It’s no secret that neonicotinoids can harm bees and other insects—they’re designed to kill pests, after all. But an increasing body of evidence is uncovering just how serious an impact these pesticides are having on the environment.

Several new studies seem to have put the nail in the coffin for neonicotinoids, showing that they harm bees and don’t even improve crop yields. And worryingly, scientists at the University of Iowa have found traces of the pesticides in drinking water for the first time. So should we be alarmed? And why haven’t the chemicals been banned?

Neonicotiniods—or neonics—have been a go-to bug buster for many years; they were developed in the 1980s and '90s as a more environmentally “friendly” alternative to traditional insecticides. Rather than having to spray the chemicals over crops, the seeds are coated, supposedly protecting the plants from being eaten by insects during germination and early growth.

Even though farmers use relatively small amounts of the chemicals, they are still leaching into the environment. According to Prof. Nigel Raine, the Rebanks Family Chair in Pollinator Conservation at the University of Guelph in Canada, almost all of the chemical ends up in the environment. “I've seen estimates of as little as 2 to 20 percent of the treatment going into the actual crop,” he said. “So if you've got potentially 98 percent of that active ingredient going into the soil and the water, that is a concern. If the pesticide is not doing its job where it should be, what impact is that having?”

In a new study in Environmental Science & Technology Letters, scientists found three common neonics in Iowa City’s drinking water: clothianidin, imidacloprid and thiamethoxam. It turns out the pesticides can withstand the standard water treatment process: The team found traces of the chemicals at concentrations of 0.24 to 57.3 nanograms per liter.

That’s low—the equivalent of a drop of liquid in 20 Olympic-sized pools—but there’s currently no defined safe level, and it’s difficult to know what the significance is. “Having these types of compounds present in water does have the potential to be concerning,” said study author Gregory LeFevre to the Washington Post, “but we don’t really know, at this point, what these levels might be.”

A mountain of research

Although there were calls to evaluate neonics shortly after their introduction, it wasn’t until the mass decline in honeybee populations in 2006 that concern properly set in. Dubbed colony collapse disorder, the phenomenon wiped out millions of bees across North America, with beekeepers waking up to find piles of dead bees in and around their hives.

A landmark 2015 study showed that neonics harm queen honeybees, and a raft of research in other pollinators has built on this, revealing that the chemicals impair flight, reduce egg development and cause bees to hatch smaller.

Two new studies give a wider view on this. In the first, scientists carried out some large-scale field experiments in the U.K., Hungary and Germany that showed the pesticides have a negative effect on honeybees, bumblebees and solitary bees. In their paper, the researchers conclude that neonics may cause “a reduced capacity of bee species to establish new populations in the year following exposure.” On the same day, Canadian scientists published “realistic” research showing that “neonicotinoids increased [honeybee] worker mortality and were associated with declined in social immunity and increased queenlessness over time.”

Corporate controversy

Unfortunately, the stark polarization on the issue—namely the agrichemicals industry supporting neonics on one side and the environmentalists pushing for a ban on the other—is making it difficult to see what’s really happening.

The companies producing the pesticides—the three biggest being Syngenta, Bayer CropScience and Monsanto—have all at one time committed to funding research into the declining bee population problem, and one of the new studies was industry funded. According to The Economist, Bayer and Syngenta are saying the latest results “don’t warrant a ban on the chemicals.”

It’s easy to see big bad corporations on one side and innocent bees on the other, but in reality, the issue is much less clear—and there is still a lot we don’t know. “Everybody has a particular agenda—industry, environmental groups, the media—but it should always be about what the data is telling us,” said Ryan Prosser, assistant professor of environmental toxicology at the University of Guelph. “It’s important to try to understand that this is a complex issue. We need to have a wide perspective, not just a narrow focus on banning a chemical—that might not be the solution to our problem.”

If neonics are banned, what will happen? Some say taking neonics off the market could make farmers use other products, which may be even more harmful—an idea conservative organizations like safechemicalpolicy.org are pushing in a bid to protect neonics from a potential ban.

Yet this argument might not hold up, in light of another new study. A team at Purdue university looked at corn in the state of Indiana and found “no benefit of the insecticidal seed treatments for crop yield during the study.” They also showed that 94 percent of honeybee foragers are at risk of exposure to neonics—even lethal levels—when the corn is sown.

So it’s not the case that farmers need neonics to improve yield, said Prof. Raine: “If the evidence to support that is not as strong as we perhaps thought it was, then that may change the balance of decision making.”

A call for evidence-based policy

Neonicotinoids have already been banned in Europe and although the U.S. has yet to follow suit, regional bans are in place in Maryland, Oregon and Washington. A more nuanced approach in Ontario, Canada, may seen an end to the prophylactic use of the chemicals, and the PMRA—the organization that regulates pesticides in Canada—is due to decide whether to ban imidacloprid—a move that Dr. Prosser says “may be a knee-jerk reaction.”

The EPA is working on the issue too, with five of the main neonics—imidacloprid, clothianidin, thiamethoxam, dinotefuran and acetamiprid—scheduled for review in 2018. The EPA has started a range of risk assessments to determine the effect of neonics on pollinators, aquatic animals and humans, but will the results make a difference to the decision? EPA Administrator Scott Pruitt has already greenlighted one pesticide believed to damage brain development in children, so there’s little evidence to suggest he might support a ban.

According to Prosser, more evidence will help. “Pollinators are facing a lot of issues; banning neonics might not solve the problem,” he explained. “It’s easy to vilify a chemical. That’s not to say it doesn’t play a role, but it’s important to step back and look at the bigger perspective: What are the agricultural needs? That’s important to society. And what are the scientists saying? Most will say it’s a multifaceted problem that we don’t know everything about.”

While there is clearly a need for more research, Raine thinks we know enough to limit our use of neonics, especially prophylactically. “There is sufficient concern and evidence now to say that there is potential for harm to bees,” he said. “Although pollinator health and supporting them in an agricultural landscape, or an urban landscape, or any kind of human-affected landscape is not just about controlling pesticide exposure, insecticides are clearly one of the environmental stress factors we should be concerned about, and we should mitigate the impacts on pollinators where we can.”

Research can take years to find answers. In the meantime, there are moves to mitigate the impact of neonics by avoiding their use—stores like Walmart and True Value have committed to eliminating neonics from products on their shelves, and will stop selling plants treated with the chemicals.

Although this is a step forward, a 2016 report by Friends of the Earth found that pesticides could be found in the “bee-friendly” plants being sold across the U.S.; there is also peer-reviewed evidence of a similar situation in the U.K. Friends of the Earth U.S. is asking consumers to take action—to join their BeeAction campaign and sign a petition to garden retailers asking that they stop selling neonicotinoid treated plants and products that contain the pesticides.