Geogenic and anthropogenic interactions at a former Sb mine: environmental impacts of As and Sb.

Mining activities are acknowledged to introduce contaminants into localised environments and cause wider spread diffuse pollution. The concentration, distribution and fate of arsenic (As) and antimony (Sb) were studied at the former metalliferous Louisa Mine at Glendinning, Scotland. Soils and surface water were sampled and subsequently analysed to map the distribution of contamination and identify pollution sources. The maximum concentrations of As and Sb of 15,490 and 1504.2 mg kg-1, respectively, were determined in soils associated with the ore processing area and spoil heaps. The fractions of dissolved As and Sb in soils were < 1 and < 5% of total soil content, respectively, confirming findings of previous studies that As and Sb are relatively immobile. Yet, the concentrations of As and Sb released by soils exceeded regulatory limits. Concentrations of As and Sb in surface water in the immediate vicinity of the mine were impacted by a gully discharge, but rapidly diluted. While the concentrations affected by the run-off waters did not exceed EU environmental standards for freshwater, the concentrations of both, As and Sb, sharply increased above the said environmental standards approximately 100 m downstream of the mine site. The unaltered As-to-Sb ratio in water samples suggests a geogenic source. While there is a justifiable concern about the soil pollution caused by the historic mining in the area, the Glenshanna Burn is affected more by indigenous geochemical processes than the derelict mine.

Physiographical variability in arsenic dynamics in Bangladeshi soils.

Rice plants grown on soils with elevated arsenic have been shown to have increased arsenic content in their grains. To gain a better understanding of the likelihood of high grain arsenic in rice grown in different soils, it is important to understand the factors affecting the bioavailability and mobility of arsenic. Paddy soils from six different physiographic regions of Bangladesh were collected, and diffusive gradients in thin-films (DGT) were used to assess the porewater and solid phase arsenic. While significant differences were identified in total soil arsenic (1.4-9.8mg/kg), porewater arsenic (AsCsoln) (5.6-64.7µg/l), labile arsenic (AsCDGT) (6.3-77.6µg/l), and solid phase pool of arsenic (AsKd) (52-1057l/kg), importantly arsenic resupply capacity was not different between the physiographic regions. All soils had a high ratio of DGT to porewater arsenic (~1), this in conjunction with the porewater arsenic values and the high AsKd values suggesting a large solid phase pool of arsenic capable of contributing towards the resupply/transport of the labile pool of arsenic in the soil porewater. This indicates that there is less difference in soil arsenic availability than might be predicted based solely on total soil arsenic content between the physiographic regions.

Insights into the biodegradation of weathered hydrocarbons in contaminated soils by bioaugmentation and nutrient stimulation.

The potential for biotransformation of weathered hydrocarbon residues in soils collected from two commercial oil refinery sites (Soil A and B) was studied in microcosm experiments. Soil A has previously been subjected to on-site bioremediation and it was believed that no further degradation was possible while soil B has not been subjected to any treatment. A number of amendment strategies including bioaugmentation with hydrocarbon degrader, biostimulation with nutrients and soil grinding, were applied to the microcosms as putative biodegradation improvement strategies. The hydrocarbon concentrations in each amendment group were monitored throughout 112 days incubation. Microcosms treated with biostimulation (BS) and biostimulation/bioaugmentation (BS + BA) showed the most significant reductions in the aliphatic and aromatic hydrocarbon fractions. However, soil grinding was shown to reduce the effectiveness of a nutrient treatment on the extent of biotransformation by up to 25% and 20% for the aliphatic and aromatic hydrocarbon fractions, respectively. This is likely due to the disruption to the indigenous microbial community in the soil caused by grinding. Further, ecotoxicological responses (mustard seed germination and Microtox assays) showed that a reduction of total petroleum hydrocarbon (TPH) concentration in soil was not directly correlable to reduction in toxicity; thus monitoring TPH alone is not sufficient for assessing the environmental risk of a contaminated site after remediation.

