Release of vanadium from oxidized sediments: insights from different extraction and leaching procedures.

Although the attention for vanadium (V) as a potentially harmful element is growing and some countries adopted threshold values for V in soils, sediments, groundwater, or surface water, V is generally of little importance in environmental legislation and the knowledge about the behavior of V in the environment is still limited. In the present study, the release of V from oxidized sediments, sediment-derived soils, and certified reference materials was investigated by means of several types of leaching tests and extractions that are frequently used for soil and sediment characterization. The pHstat leaching tests and single and sequential extractions applied in this study show that V generally displays a very limited actual and potential mobility in sediment. "Mobile" V concentrations, as estimated by the amount of V released by a single extraction with CaCl2 0.01 mol L(-1), were low, even in the most contaminated sediment samples. Only under strongly acidifying conditions (pH 2), such as in the case of ingestion of soil or sediment or in accidental spills, a substantial release of V can be expected.

Strategic selection of an optimal sorbent mixture for in-situ remediation of heavy metal contaminated sediments: framework and case study.

Aquatic sediments contaminated with heavy metals originating from mining and metallurgical activities pose significant risk to the environment and human health. These sediments not only act as a sink for heavy metals, but can also constitute a secondary source of heavy metal contamination. A variety of sorbent materials has demonstrated the potential to immobilize heavy metals. However, the complexity of multi-element contamination makes choosing the appropriate sorbent mixture and application dosage highly challenging. In this paper, a strategic framework is designed to systematically address the development of an in-situ sediment remediation solution through Assessment, Feasibility and Performance studies. The decision making tools and the experimental procedures needed to identify optimum sorbent mixtures are detailed. Particular emphasis is given to the utilization and combination of commercially available and waste-derived sorbents to enhance the sustainability of the solution. A specific case study for a contaminated sediment site in Northern Belgium with high levels of As, Cd, Pb and Zn originating from historical non-ferrous smelting is presented. The proposed framework is utilized to achieve the required remediation targets and to meet the imposed regulations on material application in natural environments.

Monitored natural attenuation (MNA) of contaminated soils: state of the art in Europe--a critical evaluation.

The use of natural attenuation (NA) processes for contaminated site cleanup and remediation has been gaining more attention over the last few years. However, the need for an inventory of the existing information concerning monitored natural attenuation (MNA), including the existing return on experience, has been sounding increasingly louder over recent years as well. This paper will focus on the application of MNA throughout Europe. First, a literature study and a survey were performed in order to collect all available data on both qualitative and quantitative aspects of MNA. Secondly, a questionnaire was created and sent out to experts in the field of regulation and research from six countries, including Finland, Spain, and the UK. Thirdly, further contributions from a SNOWMAN workshop concerning MNA (November 7th, 2011, Paris) were included in this paper. The result is a state of the art concerning MNA for several countries, including the legal framework and existing protocols, a comparison between different countries, and an overview of some existing MNA cases throughout Europe combined with a discussion on relevant aspects related to "return on experience". The results demonstrate that MNA is now considered to be a conventional remediation technique in most countries that were included in this study. Although MNA is currently being applied for the remediation of contaminated sites, some countries still don't recognise it as an official remediation technique (e.g. Finland). This study also confirms and illustrates the differences concerning the MNA approach that exists between different countries, as well as the differences in application levels. However, it is important to note that at the same time a certain level of coherence exists concerning the MNA approach, e.g. with regard to the importance of biodegradation processes. Furthermore, the main outcome of this study emphasises the clear need to systematically collect and share information concerning existing MNA cases. Only then a clear return of experience will be possible.

Arsenic pollution at the industrial site of Reppel-Bocholt (north Belgium).

An industrial site, polluted with As and heavy metals, was investigated by combining chemical (sequential extractions and pHstat leaching tests), physical and mineralogical characterization of soil samples and slag fragments, and by the analysis of soil porewater aimed at assessing the distribution, speciation and mobility of heavy metals and As. On the site itself, arsenic concentrations up to 3.6% in surficial soil samples and up to 22% in slag fragments were found, together with elevated concentrations (percentage level) of Cu, Co, Ni, Zn and Pb. High concentrations of arsenic (up to 38,000 microg/l) and heavy metals (up to 1700 microg/l Cu and 4700 microg/l Zn) were also found in the in situ sampled soil porewater, highlighting the considerable availability of As, Zn and Cu for uptake by plants and leaching to the ground water. Sequential extractions also indicated a high availability of arsenic and copper in most samples and slag fragments of the industrial site, although poorly reactive phases were encountered as well. pHstat leaching tests confirmed that the present leaching of contaminants is alarming. Moreover, soil acidification will enhance the leaching of contaminants, emphasizing that remediation of the industrial site is urgent. Small scale variability of total metal concentrations and metal speciation, both in the horizontal and vertical direction, and the occurrence of a camouflage layer underline the importance of elaborate sampling for pollution assessment on an industrial site.