How environmental scientist Melanie Kah changed her mind about nanopesticides

In 2012, the US Environmental Protection Agency approved the first nanoscale pesticide: a nanosilver product designed to prevent microbial growth on textiles. Approval for agricultural nanopesticides did not seem far behind, and many environmental scientists were concerned, says Melanie Kah of the University of Auckland, who at the time was surveying nanopesticides from the perspective of a soil scientist looking at contaminants. Using nanotechnology to deliver pesticides could decrease the overall volume applied to crops, but such nanoproducts might also pose risks—for example, to soil-dwelling nematodes and microbes or to bees and other pollinators.

To get a handle on the agrochemical nanoproducts on the market, Kah and her colleagues cataloged what they could find and published an assessment in 2013 (Crit. Rev. Environ. Sci. Technol., DOI: 10.1080/10643389.2012.671750). Companies had not always advertised what they were developing, and a lot of uncertainty surrounded these products. Naomi Lubick talked with Kah about why she and other environmental scientists are now less worried about the risks of nanoproducts, even though a complete picture of their use remains elusive. This interview was edited for length and clarity.

How has the research on nanopesticide risks changed over the past decade?

I started my research being concerned from a regulatory risk-assessment perspective. Regulatory bodies have been really proactive in supporting the development of tests on nanoproducts. Few tests were available a decade ago, but that may be because there were so few nanoproducts on the market. The Organisation for Economic Co-operation and Development has been playing a great role, continuing to shepherd the development of ecotoxicity and human health testing for nanomaterials.

One way to see the past 10 years is to think of different generations of nanoproducts. We started with things like titanium dioxide nanoparticles and carbon nanotubes. Researchers thought nanoparticles would harm a plant, but instead they found that some nanoparticles can make it stronger. This is work that Jason White of the Connecticut Agricultural Experiment Station and his colleagues are pursuing now: nanoforms of metals applied at the right time in a plant’s development as a kind of fertilizer or to boost a plant’s defense systems (Nat. Nanotechnol. 2019, DOI: 10.1038/s41565-019-0439-5).

Second-generation products involve using nanomaterials to encapsulate and deliver an active ingredient or to change the ingredient’s chemistry. Maybe a nanomaterial would make a pesticide more mobile or make it compatible with other products, like fertilizers that could be applied at the same time. Companies are still trying to develop these products and bring them to market, but they are not publishing in the scientific research literature, so it’s hard to see what they are doing.

Now we are on the third generation: a combination of different technologies that may end up with some very complex formulations, which may be tricky. For example, Neena Mitter at the University of Queensland is using RNA interference delivered by nanoscale clay materials. It’s a new way to deliver bits of genetic material to control plant pathogens and pests, with great specificity and efficiency (Nat. Plants 2017, DOI: 10.1038/nplants.2016.207).

I think this third generation is trying to use nanotechnology to target pests and consider the host in a more careful manner, as well as nontarget organisms. Conventional pesticides are more basic: you just want to kill the pest.

What eased your concerns about the potential effects of nanopesticides?

The uncertainty has decreased over the last 15 years due to a huge amount of research—definitely on nanoagrochemicals but also for nanoparticles in general, which is a huge body of work. I’m mainly aware of environmental aspects, but the impact on human health probably has gone in a similar way because of medical research.

The suspicion was that when the particle size becomes smaller, the behavior is going to be drastically different, and some completely new reactions and interactions with living organisms are going to happen. Research has shown that some unexpected things happen. But we can test for them. The research and testing decrease the level of uncertainty and allow the perception of risk to be more fact based, so you can balance the risk and the potential benefits.

Where do you see this work headed in the next 20 years?

More and more, I think nano is going to be an enabling technology. I think there is certainly more need for research on nanofertilizers.

I hope all the research will contribute to a deep reflection on how we use chemistry and technology to grow our food. In some contexts, no technology is necessary. In others, high tech and new chemistry might be needed.

Right now, there’s more potential for nanoproducts for high-value crops in developed countries, such as to help grow grapes for wine or to treat canker in citrus trees. Nanoproducts can be costly to develop and to make, and it’s worth it for high-value crops.

We may have to use nanomaterials to solve some problems in the future, such as resistance to certain conventional pesticides. If we have a new crop disease in the future, nanotechnology might provide solutions.

What advice do you have for scientists who want to work on nanoagrochemicals?

Don’t ignore the risk aspect and only focus on the benefits or say nanotechnology is a magic bullet. I think this is an extreme that we should avoid.

From my perspective, it’s really a balance. Let’s compare new products to conventional products and be critical about both. Agrochemicals are always associated with risk. If we can reduce the risk, that’s great, but I don’t think a revolution is coming.

In the scientific literature, there are some newcomers who have no background in agronomy or pesticide science or who would just suggest that nanotechnology is going to change everything. I hope that this is going to evolve by more collaboration, more interdisciplinary conversations, so that people who have been developing pesticides for 30 years can actually tell the newcomers, “Look, we’ve tried this. Now let’s try and build on what you can do and what we’ve tried before.”

Naomi Lubick is a freelance writer based in Stockholm who covers earth and environmental sciences. A version of this story first appeared in ACS Central Science: cenm.ag/kah.