The potential applications of SOS-lux biosensors for rapid screening of mutagenic chemicals.

The environmental fate and potency of mutagenic compounds is of growing concern. This has necessitated the development and application of rapid assays to screen large numbers of samples for their genotoxic and carcinogenic effects. Despite the development of biosensors for genotoxicity assessment, these have not been calibrated against traditional microbial bioassays. In this study, assays using the SOS-lux-marked microbial biosensors Escherichia coli K12C600 and E. coli DPD1718 were refined and optimised to screen selected mutagenic chemicals. The response of the biosensors was compared with the mutagenic response of the traditional Salmonella mutagenicity assay. For the chemicals tested (acridine, B[a]A, B[a]P, chrysene, mitomycin C and sodium azide), E. coli DPD1718 was consistently more sensitive than E. coli K12C600. The biosensors were of comparable sensitivity to the Salmonella assay but were more rapid, reproducible and easier to measure. These data validate the adoption of optimised assays making use of microbial biosensors for routine screening of test chemicals.

The biodegradation of cable oil components: impact of oil concentration, nutrient addition and bioaugmentation.

The effect of cable oil concentration, nutrient amendment and bioaugmentation on cable oil component biodegradation in a pristine agricultural soil was investigated. Biodegradation potential was evaluated over 21 d by measuring cumulative CO(2) respiration on a Micro-Oxymax respirometer and (14)C-phenyldodecane mineralisation using a (14)C-respirometric assay. Cable oil concentration had a significant effect upon oil biodegradation. Microbial respiratory activity increased with increasing cable oil concentration, whereas (14)C-phenydodecane mineralisation decreased. Bioaugmentation achieved the best cable oil biodegradation performance, resulting in increases in cumulative CO(2) respiration, and maximum rates and extents of (14)C-phenyldodecane mineralisation. Generally, nutrient amendment also enhanced cable oil biodegradation, but not to the extent that degrader amendment did. Cable oil biodegradation was a function of (i) cable oil concentration and (ii) catabolic ability of microbial populations. Bioaugmentation may enhance cable oil biodegradation, and is dependent upon composition, cell number and application of catabolic inocula to soil.

Impact of carbon nanomaterials on the behaviour of 14C-phenanthrene and 14C-benzo-[a] pyrene in soil.

The impact of fullerene soot (FS), single-walled (SWCNTs) and multi-walled (MWCNTs) carbon nanotubes on the behaviour of two (14)C-PAHs in sterile soil was investigated. Different concentrations of carbon nanomaterials (0, 0.05, 0.1 and 0.5%) were added to soil, and (14)C-phenanthrene and (14)C-benzo[a]pyrene extractability assessed over 80 d through dichloromethane (DCM) and hydroxypropyl-ß-cyclodextrin (HPCD) shake extractions. Total (14)C-PAH activity in soils was determined by combustion, and mineralisation of (14)C-phenanthrene was monitored over 14 d, using a catabolically active pseudomonad inoculum. No significant loss of (14)C-PAH-associated activity from CNM-amended soils was observed over the 'aging' period. CNMs had a significant impact on HPCD-extractability of (14)C-PAHS; extractability decreased with increasing CNM concentration. Additionally, (14)C-phenanthrene mineralisation was inhibited by the presence of CNMs at concentrations of ≥ 0.05%. Differences in overall extents of (14)C-mineralisation were also apparent between CNM types. It is suggested the addition of CNMs to soil can reduce PAH extractability and bioaccessibility, with PAH sorption to CNMs influenced by CNM type and concentration.

Mineralisation of target hydrocarbons in three contaminated soils from former refinery facilities.

