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 bacterivo rus ciliates was investigated. The presence of HA resulted in a statistical ly 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 availabi lity of Cu with respect to bacterial cell surface binding and uptake. For c iliates, 10 mg HA L-1 significantly reduced uptake of Cu by Uronema, but di d 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 t han 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 cili ate(-1)), The lower % reduction attributable to fed ciliates in the presenc e of HA suggests that some of the Cu associated with HA is available throug h trophic processes. (C) 1998 Elsevier Science Ltd. All rights reserved.