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Publication #PI-71

Pesticide Toxicity Profile: Hydrocarbon Fumigants1

Frederick M. Fishel2

This document provides a general overview of human toxicity, a listing of laboratory animal and wildlife toxicities, and a cross-reference of chemical, common, and trade names of hydrocarbon fumigants registered for use in Florida.

General

The hydrocarbon fumigants have been used for many years throughout the United States. This chemical family of fumigants consists of four members—chloropicrin, 1,3-dichloropropene, methyl bromide, and paradichlorobenzene. As a fumigant group, they are some of the most important pest control tools used in the world. In Florida, chloropicrin, 1,3-dichloropropene, and methyl bromide are extremely effective in controlling vegetable, citrus, field crop and ornamental plant diseases, insects, and nematodes. They are non-selective pressurized gases or liquids that change into the gaseous phase. Their function relies on their remarkable capacities for diffusion, providing a thorough pest kill. Because of 1,3-dichloropropene's and methyl bromide's high acute toxicity or carcinogenic effects, they are classified as restricted-use pesticides. Chloropicrin is classified as restricted-use based solely on its acute toxicity; studies have concluded that it is not considered to be a carcinogen. Methyl bromide is an odorless, colorless gas that has been used as an agricultural soil and structural fumigant since the 1940s. However, at the time of this publication, the amount of methyl bromide produced and imported in the US has been incrementally reduced in a phase-out. The only uses allowed are those deemed as “critical uses.” This exemption allows methyl bromide use for purposes where no viable pest control alternatives exist. The phase-out falls under the Clean Air Act because methyl bromide has been identified by the EPA as a Class 1 ozone-depleting substance. Methyl bromide products are labeled DANGER. Many methyl bromide formulated products also contain chloropicrin. In agricultural applications, methyl bromide is injected into the soil and immediately covered with tarps that must remain in place for at least 48 hours for effectiveness. 1,3-dichloropropene is a colorless liquid that may be soil- or tarp-sealed following application, with some product labels requiring tarp-sealing for up to 14 days following treatment. Like methyl bromide products, many 1,3-dichloropropene products also contain chloropicrin. Chloropicrin is a pressurized gas that has uses besides agricultural and structural, such as treatment of wood products for control of decay organisms and wood borers. Products containing chloropicrin are classified as restricted-use due to acute toxicity and bear the signal word, DANGER. Paradichlorobenzene products are crystalline formulations used as moth repellents in areas where clothes and fabrics are stored; they are also sold as air fresheners and deodorizers and have activity as retardants of mold and mildew.

Toxicity

Chloropicrin is severely irritating to the upper respiratory tract, eyes, and skin. Inhalation sometimes leads to vomiting. Ingestion could be expected to cause inflammation of the stomach and intestines due to the chemical's corrosiveness. In cases where the air concentration level of chloropicrin is at least 0.1 ppm, a respirator will be required for applicators and handlers. Liver, kidney, and cardiac toxicity are seen in laboratory animals, but there are limited data available for 1,3-dichloropropene. It appears that risk of such toxicity is relatively low for humans except via ingestion of large quantities. Similar irritating effects are seen as those associated with chloropicrin. Methyl bromide is severely irritating to the lower respiratory tract and can cause fluid accumulation in the lungs, hemorrhage, or pneumonia. The onset of these respiratory problems may be delayed 4 to 12 hours after exposure. Methyl bromide is considered a central nervous system depressant, but may also cause convulsions. Early symptoms of acute poisoning include headache, dizziness, nausea, vomiting, tremor, slurred speech, and failure of muscle coordination. If liquid methyl bromide contacts the skin, severe burning, itching, and blister formation occur. Approximately 1,000 human exposure incidents caused by methyl bromide have been reported, most as a result of inhalation. There are currently few toxicity concerns associated with paradichlorobenzene-containing products, many used within the home. Its vapor is only mildly irritating to the nose and eyes. Although accidental ingestions, especially by children, have been fairly common, symptomatic human poisonings have been rare. Other isomers of dichlorobenzene are more toxic than the isomer found in these products. Ecologically, the main concern is with chloropicrin's toxic effects on fish. Labels will carry statements expressing this concern in the Environmental Hazards section. Mammalian toxicities for the hydrocarbon fumigants are shown in Table 1. Table 2 lists the toxicities to wildlife, if known, by the common name of the pesticide. Table 3 provides a cross-listing of some of the trade names that these products are registered and sold by in Florida.

Additional Information

Crop Protection Handbook. 2005. vol. 91. Willoughby, Ohio: Meister Publishing Co. http://www.meistermedia.com/publications/handbook.html.

Nesheim, O.N., Frederick M. Fishel, and Mark Mossler. 2002. Toxicity of pesticides. UF/IFAS EDIS Document PI-13. http://edis.ifas.ufl.edu/pi008.

Reigart, J.R. and J.R. Roberts. 1999. Recognition and management of pesticide poisonings, 5th ed. United States Environmental Protection Agency Publication EPA-735-R-98-003.

Seyler, L.A., et.al. 1994. Extension toxicology network (EXTOXNET). Cornell University and Michigan State University. http://extoxnet.orst.edu/index.html.

Tables

Table 1. 

Hydrocarbon fumigant mammalian toxicities (mg/kg of body weight).

Common name

Rat oral LD50

Inhalation LC50

Chloropicrin

250

150 (rabbit)

1,3-dichloropropene

127 (DD-92®)

904 (rat, Telone®)

Methyl bromide

100

302 (rat, LC100)

Paradichlorobenzene

---

---

Table 2. 

Hydrocarbon fumigant wildlife toxicity ranges.

Common name

Bird acute oral LD50 (mg/kg)*

Fish (ppm)**

Bee

Chloropicrin

---

HT

PNT

1,3-dichloropropene

---

---

---

Methyl bromide

---

---

PNT

Paradichlorobenzene

ST

MT

---

* Bird LD50: Practically nontoxic (PNT) = >2,000; slightly toxic (ST) = 501 – 2,000; moderately toxic (MT) = 51 – 500; highly toxic (HT) = 10 – 50; very highly toxic (VHT) = <10.

** Fish LC50: PNT = >100; ST = 10 – 100; MT = 1 – 10; HT = 0.1 – 1; VHT = <0.1.

Bee: HT = highly toxic (kills upon contact as well as residues); MT = moderately toxic (kills if applied over bees); PNT = relatively nontoxic (relatively few precautions necessary).

Table 3. 

Cross-reference list of common, trade, and chemical names of hydrocarbon fumigants.

Common name

Trade names*

Chemical name

Chloropicrin

Chlor-O-Pic®, Chloropicrin®, Timber Fume®

Trichloronitromethane

1,3-dichloropropene

Curfew®, Telone®, Tri-Lone®

1,3-dichloropropene

Methyl bromide

Metabrom®, Meth-O-Gas®, Methyl Bromide®

Bromomethane

Paradichlorobenzene

Many home products

1,4-dichlorbenzene

*Does not include manufacturer's prepackaged mixtures.

Footnotes

1.

This document is PI-71, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date September 2005. Revised September 2012. Reviewed September 2015. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Frederick M. Fishel, professor, Agronomy Department, and director, Pesticide Information Office; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use pesticides safely. Read and follow directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.