| Summary: | Mercury bioavailability was assessed by exposing the dipteran <i>Chironomus riparius</i> for the whole life cycle to legacy-contaminated fluvial sediments (0.038–0.285 mg Hg kg<sup>−1</sup> d.w.) and analyzing tissue concentrations in larvae at different exposure times (7, 11, and 16 days) and in adults. In the same experiment, diffusive gradients in thin-film passive samplers (DGTs), both piston- and probe-shaped, were co-deployed in the same sediments and retrieved at the same times as the organisms. To compare the two approaches, results showed a good agreement between accumulation kinetics of <i>C. riparius</i> and DGTs, both approximating an apparent steady-state. A strong correlation was found between values in tissues and in both types of DGTs (r between 0.74 and 0.99). Concentrations in mature larvae (19–140 µg kg<sup>−1</sup> w.w.), which may represent a basal level of the aquatic food web, exceeded the European Environmental Quality Standard for biota (20 µg kg<sup>−1</sup> w.w.), which aims at protecting the top predators from secondary poisoning. Body burdens in larvae and in adults were similar, showing negligible decontamination during metamorphosis and proving an efficient mercury transfer from sediments to terrestrial food webs.
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