A comparison of hydraulic and transport parameters measured in low-permeability fractured media

Data from 90 tracer experiments performed in low-permeability fractured media have been studied to explore correlations among parameters controlling flow and transport. The original data had been interpreted by different authors using different models, which prevents direct comparison of their estimated parameters. In order to produce comparable parameters, the data have been reexamined using simple models (homogeneous domain, steady-state flow regime, single porosity). Specifically, hydraulic conductivity has been derived as the ratio of water flux to head gradient and apparent porosity as the ratio of water velocity to water flux; the former estimated from both first and peak arrival times. Hydraulic conductivity and porosity correlate along a straight line of slope 1:3 in log scale. While the regression is too noisy to be of predictive use, it lends some support to the use of a generalized cubic law. The fact that correlation for first arrival time porosity (0.77) is larger than for peak arrival porosity (0.62) suggests that first arrival is controlled by the same flow paths as hydraulic conductivity. Apparent porosity derived from peak arrival time is found to grow with travel time along a line of 0.55 slope (again log scale). The correlation coefficient ranges between 0.73 and 0.80 (depending on the data set) for hard rocks. The fact that this correlation is maintained when varying the flow rate at a given site leads us to suggest that it is caused by diffusion mechanisms. This conclusion is further supported by the increase of apparent porosity with the matrix porosity of the rock on which the experiments were performed.     

A regional flux-based risk assessment approach for multiple contaminated sites on groundwater bodies

In the context of the Water Framework Directive (EP and CEU, 2000), management plans have to be set up to monitor and to maintain water quality in groundwater bodies in the EU. In heavily industrialized and urbanized areas, the cumulative effect of multiple contaminant sources is likely and has to be evaluated. In order to propose adequate measures, the calculated risk should be based on criteria reflecting the risk of groundwater quality deterioration, in a cumulative manner and at the scale of the entire groundwater body. An integrated GIS- and flux-based risk assessment approach for groundwater bodies is described, with a regional scale indicator for evaluating the quality status of the groundwater body. It is based on the SEQ-ESO currently used in the Walloon Region of Belgium which defines, for different water uses and for a detailed list of groundwater contaminants, a set of threshold values reflecting the levels of water quality and degradation with respect to each contaminant. The methodology is illustrated with first results at a regional scale on a groundwater body-scale application to a contaminated alluvial aquifer which has been classified to be at risk of not reaching a good quality status by 2015. These first results show that contaminants resulting from old industrial activities in that area are likely to contribute significantly to the degradation of groundwater quality. However, further investigations are required on the evaluation of the actual polluting pressures before any definitive conclusion be established.     

Site-specific risk assessment in contaminated vegetable gardens

A field survey was carried on in Gy?ngy?soroszi, Hungary, near to an abandoned lead/zinc mine to analyse the metal contamination of flooded and non-flooded vegetable gardens, and to evaluate the health risks to local population. Contamination levels of arsenic, cadmium, lead, mercury and zinc were measured in soil and homegrown vegetable samples and bioconcentration factors and hazard indices were calculated. The high metal contents of flooded vegetable gardens were caused by floods, the results indicated significant differences between flooded and non-flooded vegetable gardens. The most accumulating vegetable was sorrel, the most mobile elements were cadmium and lead. Arsenic was not available for vegetables. The health risk was calculated for two exposure routes: ingestion of soil and ingestion of vegetables. The site-specific exposure parameters were established after a population based survey and a special equation was created to calculate the health risk due to homegrown vegetable consumption. The highest risk was associated with ingestion of vegetables, the most hazardous element being lead. The hazard index did not exceed the threshold value of one in flooded or non-flooded gardens. The analyses of health risk indicated that despite the high metal concentrations of soil the contamination of vegetable gardens does not pose an unacceptable risk to the inhabitants of the village.     

A rule-based screening environmental risk assessment tool derived from EUSES

Within the context and scope of the forthcoming European Union chemical regulations (REACH), there is a need to be able to prioritise the chemicals for evaluation. Therefore, a simple, pragmatic and adequately conservative approach for the identification of substances of very low or no immediate concern at an early stage is presented. The fundamental principles and basic concepts are derived from the EU Technical Guidance Document and EUSES, and are translated into an easy-to-use rule-based system. For this development, the effect on risk characterisation ratios (RCRs) of the key environmental parameters in EUSES was quantified (taking into account several standardised chemical release scenarios). Using statistical analysis, ranges were identified for each key parameter, within which the end result of the assessment was not significantly affected. This information was then translated into a lookup table from which environmental risk characterisation ratios can be directly read as a function of a few parameters.     

