Although dioxins and related compounds (DXNs) are toxic, they can be kept away from living matter through the DXN abatement strategy involving adsorption and suppressed formation. Although DXNs are inevitably generated through fire-handling, nature and humans have achieved the ability to coexist in a divided state, which makes keeping them away from living matter possible. This natural mechanism of “divided coexistence” is frequently found, e.g. biological utilization of toxic but essential elements such as selenium in blood, confinement of heavy metals in sediment soil, and stabilization of thermally activated hexavalent chrmium (Cr (VI)) by biomass organic substances. These mechanisms have apparently been achieved as a result of long-term interaction between nature and living matter, and has hence enabled the coexistence of nature-based hazardous metals in the living sphere. It must be noted here that the mechanism does not function for all hazardous substrates. Chemicals with high mobility and persistence, like POPs chemicals, are potentially ingested; in other words, “divided coexistence” may be impossible for those chemicals.

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The aryl hydrocarbon receptor (AhR) is a pivotal chemical sensor that transduces external and internal stimuli into biological responses. AhR was originally thought to be involved in not only xenobiotic metabolism but also carcinogenic and toxicological responses against environmental pollutants, such as polycyclic aromatic hydrocarbons and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, recent studies demonstrate that the AhR plays multiple intrinsic roles in host defense and homeostasis. This includes immunity, stem cell maintenance, and cell differentiation upon binding with an increasing number of newly defined dietary, cellular, and microbe-derived ligands. In addition, AhR is a convergence point for several signaling cascades, which may be involved in the diverse diseases caused by binding of the persistent ligand TCDD with extremely high affinity to AhR. A comprehensive understanding of physiological and pathological processes initiated by endogenous AhR agonists and antagonists may allow for the therapeutic regulation of AhR activity. Thus, the AhR can be a valuable diagnostic marker and therapeutic target for human diseases.

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At the 2002 World Summit on Sustainable Development (WSSD), a transparent, scientifically based goal with regard to the management of hazardous chemicals was adopted by participants in their statement, “We aim to achieve by 2020 to ensure that chemicals be used and produced in a way that minimizes the significant adverse effects on human health and the environment by using evaluation procedures.” Aiming to achieve this WSSD 2020 target, the international community is promoting a management policy regarding harmful chemical substances, including persistent organic pollutants such as dioxins throughout their life cycle. In this paper, after determining global trends in chemical substance management and clarifying the position of measures against dioxins, the actual details of risk management for dioxins focusing on the aryl hydrocarbon receptor (AhR) and dioxin-like compounds (i.e. must elicit AhR-mediated biochemical and toxic responses, and must show environmental persistence and bioaccumulation) is summarized and an approach is introduced.

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A copious amount of chemical substances can be found within our modern living environments. The Chemical Abstracting Service (CAS) in the United States has already created a register to track them, which currently exceeds 140 million different ones. The toxicity of each chemical substance is evaluated through a general toxicity test. In this paper, the 50 % lethal dose (LD50) and the no-observed adverse effect level (NOAEL) are compared in order to evaluate the level of toxicity. Humans are exposed to these environmental pollutants via a number of different routes. Subsequently, many chemical substances are detoxified through means such as absorption, distribution and the metabolism process. However, some environmental pollutants result in metabolic activation by cytochrome P450 ; its active metabolites convert into highly toxic substances. This paper provides an outline of the toxicity test and cytochrome P450. Moreover, a few examples of metabolic activation are given and the importance of the toxic evaluation of the chemical substances and their metabolites is asserted.

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article provides an overview of current knowledge on microbial degradation and transformation, as well as plant uptake of dioxins and dioxin-like compounds. Higher chlorinated dioxins can be reductively dechlorinated by anaerobic bacteria such as Dehalococcoides. Lower chlorinated dioxins can be cometabolically degraded by aerobic bacteria such as Sphingomonas, Pseudomonas and Burkholderia. Chlorinated dioxins can also be degraded under aerobic conditions by white-rot fungi that utilize cytochrome P450 and extracellular lignin-degrading peroxidases. Plants of the Cucurbitaceae family can uptake chlorinated dioxins from soil and translocate them to stems and leaves. Rhizodegradation of dioxin-contaminated soils is an effective and environmentally-friendly means of remediation.

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“Best available techniques (BAT)” and “best environmental practices (BEP)” are used to discuss technology and management systems that minimize unintentional-formation chemicals listed in Annex C of the Stockholm Convention on Persistent Organic Pollutants (POPs). Considering technological, economical, and regional features for each of the contracting countries of the Stockholm Convention, activities to minimize unintentional-formation chemicals are promoted based on the Guidelines on BAT and Provisional Guidance on BEP. Guidelines also contain definitions of terms, sources of unintentional-formation chemicals, release limitations, factors related to unintentional formation, flue gas treatment techniques, and application of BAT/BEP to each source. Japan has already undertaken several actions, including consolidation of the legal system, application of control techniques, efforts on PCB as a by-product in organic pigment, and so on. Recently, application of BAT/BEP is also discussed for POPs listed in Annex A (elimination) and Annex B (restriction) as chemicals of unintentional formation. This shows how the various issues involving open burning of electronic waste have proliferated as one of the novel sources and by unintentional formation from thermal destruction of new POPs in Annex A.

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