Watermelon (left) and celery (right) are two of more than a dozen fruits and vegetables being studied by Dawn Reinhold’s lab to assess their uptake and bioaccumulation of antimicrobials from irrigated water. Photo: Shannon Henderson

Using plants to protect water and health

Plants are commonly viewed as a source of food or medicinal ingredients, or as ornamentals that add beauty and color to our surroundings. For Michigan State University AgBioResearch scientist Dawn Reinhold, plants are also a crucial component of natural treatment systems that can be used to protect both the environment and human health.

Dawn Reinhold“Plants play a very active role in helping to mitigate various pollutants,” said Reinhold, assistant professor in the MSU Department of Biosystems and Agricultural Engineering. “Plants are often overlooked when people are studying the environmental fate of chemicals and contaminants, but we’ve demonstrated time and again in our research that plants have a direct effect on improving the outcome of environmental fate by decreasing pollutant concentrations in waters and soils, which can potentially affect human health.”

A key research focus for Reinhold is the understanding and engineering of plant-based ecosystems for the protection and treatment of water resources. She and members of her lab are examining the abilities of food crops to phytoaccumulate (a process by which a plant takes up chemicals) antimicrobials from biosolids (nutrient-rich organic materials resulting from the treatment of sewage sludge, often used as fertilizer) and wastewater used for irrigation, and what the relevance of this phytoaccumulation is to the environmental fate of chemicals and human health risk.

Two of the most common antimicrobial agents used in consumer products are triclosan and triclocarban. According to the scientific literature, these compounds have been used as antimicrobial agents in soap since the 1960s. In recent years, the use of antibacterial agents in consumer products has skyrocketed — they are found in soaps, lotions, cosmetics, toothpaste, deodorant and other personal hygiene products.

“Most of these products get washed down the drain, and are not transformed in conventional wastewater treatment plants,” Reinhold said. “Untransformed, these chemicals enter the environment through wastewater treatment effluent and biosolids. Triclosan is one of the most frequently detected chemicals in streams across the United States, and both triclosan and triclocarban are found in high concentrations in sediments and sewage sludge, where they can persist for years. These agents adversely affect ecosystems and, at high concentrations or with continuous exposure, can potentially affect human health.”

To help address this problem, Reinhold and members of her lab first conducted vegetated soil column studies to look at biosolids application, which introduces triclocarban and triclosan to soil and water resources. Pumpkin, zucchini and switchgrass were grown in soil columns to which biosolids were applied. Leachate from soil columns was assessed every other week for triclocarban and triclosan. At the end of the trial, concentrations of the two agents were determined for soil, roots, stems and leaves.

“Our results showed that plants can, indeed, reduce leaching of antimicrobials to water resources,” Reinhold said. “Further, our outcomes indicated that phytoaccumulation of antimicrobials in pumpkin and zucchini reduce concentrations of anti microbials in agricultural fields, and that the consumption of these crops from fields where biosolids are applied present minimal risk to human health.”

In the next phase of this research, Reinhold and her team are screening 12 to 15 vegetable and fruit crops using hydroponics (the cultivation of plants in a nutrient solution rather than in soil) to investigate the relevance of bioaccumulation of antimicrobials from irrigation waters to human health risk and environmental fate.

“To build on our biosolids work, we want to evaluate the hypothesis that food crops will phytoaccumulate antimicrobials when irrigated with municipal wastewater treatment plant effluents and that, though it will affect the fate of antimicrobials in agricultural fields, phytoaccumulation of antimicrobials will not present a significant health risk,” Reinhold said. “Repurposing treated municipal wastewater for irrigation could also help remedy the negative impact that antimicrobials have on aquatic ecosystems when it’s discharged into surface waters.”

Once their hydroponic study is complete, Reinhold and her team will do some modeling to predict plant uptake, microbial degradation and the fate of the chemicals in these systems. The results from the modeling will then be expanded into a greenhouse study that uses wastewater and biosolids so that estimates can include both sides of the bioaccumulation coin.

“The ecosystem is much more sensitive to these chemicals than humans,” Reinhold said. “This makes sense if you think about it because antimicrobials are designed to kill microorganisms, and river and soil communities are built on microorganisms. Our findings demonstrate that soils and plants have a greater capacity to handle these wastes and break down the antimicrobials — and can do so without acute human health risks — whereas the capacity of aquatic systems to assimilate antimicrobials without adverse effects is currently being exceeded. So we’re looking at the concentration levels of these compounds and asking whether this is something we need to be concerned about. And in aquatic systems, it definitely is.”