Model comparison for risk assessment: a case study of contaminated groundwater

Many environmental multimedia risk assessment models have been developed and widely used along with increasing sophistication of the risk assessment method. Despite of the considerable improvement, uncertainty remains a primary threat to the credibility of and users' confidence in the model-based risk assessments. In particular, it has been indicated that scenario and model uncertainty may affect significantly the assessment outcome. Furthermore, the uncertainty resulting from choosing different models has been shown more important than that caused by parameter uncertainty. Based on the relationship between exposure pathways and estimated risk results, this study develops a screening procedure to compare the relative suitability between potential multimedia models, which would facilitate the reduction of uncertainty due to model selection. MEPAS, MMSOILS, and CalTOX models, combined with Monte Carlo simulation, are applied to a realistic groundwater-contaminated site to demonstrate the process. It is also shown that the identification of important parameters and exposure pathways, and implicitly, the subsequent design of uncertainty reduction and risk management measures, would be better-formed.     

Risk assessment and prioritisation of contaminated sites on the catchment scale

Contaminated sites pose a significant threat to groundwater resources worldwide. Due to limited available resources a risk-based prioritisation of the remediation efforts is essential. Existing risk assessment tools are unsuitable for this purpose, because they consider each contaminated site separately and on a local scale, which makes it difficult to compare the impact from different sites. Hence a modelling tool for risk assessment of contaminated sites on the catchment scale has been developed. The CatchRisk screening tool evaluates the risk associated with each site in terms of its ability to contaminate abstracted groundwater in the catchment. The tool considers both the local scale and the catchment scale. At the local scale, a flexible, site specific leaching model that can be adjusted to the actual data availability is used to estimate the mass flux over time from identified sites. At the catchment scale, a transport model that utilises the source flux and a groundwater model covering the catchment is used to estimate the transient impact on the supply well. The CatchRisk model was tested on a groundwater catchment for a waterworks north of Copenhagen, Denmark. Even though data scarcity limited the application of the model, the sites that most likely caused the observed contamination at the waterworks were identified. The method was found to be valuable as a basis for prioritising point sources according to their impact on groundwater quality. The tool can also be used as a framework for testing hypotheses on the origin of contamination in the catchment and for identification of unknown contaminant sources.     

Model selection and evaluation for risk assessment of dioxin-contaminated sites

The general European population has a total intake of dioxins and dioxin-like chemicals near the limit recommended by the European Union, making additional exposure above background levels undesirable. For populations living near dioxin-contaminated sites, additional exposure may occur by intake of locally produced food, inhalation of particles, dermal contact with soils, or other exposure pathways. Risk assessment tools are required to estimate risks associated with contaminated sites and to set priorities for site remediation. Here, we review several multimedia models that can be applied as tools to support risk assessment. We then present a strategy to select, apply, evaluate, and adapt a model to address a specific situation. The case study we consider is a risk assessment of generic background dioxin exposure in Sweden, and we compare the predictions with environmental observations and exposure data from Sweden. Arguments are presented for selecting the CalTOX model for this case study. We demonstrate the application, evaluation, and adaptation of the model and discuss the requirements for extending the analysis to conduct risk assessment for subpopulations living near dioxin-contaminated sites.     

An intelligent data collection tool for chemical safety/risk assessment

REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) is the new European chemical legislation which aims to assess risk or safety of tens of thousands of chemicals to improve the protection of human health and the environment. The chemical safety assessment process is of an iterative nature. First, an initial, worst-case assessment is conducted after which refinements are made until no risk has been estimated or the risk is adequately controlled. Wasting time and resources on additional testing and implementing risk management measures with low effect on risk conclusions should be avoided as much as possible. This paper demonstrates the usefulness of an intelligent data collection strategy based on a sensitivity (and uncertainty) analysis on the risk assessment model EUSES to identify and order the most important "within-EU-TGD-reducible" input parameters influencing the local and regional risk characterisation ratios. The ordering can be adjusted for the costs involved in additional testing (e.g. ecotoxicity, physico-chemical properties, emission estimates, etc.). The risk refinement tool therefore reduces the resources needed to obtain a realistic risk estimate (both less conservative and less uncertain) as efficient as possible.     

Isotopes as tracers in a contaminated fractured chalk aquitard

Clusters of industrial plants often generate contaminant plumes with several potential sources. Prevention of further pollution and designing suitable remedial measures require identification of the contributing source among all potential ones and the sorting of currently active sources from historical ones. In the study area, an industrial complex in the Negev desert, Israel, contaminants could not serve as indicators for the contamination sources because of their extensive spatial distribution across the site. However, stable isotopes of oxygen, hydrogen and sulfur, as well as tritium, proved to be efficient tools for this task. The isotopic characterization of the potential end members provided the criteria for constraining a contaminating source when several alternative sources appeared viable. The isotopic fractionation of oxygen and hydrogen isotopes could be tied to the various disposal phases of the industrial wastewater. The three case studies presented here confirm the important role of isotopes as tracers in contaminated sites.     

