Effects of Organic Matter Concentration in Soil on Phytoavailability of Cadmium in Medicinal Plants

Abstract

The safety of plant species used as a source for herbal medicines and dietary supplements has recently been questioned due to poisonings associated with the presence of cadmium (Cd) in these plants. These plants can derive Cd from their presence in the soil. Organic matter (OM) concentrations in soils could affect the availability of Cd for plants. To determine the effect of OM concentration in soil on the concentration of plant available Cd and uptake of this toxic element by medicinal plants, soil and plant samples were collected from 102 fields supporting for 5 species of medicinal plants in 6 province of South Korea. Concentrations of OM and dissolved organic carbon (DOC) in soils affected the phytoavailability of Cd. One M NH4OAc extractable Cd concentration in soil increased with increasing OM concentrations. There were significantly positive relationships between 1 M NH4OAc extractable Cd concentration and OM concentration in soil and between 1 M NH4OAc extractable Cd concentration and DOC concentration. Likewise, OM and DOC concentrations significantly affected Cd concentration in medicinal plant soils. Cadmium concentration in medicinal plants increased with increasing OM concentration in soil [Cd concentration (mg kg-1) = 0.179 + 1.424 × 10-3 OM concentrations, R2 = 0.042*] and with DOC concentration [Cd concentration (mg kg-1) = 0.150 + 5.870 × 10-4 DOC concentrations, R2 = 0.124***]. These results might result from Cd-DOC complex which is easily absorbed Cd form by plant root. Dissolved organic carbon concentration had more positive relationship with Cd concentration in medicinal plants and 1 M NH4OAc extractable Cd concentration in soils than OM. Cadmium concentration in all 5 species of medicinal plant (Atractylodes macrocephala Koidzumi, Astragalus membranaceus, Codonopsis lanceolata, Platycodon grandiflorum, and Rehmannia glutinosa) significantly increased with increasing DOC concentration in soil. From the above results, formation of Cd-DOC complex caused by OM application might be mainly attributed to increase in Cd concentration in medicinal plants.