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PCNB

Publication Date: 9/93

TRADE OR OTHER NAMES

Trade names for products containing PCNB include Avicol, Botrilex, Folsan, Saniclor, Terraclor, Tubergran and Turcide. The fungicide is often used in combination with insecticides and fungicides including carbaryl, imazalil, tridimenol, etridiazole and fuberidazole.

INTRODUCTION

PCNB is a organochlorine fungicide used for seed and soil treatments at planting. It is also know as quintozene. It is used on a variety of vegetable and field crops including lettuce, cotton, brassicas, tomatoes, flowers and bulbs and on turf grass. Depending on the producer and the manufacturing procedure, PCNB impurities can include hexachlorobenzene, pentachlorobenzene and tetrachloronitro-benzene.

Most products containing PCNB have been cancelled for use in the United States.

TOXICOLOGICAL EFFECTS

ACUTE TOXICITY

Depending on the formulation PCNB carries the signal word WARNING or CAUTION on the label. The WARNING signal word denotes a moderately toxic compound and the CAUTION signal word denotes a slightly toxic compound.

The lethal dose for humans is between 500 to 5,000 mg/kg (2). PCNB has a rat oral LD50 of around 1,500 mg/kg when fed in oil, but when administered in water, the LD50 was significantly higher (greater than 12,000 mg/kg) (9).

Humans exhibited no skin irritation after a 48-hour, contact but a sensitivity reaction occurred in 20% of the subjects after a second skin exposure. This indicates that allergic reactions to repeated exposure may occur (7).

CHRONIC TOXICITY

Rats fed diets containing PCNB over a wide range of doses (3 mg/kg to 150 mg/kg) for three months had elevated liver to body weight ratios in all groups except in females at the low dose (9). No blood chemistry changes were seen. In another experiment, rats fed diets containing high levels (250 mg/kg) of the fungicide in their food for 90 days showed decreased growth (7).

Dogs fed diets containing relatively low doses for two years showed no growth related effects or blood changes. Microscopic structural changes were confined to liver-cell enlargement (7).

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 (2). It is unlikely that this compound would present a significant reproductive risk to humans chronically exposed.

Teratogenic Effects

Early studies showed defects in kidney formation in offspring when PCNB products containing hexachlorobenzene were administered to pregnant mice. In a later study, feeding pregnant rats moderate doses (125 mg/kg) of pure PCNB during active organ formation did not result in fetal toxicity or birth defects. At very high doses (500 mg/kg) female mice produced offspring with missing kidneys and cleft palate (2). Several of the other products found in the PCNB fomulation are not teratogenic in rats or mice.

Mutagenic Effects

It appears from limited test information that PCNB is either not mutagenic or weakly mutagenic (2).

Carcinogenic Effects

As with the teratogenic data, early cancer studies were performed with PCNB that contained hexachlorobenzene. These studies showed that mice given very high dose of 464 mg/kg by stomach tube from days 7 to 28 and then placed on diets of about 50 mg/kg for 18 months, developed liver tumors (2).

Organ Toxicity

Cats given very high oral doses of 1,600 mg/kg showed some blood chemistry changes (methemoglobin formation) after 24 hours. There was slight recovery after 48 hours. This condition changes the bloods ability to bind and carry oxygen throughout the body (7).

Fate in Humans and Animals

In mammals PCNB is eliminated unchanged in the feces or as metabolites in urine. The speed and thoroughness of absorption varies among species.

Eggs from chickens fed low doses of PCNB in their diets were considered safe for human consumption. Only trace amounts were found in the milk of cows fed 25 mg/day.

Storage in the tissues did not occur in rats, dogs, or cows. The major metabolites are the aniline (PCA) and sulfide (MPCPS) and are found primarily in the body fat, with minimal amounts in the muscles. Impurities account for the prominent persistent residues. There is some evidence that pentachlorphenol is formed directly from PCNB (2).

ECOLOGICAL EFFECTS

The LD50 of PCNB is greater than 3,700 mg/kg in mallards and 170 mg/kg in bobwhite quail. No tissue buildup was observed (4). Examination of various organs failed to reveal lesions. This would indicate that PCNB is either only slightly toxic or practically non-toxic to birds.

PCNB 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. Algae accumulate the greatest amount. The bioconcentration factor for algae was estimated to be roughly 14,000 times the background water concentration of PCNB (2, 8).

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 (4). Metabolites in the soil include aniline, pentachlorabenzene, hexachlorabenzene, and sulfide. These will persist for two or three years. Under oxygenated conditions, many soil bacteria aid in the breakdown of this product (8).

Plants take up PCNB from both soil and water (4). One week after young cotton plants were treated with 300 ppm PCNB, they contained 91 ppm of the parent compound and 2.0 ppm pentachlorobenzene, 2.77 ppm hexachloro-benzene, 0.65 ppm aniline, 1.36 ppm sulfide, and traces of other metabolites.

PCNB is unchanged by sunlight. It is not expected to leach extensively, but it has been found in drinking water in Ohio and in ground water in California and Ontario, Canada (8).

PHYSICAL PROPERTIES AND GUIDELINES

Exposure Guidelines:

NOEL (dog): 0.75 mg/kg/day
ADI: 0.007 mg/kg/day (EPA)
RfD: 0.003 mg/kg/day
LEL: 4.5 mg/kg/day (dog)

Physical Properties:

CAS #: 82-68-8
Chemical name: pentachloronitrobenzene
Chemical class/use: nitro aromatic fungicide
Solubility in water: 0.44 mg/l
Solubility in other solvents: slightly soluble in alcohols; freely soluble in benzene and chloroform.
Melting Point: 144 degrees C
Vapor Pressure: 1.1 x 10 to the minus 4 mm Hg

BASIC MANUFACTURER

Uniroyal Chemical
World Headquarters
Middlebury, CT 06749
Telephone: 203/573-200
Emergency: 209/224-8910

Review by Basic Manufacturer:

Comments solicited: October, 1991
Comments received:

REFERENCES

  1. Shepard, Thomas H. (1986). Catalog of Teratogenic Agents. The John Hopkins University Press, Baltimore, MD.
  2. National Library of Medicine (1992). Hazardous Substances Databank. TOXNET, Medlars Management Section, Bethesda, MD.
  3. U. S. Environmental Protection Agency (1976). Initial Scientific Review of PCNB, Substitute Chemical Program. Office of Pesticide Programs, Criteria and Evaluation Division.
  4. Scott Products (No date). PCNB. Technical Data, 34 pages.
  5. U. S. Environmental Protection Agency (1968-81). Pesticide Abstracts, Office of Pesticides and Toxic Substances, Management Support Division, 75- 0098, 78-2944, 79-1635, 80-0246, 81-1983.
  6. Food and Drug Administration (1986). The FDA Surveillance Index. Bureau of Foods, Dept of Commerce, National Technical Information Service, Springfield, VA.
  7. Edwards, I. Ralph, Donald G. Ferry, and Wayne A. Temple.
  8. Fungicides an Related Compounds. in Handbook of Pesticide Toxicology, Volume 3 Classes of Pesticides. Wayland J. Hayes and Edward R. Laws Editors. Academic Press, Inc. NY.
  9. Howard, Philip H. (1991). Handbook of Environmental Fate and Exposure data for Organic Chemicals, Volume III. Lewis Publishers, Chelsea, MI.
  10. The Agrochemicals Handbook. 1991. Royal Society of Chemistry. Cambridge, England.