Forensic Toxicology
THE FOLLOWING ARTICLE APPEARED IN THE
OCTOBER 1998 ISSUE
THE POISON SLEUTHS
DEATH BY ALUMINIUM PHOSPHIDE
-Dr. Anil Aggrawal
"Good morning doctor. Oh, my God, what are you doing today? You have the dead body of a young lady today. What happened to her? Please tell me."
"Good morning Tarun. The name of this young lady is Sushila, and she was found dead in her bed today morning. It is suspected that her husband gave her something in her food, which took her life. I will tell you some details, which will put the whole crime in perspective for you. She was married to a young boy Suresh only 2 months back. Suresh is a petty clerk in a bank, and it appears that there was a dowry demand in the house, which was not properly catered to, by the bride's side. Because of this there was a lot of tension in the house, and Sushila had complained several times to her parents about it. Now suddenly she is found dead in her bed. It is suspected by Sushila's parents, as well as by the police that Sushila has been given some poison by Suresh and his parents to do away with her."
"What makes them think that? Do they have any proof against them?"
"Well, the main thing is that there is a very strong motive for Suresh's parents to kill Sushila- dowry. They could get their son married again for better dowry. It seems a reasonable motive. Moreover brides don’t usually die so mysteriously just after 2 months of their marriage, until and unless there is some serious trouble with the marriage."
"But it is quite possible that she committed suicide. What makes the police think that it is a case of murder?"
"Well it could be. But Suresh and his parents are going one step further. They are alleging that she may have died of some natural disease. In fact Suresh has alleged that she had some gynecological problem about which she once discussed with him."
"Really? Did you find any evidence of a fatal disease in her body? And by the way, have you found something in her stomach?"
"Tarun, I didn’t find any fatal disease in her body. If she had any of it, like leukemia, or other cancers, or some gynecological trouble, I would surely have found out. I have indeed analyzed the contents of Sushila's stomach and I have found out lot of Aluminum hydroxide in her stomach."
"Aluminum hydroxide? Doesn't seem like a poison to me. It is a very weak alkali though. Can it kill someone?"
"You are right. Aluminum hydroxide generally doesn't kill a person. But just by it's presence, I have come to know of the poison, which might have been administered to her."
"And what that poison is doctor? Please tell me. I am getting curious."
"Tarun, it is Aluminium Phosphide, a very dangerous poison. It is available in the market at tablets of Celphos, Quickphos or Fumigant. The last trade name is perhaps quite apt. These tablets are used for killing insects in the grains such as wheat and rice. Generally people buy these tablets and mix them with stored wheat. Insects which would otherwise appear in these grains after some time, generally don’t appear if you preserve the grains along with these tablets."
"Oh, I see. I have heard about such tablets. But how do they prevent insects from breeding inside the grains."
"Tarun, when Aluminium Phosphide comes in contact with water, or moisture in the air, it liberates a very dangerous gas phosphine. This gas is actually dangerous for the insects, and they can't breed inside the grains. Since you are so good in chemistry, I will give you the exact chemical equation of this chemical reaction. The chemical equation for the liberation of phosphine is:
2 AlP + 6 H2O = 2 Al(OH)3 + 2 PH3
I hope it is quite clear to you. The gas phosphine is liberated and aluminum hydroxide is left behind."
"Yeah it indeed is clear to me. Tell me why such a dangerous poison is freely available in the market. I agree that it is such a good fumigant, but keeping in mind its poisonous nature, can't the scientists find some better alternative?"
"That's a good point of discussion Tarun. In fact there has been much debate and discussion on this already. But I don’t want to go into that. For the time being I will tell you why they are finding it so hard to abandon it. Aluminum phosphide is commonly used as insecticide, rodenticide and fumigant all over India and even in developed countries. To be sure, there are several other fumigants available, such as ethylene dichloride, ethylene dibromide, carbon tetrachloride mixture and methyl bromide. But only aluminum phosphide is considered as an ideal fumigant over all other fumigants. It has almost all the properties of an ideal fumigant…."
"Really? What are those? Please let me know."
