Carbon disulphide

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Carbon disulphide (CS2) was one of the first fumigants employed on a large scale. Its use in France, in 1869, against the grape phylloxera is a landmark in the history of applied entomology. It was injected into the soil to control the insects infesting the roots of the grapevine. For many years afterwards, CS2 was widely used as a soil or space fumigant. Its tendency to burn or explode presents a hazard, and many explosions have been recorded during its use as a fumigant (Hinds, 1911; Fleming and Baker, 1935).

Carbon disulphide penetrates well and is still the only fumigant used in certain parts of the world. It is of practical value in tropical countries where the high temperatures favour volatilization.

Carbon disulphide is commonly formulated in mixtures with nonflammable ingredients for fumigating grain.

TOXICITY

Judged on the basis of lethal dosages, CS2 ranks rather low among the insect fumigants because relatively large dosages by weight are required.

Carbon disulphide is toxic to humans. Because it is used in certain manufacturing processes, it is an important industrial poison. High concentrations of the vapour produce a narcotic effect and, if exposure is continued, unconsciousness and death may ensue from paralysis of the respiratory cent ret Repeated exposure to low concentrations for periods of a few weeks or longer may result in a variety of nervous manifes tations, which may make correct diagnosis difficult (Canada, Department of National Health sod Welfare, 1957). Persons exposed to low concentrations may lose their ability to detect the odour of the chemical and thus may continue to work in a toxic atmosphere without being aware of it (Hinds, 1917).

PROPERTIES OF CARBON DISOLPHIDE
Alternative name : carbon bisulphide
Abbreviation used in this manual: CS
2

Odour Sweetish when pure; impurities, such as hydrogen sulphide, give characteristic unpleasant odours
Chemical formula CS2
Boiling point 46.3C
Freezing point -111 C
Molecular weight 76.13
Specific gravity  
gas (air = 1) 2.64
liquid (water at 4C = 1) 1.2628 at 20C
Latent heat of vaporization 84.1 cal/g
Flammability limits in air 1.25 to 44% by volume
Solubility in water 0.22 g/100 ml at 22C
Pertinent chemical properties Flash point about 20C and ignites spontaneously about 100C
Method of evolution as fumigant By evaporation of liquid; now used more often in nonflammable mixtures
Commercial purity 99.99%

Natural vapour pressure at different temperatures

0C (32 F) 127.3 mm Hg
10C (50F) 198.1 mm Hg
20C (68F) 297.5 mm Hg
25C (77F) 351.1 mm Hg
30C (86F) 432.7 mm Hg
40C (104F) 616.7 mm Hg

Weights and volumes of liquid

1 lb (avdp) at 20C has volume 359.2 ml
1 U.S. gal weighs 10.53 lb (4.775 kg)
1 Imp gal weighs 12.63 lb (5.728 kg)
1 kg has volume 791.89 ml
1 litre weighs 1.2628 kg

Dosages and concentrations of gas in air (25C and 760 mm pressure)

By volume

Weight per volume

Parts per million Percent g/m lb/1 000 ft
20 0.002 0.06  
50 0.005 0.15  
100 0.01 0.31  
200 0.02 0.62  
321 0.032 1.00  
500 0.05 1.56 0.10
1 000 0.10 3.11 0.19
5 138 0.514 16.00 1.00
20 000 2.0 62.28 3.89

1 Ounces per 1000 cubic feet or milligrammes per litre

Absorption of high concentrations may take place through the skin as well as by inhalation. Prolonged contact of the skin with high concentrations of vapour or with the liquid may result in severe burns, blistering or neuritis (Canada, Department of National Health and Welfare, 1957).

A full discussion of the toxicology of CS2 is given in a joint FAD/WHO report (1965a).

EFFECT ON PLANT LIFE

Hinds (1917) found that CS2 in insecticidal fumigations did not reduce the viability of dry seeds (normal moisture content for safe storage). The percentage germination of moist seeds was significantly lowered. Kamel and Shahba (1958) found that the germination of cereal grains (wheat, barley, millet and rice) was not affected with normal fumigation concentrations (250 g/m for 24 hours). Fifteen kinds of vegetable seeds were also not affected, the only exception being eggplant seeds. King et al (1960) experimented with CS2 as an ingredient of fumigant mixtures with carbon tetrachloride and sulphur dioxide. The seeds used were barley, oats, wheat, rice, cotton and two varieties each of maize and grain sorghum. They concluded that the CS2 in combination tended to reduce germination, especially after prolonged storage. The reduction was greater when sulphur dioxide was included in the formulation.

Growing plants and nursery stock are severely injured or killed when treated with gaseous CS2. However, CS2 applied as a dilute emulsion in water to the earth surrounding the roots of evergreen and deciduous nursery stock in the field is effective against some insects, such as the larvae of the Japanese beetle, without causing injury. For details of these treatments and the specific plant reactions to them, the original work of Fleming and Baker (1935) should be consulted.

