Lindane
Lindane is an organochlorine insecticide which has been used on a wide
range of soil-dwelling and plant-eating (phytophagous) insects. It is
commonly used on a wide variety of crops, in warehouses, in public health
to control insect-borne diseases, and (with fungicides) as a seed treatment.
Lindane is also presently used in lotions, creams, and shampoos for
the control of lice and mites (scabies) in humans.
Technical lindane is comprised of the gamma-isomer of
hexachlorocyclohexane, HCH. Five other isomers (molecules with a unique
structural arrangement, but identical chemical formulas) of HCH are
commonly found in technical lindane, but the gamma-isomer is the predominant
one, comprising at least 99% of the mixture of isomers. Data presented
in this profile are for the technical product unless otherwise stated;
lindane, HCH, or BHC refer to technical lindane, i.e., Gamma-hexachlorocyclohexane.
Gamma-HCH has been shown to be the insecticidally effective isomer.
Lindane may also be found in formulations with a host
of fungicides and insecticides. It is available as a suspension, emulsifiable
concentrate, fumigant, seed treatment, wettable and dustable powder,
and ultra low volume (ULV) liquid.
IUPAC Name:
gamma 1α,2α,3β,4α,5α,6β-hexachlorocyclohexane
Chemical Formula:
C6H6Cl6
NOTE: Lindane (or hexachlorocyclohexane,
HCH) has historically and widely been inappropriately referred to as
"benzene hexachloride" or "BHC". This compound should not be confused
with hexachlorobenzene, or HCB.
LD50/LC50:
Lindane is a moderately
toxic compound via oral exposure, with a reported oral LD50 of 88 to
190 mg/kg in rats. Other reported oral LD50 values are 59 to 562 mg/kg
in mice, 100 to 127 mg/kg in guinea pigs, and 200 mg/kg in rabbits.
Gamma-HCH is generally considered to be the most acutely toxic of the
isomers following single administration. It is moderately toxic via
the dermal route as well, with reported dermal LD50 values of 500 to
1000 mg/kg in rats, 300 mg/kg in mice, 400 mg/kg in guinea pigs, and
300 mg/kg in rabbits. Effects of high acute exposure to lindane may
include central nervous system stimulation (usually developing within
1 hour), mental/motor impairment, excitation, clonic (intermittent)
and tonic (continuous) convulsions, increased respiratory rate and/or
failure, pulmonary edema, and dermatitis. Other symptoms in humans are
more behavioral in nature such as loss of balance, grinding of the teeth,
and hyper-irritability. Most acute effects in humans have been due to
accidental or intentional ingestion, although inhalation toxicity occurred
(especially among children) when it was used in vaporizers. Workers
may be exposed to the product through skin absorption and through inhalation
if handled incorrectly. Lotions (10%) applied for scabies have resulted
in severe intoxication in some children and infants. It is reported
that single administrations of 120 mg/kg inhibited the ability of white
blood cells to attack and kill foreign bacteria in the blood of rats,
and 60 mg/kg inhibited antibody formation to human serum albumin. It
is not clear whether these effects were temporary, or for how long they
may have lasted.
Effects
on birds: Lindane is moderately to practically
nontoxic to bird species, with a reported LD50 of more than 2000 mg/kg
in the mallard duck. The LC50 values of lindane in pheasant and bobwhite
quail are 561 ppm and 882 ppm, respectively. Egg-shell thinning and
reduced egg production has occurred in birds exposed to lindane. Lindane
can be stored in the fat of birds; birds of prey in the Netherlands
contained up to 89 ppm in their fat. Residues can also find their way
into egg yolks at measurable concentrations for 32 days after dosing.
Effects
on aquatic organisms: Lindane is highly to very
highly toxic to fish and aquatic invertebrate species. Reported 96-hour
LC50 values range from 1.7 to 90 ug/L in trout (rainbow, brown, and
lake), salmon, carp, largemouth bass. Water hardness did not seem to
alter the toxicity to fish, but increased temperature caused increased
toxicity for some species and decreased toxicity for others. Reported
96-hour LC50 values in aquatic invertebrates were: in Daphnia, 460 ug/L;
in scuds, 10-88 ug/L; and in Pteronarcys (stone flies), 4.5 ug/L. The
bioconcentration factor for the compound is 1400 times ambient water
concentrations, indicating significant bioaccumulation.
Effects
on other organisms: ***Lindane is highly toxic
to bees***.
Breakdown
in soil and groundwater: Lindane is highly persistent
in most soils, with a field half-life of approximately 15 months. When
sprayed on the surface, the half-life was typically much shorter than
when incorporated into the soil. It shows a low affinity for soil binding,
and may be mobile in soils with especially low organic matter content
or subject to high rainfall. It may pose a risk of groundwater contamination.
The pesticide has been found in a significant number of groundwater
samples in the USA and Italy.
Breakdown
in water: Lindane is very stable in both
fresh and salt water environments, and is resistant to photodegradation.
It will disappear from the water by secondary mechanisms such as adsorption
on sediment, biological breakdown by microflora and fauna, and adsorption
by fish through gills, skin, and food.
Breakdown
in vegetation: Plants may pick up residues from
not only direct application, but through water and vapor phases. Persistence
is seen when plants are rich in lipid content, and crops like cauliflower
and spinach will build up less residue than crops like carrots. The
metabolism in plants is not well understood, but carrots are estimated
to metabolize lindane with a half-life of just over 10 weeks (based
on plant uptake) whereas it may have a half-life in lettuce of only
3 to 4 days.
Physical
Properties:
- Appearance: Lindane is a
colorless crystal compound.
- Chemical Name: gamma-1,2,3,4,5,6-hexachlorocyclohexane.
- CAS Number: 58-89-9.
- Molecular Weight: 290.85.
- Water Solubility: 7.3 mg/L
@ 25°C.
- Solubility in Other Solvents:
v.s. in acetone, benzene, and ethanol.
- Melting Point: Approximately
113°C.
- Vapor Pressure:
5.6 mPa @ 20°C.
- Partition Coefficient:
Not Available.
- Adsorption Coefficient:
1100.
Sources: Oregon University
and The World Health Organisation
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