Problems Admitted in Initial Lab Tests on Recalled Melons

State officials now admit that early laboratory tests after the July 4 watermelon recall were beset by problems, adding to the confusion that led growers to criticize the state’s action halting the harvest until a program to clear unaffected fields could be set up.

Despite early lab tests suggesting that as many as 20 watermelon growers in four counties illegally used a highly toxic pesticide on their fields, the state testing program has turned up evidence of contamination in only one farm’s crops.

Scientists for the state Department of Food and Agriculture late last week described their initial problems in testing for aldicarb, the pesticide that may have poisoned more than 500 people who consumed California-grown watermelons.

For several hours on July 4, when the first samples of watermelons linked to pesticide poisonings were being tested, department chemists checked for the wrong compound--the pesticide itself rather than the active breakdown product present in fruit, said George Tichelaar, the department’s laboratory services chief.

Only after checking with a chemist for the pesticide’s manufacturer did the scientists here realize their mistake and confirm that the melons were contaminated.

In the days that followed, the department’s Fresno laboratory got false results, incorrectly implicating several growers, because of technical problems in setting up mass testing of thousands of melons taken from fields waiting for harvest. A list was released of four growers whose melons were thought to be contaminated, although all but one were cleared just a few days later.

Among the fields that were first thought to have pesticide-tainted melons, but in fact did not, was one operated by California State University at Fresno, according to documents obtained by The Times.

But scientists at the Food and Agriculture Department laboratory in Sacramento say they quickly corrected the problems, and they express confidence in the methods used to clear hundreds of watermelon fields around the state.

Based on an improved testing procedure that includes confirmation of positive results on three different testing systems, the department last Monday placed a quarantine on 110 acres of watermelons owned by Kern County growers Jim and Gary Icardo. These are the only fields that have so far failed to pass the mandatory aldicarb testing program, according to department spokeswoman Jan Wessell.

“If it (the pesticide) doesn’t show up in our tests, I know it’s not there,” Tichelaar said.

Sample of 20 Melons

But because the department is testing a sample of 20 melons taken from each field, and because the testing methods can miss low levels of the pesticide, the possibility remains that watermelons now on the market contain low levels of aldicarb.

Those amounts would be unlikely to cause any immediate health effects, according to health officials. The U.S. Environmental Protection Agency standards allow such low levels in oranges, one of the food crops to which aldicarb may be applied legally.

And thus far, a statewide search has turned up no confirmed cases of pesticide poisoning from eating melons with stickers showing they were harvested from fields that have been cleared by the department’s testing.

“There is a high probability of catching a contaminated field,” said Dr. James Stratton, a medical epidemiologist with the state Department of Health Services. “But from a public health standpoint, we have to make the assumption that no system like this can be 100% perfect.”

That is why, Stratton said, state health officials are in daily contact with 10 poison control centers and 61 local health officers around the state in a search for outbreaks of food poisoning connected to eating watermelons.

No New Poisonings Confirmed

Since stickered watermelons first began appearing on market shelves, health officials have investigated about a dozen cases of illnesses that followed watermelon consumption. But in every case in which samples of fruit have been recovered and tested, no traces of the pesticide could be found, according to Stratton and Tichelaar.

The problem in identifying cases of aldicarb poisoning is that the symptoms are similar to those of flu-like viral infections that are common in the summer months, Stratton said.

The poisoning victims do not have a fever. They may experience vomiting, diarrhea, abdominal pain, muscle weakness, excessive sweating and blurred vision. The pupils of the eye become pinpoint-size and do not react to changes in light--symptoms that are not present in the flu, but that are usually difficult for patients themselves to document. The worst effects of poisoning are seen within a few hours of ingestion and then usually disappear without treatment, although high doses of aldicarb can be fatal.

No deaths have been connected to the tainted watermelons.

Growers Initially Skeptical

In the early days of the recall, skeptical growers questioned whether there had been any aldicarb poisoning. In fact, state health officials also wondered at first whether the levels of aldicarb found in melons during the first week of the crisis could cause any symptoms at all.

But unpublished studies conducted by Union Carbide, which manufactures aldicarb under the brand name Temik, show that extremely low doses can have a pronounced effect on human enzymes needed for proper nerve transmission. In these experiments, which were conducted 15 years ago in human volunteers, the subjects quickly swallowed small amounts of the pesticide dissolved in water. Several developed outward symptoms of poisoning, and all had blood changes caused by the chemical.

Tichelaar and other Food and Agriculture Department scientists explained that developing techniques to pick up low levels of a pesticide in a food product is as much art as science.

The first testing method used in the department’s Fresno laboratory confused an unrelated, naturally occurring chemical found in some of the melons with aldicarb, Tichelaar said.

With the help of a Union Carbide chemist, state scientists were able to adjust their techniques and increase their ability to find extremely small quantities of the pesticide.

Sheer Volume of Melons

Once the testing procedures were worked out, the most difficult problem facing the laboratory scientists was managing the huge volume of watermelons. As many as 1,600 melons--eight tons of fruit--moved through three department laboratories in a single day. Last weekend, the Sacramento laboratory was virtually knee-deep in watermelons. None of the melons could be discarded until a sample of it was tested and found to contain no detectable levels of the pesticide products.

Any melon that was found positive has been frozen and retained for further testing.

The freezer in the Sacramento laboratory is now filled with watermelons, Tichelaar said.

While Food and Agriculture Department officials say that the illegal use of aldicarb in just a few fields could account for all the cases of poisoning, some state health officials still wonder whether the use of the chemical might have been a more widespread practice.

Tichelaar’s chemists may have an answer. They are now beginning to test soils taken from melon fields, another way of finding out if the pesticide has been illegally applied.