Analysis of Shellfish Tissue for Cadmium, Mercury and Nickel

Significance of the Topic

Shellfish are excellent bioindicators of coastal pollution because they filter and concentrate trace metals in their tissues. Toxic metals such as cadmium, mercury and nickel pose health risks to humans and ecosystems, requiring reliable analytical protocols for seafood safety and environmental monitoring.

Study Objectives and Overview

This application note describes the development and validation of an acid digestion method for freeze-dried shellfish tissue, followed by atomic absorption spectroscopy (AAS) analysis of cadmium, nickel and mercury. The study compares two digestion approaches, applies the method to two shellfish samples and uses a NIST bovine liver reference material (1577) for quality assurance.

Methodology and Sample Preparation

Two digestion procedures were evaluated: a nitric acid digestion previously used for mercury and a modified version with hydrogen peroxide. A 1 g sample of NIST 1577 and 0.1 g aliquots of shellfish tissue were digested in 10 mL concentrated HNO3 at 125 °C for three hours. After cooling, solutions were diluted to defined final volumes (50–125 mL) for metal determination. Working standards were prepared in dilute HNO3, and ammonium dihydrogen phosphate was used as a modifier for cadmium.

Instrumentation Used

• Agilent SpectrAA-300GZ with Zeeman background correction and PSD-96 autosampler for cadmium and nickel. Cadmium was atomized from a pyrolytic forked platform; nickel from a pyrolytic-coated tube wall.
• Agilent SpectrAA-20ABQ with VGA-76 cold vapor generation and MCA-90 mercury concentration accessory for mercury analysis.
• Hollow cathode lamps for each element, argon as inert gas and standard instrument parameters optimized for peak area (Cd, Ni) and peak height (Hg).

Main Results and Discussion

Calibration curves for cadmium (228.8 nm) and nickel (232.0 nm) were linear with low background. NIST 1577 cadmium results agreed closely with the certified value; shellfish sample 1 showed elevated cadmium likely due to contamination or inhomogeneity, while shellfish 2 was within acceptable limits. Nickel results for both shellfish samples were consistent, indicating homogeneous metal distribution. Mercury measurements by cold vapor AAS matched the certified NIST value, confirming the digestion and analysis procedure’s suitability for volatile metals.

Benefits and Practical Applications

• Provides a validated, rapid workflow for multielement quantification in seafood.
• Ensures accuracy through reference material validation and recovery studies.
• Applicable to environmental surveillance around industrial and mining areas.

Future Trends and Possibilities

Advancements may include coupling digestion methods with ICP-MS for lower detection limits, fully automated microwave digestion systems, expanded monitoring of emerging contaminants and development of portable field-deployable sensors for real-time metal analysis.

Conclusion

The presented acid digestion and AAS protocols enable accurate determination of cadmium, nickel and mercury in shellfish tissue. Validation with NIST 1577 confirms method reliability, making it suitable for routine environmental and food safety monitoring.

References

• S J Evans, M S Johnson and R T Leah. Varian Instruments At Work AA-60, May 1986.
• L M Beach. Varian Instruments At Work AA-90, June 1989.
• L M Beach. Varian Instruments At Work AA-105, February 1992.
• J H Moffett. Varian Instruments At Work AA-104, December 1991.
• L M Beach. Varian Instruments At Work AA-108, October 1992.