Dioxin- and POP-contaminated sites—contemporary and future relevance and challenges

BACKGROUND, AIM AND SCOPE: Once they have been generated, polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and other persistent organic pollutants (POPs) can persist in soils and sediments and in waste repositories for periods extending from decades to centuries. In 1994, the US EPA concluded that contaminated sites and other reservoirs are likely to become the major source of contemporary pollution problems with these substances. With this in mind, this article is the first in a new series in ESPR under the title 'Case Studies on Dioxin and POP Contaminated Sites--Contemporary and Future Relevance and Challenges', which will address this important issue. The series will document various experiences from sites contaminated with PCDD/F and other POPs. This article provides an overview of the content of the articles comprising the series. In addition, it provides a review of the subject in its own right and identifies the key issues arising from dioxin/POP-contaminated sites. Additionally, it highlights the important conclusions that can be drawn from these examples. The key aim of this article and of the series as a whole is to provide a comprehensive overview of the types of PCDD/F contaminated sites that exist as a result of historical activities. It details the various processes whereby these sites became contaminated and attempts to evaluate their contemporary relevance as sources of PCDD/Fs and other POPs. It also details the various strategies used to assess these historical legacies of contamination and the concepts developed, or which are under development, to effect their remediation. MAIN FEATURES: Special sessions on 'Contaminated sites--Cases, remediation, risk and policy' were held at the DIOXIN conferences in 2006 and 2007, and this theme will be continued at DIOXIN 2008 to be held in Birmingham. Selected cases from the approximately 70 contributions made to these sessions, together with some additional invited case studies are outlined together with the key issues they raise. By evaluating these cases and adding details of experiences published in the current literature, an overview will be given of the different features and challenges of dioxin and POP-contaminated sites. RESULTS: This article provides a systematic categorisation of types of PCDD/F and POP-contaminated sites. These are categorised according to the chemical or manufacturing process, which generated the PCDD/Fs or POPs and also includes the use and disposal aspects of the product life cycle in question. The highest historical PCDD/F and dioxin-like polychlorinated biphenyl (PCB) contamination burdens have arisen as a result of the production of chlorine and of chlorinated organic chemicals. In particular, the production of chlorinated pesticides, PCBs and the related contaminated waste streams are identified being responsible for historical releases of toxic equivalents (TEQs) at a scale of many tonnes. Along with such releases, major PCDD/F contaminated sites have been created through the application or improper disposal of contaminated pesticides, PCBs and other organochlorine chemicals, as well through the recycling of wastes and their attempted destruction. In some extreme examples, PCDD/F contaminated sites have also resulted from thermal processes such as waste incinerators, secondary metal industries or from the recycling or deposition of specific waste (e.g. electronic waste or car shredder wastes), which often contain chlorinated or brominated organic chemicals. The examples of PCDD/F and dioxin-like PCB contamination of fish in European rivers or the impact of contaminated sites upon fishing grounds and upon other food resources demonstrate the relevance of these historical problems to current and future human generations. Many of the recent food contamination problems that have emerged in Europe and elsewhere demonstrate how PCDD/F and dioxin like PCBs from historical sources can directly contaminate human and animal feedstuffs and indeed highlight their considerable contemporary relevance in this respect. Accordingly, some key experiences and lessons learnt regarding the production, use, disposal and remediation of POPs from the contaminated sites are summarised. DISCUSSION: An important criterion for evaluating the significance and risks of PCDD/Fs and other POPs at contaminated sites is their present or future potential for mobility. This, in turn, determines to a large degree their propensity for off-site transport and environmental accessibility. The detailed evaluation of contaminated site cases reveals different site-specific factors, which influence the varied pathways through which poor water-soluble POPs can be mobilised. Co-contaminants with greater water solubility are also typically present at such sites. Hence, pumping of groundwater (pump and treat) is often required in addition to attempting to physically secure a site. At an increasing number of contaminated sites, securing measures are failing after relatively short time spans compared to the time horizon, which applies to persistent organic pollutant contamination. Due to the immense costs and challenges associated with remediation of contaminated sites 'monitored natural attenuation' is increasingly gaining purchase as a conceptual remediation approach. However, these concepts may well prove limited in their practical application to contaminated sites containing persistent organic pollutants and other key pollutants like heavy metals. CONCLUSIONS: It is inevitable, therefore, that dioxin/POP-contaminated sites will remain of contemporary and future relevance. They will continue to represent an environmental issue for future generations to address. The securing and/or remediation of dioxin/POP-contaminated sites is very costly, generally in the order of tens or hundreds of millions of dollars. Secured landfills and secured production sites need to be considered as constructions not made for 'eternity' but built for a finite time scale. Accordingly, they will need to be controlled, supervised and potentially repaired/renewed. Furthermore, the leachates and groundwater impacted by these sites will require ongoing monitoring and potential further remediation. These activities result in high maintenance costs, which are accrued for decades or centuries and should, therefore, be compared to the fully sustainable option of complete remediation. The contaminated site case studies highlight that, while extensive policies and established funds for remediation exist in most of the industrialised western countries, even these relatively well-regulated and wealthy countries face significant challenges in the implementation of a remediation strategy. This highlights the fact that ultimately only the prevention of contaminated sites represents a sustainable solution for the future and that the Polluter Pays Principle needs to be applied in a comprehensive way to current problems and those which may emerge in the future. RECOMMENDATIONS AND PERSPECTIVES: With the continuing shift of industrial activities in developing and transition economies, which often have poor regulation (and weak self-regulation of industries), additional global challenges regarding POPs and other contaminated sites may be expected. In this respect, a comprehensive application of the "polluter pays principle" in these countries will also be a key to facilitate the clean-up of contaminated areas and the prevention of future contaminated sites. The threats and challenges of contaminated sites and the high costs of securing/remediating the problems highlight the need for a comprehensive approach based upon integrated pollution prevention and control. If applied to all polluting (and potentially polluting) industrial sectors around the globe, such an approach will prove to be both the cheapest and most sustainable way to underpin the development of industries in developing and transition economies.     

