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Rachel Carson’s Silent Spring may be old enough to be a classic, but the , and kill birds. Yes, DDT is still present in the layers of the ecosystem.  And it’s left another legacy: a reactionary system of pesticide approval. Starting with the widespread DDT panic, regulatory bodies have again and again jumped at new pesticides that seem safer—though their apparent safety is largely a factor of their limited lifespan.  Research published this month shows that, once again, the current reigning class of pesticides, neonicotinoids, are more dangerous than originally thought.

The new study, published in Nature, is quite damning: In areas heavily treated with neonicotinoids there was a 3.5 percent decline in bird populations. The most vulnerable species—the Barn Swallow, Yellow Wagtail, Common Starling, and Mistle Thrush—experienced significant population declines.. The researchers suggest that the pesticides are so effective at killing the insects that the birds relying upon those bugs can’t find enough to feed their chicks.

“I think our results are alarming,” study author Caspar Hallmann, a professor of experimental plant ecology at Radboud University in the Netherlands, said. “Something must be done. 

Neonicotinoids were first approved for use in early 1990s, and their ease of application has catapulted them to pesticide dominance. The chemicals can be sprayed on the field, but more often application starts even sooner. Often, crop seeds are sold with the chemicals already applied, a prophylactic approach. A plant grown from such a seed will deliver neurotoxins to insects that try to feed on it, even if the insect doesn’t pose a threat to the plant (like the hoards of they’re killing off).

“A good product is one that is selective for the pest you want to control,” says , a research scientist and Carleton University biology professor. The way neonicotinoids work is the complete opposite.

Of course, to be approved for use, the for safety. The EPA’s findings indicated that the pesticides posed no danger to birds and other animals that ate them directly. However, Mineau says the chemicals’ overall potential impact on the ecosystem was ignored.

Now, after decades of use, the effects are obvious.

The new study indicates that high concentrations of imidacloprid (an active ingredient in neonicotinoids) have leached into the environment, and are affecting non-target insects, beyond pests.

Neonicotinoids threaten the environment in many ways, Mineaus says. Not only do they kill insects, they linger in the soil. The chemicals break down into compounds that are even more toxic than the original, according to the , an independent scientific group that assesses pesticide risk in Europe. Long-term exposure can cause chronic or lethal neurological issues for several animals, including birds, the task force found.

So why were they approved so speedily? “The regulatory bodies at the time were desperate for something new to come along and were willing to disregard a lot of red flags,” Mineau says. That’s because organophosphates, the predecessors to neonicotinoids, were embroiled in controversy after being linked to neurotoxicity problems in people, children, and wildlife. One popular pesticide at the time, granular carbofuran, is estimated, at its peak, to have  annually before it was . Agriculture needed an alternative, fast.

What is so disturbing is that the organophosphates had originally been approved in the 1960s, in reaction to the quick turn away from DDT, following Silent Spring. One pesticide class after another has been proven dangerous, but this has done nothing to convince regulators that the next promising compound may actually turn out to be just the next bandage on a perpetual problem.

The Natural Resource Defense Council has already against the Environmental Protection Agency requesting that approval of neonicotinoids be revoked, and other conservation groups are . The EPA’s , as they routinely do for approved chemicals, but a final decision isn’t expected before 2019.