Determination of Mercury in Fish Tissue, a Rapid, Automated Technique for Routine Analysis

Importance of the Topic

The monitoring of mercury levels in fish tissues is critical due to the neurotoxic effects of methylmercury on human health and ecosystems. Routine, high‐throughput analysis methods support environmental surveys and food safety programs by providing reliable data on mercury contamination in seafood.

Objectives and Study Overview

Researchers at the University of Liverpool conducted an extensive survey of 18 sites in the Irish Sea, analyzing over 8 000 fish across seven species over 15 months. The main goal was to establish a rapid, cost‐effective, and automated protocol for batch analysis of fish muscle for mercury content, minimizing technician workload and maximizing throughput.

Methodology and Instrumentation

The procedure employs cold‐vapor atomic absorption spectroscopy with continuous flow vapor generation. Key instrumentation includes:

• Agilent AA-1275 atomic absorption spectrophotometer
• Agilent Model 76 Vapor Generation Accessory (VGA-76)
• Agilent PSC-55 programmable sample changer
• Apple IIe microcomputer for automation and data processing

A single‐step digestion uses concentrated nitric acid, followed by dilution. Stannous chloride (25 % w/v SnCl₂ in 20 % v/v HCl) is selected as the reducing agent due to minimal matrix interference compared to sodium borohydride. Operating parameters are optimized for routine use:

• Sample flow: 6.5 mL/min
  
• Reagent flows: 1 mL/min each for reducing agent and water
  
• Inert gas: nitrogen to strip vapor
  
• Delay time: 70 s; rinse time: 30 s; integration: four replicates with 4 s hold
  
• Wavelength: 253.7 nm

Main Results and Discussion

The optimized method achieved:

• Routine relative standard deviations below 0.5 %
• Recoveries of 92–102 % for spiked fish samples
• Inter-laboratory agreement at 95–104 % (mean 96.2 %) compared with a reference laboratory
• Throughput of up to 134 samples per day

The use of stannous chloride eliminated the severe suppression seen with sodium borohydride in fish digests. Temperature‐controlled automatic reslope calibration maintained performance stability despite laboratory temperature fluctuations.

Benefits and Practical Applications

The developed protocol offers:

• High throughput with minimal glassware and single‐reagent digestion
• Low operational cost and reduced contamination risk
• Fully automated sample handling and data acquisition
• Robust accuracy and precision suitable for regulatory monitoring and research surveys

Future Trends and Possibilities

Potential developments include expanding the automated vapor generation approach to other hydride‐forming elements (e.g., arsenic, selenium), integrating real‐time data analytics, and miniaturizing components for field‐deployable monitoring systems. Advances in software control and robotics may further increase sample throughput and reduce human intervention.

Conclusion

The rapid, automated cold‐vapor AAS method using simple nitric acid digestion and stannous chloride reduction provides a reliable, efficient solution for large‐scale mercury analysis in fish muscle. Validation against reference materials and inter-laboratory studies confirms its suitability for routine environmental and food safety monitoring.

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