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Extension Toxicology Network

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.


Publication Date: 9/93


Trade names for products containing dienochlor include Pentac WP and Pentac Aquaflow. The compound may be found in formulations with a wide variety of other common pesticides.


Dienochlor is an organochlorine insecticide with contact action. It is used for the control of plant damaging mites on a variety of ornamental shrubs and trees outdoors and in greenhouses. The compound may also be used on non-food ornamental crops. Dienochlor disrupts the egg laying ability (oviposition) of female mites. Dienochlor is a General Use Pesticide.


Acute Toxicity

Products containing dienochlor are highly toxic when inhaled and thus require the signal word WARNING on the label. Symptoms of acute dienochlor exposure are similar to those of other organochlorine compounds and may include, stimulation of the central nervous system (tremors, convulsions, agitation and nervousness), slowing of breathing, nausea, vomiting and diarrhea (1). The oral LD50 for technical dienochlor is greater than 3,160 mg/kg in male rats (2) indicating that the compound is only slightly toxic by this route of exposure. The oral LD50 for a lower concentration of the compound (38% ranges from 5,100 mg/kg to 20,000 mg/kg in rats) is greater than 5,000 mg/kg in rabbits, and is 16,900 mg/kg in mice. Dienochlor is only slightly toxic by exposure through the skin (dermal). The LC50 for the compound is greater than 3,160 mg/kg in rabbits(3). Acute inhalation studies with the product Pentac 50 WP indicate that the compound is highly toxic by this route of exposure. The LC50 value for the product ranged between 1.4 mg/l and 2.4 mg/l in rats (3). Dienochlor is not a primary skin irritant or a skin sensitizer and is only a mild eye irritant. Rabbits exposed to a single dose of the technical product (dose undisclosed) experienced corneal opacity and irritation. The condition abated completely within seven days (3).

Chronic Toxicity

Only two sub-chronic feeding studies were found. Both studies were conducted over three month periods. One study established a no observable effect level (NOEL) in rats of 6.3 mg/kg/day. Above this dosage the rats experienced a reduction in body weight gain. The other study noted a no effect level of 16 mg/kg for mice. At the next highest dose administered (64 mg/kg), the mice experienced increased mortality, inactivity, hunchbacked- walk, decreased body weight gain, changes in blood and urine chemistry, and altered organ weights. Rats fed dienochlor in their diets over two weeks had no effects at or below 5 mg/kg/day. The limited evidence indicates that there is a very close threshold for chronic effects in mice. There is only a small difference in the amount of dose between 16 and 64 mg/kg (in relation to the LD50) for the species. The numerous chronic symptoms of dienochlor exposure indicate that there may be a risk to humans exposed to low to moderate levels of the compound over time.

Reproductive Effects

No data on reproductive effects of dienochlor were found.

Teratogenic Effects

No birth defects appeared in the offspring of pregnant rats fed up to 50 mg/kg dienochlor in their food. Maternal toxic effects (unspecified) were noted at doses of 17 mg/kg. The time of exposure for the two studies was not noted (3).

Mutagenic Effects

At least eight separate tests evaluating the mutagenicity of dienochlor have produced mixed results. Test results have shown the compound to be non- mutagenic or weakly mutagenic (3). This suggests that the mutagenic risk to humans would be minimal.

Carcinogenic Effects

No information was available on any cancer related effects from dienochlor exposure.

Organ Toxicity

The results from a single study indicated that the spleen and thymus showed evidence of atrophy. The report summary compiled by the EPA also indicated altered organ weights. The effects were noted at a dose of 64 mg/kg/day. The specifics of the change or the organs affected were not noted (3).

Fate in Humans and Animals

Female rats fed a single, low dose (1 mg/kg) of dienochlor excreted nearly ninety percent of the breakdown products of the compound in the feces and only two percent in the urine (4). Nearly all of the dienochlor was broken down in the rats within one day. The compound is poorly absorbed through the stomach and intestines. At this dose after four days, only two percent of the initial dose remained in the rat in the liver, kidneys, stomach and intestines. Absorption of the compound is very slow. This may account for its low oral toxicity (high oral LD50). When the compound was administered on the skin of the rats only a very small amount passed through the skin to the blood stream (2%) (4). The authors indicated that even less would penetrate the skin of humans. Only one percent of the applied dose was detected in the urine and less than 0.2 percent in the tissues.


Dienochlor is practically non-toxic to bobwhite quail and to mallard ducks. The LD50 for the compound in the quail is 705 mg/kg and the LC50 for dienochlor in mallards is nearly 4,000 mg/kg diet. A study with Japanese quail produced an LD50 of 4,319 mg/kg but was deemed inadequate for several reasons by the EPA (6). No other studies with birds were found. The effect of this organochlorine compound on avian reproduction remains unevaluated. Tests with several species of fish have indicated that the compound is highly to very highly toxic to this group of organisms. The LC50 for dienochlor is 0.6 mg/l for bluegill sunfish and 0.05 mg/l for rainbow trout (6). Dienochlor is only moderately toxic to the freshwater invertebrate Daphnia magna. There are no data available on the potential of the compound to accumulate in aquatic organisms. The compound is practically non-toxic to bees (2).


There is very little information about the fate of the compound in the environment. Few studies have been conducted in this area. One study indicated that the compound is non-persistent (5). A non-persistent compound only lasts in the environment from a few hours to up to twelve weeks.

Dienochlor is readily broken down by the action of sunlight (5).

Exposure Guidelines:

NOEL (rat): 6.25 mg/kg/day

Physical Properties:

Common Name: dienochlor
CAS #: 2227-17-0
Chemical Name: decachlorobis(2,4-cyclopentadien-1-yl)
Chemical class: organochlorine
Chemical Use: miticide
Solubility in water: practically insoluble in water
Solubility in solvent: Slightly soluble in hot ethanol, acetone and cyclohexanone. Moderately soluble in benzene, xylene, and other aromatic hydrocarbons.
Partition coefficient: 1411-2011 (octanol/water)
Melting Point: 122-123 degrees C
Vapor pressure: 1.3 mPa at 25 degrees C


Sandoz Crop Protection Corporation
1300 E. Touhy Avenue
Des Plains, Il 60018
Telephone: 708-699-1616
FAX: 708-390-3940

Review by Basic Manufacturer:

Comments solicited: June, 1993
Comments received: June, 1993


  1. The Agrochemicals Handbook. 1991. The Royal Society of Chemistry. Cambridge, England.
  2. The Farm Chemicals Handbook. 1992. Meister Publishing. Willoughby, OH.
  3. Dienochlor. Tox Oneliners. 1990. US Environmental Protection Agency. Office of Pesticides/HED/SACB.
  4. Quistad, G.B., K.M. Mulholland and W.S. Skinner. 1986. The Fate of Dienochlor Administered Orally and Dermally to Rats. Toxicology and Applied Pharmacology 85(2):215-220.
  5. Quistad, G.B., and K.M. Mulholland. 1986. Photodegradation of Dienochlor. Journal of Agricultural Food Chemistry. 31(3):621-624.
  6. Dienochlor. Ecological Effects Branch. US Environmental Protection Agency. Reviewed 12/15/81.