The speciation of dissolved copper, cadmium and zinc in Manila Bay, Philippines I.B. Velasquez a, * , G.S. Jacinto a , F.S. Valera b a Marine Science Institute, University of the Philippines, Diliman 1101, Quezon City, Philippines b Institute of Chemistry, University of the Philippines, Diliman 1101, Quezon City, Philippines Abstract At present, there is a very limited information on the levels and distribution of dissolved metals in Manila Bay. In this study, the horizontal and vertical distribution of operationally defined species (labile, bound and total) of dissolved copper (Cu), cadmium (Cd) and zinc (Zn) were determined using differential pulse anodic and cathodic stripping voltammetry in water samples obtained from 18 stations in November 1998. In addition, the 24-h variability in the concentrations of these species at different depths in the water column was determined. These measurements were complemented by the determination of temperature, salinity, dissolved oxygen, chlorophyll a, particulate organic carbon and nutrients. Results showed that more than 50% of total dissolved copper and cadmium were labile while 50% of total dissolved zinc was organically bound. Vertical profiles showed that Cu, Cd and Zn con- centrations were generally high at the surface. Zinc and cadmium were characterised by the presence of a mid-depth minimum while copper did not show any clear vertical trend. Dissolved Cu concentrations during the spatial and diurnal samplings ranged from 0.32 to 6.95 nM and 1.52 to 45.65 nM, respectively. For Cd, the concentrations in 18 stations ranged from 0.05 to 2.92 nM, and from 0.03 to 2.42 nM over a 24-h period. Zn concentrations ranged from 2.48 to 147.43 nM and 2.87 to 88.27 nM during the spatial and diurnal samplings, respectively. The large variation in the concentration of Cu, Cd and Zn in the bay was observed to be associated with the presence of a large vertical density gradient in the water column, which appeared to limit the exchange of materials between the surface and bottom waters. Elevated levels of these metals near point sources suggest anthropogenic inputs in the bay. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Speciation; Labile; Voltammetry; Copper; Cadmium; Zinc; Manila Bay 1. Introduction Elevated metal concentrations can be observed in estuarine systems due to input of contaminants from various sources. Physical transport of materials from rivers and discharges from urban and industrial areas together with the natural biogeochemical cycling of pollutants can contribute to the natural variability in concentration, distribution and fate of these metals in coastal estuaries (Dassenakis et al., 1997). Metal speci- ation studies can help in the measurement and under- standing of the transformation of trace elements from its three major forms in the dissolved phase namely: (1) the free hydrated metal ion, (2) inorganic complexes and (3) organic complexes (Muller, 1996; Kozelka and Bruland, 1998). Among the three major forms, the free hydrated metal ion has been observed to be bioavailable and very toxic to phytoplankton while the inorganic and organic complexes are considered not bioavailable to organisms (Sunda and Guillard, 1976; Muller, 1996; Kozelka and Bruland, 1998). The free hydrated metals are present in trace amounts ranging between the concentration win- dow of essential and toxic levels (Florence, 1982). In this study, a combination of operationally defined physical and chemical separation techniques was utilised in the measurement of the different species of copper (Cu), cadmium (Cd) and zinc (Zn). The kinetically labile or bioavailable Cu, Cd and Zn (sum of free hydrated metal and inorganic complexes), bound Cu, Cd and Zn (organically bound complexes) and total Cu, Cd and Zn were measured in Manila Bay. Very little is known on the levels and distribution of metals in the country specifically in the marine environment. Hence this study * Corresponding author. 0025-326X/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0025-326X(02)00049-8 www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 45 (2002) 210–217