Dioxinsfurans

Dioxinsfurans

Potential exposure

Dioxins and furans include two classes of halogenated aromatic

hydrocarbons, or congeners. Furans are often referred to as "dioxin-like

compounds" because their structure and toxicity are similar to dioxins. Dioxin-

like compounds are by-products of chlorination processes, for example chlorine

bleaching in pulp and paper mills. These compounds are also products of

combustion of chlorinated precursor compounds. Dioxins and furans are

persistent in the environment and tend to bioaccumulate in the food chain.

Ecological receptors are often exposed to mixtures of these compounds in food,

soil, and water. Humans may be exposed primarily through their diet and dermal

absorption from contaminated ash, soil, and dust.

Physical and chemical properties of 2,3,7,8-TCDD

Property

Value

Molecular weight

322 g/mol

Water solubility

19.3 ng/L

7.4 10-10 mm Hg at 25 0C

Vapor pressure

1.15 103 to 3.8 107

Koc

log Kow

6.64

1.62 10-5 atm-m3/mol

Henry's Law Constant

Toxicity

Exposure to dioxins and furans has been shown to cause acute toxicity to the

liver in rodents and rabbits and the thymus in guinea pigs. Epidermal effects,

such as chloracne, have been seen in subchronic studies with rodents and

monkeys. Other effects due to chronic exposure to dioxin-like compounds are

wasting syndrome, hepatotoxicity, enzyme induction, and endocrine effects. In

general, congeners without lateral substitution of chlorines and with greater

number of chlorine substitutions are more toxic than other congeners.

There is evidence from animal and epidemiological studies that dioxins are

furans are immunotoxic. These compounds have also been found to cause

developmental and reproductive toxicity in animals and humans. For example, in

the Yusho and Yu-Cheng poisoning episodes, the following developmental

effects occurred in babies born to mothers who consumed rice oil contaminated

with furans and other dioxin-like congeners: fetal death, growth retardation,

D36

Appendix D Toxicological Profiles