142
R.T. Vinarao et al.
digested with aqua regia and potassium permanganate (KMnO 4 ). Distilled water
was added to the digestates as stated in USEPA 7471 (USEPA 1994). Sodium
chloride-hydroxylamine was added prior to quantification using the Cold Vapor
Technique Flow Injection Mercury System.
Heavy Metal Analysis in Water
The analyses of metals in seawater was based on the American Public Health
Association (APHA) method (APHA 1980). The water samples were digested with
different acids and reagents: HNO 3 for Pb (APHA 3030E); HNO 3 and HCl for Cd
(APHA 3030F); H 2 SO 4 and potassium persulfate (K 2 S 2 O 8 ) for As (APHA 3114B);
and H 2 SO 4 , HNO 3 , KMnO 4 and K 2 S 2 O 8 for Hg (APHA 3112B). They were filtered
using prewashed and pre-weighed membranes and diluted to 100 mL with distilled
water. Water samples were analyzed following the same analytical technique as used
for oyster tissues and sediments.
Quality Control
Standard stock solutions were prepared from ultra-high purity grade chemicals
(99.99 % pure). All working standards and samples were prepared in duplicates
and average readings were taken from three instrument readings for all the heavy
metals. Operational conditions such as limit of detection were adjusted according
to the instrument and method requirements. The duplicate relative percentage
difference (RPD) for all laboratory duplicates was Ä20 %. Concentrations were
computed by the standard calibration method. Calibration curves were composed
of at least three standard concentrations where computation for linearity was based.
The instrument detection limits were determined from three standard deviations
obtained from seven blanks. Percent recoveries of oysters, sediment and water
samples are in the range of 80–120 %. Regular measurements of laboratory blanks
and spikes for all metals and proficiency tests for water were done to assure quality
control of the analysis. Blank digestion was also performed to quantify possible
contamination during sample preparation and analysis.
Statistical Analysis
Within and between group differences were assessed using one-way analysis of
variance (ANOVA) and Duncan’s Multiple Range Test (Bewick et al. 2004).
Relationships between the heavy metal concentration in oyster tissues, sediments
and water were evaluated by linear regression and by determination of Pearson
correlation coefficients. All errors were calculated at 95 % confidence level.
R.T. Vinarao et al.
digested with aqua regia and potassium permanganate (KMnO 4 ). Distilled water
was added to the digestates as stated in USEPA 7471 (USEPA 1994). Sodium
chloride-hydroxylamine was added prior to quantification using the Cold Vapor
Technique Flow Injection Mercury System.
Heavy Metal Analysis in Water
The analyses of metals in seawater was based on the American Public Health
Association (APHA) method (APHA 1980). The water samples were digested with
different acids and reagents: HNO 3 for Pb (APHA 3030E); HNO 3 and HCl for Cd
(APHA 3030F); H 2 SO 4 and potassium persulfate (K 2 S 2 O 8 ) for As (APHA 3114B);
and H 2 SO 4 , HNO 3 , KMnO 4 and K 2 S 2 O 8 for Hg (APHA 3112B). They were filtered
using prewashed and pre-weighed membranes and diluted to 100 mL with distilled
water. Water samples were analyzed following the same analytical technique as used
for oyster tissues and sediments.
Quality Control
Standard stock solutions were prepared from ultra-high purity grade chemicals
(99.99 % pure). All working standards and samples were prepared in duplicates
and average readings were taken from three instrument readings for all the heavy
metals. Operational conditions such as limit of detection were adjusted according
to the instrument and method requirements. The duplicate relative percentage
difference (RPD) for all laboratory duplicates was Ä20 %. Concentrations were
computed by the standard calibration method. Calibration curves were composed
of at least three standard concentrations where computation for linearity was based.
The instrument detection limits were determined from three standard deviations
obtained from seven blanks. Percent recoveries of oysters, sediment and water
samples are in the range of 80–120 %. Regular measurements of laboratory blanks
and spikes for all metals and proficiency tests for water were done to assure quality
control of the analysis. Blank digestion was also performed to quantify possible
contamination during sample preparation and analysis.
Statistical Analysis
Within and between group differences were assessed using one-way analysis of
variance (ANOVA) and Duncan’s Multiple Range Test (Bewick et al. 2004).
Relationships between the heavy metal concentration in oyster tissues, sediments
and water were evaluated by linear regression and by determination of Pearson
correlation coefficients. All errors were calculated at 95 % confidence level.