Phytosanitary Solutions

Phosphine gas

Hydrogen phosphide

PH₃

Aluminium phosphide(ALP) is Solid; emits phosphine gas.

Pure Phosphine is odourless, however due to impurities it has Garlic-like, decomposing fish and stale urine odour.

-87.7°C

ALP : 2530°C

-138.5°C

34.04

i) At gaseous stage :

1.214

2.85 g/cm³   (20°C)

Explosive at 1.79% by volume in air. Auto-ignites at 38°C.

26 cc/100 cc at 17°C

Explosive when in contact with moist air. Corrosive to certain metals.

As the fumigant remains in a state of gas, the weight/volume ratio is not relevant.

The reading in Rekin Phosphine Monitor is shown in mg/l.

We should know that 1 mg/l is equal to 1 g/m³ and 1 g/m³  of phosphine gas is equal to 718 ppm.

Phosphine gas 40 mm Hg @ ­129.4 C

Mode of Action:

AlP + 3H₂0 = Al (OH)₃+ PH₃ (in air)

AlP + 3HCl = AlCl₃ + PH₃ (in air and stomach)

Phosphine gas is absorbed through the skin of the insects resulting in their kill.

0.3 ppm

Method of Evolution as Fumigant

Aluminium phosphide is available in pellets or tablets which contains gas with inert material and also ammonium carbamate. The addition of ammonium carbamate serves to reduce the danger of flammability of phosphine gas as it gives off carbon dioxide and ammonia.

Effect on Metals, Paints, Enamels, Plastics, etc.

Metals: Copper, Brass, Gold, silver: causes severe damage;

Other Metals: affects to some extent in high humidity.

Paints, enamels: No information.

Effect On Planting Material:

Germination of seeds: Germination not affected.

Phytotoxicity: No information is available.

Effect on Plant Products

No adverse effect on vitamins, particularly Vitamin A and B₂. No adverse effect on baking quality of flour made from fumigated wheat.

It is toxic to Human beings and animals.

LD₅₀ = 11.5 mg/kg

Conversion: Extensive work carried out so far has not indicated phosphine reacting with contents and leaving a permanent residue. The indications so far are that if such residues are left, they are extremely small and difficult to detect. However, phosphine has been found as residue in food grains in very low concentrations and further reduces after aeration.

Tolerance:

The fact that phosphine aerates rapidly from foodstuff and that a residue of 0.1 ppm in a raw cereal would yield a residue below 0.01 ppm, the Codex Alimentarius Commission found no necessity to fix Acceptable Daily Intake (ADI).

Phosphine is the toxic gas that is formed from hydrolytic reaction of aluminium phosphide. Immediately on contact with moisture, there is decomposition of ammonium carbamate component producing ammonia and carbon dioxide gas. Both these gases dilute the phosphine gas, which is evolved during subsequent hydrolysis, thus preventing explosion. As the breakdown progresses, the outer appearance of the tablet preparation will change from shiny grey-green to white. The tablet then disintegrates into a pile of grey white dust. The residue dust is aluminium hydroxide which may contain traces of aluminium phosphide.

Phosphine is an extremely useful fumigant in Phytosanitary treatment. It is highly toxic to pupal, larval and adult stages of insects. Its ovicidal properties are however a limiting factor. Because of this, the exposure period is longer than MB.

Phosphine is highly toxic to human beings. The gas is not absorbed through the skin. There is no evidence for cumulative effect from intermittent, low level exposures of 10 ppm or less. At higher concentrations, inhalation of phosphine may produce symptoms including nausea, vomiting, diarrhea, headache, chest pain, and massive accumulation of fluids in the lungs before death.

Treatment: The treatment is only symptomatic and supportive.

EMERGENCY TREATMENT

A. INHALATION:

(i) Remove patient from exposure, keep at rest. Rescuers should follow full safety  procedures.

(ii) If the patient is unconscious, place in semi-prone recovery position or otherwise maintain the airway.

(iii) If patient is conscious but has difficulty in breathing, treat in a seated position and give oxygen if available.

(iv) Allow patient to recline with the legs slightly elevated.

(v) If breathing stops, immediately ventilate the patient artificially (mouth to mouth/nose or mechanically with oxygen available).

(vi) If the heart stops, begin cardiopulmonary resuscitation-CPR.

B. SKIN:

(i) Remove contaminated clothing. Wash contaminated skin with soap & water.

C. EYE:

(i) Immediately flush with large amounts of water for at least 15 mins., occasionally lifting  upper and lower lids.

·         At relative humidity of over 75%, maximum release of PH₃ occurs in 45 hours at 25°C;

·         For bag stacks a minimum of 7 days exposure at a dosage of 6 to 9 tablets per tonne at 25°C gives best kill of insects;

·         Perfect gas-tight enclosures give desired results; gas loss could be unmanageable at temperature exceeding 25°C _;

Only trained fumigation operator knowing toxicological and technological properties should use.

·         Fumigation should not be attempted at Relative Humidity less than 50% (grain moisture contents around 10%);

·         Some insect species are highly tolerant of PH₃ especially at low temperatures and short exposures;

·         Oil bearing commodities tend to air slowly and have to be checked for residual PH_3;

·         Odour threshold is 2 ppm; unfavourable on long exposures;

·         Flammability hazard;

·         Brass and copper are attacked.