CAN ROOT FUNGI INTERRUPT TROPHIC TRANSFER OF URANIUM FROM SOIL TO PLANTS TO SHEEP TO NAVAJO PEOPLE?

The Cold War drove intense uranium mining in the American Southwest, without regulation or attention to environmental impact. As a result, the Navajo Nation is peppered with hundreds of abandoned mines, and the Diné people experience elevated rates of certain cancers and kidney disease [1]. Traditional consumption of mutton is one significant exposure pathway; sheep graze on plant shoots that have grown in uranium-contaminated soil. The livers and kidneys of the sheep, consumption of which has cultural importance, are particularly enriched in uranium [2]. How might chronic U exposure through the food chain be reduced in an economically feasible and culturally considerate manner?

To explore a possible new approach to this problem, we grew sunflowers with and without symbiotic root fungi (arbuscular mycorrhizal fungi). We aimed to learn whether the presence of fungi can cause plants to sequester the uranium they take up in their roots, thus reducing the amounts in shoots and leaves and potentially available to herbivores, as observed in two previous studies [3,4]. In greenhouse experiments, we investigated how soil mineralogy and fungal colonization influenced uranium uptake and translocation by using soil media of differing clay content, watering with different concentrations of uranium, and inoculating roots of some plants with fungi. Statistical analysis of U concentrations in plant tissues (determined by ICP-MS) suggests that the fungi do decrease translocation of uranium to shoots in our highest [U] experiments, consistent with [3], although the small number of replicates in our pilot study prevents us from drawing a robust conclusion (p=0.22). Results also suggest that kaolinite causes increased uptake under certain conditions, indicating that sorption of U onto kaolinite surfaces may be an important variable governing bioavailability of this radioactive and toxic metal. Our work represents a first step toward assessing whether stimulation of naturally-occurring arbuscular mycorrhizal fungi in Navajo grazing lands could mitigate uranium exposure and under what conditions such an approach might work best.

[1] Brugge & Goble (2002) Am J Public Health 92, 1410; [2] Lister et al. (2021) J Vet Med Animal Sci. 4(1), 1055; [3] Rufyikiri et al. (2004) Env Pollution 130, 427; [4] Chen et al. (2005) Plant and Soil 275, 349