The effect of humic acid on uptake/adsorption of copper by a marine bacterium and two marine ciliates

The effect of humic acid (KA) on Cu uptake by a bacterium and two bacterivorus ciliates was investigated. The presence of HA resulted in a statistically significant (p<0.001) decrease in Cu associated with bacteria that were exposed to 67 mu g Cu L-1. Complexation of Cu appears to lower the availability of Cu with respect to bacterial cell surface binding and uptake. For ciliates, 10 mg HA L-1 significantly reduced uptake of Cu by Uronema, but did not reduce uptake of Cu by Pleuronema. Uronema exposed to 67 mu g Cu L-1 accumulated 54% less Cu when 10 mg I-IA L-1 was present (0.50 pg ciliate(-1) vs 0.23 pg ciliate(-1)). Uronema feeding on V. natriegens, took up less than half as much Cu as unfed Uronema when exposed to Cu without HA (0.41 pg Cu fed ciliate(-1) vs 0.86 pg Cu unfed ciliate(-1), but only 40% less when exposed to Cu and HA ( 0.31 pg Cu fed ciliate(-1) vs 0.51 pg Cu unfed ciliate(-1)), The lower % reduction attributable to fed ciliates in the presence of HA suggests that some of the Cu associated with HA is available through trophic processes. (C) 1998 Elsevier Science Ltd. All rights reserved.