EFFECT ON PLANT PRODUCTS

Certain fruits (strawberries, raspberries, blackberries, peaches, plums, red currants and gooseberries) in marketable condition were found to be tolerant to fumigation with CS2 at 100 g/m (6.25 lb/1 000 ft ) for 2 hours at 27C. Their flavour and appearance were not affected. Blueberries did not keep well following treatment, and part of the bloom was removed (Osburn and Lipp, 1935). There appears to be no record of the application of CS2 fumigation to fruit in commercial practice.

Previously, CS2 WAS used extensively in fumigation chambers for the treatment of plant products, such as dried beans and peas. Although still used to some extent for this purpose, it has been largely replaced by methyl bromide, which is nonflammable and more easily volatilized.

Majumder et al (1961) reported that CS2 affects the taste of coffee when used to fumigate monsooned (high moisture content) beans and Calderon et al (1970) that it reducer) loaf volume of bread made from fumigated wheat .

RESIDUES IN FOODSTUFFS

Theoretically, from the results of in vitro studies, CS2 may react with peptides and amino acid groups in foodstuffs of vegetable origin (FAO/WHO, 1965a). However, reaction products of CS2 fumigation in foudstuffs have not, apparently, been demonstrated as residues.

The available information refers to the possibility of CS2 itself appearing as residue in fumigated material. Studies of the retention of the fumigant in flour, wheat, rolled oats and the ingredients of bread showed that residues following normal aeration will not persist in cooked foods, such as bread and rolled oats (Lynn and Vorhes, 1957; Munsey et al 1957) .

METHODS OF ANALYSIS

Determination of Vapours

For determination of insecticidal concentrations in the field the thermal conductivity analyser may be used after appropriate calibration for CS2

(Kenaga, 1958). A chemical method that is fairly rapid and convenient has been described by Fleming and Baker (1935). It is based on direct iodometric titration after the vapours are absorbed by alcoholic potassium hydroxide.

For protection of personnel from the poisonous effects of low concentrations and for the measurement of higher levels, glass detector tubes with ranges as low as 5 ppm and up to 3 200 ppm are available. Also infra-red gas analyzers can be used for carbon disulphide. Instruments that will detect concentrations from 0.5 ppm to more than 39 000 ppm can be obtained.

Determination of Residues

Dunning (1957) and Keppel and Munsey ( 1957) described adaptations of Lowen's dithiocarbamate method for the determination of CS2 in fumigated products. Berck (1965a) included it among the fumigant gases which may be analysed by gas chromatography. Bielorai and Alumot (1966) described an electron-capture yes chromatography method sensitive to parts per thousand million, although with standard mixtures the recovery was 50 percent or less. Whitney (1962) discussed methods of inhibiting CS2 decomposition during gas chromatography procedures.

APPLICATION

Carbon disulphide is available in metal cans or drums of various sizes and is readily poured from a large container into a smaller one for application .

The boiling point of CS2 (46C) is well above normal temperatures, and in space fumigations some means of rapid volatilization must be provider! in order that the needed concentrations may be reached as quickly as possible. For small-scale work, the liquid may be poured onto some absorbent material such as jute cloth (burlap), which is then suspended in the space. The liquid may also be applied as a fine spray from a spray pump, preferably from outside the building.

An apparatus for rapid vaporization of CS2 for use in atmospheric fumigation chambers is described by Weigel et al (1927). The CS2 is poured into a shallow pan containing coils of 0.5 inch (1.3 cm) seamless copper tubing through which hot water is circulated. The temperature of the water must be kept well below 96C because this is the lowest temperature reported for the ignition of CS2 in contact with copper. The authors recommend that the temperature of the water in the coil should not exceed 84C.

Grain fumigation with CS2 is discussed in Chapter 10.

PRECAUTIONS

Flammability

The low ignition temperature of CS2 makes it a dangerous fire hazard.

Cans or drums containing liquid CS2 should be stored in cool, shaded, well-ventilated rooms, never under direct sun. In very hot weather, it may be necessary to spray the containers with cold water to prevent excessive rise in temperature. Contact of the vapour with a steam pipe or an electric light bulb may be enough to ignite it. Even the heat generated by a heavy blow could set off an explosion. The spark from static electricity or from an electric motor is a particularly dangerous source of ignition.

Great care must therefore be exercised in handling this material and strict precautions must be adopted during fumigation. If the grain to be fumigated is heating or is likely to do so, pure CS2 should not be used.

Carbon tetrachloride

Carbon tetrachloride (CT) may be used alone as a fumigant but because of its low toxicity to insects, high dosages or greatly prolonger) exposure periods are needed. It has, however, been used alone for grain fumigation, usual ly when there is a shortage of more toxic materiaIs.

At recommended insecticidal concentrations, CT does not affect the germination of seeds (King et al, 1960) hut it may be injurious to growing plants, nursery stock, fruit and vegetables*. Majunder et al, (1961) reported that the taste of coffee may be affected from monsooned (high moisture content) beans fumigated with CT.

* Roth (personal communication, 1967) states that CT in high concentrations near the saturation limit in air for exposures of 4 hours and upward at 25 to 30C was injurious to seeds of the conifers Pinus, Picea, Larix and Thuja but apparently nut of Cupressus.

