In his public plea for the Environmental Protection Agency to reject registration of a potent new weedkiller, Christopher Lish of Olema, California, revisited a decades-old warning from environmental prophet Rachel Carson: "As crude a weapon as the cave man's club, the chemical barrage has been hurled against the fabric of life."

Lois Rose, a registered nurse in South Milwaukee, Wisconsin, posted her own, less ornate caution to the EPA website: "Stop listening to the chemical lobby and start listening to the humans affected by these poisons."

As a federal decision looms over whether to approve Dow AgroSciences' proposed Enlist Duo herbicide -- a mix of 2,4-D and glyphosate, the main ingredient in Monsanto's Roundup weedkiller -- challenges from critics across the country have poured in. And children's health advocates are among the most vocal.

More than half a million people shared their thoughts before the EPA closed its public comment period on Monday. Among the submissions was a letter signed by 35 doctors, scientists and researchers, which highlighted human health risks they suggested had been overlooked by the agency -- especially for "young children in residential communities, schools, and daycare centers near the 2,4-D-sprayed fields."

On Wednesday, an environmental nonprofit released a report, including an interactive map, that warns the new weed-killing recipe may soon be sprayed on corn and soy fields within a thousand feet of more than 18,000 U.S. schools. Around 5,600 schools are within 200 feet of fields that could potentially be sprayed, according to the Environmental Working Group's new analysis. The EPA's proposed approval of the double herbicide calls for a 200-foot buffer zone around locations where it is sprayed.

"The analysis is pretty scary," said Mary Ellen Kustin, senior policy analyst with the Environmental Working Group. "To think that there are this many schools so close to fields that may be turned over to this new cropping system."

Inhalation of drifting herbicide is the key concern, Kustin noted, although children may be exposed via other routes such as dust tracked around on shoes, clothes and the like.

Industry representatives, meanwhile, call the group's claims "inflammatory," "specious" and "irresponsible." They suggest the federal government is poised to approve the chemical spray with good reason: The herbicide is safe and a necessary solution for struggling American farmers.

"Regulatory and health and safety organizations worldwide have reviewed the database on 2,4-D and found little concern for adverse effects when the product is used as directed," Garry Hamlin, a spokesman with Dow AgroSciences, told The Huffington Post in an email. He added that the 2,4-D in the company's product has been formulated to reduce volatilization and drift: "This is not your granddad's 2,4-D."

The U.S. Department of Agriculture estimates that if Enlist Duo is green-lighted, agricultural use of 2,4-D would at least triple by 2020 to between 77.8 and 176.2 million pounds annually. The latter herbicide was first introduced on the market in 1946 and is also commonly used by homeowners to kill weeds in their lawn -- much to the chagrin of environmental health advocates.

Chensheng Lu, an environmental health expert at the Harvard School of Public Health, is among those not comforted by industry's claims. "The reproductive hazards [of 2,4-D], as well as the concern of cancers, have been well documented," said Lu, one of the signatories on the EPA letter. "The EPA should at least host a scientific advisory panel meeting to gather independent review of Enlist Duo."

To the list of potential health risks for children exposed to even tiny amounts of the double herbicide, Warren Porter, a toxicologist at the University of Wisconsin, Madison, and another signatory, added attention deficit hyperactivity disorder, asthma and immune disorders.

The EPA's assessment, he said, misses emerging evidence that certain chemicals in minute amounts can disrupt human hormones and therefore mess with multiple systems in the body. Research suggests both 2,4-D and glyphosate carry that capacity.

"Why should we be supporting some kind of a policy that is going to directly impact the health of our children?" said Porter. "The EPA seems totally in the pocket of Dow right now."

The EPA stated that it will review all comments before its final decision, which is expected sometime late summer or early fall. "Our proposal was based on an extensive assessment," the agency told HuffPost in an email, adding that it had looked at herbicide drift and risks to kids, among critics' concerns.

Another worry is potential interactions between glyphosate and 2,4-D, as well as with other ingredients in Enlist Duo. In its environmental risk assessment, the EPA acknowledges that "there could be additive, synergistic, or interference between the two herbicides," potentially increasing or decreasing the overall toxicity of the product.

Fifty years ago, Rachel Carson wrote in Silent Spring of a pesticide combination that resulted in health risks "up to 50 times as severe as would be predicted on the basis of adding together the toxicities of the two."

The EPA did not include any such potential synergisms in its human health risk assessment. While the potential for drift is discussed, the agency also dismissed it from aggregate exposure calculations, determining it didn't pose a sufficient risk.

In addition to the EPA's verdict on the dual herbicide, Dow AgroSciences also awaits final word from the USDA regarding its herbicide-resistant seeds, the other component of its Enlist system. Corn and soy crops would be genetically modified to withstand exposure to 2,4-D and glyphosate, theoretically leaving only the weeds vulnerable to the chemicals.

Weeds, however, may evolve to withstand exposure, as farmers learned after years of employing Monsanto's genetically engineered Roundup Ready seeds. Repeated application of a herbicide can literally weed out the weak weeds, giving the rare resistant ones the opportunity to reproduce and eventually dominate.

More than 70 million acres of farmland in the U.S. are now infested with glyphosate-resistant "superweeds." And that number is rising.

"As a farmer located in Iowa, I look forward to approval of this herbicide option," wrote Fred Wirtz of West Bend, Iowa, in a comment posted on the EPA's website. "Weed resistance to gly[ph]osate and other herbicides is becoming an increasing concern, and this will provide a valuable additional option to protect the crop."

Approval of Enlist Duo should keep farmers from unleashing other -- potentially more toxic -- herbicides, as well as larger quantities of Roundup, said Dow's Hamlin.

Mike Owen, a weed expert at Iowa State University, agreed that the product would be a useful tool for farmers.

While he was among those who first warned of the likelihood of Roundup resistance in the early 1990s, Owen is hopeful that more stringent restrictions included on the Enlist Duo product label will result in more sustainable use. Dow AgroSciences provides specifics on application rates and advises rotating use of Enlist Duo with other herbicides and non-chemical practices such as mechanical cultivation.

Diversifying crops and methods to manage weeds, Owen emphasized, is the real key to getting off what many now call the "pesticide treadmill." He pointed to one factor thwarting that effort: the growing size of the average American farm. "There are fewer farmers farming larger areas over greater distances," Owen said. "And many want to spray one herbicide over all their acres."

Dow AgroSciences also advises on appropriate spray nozzles and weather conditions, among other factors that affect drift. The label, for example, warns applicators not to spray "at wind speeds greater than 15 mph" or in "areas of temperature inversions."

But even if a farmer perfectly adheres to all the label's directions, there is still the chance of dangerous drift, said Porter of the University of Wisconsin. And again, young children may be particularly vulnerable to any toxic effects.

"If the wind is blowing, or even if not, stuff is going to move in all dimensions," said Porter. "They could be well outside the buffer zone, but still get a dose that could affect their immune system, their endocrine system, their nervous system."