Due to its toxicity, mercury is increasingly being phased out. Before the adverse effects of mercury were known, it was used in numerous products, in a variety of industrial processes and in crop protection products. This led to emissions into the environment, and consequently to humans and the ecosystem being exposed to mercury contamination.
Mercury contamination occurs in a diffuse manner, including via stalk-emission from coal-fired power plants, contamination of surface water with mercury-containing sediments, emissions by evaporation of mercury during the extraction of gold from amalgam during ASGM operations, and as hotspots from chlor-alkali sites etc. The site assessment and remediation/implementation of risk reduction measures for all these diverse sites demand unique, tailor-made approaches. However, the common factors are that the fat and transport of mercury on these sites are complicated and difficult to assess, and that risk reduction measures are costly and far-reaching. This particularly applies to ASGM. As the sustainable management of sites contaminated with mercury (site assessment, remediation assessment, remediation and aftercare) is complex and expensive, the use of innovative and efficient site assessment and remediation approaches and techniques is crucial to make the sustainable management of these sites feasible.
Site authorities/owners confronted with mercury contamination often have one or more of the following questions. TAUW is able to answer these questions and assist you with the sustainable management of mercury-impacted sites in an appropriate, site-specific way.
Consultancy is required to put the risks posed by a site contaminated with mercury into perspective. This includes a solid risk assessment. This risk assessment should be based on a robust Conceptual Site Model (CSM) that clearly describes the source-pathway-receptor linkage. Representative data must also be used to develop a risk-based remediation approach using innovative solutions for sites where the investigation and remediation of mercury contamination are challenging. TAUW focuses on such innovative solutions and the site-specific social and economic restrictions and opportunities during all phases of the sustainable management of sites contaminated with mercury.
The nature of elemental mercury and the non-uniform distribution of this contaminant in the soil matrix (Nugget effect) make traditional ground penetrating techniques very challenging. In addition, intrusive sampling operations using drilling techniques or excavation pits may allow mercury to migrate to deeper soil layers. There is a need to optimise the investigative costs using innovative in-situ investigative techniques, such as passive vapor sampling to map the hotspots, Membrane Interface Probe (MIP) for real-time vertical profiles, XRF technology to identify (metallic) mercury in soil and gamma-ray spectrometry for sediment surveys.
Due to the bioaccumulative and toxic properties of mercury (especially inorganic methylmercury), bioaccumulation and biomagnification of mercury in aquatic and terrestrial food chains play an important role in the global mercury cycle. Via the consumption of animal products and crops, bioaccumulated mercury can also eventually lead to risks to human health. Reducing ecological risks/risks to human health is often the main driver for managing sites contaminated with mercury. ERA is a necessary and powerful tool to effectively reduce ecological risks. As such, it should be incorporated into the decision making and design phase of (cost-)effective remedial measures. It allows realistic and clear remediation goals, targets and evaluation frameworks to be determined. Furthermore, ERA offers the opportunity to involve stakeholders in decision making and increases the acceptance of the remedial measures and their results.
Prior to the implementation of the remediation phase, a range of different goals and techniques must be evaluated to select the best remediation approach. The techniques may include excavation, pump and treat, immobilisation, capping, thermal treatment and soil washing. TAUW employs the ROSA (RObust Sanitation Analysis) guideline. This offers practical advice and tools for selecting remediation options. Feasibility, duration, nuisance and aftercare are also considered. The REC model compares the different remediation techniques based on Risk reduction, Environmental merit and Costs. These models appear to be very suitable tools for multivariate analyses of this kind. The remediation plan pays particular attention to health and safety aspects when working with soil contaminated with mercury. We take care of the entire remediation process, including cost calculations, permits, tendering, management and supervision.
Accumulation of heavy metals in the sediments of rivers exposed to mining and industrial waste is a common phenomenon across the globe. Once heavy metals enter the river, depending on the physico-chemical characteristics of the river, they may be adsorbed by suspended particulate matter and later deposited to the sediments by gravity. During the past few centuries, both river bed sediments and flood plain sediments of impacted river courses have become sinks for heavy metals.
As contaminated sediments can act not only as a sink but also as a source of heavy metals to the aquatic environment and the organisms inhabiting it, heavy metal pollution in the aquatic environment has attracted extensive attention due to its environmental persistence, potential long-term adverse effects on human health and accumulation in the food chain. Among the heavy metals typically present, mercury is one of those attracting the greatest concern due to its high level of (eco-)toxicity.