Dioxins and furans
Dioxins/furans (PCDDs / PCDFs)
Polychlorinated dibenzopdioxins (PCDDs) and dibenzofurans (PCDFs) are a large group of polyhalogenated heterocyclic compounds characterized by structural diversity. Chlorine and, to a lesser degree, bromine derivatives are predominant. PCDDs / PCDFs combine eight homologous groups of dioxins and 8 homologous groups of furans, differing in number of connected halogen atoms and their location within a homologous series.
PCDDs are colorless and odorless crystalline substances. They have low hygroscopicity and high adsorption capacity. The dioxin molecular weight is 32.97; density at 25°C - 1.827 g/cm3, boiling point – 421.2°C, melting temperature - 290-305°C. Saturated vapor pressure at 25°C is 1*10-9 mmHg, Henry’s Law Constant Pa•m3/mol 7.26 at 25°C.
Solubility of dioxins and dioxin-like compounds in water is very low and does not depend on temperature.
Solubility in fats and organic solvents is not high either. Despite very poor dissolution of dioxins in water, and good or moderate in fats or organic solvents, these values, given high toxicity of dioxins, are sufficient to penetrate the body in a number of ways and in such quantities as to have toxic effects.
PCDDs/PCDFs are not produced intentionally in any industry. Natural formation of these compounds in the environment has not been discovered.
A wide range of dioxins is formed as byproducts in the chemical industry, especially in the industrial manufacture of chlorine, as well as in other industries.
The main industrial sources of dioxins unintentional production and release into the environment are:
Other sources of dioxins unintentional production and emissions:
There is evidence that certain amount of dioxins is formed during production of bromine organic compounds, and large quantities are formed during their pyrolysis. PBDDs and PBDFs are formed during thermolysis of polybrominated diphenyl ethers at 510-630°C. Release is around 10%. Similar results are obtained by pyrolysis of these compounds at 700-900°C. PBDFs are formed during pyrolysis of PBB, and PBDFs and PBDDs - during pyrolysis of brominated phenols and tetrabromdiphenylpropane.
Dioxins are also formed during other chemical processes when chlorine, inorganic halides, chlorine and bromine organic compounds are produced for captive use, including as catalysts and solvents.
Dioxins source inventory is a very complex task. Many sources of dioxins, despite low content must also be taken into consideration in case of large production volumes and constant human contact with these products.
The Republic of Belarus, fulfilling international agreements, regularly submits reports on dioxins/furanes release into the environment.
The total annual emissions of polychlorinated debenzo-n-dioxins and debenzofurans are 141.95 gram of toxic equivalent (TEQ), including in air - 36.6 TEQ, water - 0.5, soil - 1.4, food products – 0.05, and burning residues - 103.3 TEQ.
Notwithstanding the fact that a lot is known about dioxins, many questions remain unexplored. This applies particularly to the study of technologies potentially dangerous for their emissions, distribution of dioxins and their analogues in the environment, possible transport routes and dioxins impact on human health and the environment.
In this regard, it would be useful to develop a target program to study international experience in this area and to apply in Belarus the best technological achievements in industry, agriculture and other sectors in order to minimize dioxins effects on human health.