After 40 years of use and growing concern about one of the most toxic pesticides around, the Environmental Protection Agency negotiated an agreement in August 2010 to take it off the market. Now a U.S. company wants to bring it back.

Aldicarb was responsible for the largest foodborne pesticide poisoning in U.S. history, sickening more than 1,000 people who ate tainted watermelons in 1985. Yet federal regulators continued to allow use of the pesticide on an array of foods for another 25 years, until new toxicity data last year prompted the EPA to strike a voluntary deal with manufacturer Bayer CropScience to end all uses.

But within a month of the agreement, Ag Logic LLC, a subsidiary of MEY Corp., asked the agency to register the pesticide for use on cotton and a variety of foods such as peanuts, soybeans, dry beans, sugar beets and sweet potatoes.

The prospect of a renewed battle over aldicarb concerns those who fought for years to get it banned or severely restricted.

“When you have something that’s subject to misuse, you worry about it being on the market at all,” said Lynn Goldman, dean of George Washington University’s School of Public Health and Health Services. Goldman was in the California health department at the time of the watermelon contamination and was assistant administrator for toxics and pesticides at the EPA from 1993 to 1999.

Aldicarb, known by the trade name Temik, is a member of the carbamate family, a class of pesticides introduced in the late 1950s and early 1960s. After it is applied to the soil, it is drawn up through the roots and into the flesh of a plant.

Aldicarb is effective at killing nematodes and other pests, but if not used properly it poses a serious risk to the environment, farmworkers and anyone who eats food or drinks groundwater contaminated with the residue. Even exposure levels that studies had once considered low were later found to disrupt the nervous system and can cause shaking, sweating, vomiting, diarrhea, blurred vision and trouble breathing. Children feel the effects at lower levels than adults do.

The pesticide has been classified as “extremely hazardous” by the World Health Organization (WHO) since 1975. It had been under EPA review since 1984, after it was used on potato fields on New York’s Long Island and leached into well water. That same year, a chemical in the pesticide was associated with a major catastrophe: Methyl isocyanate, or MIC, caused the death of thousands of people in Bhopal, India, when the gas leaked from a Union Carbide pesticide plant.

The U.S. watermelon outbreak occurred on the West Coast the following year. Many of those who fell ill had minor symptoms, but 17 people were hospitalized.

How aldicarb got into the fruit is not clear. Pesticides must be registered with the EPA for use on specific crops, and watermelons were not among those approved for aldicarb. Studies also found high residues even when aldicarb was applied properly on approved crops.

The EPA has the power to ban pesticides after internal review and consultation with the Department of Agriculture. But the agency often relies on voluntary agreements to reduce pesticide risks, a strategy that avoids protracted and costly legal battles, during which the chemical remains on the market.

But as the aldicarb experience shows, building a case strong enough to pressure a manufacturer into voluntarily stopping production of a profitable product can take decades – and leave the door open for another company to pick up where the previous manufacturer left off.

“The law doesn’t say if a pesticide hits a certain level of badness, it’s automatically banned,” said Goldman. “The other party has rights under the law.”

Aldicarb was among some 600 older pesticide ingredients on the market in 1988 when Congress charged the EPA with reviewing pesticides registered before November 1984 and reregistering them based on modern environmental and health standards. The agency didn’t finish until 2007, and aldicarb was the last active ingredient reviewed.

In the meantime, the agency took a patchwork approach to restricting its use. EPA toxicologists recommended in 1989 that the agency ban use of aldicarb on bananas and potatoes because they believed the crops were exposing thousands of children to risky levels of aldicarb every day, according to news reports at the time. By then, the French chemical company Rhone-Poulenc had acquired aldicarb.

But no policy was changed until company monitoring over the next two years picked up residues on potatoes and imported bananas that exceeded safe levels.

In 1990, Rhone-Poulenc suspended use of aldicarb on potatoes while it changed application instructions. The company voluntarily stopped the chemical’s use on bananas a year later.

In 1993, a study by the National Research Council urged regulators to pay attention to the eating habits of children and their potentially higher sensitivity to pesticides when setting the legal limit for residues in food, referred to as “tolerances.” That year, the EPA revoked aldicarb tolerances for bananas.

The Food Quality Protection Act of 1996 tightened pesticide regulation. The act directed the EPA to reassess pesticide tolerances to make sure children were protected from potential harm.

The law also changed the way pesticides were evaluated. The EPA started looking at the cumulative risk of pesticides that had the same physiological effects on people; and it considered a person’s total dietary exposure to a pesticide from a variety of sources.

Prompted by the National Research Council’s findings and subsequent congressional action, the EPA completed a study in 1999 that analyzed the effects of aldicarb on children. The results showed that children were two times as sensitive to aldicarb as adults were.

But it wasn’t until 2007 that EPA asked for a new test on children’s sensitivity. By then, Bayer had acquired aldicarb through a series of mergers.

As part of the re-registration decision, Bayer struck an agreement with the EPA to further whittle the pesticide’s uses by not renewing its registrations for coffee, ornamentals, pecans, sugarcane, sorghum, tobacco, and alfalfa grown for seed.

At the time of the re-registration decision, the EPA called for an update of the study evaluating children’s sensitivity to aldicarb.

Bayer completed the study in February 2010. Based on that data, the EPA decided that children were five times more sensitive to aldicarb than adults. And the agency reanalyzed potential risk from food and drink with aldicarb residue.

Though Bayer did not agree with the EPA’s findings, the results led to an agreement last summer between the EPA and BayerCropScience to take measures to protect groundwater and to immediately withdraw citrus and potatoes – the crops responsible for most exposure – from the chemical’s registered uses. Under the agreement, existing supplies of the chemical could be used through 2011.

The EPA considered the remaining uses of aldicarb safe. However, with its market diminished – aldicarb sales were $80 million for the year, down from $170 million in 1990, according to reports in Chemical Week – Bayer CropScience decided to stop making aldicarb by the end of 2014. Existing supplies would be allowed for sale through 2016 and for approved uses through August 2018.

Jack Boyne, spokesperson for Bayer CropScience, said the decision was in line with a company business plan to gradually quit the market of WHO Class I pesticides.

But production complications caused Bayer to make a business decision in March 2011 to end aldicarb manufacturing, he said.

That effectively cut off the supply.

But by then, Ag Logic had submitted its application to register aldicarb. The application seeks to put the pesticide back on the market by winning approval for use on peanuts, soybeans, dry beans, sugar beets, sweet potatoes and cotton – the remaining crops deemed safe by the EPA.

Antoine Puech, president and CEO of MEY Corporation, said he is not concerned about the safety of aldicarb as long as it is used properly. The product has a “pretty enviable safety record,” he said, adding that the only thing that changed was the EPA’s decision to increase the safety factor.

Puech said he expects a response on the proposed registration in October.

Charles Benbrook, chief scientist for The Organic Center and former executive director of the National Academy of Sciences Board on Agriculture, said there is no reason for continued use of aldicarb in food crops.

“To [Bayer CropScience’s] credit, they realized they have better, safer insecticides in their current product line to address essentially all of the uses that aldicarb has been directed to in the past,” he said. “And it’s time to let this go. It’s a very high-risk, dangerous chemical. Time to mothball it. It’s obsolete, excessively risky chemistry.”