The main focus of the current study was to identify risk scenarios where polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in wastes are distributed in the environment and transferred to humans via food and other exposure pathways. Two field studies were conducted at sites where wastes and ashes are managed and stored open, one in Thailand and one in Peru. The aim of these studies was to investigate the degree of local environmental impact. To be able to relate human exposure levels to the suggested LPCL for PCDD/F, a risk assessment was performed using a fate and exposure model (CalTOX), supported by field data from Peru. Additional human exposure from local sources was estimated in relation to inevitable human exposure related to diffuse emissions by exposure calculations. The aim of the exposure assessment was to establish whether point sources may contribute to human body burdens above the exposure levels that we are inevitably subject to from existing background levels as a result of diffuse pollution. 2.1 Dioxin contaminated waste in current case studies We identified four major waste categories as being potentially important in the context of this study: i) incineration residues, ii) chemical waste, iii) waste wood fractions and iv) waste from e-waste recycling sites A limited number of recent case studies are reported for categories i, ii and iv, while case studies for chemical waste mostly are related to historical incidents. Trading and shipping of waste wood fractions may be of special importance since there are recently reported incidents where this waste fraction has contaminated human food chains at animal food production facilities. For ashes, we only identified one study, and it is reported from Britain, where bottom ash and some fly ash from a municipal waste incinerator were recycled as path material in an allotment area. This resulted in elevated concentrations in free-range chicken eggs. All incidents for waste wood and ash are reported from European countries, but this certainly does not exclude the possibility that that serious risk scenarios exist for developing countries as well. Since these problems can arise in Europe, in spite of well established and robust regulatory frameworks and practices, the probability of similar events occurring in countries with more limited environmental control is even higher. However, environmental and food/feed control data from developing countries are often lacking. Since several hazardous pollutants may be present at high levels in waste and open waste dumping sites, some exposed subpopulations (e.g. waste pickers) are at risk for increased exposure. Management of PCDD/F contaminated waste may thus be a serious, but a so far, not well-documented problem. It can be difficult to relate an environmental impact to management of waste in areas where other sources co-exist. In the field studies in Peru and Phuket, consequences of open and unprotected storage of ash could therefore not be investigated separately from the influence of local air emissions. 2.2 Food and exposure levels related to local sources Several studies have reported local PCDD/F contamination of soils and waters related to industrial point sources, spills, accidents and other polluting activities. At these sites, elevated exposure levels of humans may occur, often related to consumption of locally produced food. In cases where abiotic media, such as soil or air, are severely polluted, direct exposure of the media, e.g. via ingestion of soil, could also result in high exposure of local inhabitants. All animal food and feed products contain PCDD/Fs as a result of accumulation from historic and current emissions from various sources. Levels of contamination in food and feed produced near local sources are therefore often related to elevated levels in the environment. This can then result in higher exposure of people residing in vicinity of the source, compared with the exposure levels for the overall population. A number of studies show that consumption of locally produced free range chickens and eggs is a high risk scenario. Some studies also show that environmental background concentrations in rural scenarios with no local pollution ‘hotspots’ can cause relatively high PCDD/F levels in free-range eggs. It is difficult to predict concentrations in eggs with high accuracy. The transfer routes between the environment and chickens are numerous and complex, and are not easily described by models. Factors such as congener composition (relative abundance of congeners) breeding and feeding conditions, soil type and vegetation cover, etc., will affect the bioaccumulation. Results from single case studies can therefore not be used to establish generic soil-to-egg transfer ratios. Production of other animal food products, such as milk and meat, is also a high risk scenario in the presence of local sources. According to dietary intake studies in different countries, generic population exposures are often close to, or exceed, the WHO Tolerable Daily Intake (TDI) value. The TDI is an estimate of the average daily intake of a contaminant that can be ingested over a lifetime without appreciable health risk. However, the intake levels differ considerably between different countries. A limited number of studies have dealt with human body burdens and dietary intakes for populations in developing countries. Since food consumption habits and living conditions differ between different countries, it may be problematic to use data from industrialised country conditions to express an opinion of the PCDD/F exposure of humans in developing countries. 2.3 Review of the BIPRO assessment In the risk assessment of PCDD/Fs conducted by a German consultant (BIPRO) for the European Commission it was assumed that the legislated maximum level in commercial eggs is correlated to human health risks based on the tolerable daily intake (TDI). Since the maximum level in food is not based on a human health risk assessment, compliance of PCDD/Fs levels in eggs (or other food items) with the legislated limits is not an indicator of the risk level and should not be used as a criteria in a risk assessment. The risk assessment by BIPRO assumes that a PCDD/F concentration of 30 pg WHOTEQ g-1 fat is acceptable in eggs. By using soil-to-egg transfer factors (so called BTF, biotransfer factors) from two studies, they estimated that the critical PCDD/F concentration of 30 pg WHO-TEQ g-1 fat in eggs corresponds to soil concentrations of 1 000 ng TEQ kg-1 d.w. (1 ppb). A consumption of one egg per day is enough to yield a significant contribution to TDI if the eggs contain 3 pg WHO-TEQ g-1 fat or more. In contrast to the conclusions in the BIPRO report, these intake calculations indicate that egg concentrations should not exceed the EU limit value (3 pg WHO-TEQ g-1 fat). A compilation of literature data showed that estimations of soil-to-egg transfer of PCDD/Fs and dl-PCBs are highly variable, and that dl-PCBs are much more available than PCDD/Fs. Considering the large variability of the soil-to-egg transfer factors, selected bio-transfer factors from only a few studies are not representative of generic scenarios. The adopted transfer factor by BIPRO was in the upper range of those calculated from the literature. Thus, there is a risk that BIPRO significantly underestimates the risk for transfer of PCDD/F into eggs at soil concentrations of 1 000 ng TEQ kg-1 d.w. (1 ppb). According to the BTFs calculated from the literature, 3 pg WHO-TEQ g-1 fat in eggs can be reached already at soil concentrations of 1-70 ng TEQ kg-1 d.w. (0.001-0.07 ppb). The TDI includes exposure both for PCDD/Fs and dl-PCBs, and both compound groups may be transferred from solid waste matrices into human food chains, even though dl-PCBs are more available than PCDD/Fs. Since BIPRO did not consider the contribution from dl-PCBs in waste to the food chain transfer, their assessment does not reflect the total risk.