Concentrations of selected elements, with special reference to Cd and Zn, in the seeds of cultivated and wild plants from the DePue Wildlife Management Area, DePue, Illinois

We examined concentrations of barium (Ba), cadmium (Cd}, copper (Cu), iron (Fe}, lead (Pb), and zinc (Zn) in buckwheat (Fagopyrum esculentum}, com (Zea mays}, giant ragweed (Ambrosia trifida), Pennsylvania smartweed (Polygonum pennsylvanicum ), and water hemp (Amaranthus rudis) seeds collected at the "3-Is" waterfowl impoundment at DePue Wildlife Management Area (DWMA), DePue, Illinois, in the autumn of 1997. Concentrations in these species (except giant ragweed) were compared with samples collected at Anderson Lake Conservation Area (ALCA}, a reference site located 146 km from DWMA. Mean Cd, Cu, Zn concentrations were lowest, and Ba and Pb were not detectable, in com seeds; Fe concentrations were lowest in smartweed seeds. Cd, Fe, and Zn concentrations were highest in seeds of water hemp, while Cu was highest in giant ragweed. Pb was detectable in some smartweed and water hemp samples. Mean and maximum Cd, Fe, and Zn concentrations were higher in buckwheat, corn, smartweed, and water hemp seeds from DWMA than in samples from ALCA. Seeds of the plant species·examined exhibited little variation in Ba and Cu concentrations between sites. Pb was detected in a lower proportion of water hemp seeds, but a higher proportion of smartweed seeds, from DWMA, when compared to ALCA. We detected a wide range of variation in Cd and Zn concentrations in seeds within and across the cell comprising the impoundment, and this was further complicated by variation among species. As a general trend, individual values tended to be higher at the north end of the easternmost cell of the impoundment, the east end of the northcentral cell, arid the central portion of the west/southcentral cell. The Zn: Cd ratio in seeds was higher in com and smartweed seeds, and lower in water hemp seeds, from DWMA as compared to seeds from ALCA. The relationship between Cd and Zn concentrations in seeds varied among species and between sites, suggesting an interaction between species and soil concentrations of these elements. Seed Cd and Zn concentrations in our study were above lower effects levels for mammals and birds observed in some studies but not in others, suggesting some poorly-definable risk to granivorous species utilizing DWMA. Cd concentrations were within known effects levels for laboratory mice, however, this group may be more sensitive to Cd exposure than wild species. Based on the information available from prior studies, it seems unlikely that concentrations of Cd and Zn observed in seeds from DWMA are high enough to cause adverse effects in ducks or gallinaceous birds that might consume them, although there might be some risk to young of these avian groups. Studies of the effects of many contaminants to wild species at environmentally realistic concentrations are lacking, making plausible inferences about risks to species consuming seeds at DWMA difficult. The bioavailability of metals present in plants needs to be considered in determining exposure risk to granivorous mammals and birds from ingesting seeds at DWMA, given the presence of elevated concentrations of elements which antagonize Cd and Zn. Additionally, the relative importance of the plant species examined as food items in the diet of each species needs to be considered, as do other exposure routes for granivorous animals. We suggest that, given elevated concentrations of Cd and Zn in the seeds of plant species growing within the impoundment (that exceed or approach effects levels in some studies) further information is needed on exposure, tissue concentration, population levels/demographics, and individual health of representative granivorous species (e.g. white-footed mice) present at DWMA.