Exposure to Metal Contaminants in Plants

Technical Outreach Services for Native American Communities

Brenda Brandon

Soil-Plant Barrier

• The barrier prevents plants from taking up excessive amounts of toxic metals.

• Most metals are not easily absorbed by roots, because they do not dissolve in water.

• High levels of metals in soils will prevent plants from growing in the first place.

In most cases, to avoid metal exposure soil should be washed away from plant parts that are to be eaten or used.

Some plants like golden weed and purple locoweed do concentrate selenium, a metal that can be toxic in high concentrations.

Pathways of Exposure to Metals in Contaminated Plants

• Ingestion (drinking tea or eating plant parts). This can be avoided by scrubbing soil from roots before using the plant.

• Inhalation (smudging). Difficult to avoid possible exposure.

• Dermal (use of contaminated plants in lodges). Also difficult to avoid possible exposure through skin.

Selenium in Soils at the BBR

• Selenium in soils at the Badlands Bombing Range (BBR) is natural, and not the result of military activity.

• Knowing levels of selenium in soil at the BBR can provide plant collection sites that are low in selenium (alternative collection sites).

Selenium• Selenium may be as high as 1 ppm in some

plants, and can be from 1,000 to 15,000 ppm in other plants.

• Selenium greater than 2 to 5 ppm in forage is potentially hazardous to domestic animals.

• Some plants in South Dakota can accumulate over 50 ppm selenium.

What We Do Not Know About Metal Contaminants in Plants

• Not all plants have been studied. We don’t know if they take up metals.

• Not all traditional medicinal plants have been studied.

• Certain ceremonial uses of plants are not scientifically understood.

• Certain studies will need to be directed by the Tribes in order to conduct them in an acceptable manner.

How Do We Study Metal Contaminants in Plants?

• Tribal Universities are starting programs to look at contaminants in plants that are important culturally to Tribes.

• Tribes can hire their own consultants to conduct studies.

• Agency for Toxic Substance and Disease Registry is conducting expert meetings to help Tribes find a way to address these types of questions in an ethical manner.