Documents polychlorinated dibenzofurans 2 results

"A general model to take into account the distribution of persistent organic pollutants (POPs) in the water column as well as POPs interaction with the atmosphere and sediments has been developed. The model has been adapted to deal with several families of POPs, including PCBs (Polychlorinated Biphenyls), PAHs (Polycyclic Aromatic Hydrocarbons), PBDEs (Polybrominated Dyphenyl Ethers) and PCDD/Fs (Polychlorinated dibenzo-p-dioxins and dibenzofurans). The simulated time series concentrations for one year are in general in good agreement with experimental observations from literature for these families of contaminants. However, specific designed campaigns still need to be performed to validate the model with a set of homogenous forcings concerning air and historical sediment concentrations as well as data on evolution of concentrations in the water column and in the surficial sediment layer. The model is being coupled with a biogeochemical model to assess the influence of phytoplankton, zooplankton and bacteria on the dynamics of POPs. In a further step, the model will be used to analyze the data obtained from different experimental campaigns carried out in Thresholds as well as mesocosm experiments."

"Evaluates the carcinogenic risks to humans posed by exposure to polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). PCDDs are formed as inadvertent by-products, sometimes in combination with PCDFs, during the production of chlorophenols and chlorophenoxy herbicides, and have been detected as contaminants in these products. PCDDs and PCDFs may also be produced in thermal processes such as incineration and metal-processing and in the bleaching of paper pulp with free chlorine. Of the PCDDs, 2,3,7,8-tetrachlorodibenzo-para-dioxin (2,3,7,8-TCDD), or "dioxin", has attracted the greatest concern. PCDDs and PCDFs are ubiquitous in soil, sediment, and air, persist in the environment, and accumulate in animal fat. Excluding occupational and accidental exposures, most human exposure to these compounds occurs from the consumption of meat, milk, eggs, fish, and related products. Occupational exposures at higher levels have occurred since the 1940s as a result of the production and use of chlorophenols and chlorophenoxy herbicides and, for PCDFs, in metal production and recycling. Even higher exposures have occurred in sporadic industrial accidents and following incidents of rice oil contamination. The evaluation, which considered abundant human and animal carcinogenicity data, found strong evidence from epidemiological studies in humans that exposure to 2,3,7,8-TCDD produces increased risks for all cancer combined, rather than for any specific site, suggesting that 2,3,7,8-TCDD is an unprecedented multi-site carcinogen with no single site predominating. Citing data from animal studies and other lines of evidence, the monograph concludes that 2,3,7,8-TCDD is carcinogenic to humans. Other polychlorinated dibenzo-para-dioxins and dibenzo-para-dioxin could not be classified as to their carcinogenicity to humans. For PCDFs, the evaluation considered evidence from two large poisoning incidents involving rice oil contamination in Japan and Taiwan. Although excessive mortality from liver cancer was observed in long-term follow-up of the Japanese cases, the report cited other factors, including a high prevalence of chronic hepatitis B infection in the geographical area concerned, as possible explanations. Evidence of carcinogenicity to human was judged inadequate. In the absence of convincing data from experimental animals, PCDFs could not be classified as to their carcinogenicity to humans."