Dietary bioavailability of Cu adsorbed to colloidal hydrous ferric oxide

The dietary bioavailability of copper (Cu) adsorbed to synthetic colloidal hydrous ferric oxide (HFO) was evaluated from the assimilation of (65)Cu by two benthic grazers, a gastropod and a larval mayfly. HFO was synthesized, labeled with (65)Cu to achieve a Cu/Fe ratio comparable to that determined in naturally formed HFO, and then aged. The labeled colloids were mixed with a food source (the diatom Nitzschia palea) to yield dietary (65)Cu concentrations ranging from 211 to 2204 nmol/g (dry weight). Animals were pulse fed the contaminated diet and assimilation of (65)Cu from HFO was determined following 1-3 days of depuration. Mass transfer of (65)Cu from HFO to the diatom was less than 1%, indicating that HFO was the source of (65)Cu to the grazers. Estimates of assimilation efficiency indicated that the majority of Cu ingested as HFO was assimilated (values >70%), implying that colloidal HFO potentially represents a source of dietary Cu to benthic grazers, especially where there is active formation and infiltration of these particles into benthic substrates.