Accumulation of Mercury and Other Heavy Metals in Some ... - NSCB

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B. Metal concentrations (dissolved) in seawaterB.1 Mercury and goldIn this section we compared dissolved metal concentrations among the 10sampling stations. The highest mercury concentration in water was observed atStation 1 with 8.91 µg/l and Station 6 with 12.29 µg/l. High concentrations werealso noted in Stations 3 to 5 (6.32 µg/l, 5.40 µg/l, and 7.16 µg/l respectively).Most of the stations that showed high mercury concentration also had high goldcontent except for Stations 7 and 8 which showed the opposite. Compared withdissolved mercury measured earlier in the bay, our results are generally higherby about an order of magnitude. It is unlikely that these results are erroneous asthe results for the reference seawater were in agreement with certified values.Such high dissolved mercury concentrations in mining areas in the Philippinesare common. In a study by Williams et al. (1995) in a nearby mining area in theeastern part of Mindanao (Philippines), dissolved mercury ranged between 0.21 -2906 µg/l within 1 km from the mine fields, and samples taken distant from thesite showed concentration range of 0.14 µg/l and 2.84 µg/l. These values arecomparable to our study area. A year later Breward (1996) did a follow-up studyfrom Mamunga River, near the mining camp and noted a maximum Hgconcentration of 1.539 µg/l. When compared with other parts of the world, ourresults are higher than what is reported by Kannan et al. (1998) for estuaries inSouth Florida but lower than in the coastal waters of North Lebanon (Shiber etal., 1978).B.2 Other metalsFor most of the other metals, Station 4 showed the highest concentration(715.41 µg/l for Al (122 µg/l), Fe (63.8 µg/l), Mn (38.9 µg/l), Zn (51µg/l) except fornickel which was highest in Station 7 (27.44 µg/l).C. Heavy metal concentrations in suspended particlesC.1 Mercury and goldMercury and gold concentrations measured in the bay ranged between 3 -13 µg Hg/g and 1 - 6 µg Au/g dry weight, respectively. The highest mercury andgold concentrations were recorded at Station 4. Other stations, which showedhigh Hg and Au concentrations, were Stations 1, 2 and 5. These were stationslocated in the proximity of the mining area. When tested to see whether therewere significant differences among all stations, the results from Kruskal-Wallistest showed very high significant differences (P < 0.001) all stations combined.C.2 Other metalsOther metals such as Cd, Co, Cu, Fe, Ni, Pb, and Zn were highest inStation 4 while Ag and Cr, which were highest in Station 6. There are few studieson metal concentrations in suspended particles particularly places close to goldmining fields (Tessier et al., 1984, Fileman et al., 1991).
D. Metal concentrations in the bottom sedimentsD.1 Mercury and goldSediments serve as sinks for heavy metals and for metals with high affinityfor organic particles such as mercury will be elevated in organic rich sediments(Skei, 1978; Luoma, 1989). Generally, as grain size decreases, the concentrationof metals adsorbed onto sediments increases, particularly across the transitionzone from silt to clay (< 4 – 63 µm) (Deely et al., 1992). Except for Station 8,which exhibited the highest Hg and Au contents (58.15 µg/g & 254.29 µg/grespectively), most of the stations with smaller particle size showed higherconcentrations for Hg and Au. Gold was also highest (254.3 µg/g) at station 8followed by station 4 (21.4 µg/g).Stations 2, 9 and 10 also serve as monitoring stations for neighboringregion (DENR-X) and the results they obtained for their June 1999 sampling(Manzano and Daitia, 1999) were about two orders of magnitude higher than ourOctober samples. This difference may be a result of differences in procedures forthe extraction of total metals from the sediments used. In our study, total metalconcentrations in the sediments were measured according to the procedurereported by Tessier et al. (1979) and Bervoets et al. (1998). Mercury in riversediments from Eastern Mindanao (Williams et al., 1995) was in the range of 0.02mg/kg and 23 mg/kg within the mining site, five times higher than what this studymeasured. Compared with other studies Sasamal et al. (1987), Craig andMoreton (1983), Park and Curtis (1997) recorded similar values.D.2 Other metalsEven for the other metals, Station 8 had the highest concentration, exceptfor lead which was high in Station 4 (331 µg/g) and Station 5 (286 µg/g). Hamilton(1989) reported similar concentrations for cadmium in the Northeast Pacific.E. Heavy metal concentrations in invertebrate species in the bayFrom the total of 10 species collected during our sampling exercise, onlyfour species were present in more than 3 stations. The other species were eitherpresent only at one or two stations. Metal concentrations varied from one stationto other and with species.E.1 Mercury and goldAmong the sampled species in the bay, Circe scripta in Station 2 had thehighest mercury content, 9.2 µg/g, followed by Placuna ephippium also in Station2 with 4.32 µg/g, Tectus fenestratus and Strombus sp. in Station 3 with 3 µg/gand 2.74 µg/g respectively. Other species that showed high mercuryconcentration include Tectus fenestratus from Station 2 with 2.72 µg/g; Anadarascapha in Station 4 with 1.66 µg/g; and Littorina scabra from Station 6 with 1.58µg/g. The rest of the species had less than 1 µg/g concentration.
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Accumulation of Mercury and Other Heavy Metals in Some ... - NSCB

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