PROPERTIES OF CARBON TETRACHLORIDE
Alternative name : tetrachloromethane
Abbreviation used in this manual : CT

Odour Characteristic and well-known
Chemical formula CCl4
Boiling point 76.8C
Freezing point -22.8C
Molecular weight 153.84
Specific gravity  
gas (air = 1) 5.32
liquid (water at 4C = 1) 1.595 at 20C
Latent heat of vaporization 46.4 cal/g
Flammability limits in air Nonflammable
Solubility in water 0.08 g/100 ml at 20C
Pertinent chemical properties Nonflammable and nonexplosive, relatively inert
Method of evolution as fumigant By evaporation of liquid. Used more often in a mixture to reduce flammability of more toxic fumigants or to act as a carrier for better distribution

Natural vapour pressure at different temperatures

0C (32F) 32.9 mm Hg
10C (50F) 56.0 mm Hg
20C (68F) 91.0 mm Hg
25C (77F) 114.5 mm Hg
30C (86F) 143.0 mm Hg
40C (104F) 215.8 mm Hg

Weights and volumes of liquid

1 lb (avdp) at 20C has volume 284.4 ml
1 U.S. gal weighs 13.3 lb (6.032 kg)
1 Imp gal weighs 15.95 lb (7.235 kg)
1 kg has volume 626.959 ml
1 litre weighs 1.595 kg

Dosages and concentrations of gas in air (25C and 760 mm pressure)

By volume

Weight per volume

Parts per million Percent g/m lb/1 000 ft
10 0.001 0.06  
50 0.005 0.31  
100 0.01 0.63  
159 0.016 1.00  
200 0.02 1.26  
500 0.05 3.14 0.20
1 000 0.10 6.29 0.39
2 543 0.254 16.00 1.00
20 000 2.0 125.85 7.86

1Ounces per 1000 cubic feet or milligrammes per litre

CT fills a useful role in the fumigation field as an ingredient of mixtures, principally for grain fumigation. It is nonflammable in any concentration in air, and serves to reduce fire hazards of other fumigants, such as ethylene dichloride, carbon disulphide and acrylonitrile. Furthermore, the distribution of some liquid-type fumigants in a grain mass is aided by the presence of CT as one of the ingredients (Berck, 1958).

TOXICITY

Although, compared with other commonly used fumigants, CT is not very toxic to insects, it is now known to be extremely poisonous to human beings. Toxicity to humans is attributed mainly to extensive liver damage (Rouiller, 1964).

Human poisoning may be acute as the result of exposure to high concentrations but in practice it more often occurs as a chronic condition from comparatively low concentrations inhaled over extended periods of time. In recent years the threshold limits established by the American Conference of Governmental Industrial Hygienists have been progressively lowered until they are now at 5 parts per million (ppm) for continuous daily exposure to CT. This fumigant is now listed by the above agency in the category of industrial substances suspected of carcinogenic potential for humans (ACGIH, 1981).

There are two important considerations in CT poisoning. According to Rowe (1957) the vapours are not detectable by smell below 70 ppm in air. It should also be made known that CT does not "mix" well with alcohol:

"Persons who are prone to imbibe too heavily or too frequently show a considerably greater susceptibility to carbon tetrachloride poisoning" (Torkelson et al 1966)

RESIDUES IN FOODSTUFFS

Evidence is strong that CT is taken up physically and without chemical reaction in grain and grain products (Pepper et al, 1947; Lynn and Vorhes, 1957). Jagielski et al (1978) found residual CT in fumigated wheat and maize three months after treatment and a substantial proportion of this appeared in milled fractions, especially the bran. Small amounts (up to 0.03 mg/kg) could be detected in bread made from the treated flour. There is no positive evidence available on the presence or absence of CT metabolites in treated grain or other foodstuffs (Kenaga, 1967).

The toxicological significance of even small amounts of residual CT is not known, but the FAO Panel of Experts on Pesticide Residues in Food (FAD/WHO, 1980) suggested that guidelines be lowered below those previously recommended. They indicated that the following levels should be used as guide lines:

Cereal grains 50 mg/kg
Milled cereal products (for baking and cooking) 10 mg/kg
Milled cereal products (for consumption Without cooking) 1.01 mg/kg
Bread and other cooked cereal products 0.01 mg/kg

METHODS OF ANALYSIS

In the field determination of this fumigant, both the thermal conductivity analyser (Kenaga, 1958) and the interference refractometer can be used. It is important to point out that such methods are not applicable to CT in fumigant mixtures and should only be employed when CT is applied alone. Glass detector tubes are available for measuring low levels of CT in the 5 to 50 ppm range.

Residual CT in cereal grains, milled products and other stored foods can be determined by gas chromatography in the parts per thousand million range (Bielorai and Alumot, 1966; Heuser and Scudamore, 1969b). A cold extraction procedure for removal of CT from wheat and maize was found more effective than steam distillation (Scudamore and Heuser, 1973). Landen (1979) described a method for microassay of CT in drinking water and beverages.


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