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The miracle of American agriculture — an amazing abundance of food — is possible because of another miracle that isn't so beneficial: powerful weedkillers. These chemical compounds — such as Monsanto's Roundup — vanquish invaders but let corn and soybeans, genetically modified to be immune, flourish. Eventually, however, overuse of one weedkiller begets weeds that evolve to be immune as well. That's what is happening across America. To combat these increasingly herbicide-resistant weeds, Dow Chemical Co. is reviving 2,4-D, a World War II-era chemical linked to cancer and other health woes. The company wants to use it in a toxic tandem with the key weedkilling chemical in Roundup. It's a one-two punch: What one doesn't kill, the other does. An elegant solution. Except ... is it safe? The U.S. Environmental Protection Agency says yes. The EPA approved the new chemical dynamic duo — called Enlist Duo — last year. But in a recent Tribune investigation called "Chemical Harvest," Tribune reporter Patricia Callahan explains that the government is weakening safety standards and downplaying the risks, especially to children. Callahan points out that with its decision, the EPA now says it is safe for Americans to have 41 times more 2,4-D in their diet than what it allowed for a decade. That level is far higher than what China allows. Or Russia, Australia, South Korea, Canada and Brazil. It's higher than what the World Health Organization recommends. Where did the EPA get the idea that the increased exposure wouldn't harm people? In Dow's own study, the company's researchers warned of kidney trouble in rats exposed to the herbicide, Callahan reports. But EPA scientists changed their analysis of that pivotal study, persuaded by a Canadian government toxicologist who decided that Dow's researchers had been overly cautious in their assessment of the risk. The EPA says that no matter how high the limit, Americans still won't ingest dangerous levels of 2,4-D. They say the chemical is safer than previously thought, and those other countries just haven't caught up yet with more recent analyses. One prominent chemical safety expert, Philip Landrigan, isn't convinced. He has urged EPA Administrator Gina McCarthy to reject Enlist Duo. He calls for the federal National Toxicology Program — a different agency that tests toxic chemicals — to assess the safety of Enlist Duo. We agree. An independent review would help assuage fears that the EPA has acted rashly. Here we could ... get further into the scientific weeds on this issue. Which are thick. Suffice to say that what we know from decades of research is obvious: Pesticides are dangerous. Children are often at greater risk of lifelong damage from doses of pesticides that wouldn't hurt their parents. That's why federal law requires the EPA to take into account the special risks that children face when exposed to pesticides. The EPA's approval of Enlist Duo is now in legal limbo. And limbo can be confusing: The EPA itself has asked a federal appellate court to rescind the agency's own approval of Enlist Duo while the agency decides whether a larger no-spray zone is needed to protect endangered plants that may grow near the edges of farm fields. Whew. But those are the rules. The EPA is rightly concerned about those plants. But what about humans? EPA officials told Callahan that they won't reopen their assessment of the human health risk from Enlist Duo. There's no added risk to people by combining the two pesticides that have long been approved individually, the EPA maintains. But where's the harm in further study to clear away all doubts? Herbicides linger in the air, the water, and in our foods. Scientists often disagree about interpretations of risks with a wide range of chemicals. The only way to sort out the risks is by further research to firmly establish safe limits. The EPA has a profound duty to make sure the modern miracle that helps Americans eat well isn't also gradually poisoning them.