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 ⁶⁵Cu by two benthic grazers, a gastropod and a larval mayfly. HFO was synthesized, labeled with ⁶⁵Cu 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 ⁶⁵Cu concentrations ranging from 211 to 2204 nmol/g (dry weight). Animals were pulse fed the contaminated diet and assimilation of ⁶⁵Cu from HFO was determined following 1–3 days of depuration. Mass transfer of ⁶⁵Cu from HFO to the diatom was less than 1%, indicating that HFO was the source of ⁶⁵Cu 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.