"Tarun, Aluminum Phosphide is highly toxic to almost all stages of insects with remarkable penetration power. It dissolves well in water, oils and fats. It is considered an ideal seed fumigant since the seeds' viability is not affected and is practically free from residual toxic hazards- provided the seeds contain less than 20% water. It is minimally absorbed and easily desorbed from the treated commodity such as wheat grains. It is non flammable at the prescribed dosage and devoid of tainting on fumigated stock. It has a distinct odor, which has been described as a fishy odor. Because of this and also because of delays in evolving phosphine provide considerable safety in handling this fumigant. Since the tablet generates the predetermined weight of gas, it is very convenient to administer the exact dose. Cost of fumigation is low and its effects on the fumigated stock last longer. It is easy to transport and handle. Treatment is more or less known, so in case accidental poisoning occurs in humans, they can be taken care of. But unfortunately no specific antidote is known. These are all very desirable properties in any fumigant, and all of these are available in aluminum phosphide."
"Doctor how can you detect phosphine in the environment?"
"Tarun, Phosphine is a colorless and odorless gas, but when it is generated from aluminum phosphide tablets available in the market, generally there are some impurities along with it. Because of this, the gas has a typical garlic odor. Besides the smell, the presence of phosphine can be detected by a simple test. When a filter paper soaked with silver nitrate solution comes in contact with the gas, it turns from brown to black. The usual fatal concentration of phosphine is 200 ppm. After the reaction with moisture, less than 25% of the original tablet weight is left behind from which the amount of aluminum phosphide consumed can be detected."
"Doctor, tell me something more about these tablets. I need to know more about them, so next time I see them, I recognize them at once."
"Tarun, the tablets are dark brown or grayish in color, 3 g in weight and measure 20 mm in diameter and 5 mm in thickness. They come in an aluminum container containing ten tablets. Aluminum phosphide is also available as 0.6 g pellets. The tablets are composed of pure aluminum phosphide (the active ingredient) and ammonium carbamate/carbonate (the inert ingredient). The ratio of the active and inert ingredient is generally about 56:44. On contact with moisture each 3 g tablet evolves about 1 g of phosphine along with carbon dioxide and ammonia, which prevents self ignition of phosphine gas. This is why it is also called "Protective gas". Carbon dioxide and ammonia are liberated by combination of water with other inert ingredients in the tablets. In fact the main function of the inert ingredients is to produce these gases, so phosphine may not ignite easily. The phosphine gas thus liberated spreads quickly and kills insects and rodents almost in all stages of development. After complete decomposition of the tablet, aluminum hydroxide is left behind as a harmless and non toxic grayish white residue."
"And this is what you have found out in Sushila's stomach. So it is almost clear that she died of Aluminum Phosphide poisoning. But how can you prove whether it is a homicidal or suicidal poisoning?"
"Tarun, Celphos poisoning is generally suicidal in nature. As I told you earlier, the tablet emits a strange fishy smell. So it is rather difficult to administer it homicidally. It is almost certain, that Sushila took it with suicidal intention. I will give my report to the police accordingly. Of course the police can still register the case as murder under Section 304B of Indian Penal Code. This section defines Dowry death. And this stipulates that the husband and his relatives are responsible for her death if the bride dies from any cause within seven years of marriage, and it is shown that she was harassed for dowry before her death. Of course, to bring Sushila's death under this section, the police would have to work hard, and prove positively beyond doubt that she was harassed for dowry, so I guess, it makes their task that much difficult."
"Oh yeah, I am sure, they will be able to do that. This was a most interesting discussion doctor. Tell me what are you going to tell me the next time?"
"Tarun, next time, I would tell you about a very interesting poison- Argemone mexicana. "
Additional notes by readers
On April 5, 2001, Sergio Salazar from Nicaragua wrote:
In Nicaragua the aluminum phosphide is named "pastilla del amor" -tablets of love- because the suicides ingest these products.
I'm a chemist and my job is analytical toxicology in the Instituto de Medicina Legal in Nicaragua. But when there are suicide by phosphine I don't know of any analytical procedure for the detection of phosphine residues.
Would you suggest me any methodology?
kind regards
Sergio Salazar