What makes cassava poisonous?

Just how lethal can a native delicacy long enjoyed by Filipinos be?

Toxic experts are eyeing cyanide as the likely cause of the poisoning of at least 110 mostly grade-school children in Bohol after they ate tasty treats made from cassava flour last Tuesday.

Thirty children died after eating the merienda. And recess will never be the same again.

According to the Plant Resources of Southeast Asia (PROSEA), a cassava’s tubers (roots) and leaves contain hydrocyanic acid (HCN).

Anyone can tell by its name that HCN is dangerous, and when it’s more than what the body can handle, this chemical compound can kill — man and animal alike, PROSEA said yesterday.

The Center for Disease Control (CDC) said in its website that cyanide

is a "rapidly acting, potentially deadly chemical that can exist in various forms, and can be a colorless gas such as HCN."

It could also come in the form of an inorganic compound such as cyanogen chloride, or in a crystal form like sodium cyanide or potassium cyanide, the CDC said.

All cassava cultivars (cultivated varieties) contain cyanogenic glucosides, according to PROSEA. Glucoside content such as HCN (or prussic acid) in the central part of fresh storage roots varies from 30 to 200 milligram (mg) per kilogram (kg), and can sometimes even be more.

"Small amounts are tolerable, but man should not consume more than one mg HCN per kg body weight per day," advised PROSEA, an international project focused on the documentation of information on plant resources of Southeast Asia.

High nitrogen and low potassium makeup in soil increases the glucoside content. The first rains after a dry season can also cause a large increase in glucoside.

"If the cells of storage roots are crushed, glucosides and enzymes make contact and the HCN is split off. This is the key to methods of removing HCN. The volatile HCN should be allowed to escape," PROSEA said.

Epidemiologist Dr. Manuel Mapue of the Department of Health (DOH) said cyanide could be produced by certain decomposing elements in the soil.

"During summer, the level of cyanide in root crops increases because the soil is dry. During the rainy days, the water (washes out the toxin)," Mapue said.

Cyanide poisoning is suspected to have caused the tragedy, Dr. Troy Gepte, an epidemiologist at the Department of Health’s (DOH) National Epidemiology Center (NEC), said yesterday.

"Toxicologists are looking closely into this but it seems that it’s cyanide poisoning," said Gepte. "I think the children ate maruya and pitsi pitsi , and cyanide is inherent in root crops like cassava."

Cassava is known as kamoteng kahoy or balinghoy in the Philippines.

Reports said the children, mostly second- and third-grade pupils studying at the San Jose Elementary School in Mabini town, started complaining of stomach pains and dizziness right after eating the merienda treats of maruya (cassava cake) and pitsi-pitsi (cassava balls) during the morning recess at around 10:30.

It didn’t take long before many of them died, most in hospitals, leaving their parents in shock and, later, agonized grief.

The number of children turning up at hospitals due to the food poisoning crisis rose to 80 as of yesterday, according to Gepte.

The death toll still stood at 30, as victims continued to receive treatment in the district hospital of Don Emilio del Valle Hospital in Ubay town and Celestina Gallares Memorial Hospital in the provincial capital of Tagbilaran City, some 100 kilometers from Mabini.

Two vendors were reportedly responsible for selling the snacks. One was identified as Aning Luyong, 60, who was also in critical condition after she reportedly ate some of the cassava cakes.

Gepte refused to blame the vendor for the incident.

"I think it’s accidental. She, herself, had been poisoned and she has reportedly been selling the products for a long time now and I don’t think she would do it deliberately," he said.

PROSEA warned that boiling is not always a guarantee that a food product is safe, as the HCN may be caught in the starch paste.

Sun-drying reduces toxicity but is not very effective either.

Another DOH epidemiologist, Dr. Chito Navarro, said cyanide is inherent in root crops.

"Cyanide can be found naturally in root crops and I think even in kaong. But if the preparation of the food is not proper, or if the food has not been rinsed and cooked well, it can cause poisoning," Navarro said.

The DOH has already coordinated with the Poison Control Center of the Philippine General Hospital (PGH) to provide the antidote for the ailing kids.

The DOH, meanwhile, is verifying reports that the cassava had been contaminated with organo phosphate, a type of pesticide used in agricultural products.

Gepte added they received information that the water used to wash the cassava came from a container contaminated with the pesticide.

"There were some children who immediately died a few minutes (after eating cassava). Symptoms of poisoning are related to the amount of cyanide ingested from the food. This could occur within 10 minutes or within a few hours," Gepte said.

