United States .
                             Environmental Protection
                             Agency
            Office of Water
            4601
                                           EPA811-F-95-003I-T
                                                 October 1995
                                 	Primary  Drinking
                             Water Regulations
                             Dioxin (2,3,7,8-TCDD)
  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
                      BlOCONCENTRATION FACTOR:
                        3.2 to 3.9 in fish; expected to biocon-
                        centrate in aquatic organisms.
                      i)
                      HENRY'S LAW COEFFICIENT:
                        1.62x10-5 atm-cu m/mole;

                      TRADE NAMES/SYNONYMS:
                        2,3,7,8-Tetrachlorodibenzo-1,4-dioxin;
                        Dioxin; Tetradioxin;
DRINKING WATER STANDARDS
  MCLG:      zero mg/L
  MCL:       3x10"8 mg/L
  HAL(child):  1 day: 1x10"6 mg/L
             10-day: 1x10-7mg/L

WEALTH 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 Ib.) child consum-
ing 1 liter of water per day, a one-day exposure of 1x1f>
6 mg/L or a ten-day exposure to 1x1f>7mg/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.
ft is  a contaminant formed in the production of 2,4,5-
[richlorophenol and of a few chlorinated herbicides such
as silvex. It may also be formed during combustion of a
rvariety of chlorinated organic compounds.
  Dioxin has been tested for use in flameproofing poly-
       esters 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 avail-
       able.

       ENVIRONMENTAL FATE
        Dioxin is  one of the most toxic and  environmentally
       stable tricyclic aromatic compounds of its structural class.
                                            d
        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 sedi-
       ments 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
 October 1995
Technical Version
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water depth increases. Many bottom sediments  may
therefore not be susceptible to significant photodegrada-
tion.
  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 demon-
strated that TCDD is generally resistant to biodegrada-
tion. 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 contami-
nated 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  biodegrada-
tion.
  If released to the atmosphere,  vapor-phase TCDD
may be degraded by reaction with hydroxyl radicals and
direct photolysis. Particulate-phase TCDD may be physi-
cally removed from air by wet and  dry deposition.
  Bioconcentration in aquatic organisms has been dem-
onstrated. 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 aquaticorganisms: snails,
fish (Gambusia), daphnia4.3-4.4; duckweed, algae, cat-
fish, 3.6-3.95.
         The major route of exposure to the general population
       results from incineration processes and exhausts from
       leaded gasoline engines.
         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
         EPA821-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 lexicological 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
October 1995
Technical Version
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