Still today river sediments can be contaminated with persistent chemicals (PCBs, dioxins, mercury) leading to exceedances of food threshold levels in fish. Environmental risk assessments of contaminated rivers exhibit multiple challenges: Often primary sources do not exist anymore (e.g. ancient sewers) or are initially not known (e.g. uncontrolled landfills next to rivers). In addition, contaminant inputs often occur via multiple pathways (sewers, tributaries) and diffuse emissions (surface run off from infrastructure systems). Back-contamination from secondary sources can occur: Not only sediments but also river banks are often significantly contaminated because of deposition of contaminated suspended material from the river water.
Here we will present the elements of an environmental risk assessment, the development of remediation targets and remediation options for contaminated rivers by using an illustrative example of a Swiss drainage channel whose sediments were contaminated over a length of about 2.3 km: a) a sampling campaign using custom-made liner-in-liner technique for optimal performance under challenging environmental conditions, b) a risk assessment approach that i) prioritizes the contaminant sources on the basis of their input paths and release potential ii) and therefrom allows to derive feasible and sustainable remediation targets and iii) the selection of most efficient remediation options.
Sampling Techniques: Due to the low aqueous contaminant concentrations, river water was sampled with passive samplers. To overcome the challenges of sediment sampling at high streaming velocities, a liner-in-liner sampling system with a core-catcher based on a mobile platform was developed. The contamination of river banks and adjacent soils was assessed, because based on the available historical information, sediments were often excavated and deposited near the channels on agricultural and residential areas. These depositions can lead to back-contamination of the sediments and may represent a potential human hazard. Several tributaries such as sewers, rivers and run-offs (spillways) were included into the sampling campaign. In addition to the relevant contaminants, soil and sediment properties such as organic carbon content and grain size distribution were addressed, to account for the relevant phase partitioning processes in river systems.
Risk assessment: Based on the conceptual site model contaminant masses, mass fluxes and concentrations were mathematically described for individual sectors of the channel. Contaminant releases for the multiple pathways were predicted: transport via infiltrating rain water, erosion of contaminated river bank material, input of contaminated sediments and water via tributaries. The remediation targets were developed in a two-step procedure: in a first step, the tolerable contamination of the sediments was derived by calculating the tolerable bioaccumulation rate via the sediment-fish pathway. In a second step the tolerable remaining input of contaminants into the channel (tolerable “back-contamination”) was calculated and therefrom the tolerable concentrations in the river banks were derived. Remediation targets for an adjacent agricultural field were derived by calculating the tolerable uptake of contaminants by cattle during grazing, which was the most sensitive use of the land.
Remediation: The channel was remediated by excavation and replacement of the river banks and sediments in the relevant sectors to the relevant depths. For this, the water flow was diverted sector-by-sector and the contaminated material was replaced. As an ecological benefit fish niches were installed and gravel of different size was used for reinstatement of the river bed, to provide optimal conditions for different fish species.
In the construction phase of large infrastructure projects such as tunnels and hydropower plants thousands of tons of construction chemicals and explosives are used. These chemicals can cause substantial environmental hazards. However, these hazards are often not anticipated upfront of infrastructure projects because of the project’s complexity: The project areas are often widespread exhibiting several construction sites with construction activities over years and various protective goods that can be affected by contaminant emissions.
The use of ammonium nitrate-based explosives and organic boosters leads to emissions of ammonium, nitrate, nitrite and nitroorganic compounds to the environment. From the application of construction chemicals (sprayed concrete, retarders, slurries, hydraulic liquids, etc.), contaminants such as hexavalent chromium, aluminium, and various organic chemicals including biocides are released to the environment.
These compounds lead to negative effects in susceptible surface waters and used groundwater. Observed effects are general ecotoxicity to aquatic life, fish toxicity (nitrite, ammonia, Al3+aq), eutrophication (nitrate), inhibition of photosynthesis (turbidity) or oxygen depletion (by dissolved organic carbon).
The emission of the substances occurs via multiple pathways: Polluted excavated material is often deposited in or along surface waters because of space shortage in the project area. From there, contaminants and fine materials are released into the water during and after the deposition. A second important emission path are tunnel effluents that are discharged to creeks with partly low runoffs. Additionally, highly contaminated material such as sludges from material recycling are deposited in project-specific landfills in the project perimeter which can lead to additional emissions.
