California overwintering monarch butterflies contain both pyrrolizidine alkaloids (PAs) and theirN-oxides. Analysis of 76 individual monarchs by TLC, HPLC, GLC, and GC-MS has shown the presence of three types of PAs, the saturated diester sarracine, the saturated monoester 7-angelylplatynecine, and the unsaturated dialcohol retronecine. Monarchs arriving at the overwintering site in Santa Cruz, California, showed a wide variation in both the type and amount of PA present. Those sampled after a PA-containing plant (Senecio mikanioides) had bloomed at the site showed an altered PA profile. While the plant was found to contain sarracine and 7-angelylplatynecine, which are nontoxic to mammals, the monarchs showed an increase in retronecine levels, a toxic PA, after the plant bloom. Apparently monarchs utilize PA-containing plants both en route to their overwintering site and at the site, and potentially alter those PAs to forms toxic to mammals.
Measured soil concentrations are often used as input in ecological uptake models to estimate the concentrations of chemicals in various organisms. In this study, modeled and measured plant and animal concentrations were compared to evaluate the validity of various uptake modeling approaches for different groups of chemicals. The models used measured soil concentration data collected during a remedial investigation at an environmentally diverse Superfund site in California to estimate metal and organic chemical plant tissue concentrations. These modeled plant tissue concentrations were then used as intake concentrations to estimate tissue concentrations in herbivores, and the resulting modeled herbivore tissue concentrations were used as intake concentrations to estimate tissue concentrations in predators. Measured chemical concentrations were determined by collecting and chemically analyzing surface soil samples and collocated plants, so that soil concentrations and tissue concentrations could be correlated. Small mammals were also sampled at the sites, as close to the location of soil and plant collection as possible. These field data were then compared with modeled plant and animal tissue concentrations. For metals, the exposure models consistently overpredicted measured tissue concentrations for both plants and animals at high soil concentrations (those exceeding "background") and underpredicted tissue concentrations at low soil concentrations. In contrast, the measured dioxin concentrations in plants and animals were consistently greater than those predicted from the models across the range of detected soil concentrations, by approximately two orders of magnitude.
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