BIOMONITORING WITH BENTHIC MACROALGAE AND DIRECT ASSAY OF HEAVY-METALS IN SEAWATER OF THE OPORTO COAST (NORTHWEST PORTUGAL)

The concentrations of dissolved Cd, Cu, Hg and Pb in seawater and alga e (Enteromorpha spp, and Porphyra spp,) were determined in parallel on three beaches located in the Oporto coast (Portugal), during 8 succes sive months, comprising periods of low and high biological productivit y, The concentrations of dissolved metals in seawater varied markedly during the sampling period and exhibited seasonality. The concentratio ns of Cd were high in autumn and winter, but low in spring, The concen trations of Cu and Hg were high in autumn, low in winter and peaked in May, The concentrations of Pb were low in autumn and winter, and also peaked in May, It is likely that biological activity was, at least pa rtially, responsible for the observed seasonal changes, The mean conce ntrations of dissolved metals in seawater were similar to those report ed for polluted and industrialized european coastal areas, Metal conce ntration factors, calculated month-to-month for each alga, metal and s ite, varied markedly during the sampling period, indicating that conce ntration factors based on single or few determinations could be mislea ding, On the contrary, mean concentration factors (calculated by divid ing the mean metal concentration in the algae by the mean metal concen tration in seawater) were relatively constant at all three sites, indi cating that in the Oporto coast, Enteromorpha spp, can be used to esti mate the mean concentration of dissolved Cd, Cu and Hg in seawater, an d Porphyra spp., the mean concentration of Cd, Cu and Pb, However, con sidering that future estimates of the concentrations of these metals i n seawater should be based on determinations of the metal contents in Enteromorpha spp, and Porphyra spp, carried out on several occasions s panning a considerable period of time, the use of these algae as monit ors of heavy metal pollution can have limited practical advantages ove r the direct assay of the metals in seawater. (C) 1997 Elsevier Scienc e Ltd. All rights reserved.