Determination of Mercury in Plastics/ Plastic Waste (Granulated or Flaked Particles)

Importance of the Topic

Mercury is a highly toxic contaminant that can accumulate in the environment and pose serious risks to human health. Plastics derived from municipal and industrial waste streams may contain trace levels of mercury from various sources such as pigments, stabilizers, or recycled content. Reliable quantification of mercury in plastic matrices is essential for regulatory compliance, quality control, and environmental monitoring.

Goals and Article Overview

This application note describes a straightforward thermal decomposition–atomic absorption spectrometry (AAS) method for determining mercury in flaked or granulated plastic waste. The study demonstrates sample preparation, calibration, instrument operation, and typical performance data using the LECO AMA254 instrument. Key objectives include achieving accurate quantification at sub-ppm levels and assessing precision for different particle sizes.

Methodology and Instrumentation

Sample Preparation and Handling

• Weigh 100–150 mg of plastic particles directly into large nickel boats (LECO 614-822-114).
• Perform blank measurements by loading empty boats three times to purge residual mercury.
• Calibrate with certified reference materials (fly ash, dry sludge) across the expected dynamic range.

Instrument Settings

• Instrument: LECO AMA254 (thermal decomposition with gold amalgamation and AAS detection).
• Drying time: 60 s; decomposition time: 200 s; cuvette clear time: 45 s; dosing delay: 0 s.
• Auto-select cell and use peak area for quantification.

Measurement Procedure

1. Load blank and calibration boats in sequence, discarding the first post-idle measurement as a conditioner.
2. Analyze samples by entering sample ID and weight, then initiating the automated sequence.
3. Verify calibration by re-analyzing a reference material within specified tolerances.

Main Results and Discussion

Two sets of plastics were evaluated at a nominal mercury level of 0.1 ppm:

• Fine particles (mean weight ~140 mg): mean concentration 0.1009 ppm, standard deviation 0.0024 ppm, RSD 2.38%.
• Coarse particles (mean weight ~108 mg): mean concentration 0.1033 ppm, standard deviation 0.0072 ppm, RSD 6.93%.

The higher variability in coarse samples reflects particle heterogeneity and highlights the importance of representative subsampling for accurate analysis.

Benefits and Practical Applications

The described technique offers:

• No wet chemistry or sample digestion—minimizing contamination and handling time.
• Rapid analysis (~8 minutes per sample) with automated loading and calibration routines.
• Low detection limits and high throughput, suitable for routine screening of recycled plastics and waste materials.

Future Trends and Possibilities

Advancements in mercury analysis for plastics may include:

• Integration of autosamplers for higher throughput and reduced operator intervention.
• Enhanced detection systems to lower the quantification limit below 0.01 ppm.
• Expansion to include speciation capabilities, differentiating inorganic mercury from organic forms within polymer matrices.
• Application to broader polymer types and complex consumer goods under circular-economy regulations.

Conclusion

The thermal decomposition–AAS method using the LECO AMA254 instrument provides a robust, sensitive, and efficient approach for determining trace mercury in plastic waste. Its simplicity and speed make it well suited for quality control, regulatory compliance, and environmental surveillance of recycled and virgin polymer materials.