A pragmatic approach for estimation of source-zone emissions at LNAPL contaminated sites

When considering natural attenuation as a remediation strategy at a site contaminated by a light non-aqueous phase liquid (LNAPL), it is important to consider the emission of contaminants from the source zone. A quantification of source-zone emissions is essential both for comparison with down-gradient mass fluxes to provide an estimate of fractional mass flux reduction, as well as for estimating the source lifetime. Because the spatial distribution of LNAPL at a field site is strongly dependent on both the spill circumstances and the heterogeneity of the geologic materials, which can be problematic for in-situ determination, alternative methods for estimating source-zone emissions are needed. In this work, a three-dimensional multiphase flow and transport modelling approach is used to investigate the relationship between the lateral extent of an LNAPL body and the emission of contaminants to groundwater at a contaminated site. For simulations involving an LNAPL release in an aquifer comprised of heterogeneous porosity and permeability distributions that were generated geostatistically, it is shown that a simple linear relationship exists between the lateral extent of the LNAPL body in the capillary fringe and the emission to the aqueous phase. The parameters describing the relationship are found to be linear functions of the groundwater flow velocity and the vertical infiltration rate. This site-specific relationship provides a simple method to estimate contaminant emissions to groundwater at LNAPL contaminated sites.     

Poplar for the phytomanagement of boron contaminated sites

Boron (B) is a widespread environmental contaminant that is mobile relative to other trace elements. We investigated the potential of hybrid poplar (Populus sp.) for B phytomanagement using a lysimeter experiment and a field trial on B-contaminated wood-waste. In both studies, poplars enhanced evapotranspiration from the wood-waste, reduced B leaching, and accumulated B in the aerial portions of the tree. When grown in a substrate containing 30 mg/kg B, poplar leaves had an average B concentration of 845 mg/kg, while the stems contained 21 mg/kg B. Leaf B concentrations increased linearly with leaf age. A decomposition experiment revealed that abscised leaves released 14% of their B during the winter months. Fertiliser application enhanced tree growth without decreasing the leaf B concentrations. Harvesting alternate rows of trees on a contaminated site would reduce leaching from the site while removing B. Harvested plant material may provide bioenergy, stock fodder, or an amendment for B-deficient soils.     

Determination of the flow-wetted surface in fractured media

Diffusion and sorption in the rock matrix are important retardation mechanisms for radionuclide transport in fractured media. For the conditions existing in a deep repository in crystalline rock, interaction with the rock matrix is controlled by the water flowrate in the fractures and the surface area in contact with the flowing water (the so-called "flow-wetted surface" (FWS)). The flow-wetted surface may be determined from the frequency of open fractures intersecting a borehole. The choice of packer distance used in these hydraulic measurements is crucial, however, since several open fractures may be found in one packer interval. The use of a packer distance that is too large may result in a considerable underestimation of the flow-wetted surface. This is especially important in zones with a high frequency of open fractures (fracture zones) where a small packer distance is a fundamental requirement. A large volume of hydraulic data has been compiled in Sweden from measurements using quite small packer distances. Over the last decade, the most common packer distance used for the hydraulic tests has been 3 m, although some new measurements using a shorter packer distance have also been performed. In several cases, the resolution of these measurements has been less than 0.5 m. All these data have been analysed in detail. From these data, the flow-wetted surface has been calculated and compared with the flow-wetted surface estimated in earlier studies. The results show the importance of using a small packer distance for carrying out borehole transmissivity measurements.     

Microbially assisted phytoremediation approaches for two multi-element contaminated sites

Phytoremediation is an environmental friendly, cost-effective technology for a soft restoration of abandoned mine sites. The grasses Agrostis capillaris, Deschampsia flexuosa and Festuca rubra, and the annual herb Helianthus annuus were combined with microbial consortia in pot experiments on multi-metal polluted substrates collected at a former uranium mine near Ronneburg, Germany, and a historic copper mine in Kopparberg, Sweden, to test for phytoextraction versus phytostabilization abilities. Metal uptake into plant biomass was evaluated to identify optimal plant–microbe combinations for each substrate. Metal bioavailability was found to be plant species and element specific, and influenced by the applied bacterial consortia of 10 strains, each isolated from the same soil to which it was applied. H. annuus showed high extraction capacity for several metals on the German soil independent of inoculation. Our study could also show a significant enhancement of extraction for F. rubra and A. capillaris when combined with the bacterial consortium, although usually grasses are considered metal excluder species. On the Swedish mixed substrate, due to its toxicity, with 30 % bark compost, A. capillaris inoculated with the respective consortium was able to extract multi-metal contaminants.     

