Survey of dioxin-like compounds in dairy feeds in the United States.

The United States Environmental Protection Agency (USEPA) has completed a survey of dioxin-like compounds (including 17 dioxin and furan (CDD/F) congeners and 12 coplanar polychlorinated biphenyl (PCBs) congeners) in dairy feeds from 10 dairy research facilities around the United States, sampling the overall mixtures and the major and minor feed components. Low levels of dioxin were found in all feed mixtures with an average concentration of 0.05 pg/g (ppt) toxic equivalent (TEQ) dry weight. This is lower than previously found in dairy feeds by about a factor of 4. While it is possible that generally lower levels of dioxins in the environment in recent years may explain this result, examinations of the data suggest that the oven drying used to prepare the wet feed samples could have resulted in a loss of dioxins from the feed materials. The percentage of the total TEQ due to CDD/Fs was about four times that of PCBs. Leafy vegetations in the feed (the silages and the hays) had concentrations about twice as high as nonleafy, protected vegetation of the feeds (the ground or meal corn, cottonseed, and others). Minor components did not significantly influence the final feed mixture concentration of dioxin TEQ. However, in one of the feed mixtures, a minor component with a high concentration of 38.5 ppt TEQ effectively doubled the concentration of the overall feed mixture.

Variables affecting emissions of PCDD/Fs from uncontrolled combustion of household waste in barrels.

The uncontrolled burning of household waste in barrels has recently been implicated as a major source of airborne emissions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). A detailed, systematic study to understand the variables affecting emissions of PCDD/Fs from burn barrels was performed. The waste composition, fullness of the barrel, and the combustion conditions within the barrel all contribute significantly to determining the emissions of PCDD/Fs from burn barrels. The study found no statistically significant effect on emissions from the Cl content of waste except at high levels, which are not representative of typical household waste. At these elevated Cl concentrations, the impact of Cl on PCDD/F emissions was found to be independent of the form of the Cl (inorganic or organic). For typical burn conditions, most of the PCDD/F emissions appear to be associated with the later stages of the burn when the waste is smoldering. Polychlorinated biphenyls (PCBs) were also measured for a subset of the tests. For the nominal waste composition, the average emissions were 76.8 ng toxic equivalency units (TEQ)WHO98/kg of waste combusted, which suggests that uncontrolled burning of household waste could be a major source of airborne PCDD/Fs in the United States.

Investigation of the potential release of polychlorinated dioxins and furans from PCP-treated utility poles.

The United States (US) Environmental Protection Agency (EPA) estimated that the use of technical grade pentachlorophenol (PCP) between 1970 and 1995 to treat wood was approximately 400,000 metric tons in the US, and that between 4800 and 36,000 g of 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalents (TEQs) were incorporated annually in treated wood. The EPA has been unable, however, to estimate the rate of release of polychlorinated dibenzo-p-dioxins and dibenzofurans (CDD/Fs) from treated utility poles into the environment. There is some evidence that CDD/Fs leach from treated poles into the surrounding soils, but these studies do not allow for the calculation of a rate of release from this mechanism. Another possible release mechanism is the volatilization of dioxins into the atmosphere, but there are no data to demonstrate, much less quantify, this release. While not directly measuring the release of dioxins from treated utility poles into the environment, this study was designed to examine the potential for such release. The general approach taken was to collect PCP-treated poles of varying ages, to remove and analyze multiple samples from each pole cross-section, and to compare the spatial distribution of CDD/F congeners among poles of different ages. Evidence of concentration-depth profile changes over time may provide insight into the potential for dioxins to migrate through and then out of PCP-treated utility poles. It was found that the CDD/F concentrations were consistently higher in the outer portions of the poles than the center. This trend tends to be most marked in older poles and for the lower chlorinated congeners. The trend for dioxins to concentrate in the outer portions of the pole over time suggest migration within the poles, and this migration may result in some environmental release. Other possible explanations were also offered.