Dioxins

Dioxins

DESIGNATIONS

Note: Strictly speaking, the designation "dioxins" refers to the group of the polychlorinated dibenzo-p-dioxins (PCDD). Chemically and toxicologically, this group is closely related to the group of the polychlorinated dibenzo-p-furans (PCDF). Thus, in a less strict sense, the designation "dioxins" may cover both groups (PCDD/F). The PCDD/F substance group consists of 210 congeners which differ in the number and position of the chlorine atoms. The basic data refer to the most toxic and best described congener 2,3,7,8-tetrachlorodibenzo-p-dioxin which is often named "dioxin" in general usage.

CAS No.: 1746-01-6
Systematic name: 2,3,7,8-Tetrachlorodibenzo-p-dioxin
Chemical name: 2,3,7,8-Tetrachlorodibenzo-p-dioxin
Synonyms, Trade names: Dioxin, 2,3,7,8-TCDD, TCDD, 2,3,7,8-Tetrachlorodibenzo-1,4-dioxin
Chemical name (German): 2,3,7,8-Tetrachlordibenzo-p-dioxin, Dioxin
Chemical name (French): Dioxine
Appearance: colourless, crystalline slivers

BASIC CHEMICOPHYSICAL DATA

Empirical formula:	C₁₂H₄Cl₄O₂
Rel. molecular mass:	321.96 g
Density:	1.83 g/cm³
Boiling point:	approx. 900°C
Melting point:	approx. 300°C
Vapour pressure:	150 x 10^-9 Pa
Solvolysis/solubility:	13 x 10^-9 g/l
Conversion factors:	1 ppm = 13.38 mg/m³ 1 mg/m³ = 0.08 ppm

Origin and use

Usage:
2,3,7,8-TCDD (like all PCDD/F) is an unwanted by-product and is produced only as an analytical standard.

Origin/derivation:
There are no known geogenic sources at present. Dioxins are created in thermal processes with lack of oxygen and temperatures of 300-800°C from organically and inorganically bonded chlorine (e.g. waste incineration or pyrolysis). Dioxins are likewise encountered during the industrial production of chlorinated compounds. Therefore, these substances may contain impurities of dioxins. Special attention has to be given to the production and processing of chlorinated aromatic substances such as chlorophenols and chlorobenzenes. Dioxins require temperatures above 1000°C to decompose completely.

Toxicity

Mammals:
Rat	LD₅₀ 22-100 µg/kg, oral	acc. RIPPEN, 1989
Mouse	LD₅₀ 70 µg/kg, oral	acc. RIPPEN, 1989
Monkey	LD₅₀ 114-280 µg/kg, oral	acc. RIPPEN, 1989
Mouse	LDLo 80 µg/kg, dermal	acc. RIPPEN, 1989
Rabbit	LDLo 10 µg/kg, oral	acc. RIPPEN, 1989
Rabbit	LD₅₀ 100-115 µg/kg, oral	acc. RIPPEN, 1989
Rabbit	LDLo 275 µg/kg, dermal	acc. RIPPEN, 1989
Hamster	_{LD₅₀ 1,160-5,000 mg/kg, oral}	_{acc. RIPPEN, 1989}
_{Guinea pig}	_{LD₅₀ 0.5-2.0 µg/kg, oral}	acc. RIPPEN, 1989
Dog	LD₅₀ 30-300 µg/kg, oral	acc. RIPPEN, 1989
Birds:
Chicken	LD₅₀ 25-50 µg/kg, oral	acc. RIPPEN, 1989

Note: The majority of the toxicological data available refers to 2,3,7,8-TCDD. In view of the fact that the toxic profiles of the PCDD/F are very similar, their potency is described by introducing toxicity equivalence factors (TEF) relative to 2,3,7,8-TCDD.

Characteristic effects:

Humans/mammals: 2,3,7,8-TCDD is the compound with the most severe toxic effect of all PCDD/F. Acute poisoning mainly affects the skin and the liver as well as the peripheral and central nervous system. Additionally, psychic disorientation and effects on the immune system (in animal experiments) have been observed. Chloracne is a typical and long-lasting symptom of acute poisoning by TCDD. The affected skin may also show overpigmentation. Liver damage results in an increased level of transaminase and fat content in the blood. Intestinal disturbances with diarrhoea have been observed as well as damage to the coronary vessels and the urinary tracts. The effects on the nervous system manifest themselves in excitability, nervousness, headaches, temporary insomnia and decrease of the visual and aural capacity. As yet, carcinogenic effects have only been established in animal experiments; teratogenic effects have not yet been proven.

ENVIRONMENTAL BEHAVIOUR

Water:
Dioxins are readily adsorbed on suspended matter because they are practically insoluble in water. The bio-availability is low, however the toxic effect on aquatic organisms is considerable.

Air:
Dioxins are found in the atmosphere adsorbed on dust particles (fly ash).

Soil:
Mobility is extremely low because of the low water solubility and high adsorption capability. Dioxins thus accumulate in soil.

Half-life:
The half-life of dioxins in soil is more than 10 years (ROTARD, 1987). The half-life in the human body is up to 6 years (BECK et al., 1987).

Degradation, decomposition products:
There is only slight degradation of dioxin by mircoorganisms. Photodegradation may occur.

Food chain:
Accumulation of dioxins in the food chain is a consequence of their solubility in fats. Bioaccumulation is high in fish as well as in fat and in the liver of terrestrial organisms. However, accumulation in plants is moderate.

ENVIRONMENTAL STANDARDS

Medium/ acceptor	Sector	Country/ organ.	Status	Value	Cat.	Remarks	Source
Soil:		D	G	5 ng/kg		unrestricted use	acc. RIPPEN, 1991
		D	G	40 ng/kg		unrestricted agricultural use	acc. RIPPEN, 1991
		D	G	100 ng/kg		exchange of soil on children’s playground	acc. RIPPEN, 1991
		D	G	1000 ng/kg		exchange of soil in settlement areas	acc. RIPPEN, 1991
		D	G	10,000 ng/kg		exchange of soil irrespective of site	acc. RIPPEN, 1991
Air:	Workp	D	L	1)	MAK		acc.RIPPEN, 1991

1) not stipulated because of proven carcinogenic effects in animal experiments (Group III A2) 1990
Limit value

Assessment/comments

Due to their extreme toxicity and the suspected carcinogenic and teratogenic effects, the emission of dioxins should be avoided as far as possible. As waste incineration and the production of chlorinated aromatic compounds are the primary sources of dioxin emissions, measures should be taken especially in these fields. Further investigations on the formation of dioxins, on technical measures to reduce dioxin emissions and on their toxicological effects are in process.

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