12 Distribution of Cd, Pb, As and Hg in Oyster Tissue, Sediment and Water. . .
141
were low and sedimentation was assumed to occur (Sakai et al. 1986; Subramanian
et al. 1987). Sampling tools were washed with fresh water and dried before the next
sample was collected. Soil samples were packed in a 16.5 14.9 cm Ziploc
TM bag,
air-dried in the laboratory at room temperature and ground to a fine mixture using a
mortar and pestle before sieving with a 2 mm mesh to obtain the 0–75 m sediment
fraction (clay/silt fraction).
Water
A series of one liter (1.0 L) water samples was collected at each sampling site at
5–10 cm from below the surface. Collected water samples were kept in pre-labeled
polyethylene plastic containers and maintained at 4
ı C in coolers.
Determination of Heavy Metal Concentrations
Metal concentrations in water, digested oyster tissues, sediment extractions and
digested sediment samples were determined using atomic absorption spectroscopy
(Analytik Jena Vario 6 AAS, Germany) for analysis of Hg and As, while inductively
coupled plasma-atomic emission spectrometry (Jobin Yvon Ultima 2 ICP, France)
was used in the determination of Cd and Pb metals. All working standards
and samples were quantified for As and Hg using Manual Hydride Generation
Technique – AAS and Cold Vapor Technique Flow Injection Mercury System,
respectively.
Heavy Metal Analysis in Oyster Tissues
For Pb, Cd and As analysis using USEPA 6010 method of preparation (USEPA
2000), oysters samples were homogenized and digested with nitric acid (HNO 3 )
then with hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl). The digestate
was then filtered and diluted to 100 mL using distilled water. Mercury levels
were analyzed according to AOAC method 977.15 (AOAC 2005). In Hg analysis,
homogenized samples were digested with sulfuric acid (H 2 SO 4 ) and HNO 3 . The
digestate was treated with H 2 O 2 and diluted with H 2 SO 4 and HNO 3 mixture.
Heavy Metal Analysis in Sediments
A portion of soil sample was digested with HNO 3 , then with H 2 O 2 and HCl. The
digestate was filtered, diluted to 100 mL with distilled water following USEPA
6010 method (USEPA 2000) and injected into the appropriate instruments for Pb,
Cd and As quantitation. In the determination of Hg, a portion of soil sample was
141
were low and sedimentation was assumed to occur (Sakai et al. 1986; Subramanian
et al. 1987). Sampling tools were washed with fresh water and dried before the next
sample was collected. Soil samples were packed in a 16.5 14.9 cm Ziploc
TM bag,
air-dried in the laboratory at room temperature and ground to a fine mixture using a
mortar and pestle before sieving with a 2 mm mesh to obtain the 0–75 m sediment
fraction (clay/silt fraction).
Water
A series of one liter (1.0 L) water samples was collected at each sampling site at
5–10 cm from below the surface. Collected water samples were kept in pre-labeled
polyethylene plastic containers and maintained at 4
ı C in coolers.
Determination of Heavy Metal Concentrations
Metal concentrations in water, digested oyster tissues, sediment extractions and
digested sediment samples were determined using atomic absorption spectroscopy
(Analytik Jena Vario 6 AAS, Germany) for analysis of Hg and As, while inductively
coupled plasma-atomic emission spectrometry (Jobin Yvon Ultima 2 ICP, France)
was used in the determination of Cd and Pb metals. All working standards
and samples were quantified for As and Hg using Manual Hydride Generation
Technique – AAS and Cold Vapor Technique Flow Injection Mercury System,
respectively.
Heavy Metal Analysis in Oyster Tissues
For Pb, Cd and As analysis using USEPA 6010 method of preparation (USEPA
2000), oysters samples were homogenized and digested with nitric acid (HNO 3 )
then with hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl). The digestate
was then filtered and diluted to 100 mL using distilled water. Mercury levels
were analyzed according to AOAC method 977.15 (AOAC 2005). In Hg analysis,
homogenized samples were digested with sulfuric acid (H 2 SO 4 ) and HNO 3 . The
digestate was treated with H 2 O 2 and diluted with H 2 SO 4 and HNO 3 mixture.
Heavy Metal Analysis in Sediments
A portion of soil sample was digested with HNO 3 , then with H 2 O 2 and HCl. The
digestate was filtered, diluted to 100 mL with distilled water following USEPA
6010 method (USEPA 2000) and injected into the appropriate instruments for Pb,
Cd and As quantitation. In the determination of Hg, a portion of soil sample was