Molecular docking: A potential tool to aid ecotoxicity testing in environmental risk assessment of pharmaceuticals

A cocktail of human pharmaceuticals pollute aquatic environments and there is considerable scientific uncertainty about the effects that this may have on aquatic organisms. Human drug target proteins can be highly conserved in non target species suggesting that similar modes of action (MoA) may occur. The aim of this work was to explore whether molecular docking offers a potential tool to predict the effects of pharmaceutical compounds on non target organisms. Three highly prescribed drugs, diclofenac, ibuprofen and levonorgestrel which regularly pollute freshwater environments were used as examples. Their primary drug targets are cyclooxygenase 2 (COX2) and progesterone receptor (PR). Molecular docking experiments were performed using these drugs and their primary drug target homologues for Danio rerio, Salmo salar, Oncorhynchus mykiss, Xenopus tropicalis, Xenopus laevis and Daphnia pulex. The results show that fish and frog COX2 enzymes are likely to bind diclofenac and ibuprofen in the same way as humans but that D. pulex would not. Binding will probably lead to inhibition of COX function and reduced prostaglandin production. Levonorgestrel was found to bind in the same binding pocket of the progesterone receptor in frogs and fish as the human form. This suggests implications for the fecundity of fish and frogs which are exposed to levonorgestrel. Chronic ecotoxicological effects of these drugs reported in the literature support these findings. Molecular docking may provide a valuable tool for ecotoxicity tests by guiding selection of test species and incorporating the MoA of drugs for relevant chronic test end points in environmental risk assessments.     

A spatially-evaluated methodology for assessing risk to a population from contaminated land

A methodology is proposed which combines quantitative probabilistic human health risk assessment and spatial statistical methods (geostatistics) to produce an assessment of risks to human health from exposure to contaminated land, in a manner which preserves the spatial distribution of risks and provides a measure of uncertainty in the assessment. Maps of soil contaminant levels, which incorporate uncertainty, are produced from sparse sample data using sequential indicator simulation. A real, age-stratified population is mapped across the contaminated area, and intake of soil contaminants by individuals is calculated probabilistically using an adaptation of the Contaminated Land Exposure Assessment (CLEA) model. An abundance of information is contained in results which can be interrogated at the population and individual level, and mapped to provide a powerful visual tool for risk managers, enabling efficient targeting of risk reduction measures to different locations.     

Development of a risk assessment methodology for evaluating potential impacts associated with contaminated mud disposal in the marine environment

In order to assess impacts associated with disposal of contaminated mud arising from Hong Kong's dredging and reclamation projects, a methodology has been formulated to determine the level of risk posed by consumption of seafood/marine prey species to humans and to the Chinese White Dolphin (Sousa chinensis). This methodology improves on previously used techniques by incorporating risks for organic contaminants, accounting for doses from sources other than seafood, and incorporating additional local knowledge on Sousa chinensis behaviour. It thus represents an advance in risk assessment techniques and a new integration of risk assessment and monitoring in environmental management.     

Polychlorinated biphenyls in small mammals from contaminated landfill sites

PCBs in small mammals living in a contaminated landfill site varied in both concentration and congener composition, reflecting both the feeding strategy of each species and the chlorination of the congeners. Body concentrations of SigmaPCB on a 1:1:1 Arochlor (1242:1254:1260) basis gave a rank order of Sorex araneus > Apodemus sylvaticus > Microtus agrestis. Comparisons with data for other PCB-contaminated sites suggest that the SigmaPCB values in S. araneus from the landfill site may be of sufficient magnitude to inhibit reproductive capability and to cause other major organ dysfunction. There were also inter-specific differences in the whole body concentrations of the individually quantified congeners. For S. araneus, the rank order of concentrations of the selected ICES 7 marker PCB congeners was: No. 153>138>180>118>28>101>52. In M. agrestis the rank order was: No. 28>118>153>138>180, 52>101. The congener order for A. sylvaticus differed from both S. araneus and M. agrestis, but was more similar to the latter, being: No. 153>138>118>180>28>52, 101. The contribution of the different congeners to SigmaPCB in the mammals reflects the degree of chlorination of different congeners but varies with feeding strategy of the species. In the insectivorous S. araneus, heavily chlorinated congeners (Nos 153, 138 and 180) are most abundant, whereas the herbivore, M. agrestis showed congeners Nos 28 and 118 to be present in the highest amounts, whilst the equivalent pattern for the more omnivorous A. sylvaticus was intermediate between S. araneus and M. agrestis. The high concentrations of PCBs in S. araneus relative to the other species, suggests that it may serve as a useful biomarker of terrestrial environmental pollution by organochlorines.