The flux of pollutants to protective goods and therefore the environmental risk is highly variable in time and location and depends on the construction activities at the multiple construction sites as well as the environmental conditions such as seasonal variability of precipitation (snow, rain), hydraulic discharges of rivers, water levels of lakes etc. To overcome these complexities, we have established a unique method for the identification of possible environmental hazards during the entire construction works. This method is based on a holistic analysis of all project phases and processes. The project system is represented by a mathematical model that predicts contaminant fluxes and concentrations as a function of time and space in all protective goods of concern. The predicted environmental concentrations (PEC) are compared to (eco)toxicologically based reference levels (predicted no effect concentration, PNEC). This risk assessment method has already successfully been applied in several Swiss projects.
The benefit of this upfront environmental risk assessment is to anticipate possible hazards already in the planning phase of the project as an integral part of the environmental impact assessment. The risk assessment allows the identification and prioritization of the relevant processes, time points and locations, which potentially lead to critical environmental impacts. These procedure guarantees the implementation of risk reduction measures and hence investments at locations with the highest impact. Such measures include installations (such as water treatment plants), application of best-practices (e.g. for the application of emulsion explosives) or the use of environmentally friendly products.
The presentation will give an overview on the method that allows for the holistic assessment of all contaminant emissions at all construction sites during the entire construction project. The strengths and limitation will be discussed as well as illustrative results from reference projects will be presented. The substances of concern, their sources and possible effects will be addressed.
The benefits of urban agriculture are many and well documented, ranging from health improvement to community betterment, more sustainable urban development and environment protection. On the negative side, urban soils are commonly enriched in toxic trace elements that have accumulated over time through the deposition of atmospheric particles (generated by automotive traffic, heating systems, historical industrial activities and resuspended street dust), and the uncontrolled disposal of domestic, commercial and industrial wastes. This in turn has given rise to concerns about the level of exposure of urban farmers to these elements and the potential health hazards associated with this exposure. Research efforts in this field have started relatively recently and have almost systematically omitted the influence of Sb and Se, and to a lesser extent of As, although all three have proven toxic effects.
In this study, the concentrations of aqua regia-extractable As, Sb and Se have been determined by GF-AAS in 42 soil samples collected with an Edelman auger from the upper 20 cm of the soil profile in seven urban gardens in Madrid. Soil physicochemical properties, i.e. soil pH, texture, calcium carbonate and organic matter contents have also been evaluated. Frequency and duration of exposure, and rates of consumption of vegetables grown in the selected urban gardens have been estimated from the results of an on-site survey. The mean concentration of As in the seven urban gardens is similar to regional background levels but the average content of Sb and Se are one order of magnitude higher, and in the case of Sb, exceeds the guideline value for agricultural land use in Madrid.
The risk for urban farmers from exposure to As, Sb and Se through four routes of exposure (accidental ingestion of soil, inhalation of suspended particles, dermal absorption and ingestion of vegetables) has been assessed. The quantitative results of the risk assessment are very sensitive to changes in the value assigned to two key variables that are affected by a high degree of uncertainty: soil ingestion rate and soil-to-plant uptake factor. For the values used in our model, taken from the USEPA’s Soil Screening Guidance and from the RAIS database, the highest contribution to the overall risk is associated with the accidental ingestion of soil particles, followed by ingestion of on-site grown vegetables and dermal absorption (inhalation of suspended particles has a negligible influence). However, changes in the soil-to-plant uptake factor within the range of published values for this variable can result in a contribution of ingestion of vegetables higher than that of soil ingestion, and in a different value of the predicted overall risk. It remains unaffected the fact that As is the contaminant of most concern given its carcinogenic nature. In terms of systemic toxicity, As is also the main contributor to the aggregate Hazard Index, followed by Sb and Se.
The estimates of overall systemic risk are more than one order of magnitude lower than the threshold values of HI=1, but that of carcinogenic risk, associated with the exposure to As, lies in the range of 10-5 - 10-6, close or even above the limit of acceptability, depending on national environmental regulations. Although risk assessments make use of very conservative assumptions, these results indicate the need for further research in order to reduce the uncertainty in some of the variables included in the model and to dissipate the concerns regarding the potential for adverse health effects associated with the practice of urban gardening.
Gardening is fun and healthy. No bigger pleasure than to harvest and eat one's own vegetables, to raise chickens and eat their eggs. Local food production has many other advantages: it contributes to a sustainable lifestyle, increases social cohesion, ….
However, in some cases, there are concerns about the presence of pollutants in home-grown food and eggs. In Flanders, with its long industrial history and high population density, diffuse soil contamination is widespread, especially in urban areas. Diffuse soil pollution cannot be linked directly to a source, and is due to all kinds of, sometimes very small, activities in the past, such as waste burning and disposal.
