Description
Octachlorostyrene(OCS) is a persistent, highly bioaccumulative,
and toxic halogenated aromatic compound. It is not commercially
manufactured, but is reportedly an inadvertent by-product
of processes that combine carbon and chlorine under elevated
temperatures. Magnesium production, chloride solvent
production, aluminum plasma etching, aluminum degassing
with hexachloroethane, chlorination of titanium, waste incineration,
and chloro-alkali production with graphite anodes
process are considered to be candidate occupations that produce
OCS. However, recent advances have been made in
process technology and pollution prevention practices in some
of these industries, such as largely eliminating the electrolytic
manufacture of chlorine and aluminum degassing with hexachloroethane,
both of which have likely resulted in reductions
in known sources of OCS.
Environmental Fate
OCS is bioaccumulative in aquatic food webs. Due to its low
water solubility (water solubility = 1.74E-03 mg l
-1; log P
(octanol–water) = 7.460), OCS tends to rapidly partition from
water and binds to sediments and suspended solids. Bioconcentration
through direct uptake may be an important
mechanism in aquatic species.
In aquatic systems, OCS is expected to adsorb to suspended
solids and sediments based on its Koc value ranging from
200 000 to 10 000 000. OCS has been detected in water at
concentrations as high as 7.2 ng l
-1, but levels typically are well
below 1 ng l
-1. While there is the potential for volatilization
from aquatic systems based on an estimated Henry’s law
constant of 2.3 ×10
-4 atm m
3 mol
-1, volatilization (vapor
pressure= 1.32E-05mmHg) is likely attenuated by adsorption
to particles. Bioaccumulation by aquatic organisms is likely
based on a bioconcentration factor that is estimated to range
from 8100 to 33 000. Field estimates of bioaccumulation factors range up to 1 400 000 (from water to rainbow trout in
Lake Ontario). Mean concentrations in Lake Ontario sediments
and rainbow trout were 13.6 ng g
-1 dry weight (ppb) and
2.6 ng g
-1 wet weight (ppb), respectively. The highest
concentrations found in fish as part of the National Study of
Chemical Residues in Fish (conducted by the US Environmental
Protection Agency (EPA)) were from Bayou D’Inde,
Louisiana (138 ng g
-1 (ppb)), Freeport, Texas (65.3 ng g
-1
(ppb)), River Rouge, Michigan (50.7 ng g
-1 (ppb)), and Olcott,
New York (49.6 ng g
-1 (ppb)). Temporal studies, while
limited, have indicated a substantial decline in concentrations
of OCS since the 1970s. In contrast, relatively low OCS levels
in freshwater mussels and fish from Belgium and Romania
ranged from 0.01 to 0.18 ng g
-1 wet weight (ppb), and those in
marine fish (bib, sole, and whiting) ranged from 0.01 to
0.02 ng g
-1 wet weight (ppb).
In terrestrial systems, OCS is expected to bind to soil
particles. In the atmosphere, OCS (in the vapor phase) is
degraded by reactions with photochemically produced
hydroxyl radicals. OCS weakly absorbs ultraviolet light
between 295 and 310 nm with slow photolysis. Major transformation
products of photolysis include heptachlorostyrene
and two isomers of hexachlorostyrene, while minor transformation
products of photolysis include pentachlorostyrene
and tetrachlorostyrene.
Monitoring of OCS in western Hudson polar bears showed
no change during 1991–2007. This suggests the persistency of
OCS in the environment, though it did not further accumulate.
