Pentachloronitrobenzene (PCNB)
PCNB is an effective organochlorine
fungicide used at planting for the
prevention and control of Rhizoctonia solani and other soil borne
diseases. PCNB works by inhibiting lipid peroxidation. This chemical
works primarily as a preventative agent through contact activity, and should
be applied before disease symptoms appear in order to achieve optimum
results. However, it does have curative properties as well. PCNB binds
rapidly to organic matter. Irrigation will not wash it off, and it has a long
residual.
Key diseases controlled or cured by PCNB include:
·
Rhizoctonia solani - root rot / stem rot
·
Pellicularia filamen-tosa - root rot / stem rot
·
Sclerotium rolfsii - bulb rot / crown rot
·
Pellicularia rolfsii - bulb rot / crown rot
·
Sclerotinia gladioli - dry rot
·
Botrytis cinerea - storage rot
·
Sclerotinia camelliae - camellia flower blight
·
Ovulinia azaleae - azalea petal blight
·
Dothistroma pini – needle blight
PCNB
is also known as quintozene or Terraclor. It may be used on a variety of
flowers and bulbs and on turf grass. PCNB impurities can include
hexachlorobenzene, pentachlorobenzene and tetrachloronitro-benzene. Because
of potential misuse and hazards, most products containing higher levels of
PCNB have been cancelled for use in the United States.
AVAILABLE FORMS
Chemtura has announced it will no longer be manufacturing or marketing Terraclor, so the wettable powder form of PCNB will no longer be available on a retail basis. Two granular forms are available: Hi-Yield PCNB Granular Fungicide (4.67%) and Hi-Yield Turf & Ornamental Fungicide (10%). A spray form is available as well, marketed as Fertilome Azalea, Camelia, & Crape Myrtle Insecticide and Fungicide (12.5%). Other products currently on the market to treat similar soil borne diseases include Aliette and FenStop, although the mode of action for each of these is different.
PHYSICAL PROPERTIES
Physical Properties:
CAS# 82-68-8 --
Pentachloronitrobenzene
A nitro aromatic fungicide.
Soluble in water at a rate of
0.44mg/l.
Slightly soluble in alcohols;
freely soluble in benzene and chloroform.
TOXICOLOGICAL EFFECTS
Acute Toxicity: The lethal
dose of PCNB for humans is between 500 to 5,000 mg. There is also a potential for allergic reaction after
repeated exposure. Humans exhibited no skin irritation after a 48-hour
contact but a sensitivity reaction occurred in 20% of the population after a
second skin exposure.
Chronic Toxicity: Rat
studies have indicated elevated liver to body rate and decreased growth after
exposure to high levels of PCNB. No measurable blood changes were seen.
Reproductive Effects: A
three-generation study of rats fed small amounts of PCNB showed no effects
from the treatment. To produce reproductive effects in mice and rats required
doses close to the lethal levels. It is unlikely that this compound would
present a significant reproductive risk to humans chronically exposed.
Teratogenic Effects: Kidney
defects were exhibited in offspring of mice given a very high dose of PCNB.
Mutagenic Effects: Tests
indicate that PCNB is not mutagenic.
Carcinogenic Effects: As
with the teratogenic data, early cancer studies were performed with PCNB that
contained hexachlorobenzene. These studies showed that mice given a very high
dose of over an extended period developed liver tumors. In 1986, the US EPA
placed PCNB in the following category: Group C - Possible
Human Carcinogen. Their analysis found evidence of thyroid follicular cell
adenomas (by both pair-wise and trend analysis) in males with a positive
trend in females.
Organ Toxicity: After
exposure to high oral doses of PCNB, several animal studies indicated blood
chemistry changes within 24 hours of exposure. The condition changes the
blood's ability to bind and carry oxygen throughout the body.
Fate in Humans and Animals: In mammals, PCNB is eliminated unchanged in the feces or
as metabolites in the urine. The speed and thoroughness of absorption varies
among species.
Ecological Effects: PCNB is
either only slightly toxic or practically non-toxic to birds, however it is highly toxic to fish.
Relatively low concentrations in water (0.3 ppm to 9.0 ppm) caused mortality
to bluegills and to trout. PCNB has been shown to accumulate in aquatic
animals and in aquatic plants.
Environmental Fate: The amount of time for one half of the PCNB fungicide to
be eliminated from an area of application is between 5 to 10 months. The soil
type is the main source of variation. PCNB is lost largely through
evaporation. PCA, one of the breakdown products of PCNB, is less toxic to
microorganisms. Metabolites found in the soil after breakdown include
aniline, pentachlorabenzene, hexachlorabenzene, and sulfide, which will for
two or three years. Under oxygenated conditions, many soil bacteria aid in
the breakdown of this product.
Plants take up
PCNB from both soil and water.
PCNB is unchanged
by sunlight. It is not expected to leach extensively, but it has been
reported in drinking water in Ohio and in ground water in California and
Ontario, Canada.
EXPOSURE GUIDELINES
Exposure is not recommended at
more than 0.007 mg/kg/day (EPA guidelines).
Information published above was
compiled from a variety of sources on August 9, 2008. Please check with your
county agricultural agent or the product label regarding any new information
or precautions after this date.
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