The presence of pollutants in home-grown food is shown in several studies, such as those resulting from the Flemish human biomonitoring program (2001-2006), and the study 'Dioxins in eggs and vegetables of private gardens' (2011). Especially with regard to the increased levels of dioxins in eggs of home-raised chickens there is a matter of concern.
How can we ensure that people can eat their home-grown vegetables and eggs from their own chickens without having to worry about their health? Together with the Service Health and Environment of the Department LNE, the OVAM sets up a system to provide suitable advice and information for citizens. The aim is not to discourage growing one's own food, but to reduce possible health risks by practical measures.
Practical guidelines are provided on how to grow vegetables and to raise chickens in allotments and private gardens in a safe way. For example, the guidelines include advices on the location of the garden in relation to heavy traffic, industry, historical contaminated sites, … When the quality of the soil is uncertain or questionable, the advice is given that one should test the soil for contamination, i.e. to take a soil sample and get it analyzed.
However, the cost of soil analyzes may be too high for private persons who are gardening for leisure. This is especially the case when one wants to raise chickens for egg production and soil testing for dioxins is needed. Therefore, on behalf of OVAM, Arcadis Belgium nv performed a feasibility study to look into the possibilities of setting up a system for soil analyzes at reduced prices. This study treats the organizational, financial and legal aspects, and includes as well an online survey of gardeners about their concerns related to soil contamination, their willingness to pay, … As part of the feasibility study, a pilot project is set up in collaboration with a local authority. In this community, soil testing at a reduced price is offered for private gardeners during a test period.
In support of previous actions, VITO developed a framework for the interpretation of the results of the analyses. For the most important pollutants, reference values were calculated for concentrations in soil that allow growing food products without health risks. The model S-Risk was used to calculate these values. With this model it is possible to define different scenario's, and to take into account the exposure route by consumption of home-grown eggs.
The advice and information system for gardeners is part of a more general approach for the management of diffuse soil contamination. This type of soil contamination is not always covered by regulation. In these cases, OVAM focuses on the avoidance of risks for human health due to diffuse soil contamination.
Abstract:
Cumene – or isopropylbenzene - is a volatile aromatic hydrocarbon with an odor threshold below the chemical-analytical detection limit. The soil contamination with cumene was caused by a road accident in which a truck loaded with Komol fell over and 10,000 l of Komol – with cumene as the principal compound - poured out all over the soil surface. In 2012, soil investigation showed:
• a soil contamination – source location – of about 750 m2 until 7 m below ground level
• a ground water contamination up to 350 m from the source location and to a depth of 25 m below ground level.
The Dutch province of North Brabant – the ‘problem owner’ - was confronted with many questions. How to assess the risks of this compound for which no general risk assessment for soil contamination exists? How to translate risk levels into remediation goals? What remediation approach will abolish all odor nuisance for the residents of the location? How to prevent nuisance during the remediation activities (as much as possible) and how to protect the health of the residents and contractor’s laborers? The province of North Brabant had to address these and many other questions in such way that the final aim of the remediation would be achieved in the most effective way and with respect to the complex situation with many stakeholders involved.
The presentation on Consoil will show the results of the investigation (conceptual model), risk assessment, in-situ remediation measurements and the applied process of a building team construction, which have resulted altogether in a successful remediation.
The soil and ground water investigation has based on a conceptual model, which gave insight in the information gabs, research questions to be answered and a clear visual insight in the contamination. The risk assessment consists of two levels: technical risk assessment concerning the human and environmental risks of the contamination and risk management (using the RISMAN method) to clarify and to address properly all project related risks. One of the most important issues of the technical assessment is the impact of the extremely low odor threshold level on the remediation goals to be achieved and the remediation activities needed to secure these goals. The conceptual model mentioned above and risk management have been the starting points of the project approach and project risks are determined and prioritized by the stakeholders involved, e.g. extreme odor nuisance, conventional explosives (second world war) and groundwater extraction. In 2012, an evaluation of the most appropriate contract form and market analyses followed the risk management session hold and as a result the building team construction has been chosen as the best suiting contract form and a short list of contractors was generated who were invited to compete for the contract. Furthermore, the advantages of the building team construction will be shown:
- the province of North Brabant is able to influence the process in such a way that the province can take its responsibility in this complex situation in which residents are involved
- members of the team (province, consultant Tauw and contractor NTP) depend on each other for the realization of the project and project risks are addressed and solved in the most effective way possible
Finally, the remediation consists of both excavation activities and in-situ measurements. The possible in-situ remediation measurements – biological, fysiological and/ or chemical - have been evaluated and it has been decided to implement a bioscreen to remediate the ground water contamination and to imply a bio blanked with a slow release compound on the floor of the excavation.