This study investigated the microbial degradation of (14)C-labelled hexadecane, octacosane, phenanthrene and pyrene and considered how degradation might be optimised in three genuinely hydrocarbon-contaminated soils from former petroleum refinery sites. Hydrocarbon mineralisation by the indigenous microbial community was monitored over 23 d. Hydrocarbon mineralisation enhancement by nutrient amendment (biostimulation), hydrocarbon degrader addition (bioaugmentation) and combined nutrient and degrader amendment, was also explored. The ability of indigenous soil microflora to mineralise (14)C-target hydrocarbons was appreciable; ≥ 16% mineralised in all soils. Generally, addition of nutrients or degraders increased the rates and extents of mineralisation of (14)C-hydrocarbons. However, the addition of nutrients and degraders in combination had a negative effect upon (14)C-octacosane mineralisation and resulted in lower extents of mineralisation in the three soils. In general, the rates and extents of mineralisation will be dependent upon treatment type, nature of the contamination and adaptation of the ingenious microbial community.

Multimedia fate of petroleum hydrocarbons in the soil: oil matrix of constructed biopiles.

A dynamic multimedia fugacity model was used to evaluate the partitioning and fate of petroleum hydrocarbon fractions and aromatic indicator compounds within the soil: oil matrix of three biopiles. Each biopile was characterised by four compartments: air, water, soil solids and non-aqueous phase liquid (NAPL). Equilibrium partitioning in biopile A and B suggested that most fractions resided in the NAPL, with the exception of the aromatic fraction with an equivalent carbon number from 5 to 7 (EC(5-7)). In Biopile C, which had the highest soil organic carbon content (13%), the soil solids were the most important compartment for both light aliphatic fractions (EC(5-6) and EC(6-8)) and aromatic fractions, excluding the EC(16-21) and EC(21-35). Our starting hypothesis was that hydrocarbons do not degrade within the NAPL. This was supported by the agreement between predicted and measured hydrocarbon concentrations in Biopile B when the degradation rate constant in NAPL was set to zero. In all scenarios, biodegradation in soil was predicted as the dominant removal process for all fractions, except for the aliphatic EC(5-6) which was predominantly lost via volatilization. The absence of an explicit NAPL phase in the model yielded a similar prediction of total petroleum hydrocarbon (TPH) behaviour; however the predicted concentrations in the air and water phases were significantly increased with consequent changes in potential mobility. Further comparisons between predictions and measured data, particularly concentrations in the soil mobile phases, are required to ascertain the true value of including an explicit NAPL in models of this kind.

When is a soil remediated? Comparison of biopiled and windrowed soils contaminated with bunker-fuel in a full-scale trial.

A six month field scale study was carried out to compare windrow turning and biopile techniques for the remediation of soil contaminated with bunker C fuel oil. End-point clean-up targets were defined by human risk assessment and ecotoxicological hazard assessment approaches. Replicate windrows and biopiles were amended with either nutrients and inocula, nutrients alone or no amendment. In addition to fractionated hydrocarbon analysis, culturable microbial characterisation and soil ecotoxicological assays were performed. This particular soil, heavy in texture and historically contaminated with bunker fuel was more effectively remediated by windrowing, but coarser textures may be more amendable to biopiling. This trial reveals the benefit of developing risk and hazard based approaches in defining end-point bioremediation of heavy hydrocarbons when engineered biopile or windrow are proposed as treatment option.

Factors affecting benthic impacts at Scottish fish farms.

The factors affecting patterns of benthic [seabed] biology and chemistry around 50 Scottish fish farms were investigated using linear mixed-effects models that account for inherent correlations between observations from the same farm. The abundance of benthic macrofauna and sediment concentrations of organic carbon were both influenced by a significant, albeit weak, interaction between farm size, defined as the maximum weight of fish permitted on site at any one time, and current speed. Above a farm size threshold of between 800 and 1000 t, the magnitude of effects at farms located in areas of elevated current speeds were greater than at equivalent farms located in more quiescent waters. Sediment concentrations of total organic matter were influenced by an interaction between distance and depth, indicating that wind-driven resuspension events may help reduce the accumulation of organic waste at farms located in shallow waters. The analyses presented here demonstrate that the production and subsequent fate of organic waste at fish farms is more complex than is often assumed; in isolation, current speed, water depth, and farr size are not necessarily good predictors of benthic impact.

