In humans acute poisoning can lead to chloracne, nausea with vomiting and irritation of the upper respiratory tract, peripheral neuropathy, disorders of the lipid metabolism and liver damage (Nau et al., 2003). Cases of poisoning like this have been reported after chemical accidents, such as in 1976 in Seveso in Italy and occupational exposure of workers in chemical factories.
Negative effects of dioxins and dioxin-like PCBs are mediated through binding to the aryl hydrocarbon receptor (AHR) (Schmid and Bradfield, 1996). Impairment of the immune system, the nervous system, the hormone balance and of reproductive functions have all been observed as chronic effects of dioxins in animal experiments. Chronic exposure to dioxins has led to various types of cancer in animals (WHO, 2002, 2010). Genotoxicity investigations have shown that dioxins have no mutagenic potential. Dioxins and dioxin-like PCBs are consequently assigned to the tumour promoter group. Tumour promoters accelerate the development of tumours from damaged cells, but are not themselves able to trigger tumour formation by damaging DNA (Nau et al., 2003).
All dioxin and dioxin-like PCB congeners are toxic to varying degrees. In order to sum up the toxicity of these various compounds and to facilitate risk assessment and regulatory control, the concept of the toxic equivalency factor (TEF) has been introduced (WHO, 2000). Various toxicity equivalency factors (TEFs) are used to express the equivalency of a given mixture: thus the most toxic dioxin 2,3,7,8-tetrachlordibenzodioxin (2,3,7,8-TCDD), the so-called Seveso dioxin, has a TEF of 1, while a less toxic mixture will have a value of 0.5 for example. All congeners found in an analysis are multiplied by their respective TEFs and are then added together. The results of analysis are expressed as a single quantifiable unit, called the TCDD toxic equivalency (TEQ) (Nau et al., 2003, EK, 2006).
Various bodies have now derived tolerable intake levels for dioxins and dioxin-like PCBs. The World Health Organization (WHO) has set a tolerable daily intake (TDI) of 1 to 4 pg WHO-TEQ per kg and day (WHO, 2000). However, due to the long half-life of dioxins and dioxin-like PCBs, this value has been revised and the tolerable intake level set for a month in order to estimate the health risk. The WHO calculated a provisional tolerable monthly intake (PTMI) of 70 pg WHO-TEQ/kg body weight and month (WHO, 2002).
In its statement of 30 May 2001 the EU’s Scientific Committee on Food, SCF, set a tolerable weekly intake (TWI) of 14 pg WHO-TEQ/kg body weight and month for dioxins and dioxin-like PCBs (SCF, 2001). For someone weighing 70 kg, this yields a weekly tolerable intake of 980 pg WHO-TEQ.