Heavy metal contamination in Thelesperma megapotamicum

Abstract

This study describes heavy metal (HM) contamination in the most commonly used herbal tea in several American Indian (AI) communities in northwestern New Mexico. The Navajo (Dine) reservation is located in an area that was heavily impacted by contamination associated with Uranium (U) mining that occurred from 1945 to 1988 and where more than 1,100 unreclaimed abandoned U mines and structures remain. The study objective was to establish the levels of HM contamination in this herb which is habitually and widely consumed in this reservation community.  The study aims were to: (1) describe the dietary behavior in Dine residents related to ingestion of harvested tea Thelesperma megapotamicum; (2) compare U and other HMs in tea in high and low vehicle traffic areas; and (3) disseminate study findings to the leadership and Dine community. A descriptive comparative design was used to compare HMs in locally harvested herbs on the reservation. The plant specimens were paired with soil samples and analyzed utilizing ICP-MS.  Samples were collected from areas spanning a 3.2 km radius from the central part of abandoned uranium mines and structures. Root samples of tea had higher concentrations of HMs than above ground plant parts for As, Cd, Cs, Mo, Pb, U and V (p < 0.05). Cadmium and Mo levels were greater in high traffic versus low traffic areas (p < 0.001).  The Cd level (0.35 mg/kg) in this popular species of tea herb exceeded the World Health Organization medicinal plant maximum permissible level.  Further research and monitoring is needed to identify factors that affect HM contamination in T. megapotamicum and other plant herbs used on the Navajo reservation as well as other U mining impacted areas.    Key words: American Indian, heavy metals, Dine/Navajo, Thelesperma megapotamicum, herbal tea, uranium, cadmium, molybdenum, mining.