The role of decision support for bioremediation strategies, exemplified by hydrocarbons for in site and ex situ procedures.

Despite the widespread availability of state-of-the-art biological techniques, remediation practitioners have been slow to adopt these technologies to assist in designing or indeed monitoring remediation strategies. In part, this is because practitioners are driven by cost and fail to see the benefit of emerging technologies, and in part because most companies have only a small portfolio of procedures available to them. Here, we review the component parts required to design a decision support tool, appraise one that the authors have developed and critically evaluate its application to case studies. If bioremediation is to become adopted, then it is likely to have to operate in parallel with other remediation methods. Furthermore, remediation strategies must couple effective technology with a transparency of information such that all parties (practitioners, developers and stakeholders) understand how decisions were reached.

The effect of agitation on the biodegradation of hydrocarbon contaminants in soil slurries.

Slurry-based mineralisation assays are widely used to investigate contaminant biodegradation in soil; however, the importance of shaking speed on microbial degradation has not been considered. This study investigated the mineralisation of (14)C-analogues of phenanthrene, hexadecane and octacosane, shaken at 0, 25 and 100 rpm. The results showed that the fastest rates and highest levels of mineralisation in 0 d aged soils were in the highly agitated conditions (100 rpm). However, the highest levels of mineralisation in 500 d aged soil were found in the gently shaken conditions (25 rpm), with the levels of mineralisation significantly (p<0.05) one third higher than under the highly agitated conditions (100 rpm). Consequently, estimation of the maximum levels of biodegradation of organic contaminants in aged soil systems should be considered under gentle mixing conditions.

Influence of hydroxypropyl-beta-cyclodextrin on the biodegradation of 14C-phenanthrene and 14C-hexadecane in soil.

Soil was spiked with [9-(14)C]phenanthrene and [1-(14)C]hexadecane at 50 mg kg(-1) and aged for 1, 25, 50, 100 and 250 d. At each time point, the microcosms were amended with aqueous solutions of cyclodextrin (HP-beta-CD) at a range of concentrations (0-40 mM). Mineralisation assays and aqueous HP-beta-CD extractions were performed to assess the effect of the amendments on microbial degradation. The results showed that amendments had no significant impact on the microbial degradation of either of the (14)C-contaminants. Further, HP-beta-CD extractions were correlated with the mineralisation of the target chemicals in each of the soil conditions. It was found that the HP-beta-CD extraction was able to predict mineralisation in soils which had not been amended with cyclodextrin; however, in the soils containing the HP-beta-CD, there was no predictive relationship. Under the conditions of this study, the introduction of HP-beta-CD into soils did not enhance the biodegradation of the organic contaminants.

Predicting the biodegradation of target hydrocarbons in the presence of mixed contaminants in soil.

The aim of this study was to investigate the prediction of (14)C-phenanthrene and (14)C-hexadecane biodegradation in the presence of other hydrocarbons in soil using beta- and alpha-cyclodextrin (CD) solutions, respectively. Prediction of the biodegradation of (14)C-phenanthrene using the beta-CD extraction was robust under single, co-contaminant and multiple contaminant conditions (r(2)=0.92, slope of best fit line=0.87, intercept=7.24, n=84). Prediction of (14)C-hexadecane using the alpha-CD extraction was robust under single and co-contaminant conditions (r(2)=0.92, slope of best fit line=0.97, intercept=1.24, n=60); however, the alpha-CD could not accurately predict (14)C-hexadecane biodegradation in the presence of multiple contaminants. The presence of multiple contaminants enhanced (14)C-hexadecane mineralisation, but did not enhance extractability. The results from this study provide further evidence for the application of HPCD extractions for the measurement of microbial accessibility in soil.

Development of an analytical procedure for weathered hydrocarbon contaminated soils within a UK risk-based framework.

