Mobility, 2,3,7,8-TCDD

An environmental protocol has been developed to assess the significance of newly discovered hazardous substances that might enter soil, water, and the food chain. Using established laboratory procedures and C-labeled 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), gas chromatography, and mass spectrometry, we determined mobility of TCDD by soil TLC in five soils, rate and amount of plant uptake in oats and soybeans, photodecomposition rate and nature of the products, persistence in two soils at 1,10, and 100 ppm, and metabolism rate in soils. We found that TCDD is immobile in soils, not readily taken up by plants, subject to photodecomposition, persistent in soils, and slowly degraded in soils to polar metabolites. Subsequent studies revealed that the environmental contamination by TCDD is extremely small and not detectable in biological samples. 

Their mobility may be increased by the simultaneous presence of organic solvents such as mineral oil. The half-life of TCDD in soil has been reported as 10-12 years, whereas photochemical degradation seems to be considerably faster but with a large variation that might be explained by experimental differences (solvents used, etc.). Highly chlorinated PCDD/PCDFs seem to be more resistant to degradation than those with just a few chlorine atoms. 

Environmental applications of SFE appear to be the most widespread in the literature. A typical example is the comparison of extraction efficiency for 2,3,7,8 -tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from sediment samples using supercritical fluid extraction and five individual mobile phases with Soxhlet extraction was made (101). The mobile phases, carbon dioxide, nitrous oxide, pure and modified with 2% methanol as well as sulfur hexafluoride were examined. Pure nitrous oxide, modified carbon dioxide and modified nitrous oxide systems gave the recoveries in the acceptable range of 80 to 100%. Carbon dioxide and sulfur hexafluoride showed recoveries of less than 50% under identical conditions. Classical Soxhlet recoveries by comparison illustrated the poorest precision with average extraction efficiencies of less than 65%. Mobile phase choice, still as yet a major question in the science of supercritical fluid extraction, seems to be dependent upon several factors polarity of the solute of interest, stearic interactions, as well as those between the matrix and the mobile phase. Physical parameters of the solute of interest, as suggested by King, must also be considered. Presently, the science behind the extraction of analytes of interest from complex matrices is not completely understood. 

TCDD was virtually undetected. The most commonly detected 2,3,7,8-substituted congener was OCDD followed by 1,2,3,4,6,7,8-HpCDD. The predominance of 1,2,3,4,6,7,8-HpCDD as the most persistent congener is associated with stationary or mobile combustion source emissions. 

Freeman RA, Schroy JM. 1985. Environmental mobility of TCDD. Chemosphere 14 873-876. 

Freeman RA, Schroy JM, Hileman FD, et al. 1986. Environmental mobility of 2,3,7,8-TCDD and companion chemicals in a roadway soil matrix. In Rappe C, Choudhary G, Keith LH, eds. Chlorinated dioxins and dibenzofurans in perspective. Chelsea, MI Lewis Publishers, Inc., 171-183. 

Palansky J, Kapila S, Manahan SE, et al. 1986. Studies on vapor phase transport and role of dispersing medium on mobility of 2,3,7,8-TCDD in soil. Chemosphere 15 1389-1396. 

In this study 154 exposed and 155 unexposed persons were examined. The exposed persons had been living in a mobile home park in which 2,3,7,8-TCDD contaminated waste oil was sprayed for dust control. The TCDD contamination dated back to 1971 when TCDD-contaminated sludge wastes were taken from a hexachlorophene production facility (11,52) Levels of 2,3,7,8-TCDD up to 2.2 ppm (mg/kg) were still present more than ten years later. No increased clinical illness was noted in the group who had lived in the contaminated mobile... 

The presence of water and/or sunlight is an important environmental parameter for the mobility of TCDD. Water appears to weaken the binding of TCDD to the soil matrix. 

The environmental behavior of chemicals with a very low volatility, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has been the subject of several studies over the last few years. The focus of these studies has varied from the development of physical property data ( 1,2) to lab and field tests of the mobility and/or fate of TCDD. 

The overall goal of this research was to study the mobility of TCDD under actual field conditions to determine the influence of such natural phenomena as rain, floods, sunlight, and heat. The Missouri Department of Natural Resources established a Dioxin Research Station at the Times Beach Site during the late Spring and early Summer of... 

For the dry and shaded control experiment (Plot D - Shaded) the surface scraping sample concentration falls within the 2 standard deviation limits about the mean. This implies that no statistically significant loss of TCDD occurred in the dry shaded plot. Therefore, the presence of water and/or sunlight are important environmental parameters affecting the mobility of TCDD in soils. 

TCDD is mobile in soils in the field environment represented by typical Times Beach, Missouri soil. 

Several medical studies are presented in Table X which have been conducted in groups outside of the industrial sector. In a medical study of exposed Seveso subjects, the prevalence of peripheral neuropathy was three times higher among those exposed persons with chloracne (57). In a study of Missouri residents from a mobile home park with soil contamination with 2,3,7,8-TCDD, some parameters of immune response were reported to differ between the exposed and unexposed (58). The U.S. Air Force completed a comprehensive medical study of the personnel of Operation Ranch Hand, the individuals who sprayed Agent Orange in Vietnam (50). Increased prevalence of enlarged livers and an increase of basal and squamous cell carcinomas was observed. 

The mobile Incinerator passed a series of trial burns (conducted between February 25 and April 8, 1985) and attained destruction and removal efficiencies exceeding 99.999 percent as required by RCRA for 2,3,7,8-TCDD-contamlnated materials burned In the system. Furthermore, the waste process streams, consisting of kiln ash and quench water, were successfully delisted. 

In 1980, Syntex, Inc., utilized a process based on photolysis to destroy approximately 13 pounds of 2,3,7,8-TCDD contained in 4300 gallons of oily trichlorophenol still-bottom residues ( ). In 1984, EPA began to use a transportable rotary kiln incinerator to detoxify solid and liquid waste which were contaminated with 2,3,7,8-TCDD (i6). Concurrent with the incineration activities, EPA began removing soils and other contaminated materials from a number of sites including a mobile home park near Grays Summit, Missouri. These activities required the application of extensive compositing techniques and statistical treatment of the data to assure the removal of... 

Eglin Air Force Base. The goals of the test effort were to evaluate the effect of time and temperature on 2,3,7,8-TCDD rernoval efficiency and to establish the importance of soil type. The samples were selected by the Air Force based on results of site surveys to yield high contamination levels in order to investigate a broad range of treatability. This testing was an extension of earlier testing performed for the EPA on two dioxin-contaminated soil samples from Missouri to support EPA s mobile incinerator trial burn in 1985 (5). 

Photolysis has had limited application for treatment of hazardous waste or detoxification of chemically contaminated materials. The susceptibility of chlorinated aromatics, including herbicides such as 2,4-D and 2,4,5-T, to UV-induced decomposition is well established (7,8). Photodecomposition of such compounds leads to successive dechlorination followed by condensation reactions to form phenolic polymers (7,8). Other research has demonstrated that CDD and CDF decompose in the presence of UV light (8,9,10) Development of a photochemical process for destroying 2,3,7,8-TCDD in a waste tar indicated similar dechlorination and condensation reactions and products (8). The high-molecular weight end products, which are similar in structure to humic acids, would be expected to have low toxicity and mobility. Therefore, essentially complete... 

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