By Ashley Stender | January 29, 2026

Many agricultural products work because they are toxic: insecticides often disrupt nervous systems, herbicides can halt basic cellular processes, and fungicides interfere with metabolism. These mechanisms can be effective in protecting crops, but they also raise questions about what happens after application. For example, some compounds persist in soil or water longer than intended. Other compounds move beyond treated fields through runoff or drift, continuing to interact with living systems long after their initial use.

For researchers developing new bioactive compounds, that reality shapes the challenge from the start. It is not enough for a compound to improve crop performance. Scientists must also understand how long it persists, where it travels once applied, and how living organisms respond to exposure before it can be considered a responsible alternative.These considerations form the basis of Aim 6: Environmental and Animal Toxicity Assessment. Built into C-SPIRIT’s research pipeline alongside discovery, annotation, pathway discovery, synthesis, and field testing, Aim 6 evaluates environmental fate and biological safety early, helping guide decisions about which compounds are worth advancing and which are not.

Where Safety Enters the Pipeline

Aim 6 is led by Karilyn Sant, an environmental toxicologist at Michigan State University whose lab focuses on researching how chemical exposures affect animals, people, and ecosystems. Sant became involved in C-SPIRIT because Director Sue Rhee recognized that evaluating safety needed to be part of the research pipeline from the outset, not something addressed after compounds were already well developed.

“I’m looking at how contaminants in the environment affect people and wildlife,” Sant says. “The goal of Aim 6 is, okay, we know these things work, they’re efficacious. Are they safe?”

That question defines her role within C-SPIRIT. Rather than assessing compounds only at the end of the process, Aim 6 is designed to operate alongside the other Aims as research progresses. “That’s my goal,” Sant explains. “I’m kind of the check and balance on safety for a lot of the other stuff.”

Following Compounds Beyond the Field

Aim 6’s work begins by examining what happens to candidate compounds once they are no longer confined to controlled testing and application.

“We start by asking, if it gets into the environment, is it going to move into animals and humans?” Sant says. “Does it stay in the body, or do we get rid of it right away? Is it likely to have an acutely toxic effect, something immediate like an allergy or other response?”

To address these questions, Aim 6 is establishing a framework that combines computational screening, cell-based assays, and organism-level testing. Computational tools are used to prioritize compounds based on predicted persistence, bioaccumulation, and hazard potential. In vitro assays using human cell lines help indicate possible impacts on human health, while in vivo testing examines how organisms respond under controlled, environmentally relevant conditions.

A central model for this work is the zebrafish, which is widely used in environmental toxicology because of its rapid development and relevance to both ecological and human health questions. “Fish are a really good predictor for what might happen out there,” Sant explains. “Because when we spray crops, a lot of that ends up in waterways.”

Aim 6 is currently building and refining these assessment approaches so they are ready as compounds from earlier Aims become available for testing. Early screening efforts and pilot studies are helping establish how toxicity data will be generated and interpreted as the pipeline advances.

Working Across Aims

Aim 6 is designed to function as part of an integrated system rather than as a downstream checkpoint. As compounds move through the C-SPIRIT pipeline, toxicity assessment informs decisions at multiple stages, shaping which candidates continue forward and how they are developed.

“Every step of that pipeline, we rule out all the things that are bad until we get down to a small group of things that we know are both effective and safe,” Sant says.

These conversations allow teams to refine their focus, prioritize candidates, and make informed tradeoffs between efficacy and safety as the pipeline narrows.

With C-SPIRIT moving into its second year, communication with Aim 6 is increasing. These inter-Aim collaborations help ensure that safety considerations are embedded alongside performance metrics, supporting coordinated decision-making across C-SPIRIT and reinforcing the pipeline’s emphasis on responsible advancement.

What Makes Safety Hard

Assessing toxicity is rarely straightforward. One challenge is the limited availability of robust toxicity data for many chemicals already in use.

“There are over 100 million registered chemicals out there,” Sant says. “But we actually only have strong toxicological data for a very small fraction of them.”

In agriculture, this gap is especially visible. Many conventional products are effective precisely because they are toxic. “That’s why they’re good pesticides,” Sant explains. Effectiveness and risk are often tightly linked, making it difficult to separate performance from potential harm.

Aim 6 operates within that reality. Its task is not simply to identify toxicity, but to understand it well enough to make informed decisions about which compounds are worth pursuing and how they might be used responsibly. “We expect to see a lot of compounds that might be neurotoxic or problematic,” Sant says. “So we know safety is going to be critical.”

At the same time, early exploratory work has provided cautious optimism. “A lot of the compounds we’re finding right now are pretty cool, because they aren’t things that we expect to be toxic at all,” she says. “Some of them are actually things that I use to help deal with toxicity from other compounds. So far, that’s been really reassuring.”

Toward Responsible Innovation

As C-SPIRIT continues to advance new bioactive compounds, Aim 6 will play a central role in determining which candidates are ready to move forward. By evaluating safety alongside performance, Aim 6 helps ensure that promising compounds are viable not only in controlled studies, but in real-world agricultural contexts. This approach aligns closely with principles of green chemistry, emphasizing effectiveness at low doses and minimizing unintended biological effects.

“We’re always asking, how much of this would need to be applied to crops versus how much would be toxic to animals?” Sant says. “We want to increase that gap as much as possible.”

The work of Aim 6 helps establish clear standards for what it means for a new bioactive compound to move forward. Those standards extend beyond whether something works, shaping how responsibility, environmental impact, and long-term consequences are weighed in decision-making.

“At the end of the day,” Sant says, “we want things that are both effective and safe.”