Interactions of copper with trace metals and thiols in the macro-algae Enteromorpha prolifera (O.F.Müll)J.Ag., grown in water of the Scheldt Estuary (Belgium and S.W. Netherlands)

Abstract

The littoral algae Enteromorpha prolifera were sampled along the Scheldt estuary at 7, 14 and 23%o salinity near Lillo, Bath and Ellewoutsdijk, respectively. E. prolifera was incubated in water from these locations, to examine its reponses to copper. In freeze-dried algae, Cu was AAS-analyzed, and the cytosolic metal-binding thiols glutathione (GSH) and phytochelatin (PC) were HPLC-analyzed. In an initial series, E. prolifera thalli were exposed to 160 nM CUSO 4. PC was below detection in controls, but ranged from 14 to 18 nmoles SH per g dry weight in Cu-exposed algae, after an 8-day exposure. At each separate sampling location, reduced GSH levels were lower when algal Cu contents were higher. However, overall correlations between algal Cu, GSH and PC were not found. This may be due to an oxidative effect of Cu upon thiols, and interactions of Cu with other trace metals. In a second series thalli of E. prolifera were incubated in estuarine water with 800 nM CU and in controls. Metal interactions were monitored for 21 days in algal subsamples. Algal metals were not in equilibrium: Fe and Pb increased during incubation, whereas Zn decreased in both controls and Cu-exposed algae. Cu increased during the first week after the addition of Cu, and Zn was higher in Cu-exposed algae than in controls. GSH correlated positively with algal Zn ( n = 27; R = +0.59; P < 0.005), and negatively with algal Fe ( n = 27; R = −0.63; P < 0.005). At the ambient metal levels in the Scheldt, PC induction may be of minor importance. GSH may be an indicator of internal metal shifts in macro-algae in general.