Technical Factsheet on: DIOXIN (2,3,7,8-TCDD)
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
Drinking Water Standards
MCLG: zero mg/L
MCL: 3x10-8 mg/L
HAL(child): 1 day: 1x10-6 mg/L; 10-day: 1x10-7 mg/L
Health Effects Summary
Acute: EPA has found dioxin to potentially cause the following
health effects from acute exposures at levels above the MCL:
liver damage, weight loss, atrophy of thymus gland and
immunosuppression.
Drinking water levels which are considered "safe" for short-term
exposures: For a 10-kg (22 lb.) child consuming 1 liter of water
per day, a one-day exposure of 1x10-6 mg/L or a ten-day exposure
to 1x10-7 mg/L.
Chronic: Dioxin has the potential to cause the following health
effects from long-term exposures at levels above the MCL: variety
of reproductive effects, from reduced fertility to birth defects.
Cancer: There is some evidence that dioxin may have the potential
to cause cancer from a lifetime exposure at levels above the MCL.
Usage Patterns
Dioxin is not produced or used commercially in the US. It is a
contaminant formed in the production of 2,4,5-trichlorophenol and
of a few chlorinated herbicides such as silvex. It may also be
formed during combustion of a variety of chlorinated organic
compounds.
Dioxin has been tested for use in flameproofing polyesters and as
an insecticide, but these uses were never exploited commercially.
Release Patterns
2,3,7,8-TCDD is released to the environment in stack emissions
from the incineration of municipal refuse and certain chemical
wastes, in exhaust from automobiles powered by leaded gasoline,
in emissions from wood burning in the presence of chlorine, in
accidental fires involving transformers containing PCBs and
chlorinated benzenes, and from the improper disposal of certain
chlorinated chemical wastes. TCDD has been released to the
environment as a low level impurity in various pesticides (such
as 2,4,5-T and derivatives) which were manufactured from
2,4,5-trichlorophenol.
Dioxin is not a listed chemical in the Toxics Release Inventory.
Data on its incidental releases are not available.
Environmental Fate
Dioxin is one of the most toxic and environmentally stable
tricyclic aromatic compounds of its structural class.
Due to its very low water solubility, most of the 2,3,7,8-TCDD
occurring in water is expected to be associated with sediments or
suspended material. Aquatic sediments may be an important, and
ultimate, environmental sink for all global releases of TCDD. Two
processes which may be able to remove TCDD from water are
photolysis and volatilization.
The photolysis half-life at the water's surface has been
estimated to range from 21 hr in summer to 118 hr in winter;
however, these rates will increase significantly as water depth
increases. Many bottom sediments may therefore not be susceptible
to significant photodegradation.
The volatilization half-life from the water column of an
environmental pond has been estimated to be 46 days; however,
when the effects of adsorption to sediment are considered, the
volatilization model predicts an overall volatilization removal
half-life of over 50 years.
Various biological screening studies have demonstrated that TCDD
is generally resistant to biodegradation. The persistence
half-life of TCDD in lakes has been estimated to be in excess of
1.5 yr.
If released to soil, TCDD is not expected to leach. As a rule,
the amount of TCDD detected more than 8 cm below the surface has
been approximately 1/10 or less than that detected down to 8 cm.
Being only slightly soluble in water, its migration in soil may
have occurred along with soil colloids and particles to which it
may have been bound. Soil cores collected from roadsides in Times
Beach, MO in 1985 which had been sprayed with waste oils
containing TCDD in the early 1970s indicated that most of the
TCDD had remained in the upper 15 cm. A mean log Koc of 7.39 was
determined for ten contaminated soils from NJ and MO. Tests
conducted by the USDA determined that vertical movement of
2,3,7,8-TCDD did not occur in a wide range of soil types.
Being only slightly soluble in water, its migration in soil may
have occurred along with soil colloids and particles to which it
may have been bound. Photodegradation on terrestrial surfaces may
be an important transformation process. Volatilization from soil
surfaces during warm conditions may be a major removal mechanism.
The persistence half-life of TCDD on soil surfaces may vary from
less than 1 yr to 3 yrs, but half-lives in soil interiors may be
as long as 12 years. Screening studies have shown that TCDD is
generally resistant to biodegradation.
If released to the atmosphere, vapor-phase TCDD may be degraded
by reaction with hydroxyl radicals and direct photolysis.
Particulate-phase TCDD may be physically removed from air by wet
and dry deposition.
Bioconcentration in aquatic organisms has been demonstrated. Mean
bioconcentration factors (BCF) of 29,200 (dry wt) and 5,840 (wet
wt) were measured for fathead minnows over a 28 day exposure; the
elimination half-life after exposure was found to be 14.5 days.
Log BCFs of approximately 3.2 to 3.9 were determined for rainbow
trout and fathead minnow in laboratory flow-through studies
during 4-5 exposures. The following log BCFs have been reported
for various aquatic organisms: snails, fish (Gambusia), daphnia
4.3-4.4; duckweed, algae, catfish, 3.6-3.95.
The major route of exposure to the general population results
from incineration processes and exhausts from leaded gasoline
engines.
Chemical/ Physical Properties
CAS Number: 1746-01-6
Color/ Form/Odor: White crystalline needles
M.P.: 305-306 C B.P.: N/A
Vapor Pressure: 7.4x10-4 mm Hg, 25 C
Density/Spec. Grav.: N/A
Octanol/Water Partition (Kow): Log Kow = 6.8
Solubility: 19.3 ng/L of water at 25 C; Insoluble in water
Soil sorption coefficient: Koc-N/A; very low mobility in soil
Odor/Taste Thresholds: N/A
Bioconcentration Factor: 3.2 to 3.9 in fish; expected to
bioconcentrate in aquatic organisms.
Henry's Law Coefficient: 1.62x10-5 atm-cu m/mole;
Trade Names/Synonyms: 2,3,7,8-Tetrachlorodibenzo-1,4-dioxin;
Dioxin; Tetradioxin;
Other Regulatory Information
Monitoring For Ground/Surface Water Sources:
- Initial Frequency- 4 quarterly samples every 3 years
- Repeat Frequency- If no detections during initial round:
- 2 quarterly per year if serving >3300 persons;
- 1 sample per 3 years for smaller systems
- Triggers - Return to Initial Freq. if detect at > 5 ng/L
Analysis:
| Reference Source |
Method Numbers |
| EPA 821-B-94-005 |
1613 |
Treatment- Best Available Technologies:
Granular Activated Charcoal
For Additional Information:
EPA can provide further regulatory and other general information:
EPA Safe Drinking Water Hotline - 800/426-4791
Other sources of toxicological and environmental fate data include:
Toxic Substance Control Act Information Line - 202/554-1404
Toxics Release Inventory, National Library of Medicine - 301/496-6531
Agency for Toxic Substances and Disease Registry - 404/639-6000
List of Contaminants
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