Cadmium (Cd) and lead (Pb) contamination in Sarangani Bay: Effect on Perna viridis L. in situ and laboratory conditions

Cd and Pb uptake by green mussels, Perna viridis was measured in situ using AAS analysis. Mussels were transplanted in 4 stations for 2 months of rainy season and 2 months of dry season. The 4 stations were established within the intertidal zone of Sarangani Bay. Station 1 was about 6o 06í 25î N latitude and 125o 09í 45î E longitude while station 2 was about 6o 01î 36î N latitude and 125o 08î 54î E longitude. Station 3 was located at about 6o 02î 53î N latitude and 125o 15î 54î E longitude while station 4 which served as the control station was situated at the Ladol Beach, Alabel, Sarangani Province. Monthly sampling of mussels was made for Cd and Pb analyses. Measurement of shell length was done. Concentrations of both metals in water and sediment were analyzed monthly. Measurement of water temperature, pH, TSS, DO and salinity was conducted. Under laboratory conditions, the rate of uptake of each metal (Cd, Pb) by green mussels exposed to 25% and 50% 96h LC50 was measured at different time points within 96 hours exposure. The depuration rate of each metal from the previously exposed mussels was measured. Cd uptake by transplanted mussels ranged from 0.006 to 0.013 mg/kg during rainy and 0.006 to 0.014 mg/kg during dry season. Pb uptake was 0.001 to 0.238 mg/kg and 0.002 to 0.271 mg/kg during rainy and dry seasons respectively. Analysis of Variance (ANOVA) showed significant difference (α\u3c0.05) of Cd and Pb uptake by green mussels among the 4 stations. Highest uptake of Cd (0.013 to 0.014 mg/kg) and Pb (0.238 to 0.271 mg/kg) was observed in station 2 which is situated near industrial zone. Both Cd and Pb concentrations were below 1.0 mg/kg value recommended safe for human consumption by Codex Alimentarius Commission (2001). In seawater, Cd concentration ranged from 0.007 to 0.017 and 0.010 to 0.026 mg/L during rainy and dry seasons respectively. Pb concentration was 0.002 to 0.232 mg/l during rainy and 0.003 to 0.494 mg/L during dry season. Cd and Pb concentrations in stations 1, 2, and 3 were higher compared with the standard values of 0.01 mg/L Cd and 0.05 mg/L Pb set by DENR for class SB waters. In sediment, Cd ranged from 0.005 to 0.026 mg/L during rainy and 0.006 to 0.029 mg/L during dry season. Pb concentration was 0.187 to 0.657 mg/L and 0.282 to 0.923 mg/L during rainy and dry seasons respectively. Cd and Pb concentrations in seawater and sediment were lower compared with other bays. Under laboratory conditions, both Cd and Pb uptake tests showed an increasing pattern of bioaccumulation. This suggests the capacity of green mussels to bioaccumulate heavy metals at higher concentration if exposed under natural habitat which is contaminated with Cd and Pb. The uptake rates (mg/kg/h) showed fluctuations at different sampling time points within 96- hour exposure, with higher rates observed during the first 24 hours. Likewise, depuration test showed progressive elimination of Cd and Pb from green mussels exposed to uncontaminated seawater. Fluctuating rates (mg/kg/h) of Cd and Pb depuration were observed with highest rates of elimination during the first 12 hours of exposure to uncontaminated seawater. The rate of Pb depuration was higher compared with Cd depuration. Generally, uptake rates were higher compared with depuration rates