A sequential ultrasonic extraction method for contaminated soils with weathered hydrocarbons is presented. The method covers the determination of total petroleum hydrocarbons between nC 8 and nC 40, and subranges of hydrocarbons including diesel range organic compounds, kerosene range organic compounds, and mineral oil range organic compounds in soils. Further modifications to the carbon banding may be made as requested for risk assessment. These include a series of ranges known as Texas banding (from the Texas Risk Reduction Program) as well as separation of the aliphatic and aromatic fractions. The method can be routinely used for measuring hydrocarbons down to 10 mg kg (-1) in soil. Lower limits can be achieved by employing a suitable solvent concentration step following extraction; however, this would result in increased cycle time. Detection limits may vary for individual carbon ranges calculated on the percentage of the full range they cover. With an extraction efficiency and recovery between >or=95 and 99%, this method can be easily positioned as a good alternative to Soxhlet extraction and shows a good potential for implementation as a standard method potentially providing further insight to the contaminated land sector.

Linking chemical extraction to microbial degradation of 14C-hexadecane in soil.

Chemical extractions have been shown to measure the biodegradable fraction of aromatic contaminants in soil; however, there is little research on the chemical prediction of aliphatic hydrocarbon degradation. The aim of this study was to investigate the potential for cyclodextrin extractions to predict hexadecane biodegradation in soil. Soils were amended with 10 or 100 mg kg(-1) of a model alkane n-hexadecane and 100 Bq g(-1) (14)C-n-hexadecane. Correlations between the extents of mineralisation and extractions of the (14)C-contaminant were determined. Solvent shake extractions and aqueous CaCl(2) extractions were poor predictors of hexadecane bioaccessibility. However, the novel HP-alpha-CD shake extraction showed close correlation (r(2)=0.90, n=36, p<0.05) to the mineralisation data. This novel extraction technique has the potential to be used to assess the biodegradable aliphatic hydrocarbon fraction in contaminated soils.

Prediction of PAH biodegradation in field contaminated soils using a cyclodextrin extraction technique.

Biodegradation has been identified as a major loss process for organic contaminants in soils and, as a result, microbial strategies have been developed for the remediation of contaminated land. Prediction of the biodegradable fraction would be important for determining bioremediation end-points in the clean-up of contaminated land. The aim of this study was to investigate the ability of a cyclodextrin extraction to predict the extent to which polycyclic aromatic hydrocarbons (PAHs) would be degraded microbiologically in field contaminated soils; further testing the robustness and reproducibility of this extraction in chemically complex systems. Dichloromethane and hydroxypropyl-beta-cyclodextrin (HPCD) extractable fractions were measured together with the PAH biodegradable fraction in each of the six field contaminated soils. The amounts of PAHs degraded by the catabolic activity of the indigenous microflora in each of the soils were correlated with HPCD-extractable PAH concentrations. The regressions showed that the amounts of lower molecular weight PAHs extracted by the HPCD were not significantly (P > 0.05) different to the amounts that were degraded. However, higher molecular weight PAHs that were extracted by HPCD did differ significantly (P < 0.05) from the amounts degraded. Although the HPCD extraction did overestimate the microbially degradable fraction of the higher molecular weight PAHs, overall the correlations between the HPCD extractable fraction and the microbially degradable fraction were very close, with mean values of the slope of line for the six soils equalling 1. This study further describes the robust and reproducible nature of the aqueous-based soil extraction technique reliably measuring the extent to which PAHs will be microbially degraded in soil.

Importance of chemical structure on the development of hydrocarbon catabolism in soil.

