Dioxin, contaminants from herbicides

Elevated human tissue dioxin levels found in certain areas after environmental contamination were described in previous publications (1-3). The highest levels were noted in human breast milk lipid a few years following heavy 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) contamination from herbicides, especially Agent Orange, sprayed in Vietnam. Elevated levels in this tissue from individuals living in the south of Vietnam decreased with time but were still above levels observed in samples from the North American continent ( ) It was hypothesized that the relatively low human tissue levels of dioxins observed in individuals living in the north of Vietnam may be attributed... 

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin TCDD) is among the most toxic compounds known today. It is an airborne contaminant from an incineration process, which has been described in Section 3.3.2. Dioxin also frequently occurs as an impurity in the herbicide 2,4,5-T. Accordingly, when the herbicide 2,4,5-T is applied to crops, dioxin is also released to the soil. Any spills of dioxin also cause soil contamination. It may be removed by extraction with coconut-activated carbon. Its half-life in soil is about one year. 

The Basic Extractive Sludge Treatment (B.E.S.T. ) process is an ex situ solvent extraction technology. The B.E.S.T. process uses one or more secondary or tertiary amines, such as diisopropylamine, to separate contaminants from soil, sediment, and sludge. This technology is applicable to most organics or oily contaminants, including polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pesticides, herbicides, dioxins, furans, and other organic compounds. 

TCDD and other chlorinated dibenzo-J -di-oxins are released during the combustion of many polychlorophenols and also occur as contaminants in various chemicals such as the herbicide 2,4,5-trichlorophenoxyacetic acid. Most high-level exposure to 2,3,7,8-TCDD and other dioxins results from accidental releases or explosions in chemical plants or storage facilities for dioxin-containing chemicals. Because of the persistence of dioxin congeners in the environment and their potential for bioaccumulation, exposure may occur via the soil, air (especially when dioxins occur as combustion products), or water. When bound to components of the soil, the health hazard from 2,3,7,8-TCDD is reduced compared to ingestion of the pure compound. However, its bioavailability varies with the specific media in which it occurs. 

A combination of the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-T (Agent Orange), was used by the US military during the Vietnam War for defoliation. Long-term health consequences from exposure to Agent Orange, in particular to dioxin contaminants, have been suspected. 

TCDD, the most toxic of the 75 dioxin isomers and possibly the most toxic manufactured chemical, contaminates phenoxy herbicides during the production process (Demers and Perrin 1995 Klaassen 1985). Conflicting literature addresses TCDD lethality in humans. Some reviews deny that human deaths result from systemic effects of TCDD (Demers and Perrin 1995). Others describe successful suicides with phenoxy herbicides (Nielsen et al. 1965). Despite extensive reports of numerous medical conditions from TCDD, the literature confirms only chloracne and transient mild hepatotoxicity in humans. Table 1-6 lists the various, but unconfirmed, signs and symptoms associated with human poisonings. Table 1-7 lists the unconfirmed psychiatric symptoms attributed to TCDD exposure. 

During the last decade, various remedial actions were carried out on dioxin-contaminated wastes in the United States and Europe. Historically, building rubble from industrial accidents was used as fill or disposed in the ocean. In 1977, about 2.2 million gallons of Agent Orange and similar herbicide formulations was incinerated on the ship Vulcanus in the Pacific (1). This solution was simplified by the ability to transfer the waste to the ship at a remote location in the Pacific and by the large quantity of liquid waste, which made the incineration on ship economically possible. The destruction efficiency of this at-sea-incineration was about 99.9% according to the limits of analytical detection at that time. 

The initial concern for the possible hazard to humans exposed to 2,4,5-T was precipitated by teratologic studies conducted by Bionetics Research Institute under contract from The National Cancer Institute (2). In these studies, large doses of 2,4,5-T were administered to pregnant rats and mice for nine of the 21 days of pregnancy. The incidence of fetal abnormalities was slightly higher in the treated animals than in control animals. Later tests indicated that these abnormalities (cleft palate) may have been caused by 27 8 ppm of 2,3,7,8-tetrachloro-dibenzo-p-dioxin present as a contaminant in the 2,4,5-T sample used in the Bionetic study (3). After the results of the study were made known, the Panel on Herbicides of the President s Science Advisory Committee studied the total 2,4,5-T situation. The report of this committee was published in March, 1971 (4). 

The vendor claims that the TDR process can be used to treat soil and sludge contaminated with polychlorinated biphenyls, polynuclear aromatic compounds, solvents, dioxins, furans, organic pesticides and herbicides, solvents, petroleum wastes, as well as nonhalogenated volatile and semivolatile compounds. The treated residuals from the process include recovered water, oil that can be used for recycling as an alternative fuel or for recycling or can be disposed, and clean soil that can be used as backfill. The volume of treated sludge is reduced by as much as 95% by this thermal process, depending on the initial level of contaminants. 

Micro-contaminants are present in chemicals at concentrations <1% of the mass. A very important class of micro-contaminants in a number of chlorinated chemicals is the chlorinated dioxins and furans. Dioxins are now classified as POPs [43], but in the late 1960s and early 1970s [201] became widely known when they were discovered to be micro-contaminants of 2,4,5-T-containing herbicides. There are numerous sources of dioxins but the most important source from synthetic chemicals is from... 

Attention In dioxin was propelled into scientific and public scruliny as the result of the use uf the herbicide 2.3.5-T l Agent Orange) during the Vietnam conflict. Also, a major localized contamination resulted from an accident in a chemical plant in Seveso, Italy, in 1976... 

CDDs are found everywhere in the environment, and most people are exposed to very small background levels of CDDs when they breath air, consume food or milk, or have skin contact with materials contaminated with CDDs. For the general population, more than 90% of the daily intake of CDDs, CDFs, and other dioxin-like compounds comes from food, primarily meat, dairy products, and fish. CDDs may be present at much lower levels in fruits and vegetables. The actual intake of CDDs from food for any one person will depend on the amount and type of food consumed and the level of contamination. Higher levels may be found in foods from areas contaminated with chemicals, such as pesticides or herbicides, containing CDDs as impurities. CDDs have been measured in human milk, cow s milk, and infant formula, so infants are known to be exposed to CDDs. 

Mixtures with other herbicides also are used for weed control. The product Agent Orange, used extensively throughout Vietnam, was about 50% 2,4-D. However, the controversy about the use of Agent Orange was associated with a contaminant (dioxin) in 2,4,5-trichlorophenoxy acetic acid (2,4,5-T) (C8H5Cl303), not with 2,4-D. It should be well understood that 2,4,5-T is different from 2,4-D but similar to 2,4-D as a herbicide component of the defoliant.39... 

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