrations in corresponding discharged septic-tank effluents (maximum, 0.243 Bq L(-1))), indicating Ra mobilization from leachfield sediments. Confidence in quantification of Ra mass balance was reduced by study design limitations, including synoptic sampling of effluents and ground waters, and large uncertainties associated with analytical methods. The trend of Ra mobilization in acidic environments does match observations from regional water-quality assessments.

Concentrations and environmental fate of Ra in cation-exchange regeneration brine waste disposed to septic tanks and accumulation in sludge, New Jersey Coastal Plain, USA

Concentrations of Ra in liquid and solid wastes generated from 15 softeners treating domestic well waters from New Jersey Coastal Plain aquifers (where combined Ra ((226)Ra plus (228)Ra) concentrations commonly exceed 0.185 Bq L(-1)) were determined. Softeners, when maintained, reduced combined Ra about 10-fold (<0.024 Bq L(-1)). Combined Ra exceeded 0.185 Bq L(-1) at 1 non-maintained system. Combined Ra was enriched in regeneration brine waste (maximum, 81.2 Bq L(-1)), but concentrations in septic-tank effluents receiving brine waste were less than in the untreated ground waters. The maximum combined Ra concentration in aquifer sands (40.7 Bq kg(-1) dry weight) was less than that in sludge from the septic tanks (range, 84-363 Bq kg(-1)), indicating Ra accumulation in sludge from effluent. The combined Ra concentration in sludge from the homeowners' septic systems falls within the range reported for sludge samples from publicly owned treatment works within the region.

Has submarine groundwater discharge been overlooked as a source of mercury to coastal waters?

We measured the mercury (Hg) in groundwater, aquifer sediments, and surface water in Waquoit Bay (Massachusetts) and found that this toxic metal (range: <3.2-262 pM) was being released within the subterranean estuary, with similarly high levels (range: 18-256 pM) found in the surface waters of the bay. None of the dissolved species (DOC, chloride, and Fe) normally observed to influence Hg partitioning correlated well with the observed Hg concentrations. It was hypothesized that this was in part due to the variable loading in time and space of Hg onto the aquifer sands in combination with the seasonality of groundwater flow through the aquifer. Aquifer sediment samples from the study site ranged from <1 to 12.5 pmol of Hg/g of sediment, suggesting log Kd values on the order of 1. We hypothesize that this was due to the low organic carbon content typical of the aquifer sediments. Last, itwas estimated that submarine groundwater discharge supplied 0.47-1.9 nmol of Hg m(-2) day(-1) to the bay, which is an order of magnitude higher than the atmospheric deposition rate for the northeastern U.S.

Novel reduction of mercury (II) by mercury-sensitive dissimilatory metal reducing bacteria

The dissimilatory metal reducing bacterium (DMRB) Shewanella oneidensis MR-1 reduces ionic mercury (Hg[II]) to elemental mercury (Hg[0]) by an activity not related to the MerA mercuric reductase. In S. oneidensis, this activity is constitutive and effective at Hg(II) concentrations too low to induce mer operon functions. Reduction of Hg(II) by MR-1 required the presence of electron donors and electron acceptors. Reduction occurred with oxygen or fumarate, but had the highest rate when ferric oxyhydroxide was used as a terminal electron acceptor. Geobacter sulfurreducens PCA and Geobacter metallireducens GS-15 reduced Hg(II) to Hg(0) with activity comparable to MR-1; however, neither the DMRB Anaeromyxobacter dehalogenans 2CP-C nor the nitrate reducer Pseudomonas stutzeri OX-1 reduced Hg(II) during growth. This discovery of constitutive mercury reduction among anaerobes has implications to the mobilization of mercury and production of methylmercury in anoxic environments.