Dioxins accumulation

This structure looks nothing like the structures of chlorine-containing compounds used in industrial processes. In fact, no dioxin is deliberately manufactured anywhere in the diverse chlorine industry. Nevertheless, dioxins are of concern for two reasons First, dioxins appear to be inevitable trace by-products of some reactions involving chlorine, particularly combustion and second, dioxins accumulate in the biosphere, where they have highly deleterious effects. 

TCP), and pentachlorophenol (PCP), in order of abundance. Minor amounts of other trichlorophenols and dichlorophenols may also be present, as well as recalcitrant polychlorinated phenoxyphenols (PCPPs) and PCDD/Fs as impurities [75, 76]. In Finland, approximately 30,000 tons of CP products were used between 1934 and 1988, when they were banned because of their potential toxicity to humans and the environment [77, 78]. The careless manufacturing and application of wood preservatives together with the lack of suitable waste disposal caused massive contamination of river sediments and sawmill sites. For example, the river Kymijoki in southern Finland was identified as the largest source of dioxins accumulating in fish in the entire Baltic area. Similar products were used in other European countries, especially Nordic countries with a large forestry industry, such as Sweden [79]. 

The main depot for dioxin accumulation in mammals is the liver and adipose tissue. When dioxin is fed to rodents with fodder, about 10% of the dose comes in the liver. Should this toxic agent be applied on rat skin, 13% of the dose is absorbed in blood already in 5 hours, and 10% remains on skin surface. 

Tubers and edible roots are featuring the highest dioxin-accumulation ability. For example, carrots can extract dioxin from soil and accumulate it up to concentrations being equal to, or somewhat exceeding, its content in soil. 

Ministry of Environment, 1999. The state of dioxin accumulation in the human body, blood, wildlife, and food Findings of the fiscal 1998 survey. 106 pp, Available at http // www.env.go.jp/en/topic/dioxin/accumulation.pdf Ministry of the Environment, Japan. 

Within the massive amounts of weedkiller being showered from American aircraft onto the jungles of Vietnam, the small amounts of dioxin accumulated. By the time the spraying had ended, an estimated 240 lb of the stuff had been dumped on Vietnam.52 A few... 

PCBS (polychlorinated biphenyls) Toxic synthetic chemicals with excellent heat resistance and low electrical conductivity properties. Now little used but considerable quantities remain in old electrical equipment. Produces dioxins and polychlorinated dibenzo-furans when burned below 1200°C. PCBs are toxic and bio-accumulative. 

Other species could feed on a different food chain to accumulate dioxins. 

Dioxins are of concern because they accumulate in the biosphere, where they have highly deleterious effects. Tests have shown that when the concentration of dioxins in the blood of laboratory animals reaches a critical level, reproductive and immune system defects result. Moreover, recent data indicate that the concentration of dioxins in the blood of the average U.S. resident has nearly reached that level. A major reason is that dioxins are not veiy water-soluble, so they accumulate in the body rather than being readily processed and excreted. Consequently, several groups, including the American Public Health Association, have issued calls for phasing out the use of industrial chlorine. 

CHLORINATED HYDROCARBONS Hydrocarbons containing chlorine atoms, e.g. trichloroethylene. Some of these chemicals accumulate in the food chain and do not readily degrade. Some plastics which contain certain chlorinated hydrocarbons release dioxins into the air, when burnt at low temperatures. 

Sacchi, G.A., P. Vigano, G. Fortunati, and S.M. Cocucci. 1986. Accumulation of 2,3,7,8-tetrachlorodibenzo-p-dioxin from soil and nutrient solution by bean and maize plants. Experientia 42 586-588. 

The toxicity of commercial or technical grades of PCP significantly exceeds that of analytical or purified PCP. Some of this added toxicity is attributed to impurities such as dioxins, dibenzo-furans, chlorophenols, and hexachlorobenzene. Pentachlorophenol is rapidly accumulated and rapidly excreted, and has little tendency to persist in living organisms. It acts by uncoupling oxidative... 

