From an Idea to the Lab: Rocky Flats Downwinders' Hemp Phytoremediation Project

Tiffany Hansen

Sep 8

5 min read

With support from a Roddenberry Foundation Catalyst Grant, Rocky Flats Downwinders launched an experimental project to ask an unusual question: Could industrial hemp take up plutonium from soil collected near Rocky Flats?

In 2018, Rocky Flats Downwinders received a Catalyst Grant from The Roddenberry Foundation to pursue an unconventional environmental research idea. The organization wanted to investigate whether industrial hemp—a plant already being studied for its ability to take up certain contaminants from soil—might also take up plutonium from soil contaminated by releases from the former Rocky Flats nuclear weapons plant. The result was the Rocky Flats Hemp Phytoremediation Project, a community-initiated pilot study that brought Rocky Flats Downwinders together with scientists and a Colorado hemp-growing company to take the question from an idea, to soil collection, to growing plants, and finally to laboratory analysis.

What is phytoremediation?

Phytoremediation is the use of living plants to remove, contain or otherwise help manage contaminants in soil, water or the environment. Industrial hemp (Cannabis sativa) was of particular interest because of previous research into its potential to accumulate certain contaminants. There was also a Colorado connection. In 2012, former Colorado legislator, rancher and Rocky Flats Grand Jury foreman Wes McKinley sponsored HB 12-1099, legislation establishing an industrial-hemp remediation pilot program to study phytoremediation using hemp grown on contaminated soil. For Rocky Flats Downwinders, that history led to another question:

Could hemp take up plutonium?

The Roddenberry Foundation Catalyst Grant

The opportunity to investigate that question came when RFD was awarded a Roddenberry Foundation Catalyst Grant. The Catalyst program was designed to support early-stage, innovative and unconventional ideas addressing significant challenges. RFD's grant supported development of a pilot project using contaminated soil from near Rocky Flats to investigate whether hemp could take up radionuclides. This was an important milestone for our organization. RFD had been formed by community members asking questions about Rocky Flats. With this project, one of those questions moved beyond discussion and into an actual experimental investigation.

Building the research team

The project depended upon collaboration.

Dr. Michael Ketterer, an analytical chemist with expertise in measuring and identifying plutonium, served as scientific consultant and performed the soil and plant analyses.

Dr. Elizabeth Pilon-Smits, a Colorado State University biologist with expertise in phytoremediation, advised the project.

RuBi Hemp Solutions, under owner Zackary Guignardi, partnered with RFD to cultivate the hemp plants in a commercial growing facility.

Rocky Flats Downwinders coordinated the project, with Tiffany Hansen participating in soil collection and later transporting harvested plant material with Ketterer for analysis.

First, they needed Rocky Flats soil

Before anyone could determine whether hemp would take up plutonium, the researchers needed appropriately characterized soil. Ketterer sought permission to collect surface soil from the Indiana Street corridor near Rocky Flats. According to contemporaneous reporting, a Jefferson County permit ultimately allowed access to a county-controlled portion of the corridor. Laboratory analysis produced an important finding even before the hemp experiment began.

Ketterer's August 2019 soil report found detectable plutonium-239+240 in all of the Rocky Flats composite samples. The measured isotope ratios differed from the ratio associated with global fallout and were consistent with weapons-grade plutonium. Ketterer concluded that essentially all of the plutonium activity measured in those samples originated from Rocky Flats. Those soils became the basis for the growing experiment.

Growing hemp in Rocky Flats-contaminated soil

At RuBi Hemp Solutions, hemp plants were grown using a control soil and five soils containing Rocky Flats-originating plutonium. According to Ketterer's final report, the five experimental soils contained plutonium-239+240 at approximately 33 to 100 Bq/kg. Two hemp strains, identified in the study as "Wife" and "Cherry," were used. The plants were harvested in fall 2019 and dried at the RuBi facility.

On November 11, Tiffany Hansen and Dr. Ketterer transported the harvested plant material into Ketterer's custody for laboratory preparation and analysis.

The plant material was dried, ground and ashed. Plutonium was chemically separated from the samples and ultimately measured using inductively coupled plasma mass spectrometry at Northern Arizona University. Then came the question that had started the entire project.

Did the hemp take up plutonium?

The pilot experiment produced evidence suggesting that it did—but the results also raised questions that prevented the experiment from providing a definitive answer.

Ketterer's final report found plutonium in the majority of hemp samples. Nearly all plant samples grown in Rocky Flats-contaminated soils contained detectable plutonium, and the three plant samples with the highest measured activities came from the contaminated-soil group. Isotopic analysis was particularly interesting. The plutonium measured in the plant material had a plutonium-240/plutonium-239 ratio of approximately 0.05–0.06, which Ketterer identified as characteristic of weapons-grade plutonium and consistent with a Rocky Flats origin. Ketterer concluded that the results appeared to suggest uptake of plutonium from the soils into the plants. But there was an important complication.

One plant grown in the control soil also contained a relatively high plutonium measurement. Ketterer noted that this result was difficult to reconcile with soil-to-plant uptake and suggested that external contamination might have occurred. There was another limitation: only the flowers and leaves were analyzed. The roots and stems were not.

So the pilot study did not establish that hemp could be deployed to remediate plutonium-contaminated land at Rocky Flats. Instead, it did what an exploratory pilot project is supposed to do: it produced an intriguing result and identified questions requiring more controlled research.

Why the project still matters

The Rocky Flats Hemp Phytoremediation Project is an important part of RFD's history for reasons beyond whether hemp ultimately proves useful for plutonium remediation.

It demonstrates what can happen when a community organization moves from asking a question to trying to investigate it. RFD secured outside funding, assembled scientific expertise, obtained and characterized soil, partnered with a commercial grower, conducted an experimental growing project and had the resulting plant material subjected to laboratory analysis. And the organization preserved the findings—including the unexpected ones.

That's important. Good research does not require an experiment to produce the answer we hoped for. It requires reporting what was actually found, acknowledging limitations and identifying what should be studied next. The hemp experiment did not prove that planting hemp around Rocky Flats could clean up plutonium contamination.

It showed that the question was worth investigating further.

And it demonstrated something else about Rocky Flats Downwinders: community members don't only have to ask for answers. Sometimes they can help begin the research needed to find them.