Occurrence of the carcinogenic Bracken constituent ptaquiloside in fronds, topsoils and organic soil layers in Denmark

Bracken (Pteridium aquilinum (L.) Kuhn) is a common fern found on all continents except Antarctica. It is under suspicion of causing cancer among people who utilizes it as food. The main carcinogenic compound is thought to be the water-soluble compound ptaquiloside. Ptaquiloside-uptake may occur not only through food, but also via drinking water as ptaquiloside might leach from plant material. The purpose of the study was to identify environmental parameters that correlate with the ptaquiloside-content in fronds, and to quantify the amount of ptaquiloside in the soil environment. The ptaquiloside-content in fronds, Oi/Oe-, and Oa/A-horizons was quantified at end of the growth season at 20 sites in Denmark. The fronds had ptaquiloside-contents between 108 and 3795 μg g−1. The Oi/Oe-horizons had contents between 0.09 and 7.70 μg g−1, while Oa/A-horizons had contents between 0.01 and 0.09 μg g−1. The ptaquiloside-content in the standing biomass, which could be transferred to the soil by the end of the growing season, ranged between 10 and 260 mg m−2, with nine sites having ptaquiloside loads over 100 mg m−2. The carbon-content in the O-horizon, the precipitation, the amount of Bracken-litter, the turnover rate and the size of Bracken-stands determined the ptaquiloside-content in the soil materials while the content in fronds was found to be a function of the frond-height and the light-exposure in the ecosystem.