PCBs can move from local sediments into the avian food web, as judged by PCB accumulation rates of tree swallows (Tachycineta bicolor) from contaminated and reference sites (Custer et al. 1998). Patterns of relative concentrations of PCB congeners change from sediment to invertebrates, and from tree swallow eggs to nestlings (Froese et al. 1998). Dioxin-like activity (TEF) measured in tree swallow tissues could predict TEF in sediments and the reverse. Models of dioxin-like activity in the sediments of Saginaw Bay, Michigan, predicted that sediments were not harmful to tree swallows from that area (Froese et al. 1998). 

Hazard of dioxin-like compounds is growing because they can be accumulated in living organisms when coming from the environment. 

Compounds of this series are actively accumulated by the inhabitants of water ecosystems (both plants and animals). It was shown that fish in rivers, polluted with dioxin-containing industrial wastewaters, could accumulate up to 0,1-0,2 mcg/kg. As much as 80% of dioxin is laid in fish skeleton and visceral fat about 10% comes in liver, and 2% - in muscles. 

I. M. Muslimova, F. F. Hizbullin.- Problem of Accumulation of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in Sludge Reservoirs of the Enterprises of Chlororganic Synthesis. Ecological Chemistry.-2001.-Vol. 10.- No. 04, p.269-274. 

PCDD/PCDFs are today found in almost all compartments of the global ecosystem in at least trace amounts. They are ubiquitous in soil, sediments and air. Excluding occupational or accidental exposures, most human background exposure to dioxins and PCBs occurs through the diet, with food of animal origin being the major source, as they are persistent in the environment and accumulate in animal fat. 

PCDD/PCDFs accumulate in human adipose tissue, and the level reflects the history of intake by the individual. Several factors have been shown to affect adipose tissue concentrations/body burdens, notably age, the number of children and period of breastfeeding, and dietary habits. Breast-milk represents the most useful matrix for evaluating time trends of dioxins and many other POPs. Several factors affect the PCDD/PCDFs content of human breast-milk, most notably the mothers age, the duration of breast-feeding and the fat content of the milk. Studies should therefore ideally... 

There are 210 different isomeric possibilities, 75 of which are PCDDs and 135 are PCDFs. The toxicity of these isomers varies greatly, and only 15 exhibit extreme toxicity, the most toxic of which is 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). The toxicity of the other isomers is therefore expressed as a toxicity equivalent of 2,3,7,8-TCDD. The PCDDs and PCDFs are poorly water soluble but are fat soluble and are therefore able to accumulate in tissue fat, thus allowing them to bio-accumulate in living organisms. The origin of dioxins in the pulp and paper industry is not entirely clear. They may be produced from the chlorination of dibenzodioxin which may be present in recycled oils used to make defoamers, but they may also arise from wood chips which have been treated with polychlorophenol to prevent sap stain formation. It is also possible that they are derived from lignin by chlorination. Dioxins are also known to be formed naturally by combustion of material such as wood, and forest fires have been particularly identified as a likely major cause of dioxin emissions. 

The chlorinated chemicals assessed do not have the same risk profile. For the more volatile chemicals the safety margins between the actual exposure and the level at which no effect on the environment would be expected is quite high. For more persistent chemicals there is a need to look to the environmental compartment where they can be accumulated (mainly in sediments and biota). For some of these chemicals the safety margin is quite low and in worst-case situations serious effects may occur. For the very persistent, bioaccumulative and toxic chemicals (like dioxins, PCBs and DDT), acceptable environmental concentrations are so low and difficult to control that the industry is committed to reducing as far as possible releases to the environment through application of Best Available Techniques (BAT), mainly with respect to dioxins. For other chemicals (PCBs, DDT), production has already been halted for some years. 

Pentachlorophenol, a large-volume fungicide and wood preservative, contains relatively high levels of hexa-, hepta- and octachlorodibenzodioxins and essentially no tetrachlorodibenzo-p-dioxins [83-85] and polychlorodibenzo-p-dioxin incineration of materials containing chlorophenols readily produces mixtures of polychlorodibenzo-p-dioxins, but 2,3,7,8-tetrachlorodibenzo-p-dioxin is a minor component. On the other hand, the highly toxic 1,2,3,7,8-pentachloro isomer is a major component of polychlorodibenzo-p-dioxins and polychlorodibenzofurans usually produce mixtures of distinctly different relative component abundances [83], On the other hand, the preferential accumulation of certain isomers in animals may prevent source identification from analyses of biological samples. 

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