On the thermally induced isomerisation of hexabromocyclododecane stereoisomers

The interconversion of the stereoisomers contained in technical 1,2,5,6,9,10-hexabromocyclododecane, a major brominated flame retardant increasingly found in the environment and in biota, was investigated at elevated temperatures. The application of pure enantiomers of the three constituents alpha-, beta-, and gamma-HBCD enabled the unambiguous elucidation of the individual isomerisation reactions as well as the quantification of all respective rate constants. At 160 degrees C the rate constants range over two orders of magnitude from 1.50x10(-3) to 1.88x10(-5)mol(%)s(-1). A preliminary mechanistic explanation for the differences of the rate constants which govern the composition of HBCD diastereomers at equilibrium is given.     

Changes in toxicity and Ah receptor agonist activity of suspended particulate matter during flood events at the rivers Neckar and Rhine — a mass balance approach using in vitro methods and chemical analysis

Background, aim, and scope  

As a consequence of flood events, runoff and remobilized sediments may cause an increase of ecotoxicologically relevant effects from contaminant reservoirs. Aquatic and terrestrial organisms as well as cattle and areas of settlement are exposed to dislocated contaminants during and after flood events. In this study, the impacts of two flood events triggered by intense rain at the rivers Neckar and Rhine (Southern Germany) were studied. Effects in correlation to flood flow were assessed at the river Neckar using samples collected at frequent intervals. River Rhine suspended particulate matter (SPM) was sampled over a longer period at normal flow and during a flood event. Three cell lines (H4L1.1c4, GPC.2D.Luc, RTL-W1) were used to compare Ah receptor agonist activity in different biotest systems. Multilayer fractionation was performed to identify causative compounds, focusing on persistent organic contaminants.     

Evidence for a significant contribution of wood burning aerosols to PM2.5 during the winter season in Paris,France

Although particulate emissions from residential wood burning have become a subject of great scientific concern for a few years, data related to their impact on the air quality of large European urban centres are still missing. In the present study, we investigated the chemical and optical properties of fine (PM_2.5) carbonaceous aerosols in Paris during the 2005 winter season in order to track the presence of wood burning emissions in such a large city. The use of a seven wavelength Aethalometer allowed us to document shortwave light absorption by brown-carbon-containing organic aerosols of biomass burning origin. In particular, a well-marked diurnal pattern of the spectral dependence of light absorption, with maxima during the night, could be observed every day of the campaign and attributed to wood burning emissions. Relatively high absorption Ångstrom exponents and WSOC/OC ratios (respectively 1.25 and 0.35 on average for the period of study) also indicated the importance of biomass burning aerosols in the Paris atmosphere in winter. Finally, a rough estimate of the contribution of wood burning carbonaceous aerosols to PM_2.5 could be achieved. This contribution was found to be as high as 20 ± 10% on average at the Paris background site investigated here.     

How to improve reliability in groundwater analysis: over a decade of experience with external quality control in field campaigns on volatile halogenated compounds

The reliability in measurement results obtained during environmental monitoring is crucial for the assessment and further planning of remediation efforts on the respective contaminated sites by the responsible authorities. A case study concerned with groundwater contaminated with perchloroethylene, trichloroethylene and 1,1,2-trichlorotrifluoroethane including their degradation products which involves private contract laboratories and an independent provider of quality assurance (QA) is presented. The experience gained with biannual monitoring campaigns over 14 years indicates that the selection of contractors on basis of accreditation status and successful performance in interlaboratory comparisons are not sufficient. Rather the auditing of the contractors by the QA provider prior to each campaign and the crosschecking of selected monitoring samples by the QA provider led to a lasting improvement of reliability in the contractors' measurement results. A mean deviation of 20% from the reference value determined by the QA provider for the crosschecked samples was reached.     

Sink–float density separation of post-consumer plastics for feedstock recycling

The paper focuses on current mechanical waste processing technologies and out-of-the-box processes linked to the processing of coal and mineral resources, to ensure high-quality feedstock recycling of polyolefin-rich post-consumer plastic fractions. Moreover, the study aims to provide the basis for the technical and economic feasibility of the chemical recycling route of this plastic fraction. When evaluating common mechanical processes, either dry or wet ones, sink–float separation in a cylindrical centrifugal force separator achieves the best results. It combines the advantages of a simple, robust apparatus of low complexity and high capacity with selective separation through the accelerated settling of particles in the centrifugal field. Furthermore, the disconnection of the separation medium feed from the solid input increases residence times. Based on the above findings, a pilot-scale plant was constructed which consists of a centrifugal force separator and a hydro jig for the pre-separation of heavy waste components. Several test campaigns were conducted to separate polyolefins from various waste fractions. Two-stage processing in the centrifugal force separator rendered almost 90 wt% of polyolefin content in the produced lightweight fraction and of polyolefin recovery. One-stage processing, on the other hand, resulted in reduced polyolefin content in the lightweight fraction.