Working On The Antidote

epte said two teams from the DOH-NEC have been dispatched to Bohol to investigate. He himself flew to the province after a hastily called press conference yesterday.

One team is composed of one toxicologist from the DOH central office and two from the PGH while the other team is composed of DOH epidemiologists from the central office and its regional office in Cebu.

According to epidemiologist Dr. Chito Navarro, the teams would determine what really poisoned the victims so the PGH experts could administer the proper antidote to them.

For cyanide poisoning, the doctors would use sodium nitrite to prevent the toxin from getting into the red blood cells and sodium thiosulfate to flush it out through the urine.

A person poisoned with cyanide dies because the chemical blocks the flow of oxygen in his body.

Navarro added that if the pesticide had been the cause of the poisoning, the experts would apply atropine, an injectable drug.

"There are many varieties (of cassava) but (those that) are poisonous cannot be usually seen. Usually, they are in the plantation. They are also used in the production of starch," he maintained.

He said the toxicity of cassava could be reduced through proper cooking and rinsing.

"The cyanide content of cassava and other root crops increases during summer because the soil is dry. We’re finding out what kind of toxin (hit the victims) and applying appropriate antidotes," Navarro said.

The extent of cyanide poisoning, he said, depends on the amount of toxin a person was exposed to and the length of time of exposure.

He added that cyanide does not give off a smell nor does it change the physical appearance of a root crop.

Those exposed to a small amount of cyanide by eating contaminated food, breathing it or absorbing it through the skin usually manifest symptoms like rapid breathing, restlessness, weakness, dizziness, headache, rapid heart rate, nausea and vomiting.

The symptoms of long-term exposure are low blood pressure, convulsions, slow heart rate, lung injury, loss of consciousness and respiratory failure.

Exposure to high levels of cyanide can also cause damage to the central nervous system, cardiovascular system and respiratory system.

The DOH does not recommend any first-aid measure for anyone who manifests such symptoms, but instead suggests bringing them to the hospital for proper treatment.

According to PROSEA, cassava leaves also contain considerable amounts of cyanogenic glucosides.

But when detoxified, cassava foliage is a good feed for animals as found in a study done by the Department of Agriculture-Philippine Carabao Center in Ubay, Bohol. The study was monitored by the DA-Bureau of Agricultural Research.

The PROSEA project is coordinated through the efforts of the Los Baños-based Department of Science and Technology-Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCARRD).

Cassava, also known as tapioca, is a common root crop in Asia.

It is ketela pohon in Java, Indonesia, and ubi kayu in Malaysia.

In Myanmar, it goes by the name palaw-pinan-u-pin, damloong cheeh in Cambodia, man tonz in Laos, man sampalang in Thailand, and san in Vietnam,

It is said that cassava, which is indigenous to tropical America, was introduced in the Philippines by Spanish explorers and tradesmen from Mexico in the 19th century.

A cassava variety is classified as bitter when the HCN is about 200 parts per million and above.

These varieties are usually used for animal feed and for industrial purposes. The most common of this type are Hawaiian 5 (popular in Mindanao, particularly in Lanao del Sur), Datu I, Java Brown, Sultan I and VCV-1.

Today, cassava is largely used as food, for starch manufacture, and to a lesser extent, for livestock feed.

"The significance and potential of cassava, especially as an animal feed, are now widely recognized in Philippine agriculture," PCARRD said.

If It’s Red, It Must Be Good

He is no agriculturist, but Sen. Juan Ponce Enrile knows a thing or two about poisonous cassava since he has been feasting on this all his life.

His word of advice: If the leaves of the plant are green, it’s poisonous. If it’s red, it’s good.

The veteran lawmaker said he knows a lot about the crop, recalling eating the crop during his days as a guerrilla in the mountains when there was no food around.

A good cassava, Enrile said, can be eaten raw unlike its poisonous counterpart, which should not be eaten under any circumstance.

Though it is easy to tell the poisonous from the safe variety, Enrile said that once the cassava is taken from the stem, it is hard to distinguish one from the other.

However, he said there was still a way of finding out simply by slicing into the cassava using a polished knife.

When the knife gathers a stain of black then the cassava is the poisonous variety.

Enrile said that all farmers know how to distinguish the two types of cassava and that it would be easy to locate the source of the deadly plant in Bohol.

While the deadly variety of cassava is inedible for humans, it could still be processed into animal feed. — With Marvin Sy