A soil was amended with (14)C-analogues of naphthalene, phenanthrene, pyrene, B[a]P or hexadecane at 50 mg kg(-1) and the development of catabolic activity was assessed by determining the rate and extent of (14)CO(2) evolution at time points over 180 days. The catabolic potential of the soil was hexadecane>naphthalene>phenanthrene>pyrene>B[a]P, determined by the decrease in lag time (as defined by the time taken for 5%(14)CO(2) to be evolved from the minerialization of the (14)C-labeled hydrocarbons). The results clearly showed the difference between constitutive and inducible biodegradation systems. The 0 day time point showed that hexadecane minerialization was rapid and immediate, with a 45.4 +/- 0.6% mineralization extent, compared with pyrene minerialization at 1.0 +/- 0.1%. However, catabolism for pyrene developed over time and after a 95 days soil-pyrene contact time, mineralization extent was found to be 63.1 +/- 7.8%. Strong regression was found (r(2)>0.99) between the maximum rates of mineralization and the partioning coefficient between the mineralized hydrocarbons, which may indicate linearity in the system.

The impact of sampling techniques on soil pore water carbon measurements of an Icelandic Histic Andosol.

The carbon in soil pore water from a Histic Andosol from Western Iceland was studied at three different scales; in the field, in undisturbed outdoor mesocosms and in laboratory repacked microcosms. Pore water was extracted using suction cup lysimeters and hollow-fibre tube sampler devices (Rhizon samplers). There were significant differences in all measured variables, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and pH values between the scales of the experiment. Gaseous constituents of soil solution and pH were more susceptible to changes in scale and the type of sampling devices used. Dissolved inorganic carbon concentrations did not differ significantly between field and mesocosm solutions but where up to 14 times lower in microcosms compared to mesocosms solutions. Rhizon samplers yielded solutions with up to 4.7 times higher DIC concentrations than porous cup lysimeters. Mesocosm surface horizon DOC concentrations were 20 and 2 times higher than in field and microcosms respectively. There was difference in DOC concentration between sampling methods (up to 8 times higher in suction cups than rhizon samplers) above 50 cm depth. Soil solution pH values did not differ between field and mesocosms and mesocosms and microcosms respectively down to 80 cm depth. Direct comparison between field and microcosms was not possible due to the nature of sampling devices. Soil solutions sampled with Rhizon samplers yielded lower pH values (up to 1.3 pH units) than those sampled with suction cups. Twenty percent of annually bound organic carbon at the soils surface under field conditions was lost by leaching of DOC and through decomposition to DIC in disturbed non-vegetated microcosms. This percentage increased to 38% in undisturbed vegetated mesocosms highlighting the importance of surface vegetation in importing carbon to soils. Increased influx of nutrients will increase growth and photosynthesis but decrease carbon sequestration in near surface horizons. Although field studies considering long-term anthropogenic changes in pedogenesis require considerable experimental duration, more rapid experiments can be conducted with confidence in micro- and mesocosms as in this research.

An ecotoxicity assessment of contaminated forest soils from the Kola Peninsula.

Point source copper and nickel contamination emanating from smelters of the Kola Peninsula, NW Russia, has been observed since the mid-1960s. Previous studies have concentrated on the spatial distribution of heavy metals and their effects on forest ecology and indigenous mammals and birds. Soil is perceived as the major repository for the metal pollutants but there is a need to link the soil concentration of pollutants on the Kola Peninsula with biological parameters. Many standard methods currently used in soil ecotoxicology are developed and refined with artificial amendments and rarely modified for use in historically contaminated environments. In this study, forest soils were sampled along a 34 km transect from the smelter and analysed both chemically and with a range of ecologically relevant biological tests. Soil respiration, total nematode count, microbial heterotrophic numbers and minimal inhibitory concentrations to copper and nickel were carried out on bulk soil. The soil pore water was tested with bacterial and fungal bioluminescence-based biosensors. The heterotrophic numbers and their inhibitory concentration showed strong correlation with heavy metal concentrations while decreasing biosensor luminescence was related to increasing copper concentrations present in the pore waters. Overall, there were considerable impacts on some microbial parameters but other measures including respiration and nematode populations were insensitive to pollutant levels. While chemical analysis of heavy metals proved essential in defining the extent of contamination, environmentally relevant ecotoxicological tests complemented these data by demonstrating pollutant impact. Ecotoxicological approaches that study both the bulk soil and pore water may represent the key to understanding the fate of heavy metal in soils.