Reference Method for the Determination of Lead in Wheel Weights, Ammunition and Fishing Sinkers and Jigheads

1. Introduction

This reference method is applicable to the analysis of lead in bulk solid material. The procedure uses a mid-level heat digestion in a 20% nitric acid solution followed by dilution and analysis using ICP-OES.

Materials composed of other metals will be digested to various degrees depending on the metal or metal alloy. The quantity of lead extracted from these materials will vary depending on composition and size of the material.

Screening of materials can be done using ED-XRF. Positive readings for lead will lead to further analysis through this procedure.

The range of concentration of lead in solids determined in this method is 0.08 to 100 %, based on the 1000 times dilution as described in this method. Lower levels may be determined using smaller dilutions.

This method is applicable to the analysis of lead in wheel weights, fishing jibs and sinkers, and ammunition used in hunting.

The laboratory conducting this analysis must be accredited for the analysis of lead by ICP-OES as per the Prohibiting the Manufacture and Import of Wheel Weights Containing Lead in Canada Regulations.

2. Interferences

  1. 2.1 Metal alloys containing lead may not be completely digested. Higher temperature digestions through the use of microwave digestion may be required.
  2. 2.2 Due to the high concentration of lead, relatively low digestion temperature and consequent large dilutions no spectral interferences (primarily Al secondary lines) of the lead lines on the ICP-OES are expected.

3. Safety and Precautions

  1. 3.1 Only personnel trained in laboratory techniques should use this method.
  2. 3.2 Proper PPE, ie. Gloves, lab coat and safety glasses, must be worn when performing this analysis.
  3. 3.3 Lead is an acute and chronic toxin, affecting the nervous system and internal organs. Gloves must be used when handling samples and solutions. Proper hygiene is essential.
  4. 3.4 Wash hands after handling samples and digestions.
  5. 3.5 Use a fume hood for the digestions.
  6. 3.6 X-Rays can cause temporary or permanent damage to the eyes. Do not open or leave open the lid of the XRF instrument when the X-Ray unit is on. Do not interfere with the interlocks that prevent the X-Rays to be operative while the lid is open.
  7. 3.7 THAs and SWPs for this method must be reviewed and signed-off before using this method.
  8. 3.8 Waste solutions must be disposed as per the local regulations for the disposal of hazardous waste.

4. Reagents

Prepare solutions in quantities as required for the analysis.

  1. 4.1 Nitric Acid, trace metal grade.
  2. 4.2 ICP-OES Calibration standards
    1. 4.2.1 Prepare multiple calibration solutions using a blank, a 10 x DL low level standard and two higher standards up to 10 mg/L to obtain the calibration curve. These solutions are prepared in 0.2 % nitric acid. The correlation coefficient for this curve must be greater than 0.9990.
    2. 4.2.2 Quality Control solutions as required for Inductively Coupled Plasma – Optical Emission Spectroscopy (ICP-OES). These solutions are prepared in 0.2 %nitric acid.
      1. Liquid Quality Control Sample
        1. Used for confirmation of a reliable calibration curve.
        2. Source from a different solution from the calibration solutions.
      2. Instrument Performance Check
        1. Used for on-going instrument verification during the run.
        2. Source from a separate solution from the calibration and Quality Control Samples.
      3. Instrument Performance Blank
        1. Used for on-going instrument verification during the run.
        2. Prepare separately from the calibration blank.
  3. 4.3 Solid Quality Control Sample
    1. 4.3.1 A reference material to be processed as a sample with each batch of samples.
    2. 4.3.2 A NIST traceable material is preferred. Alternatively, a sample designated by the laboratory as a reference material may be used.
  4. 4.4 Certified Reference material for ED-XRF, including lead metal mixtures.

5. Apparatus

  1. 5.1 Analytical Balance, capable of measuring to 0.001 ± 0.0001 g.
  2. 5.2 Digestion Block Heater
    1. 5.2.1 Class A 50 mL digestion tubes with screw on lids
    2. 5.2.2 Disposable watch glasses (polypropylene)
  3. 5.3 100, 50 and 25 mL Class A Volumetric flasks.
  4. 5.4 0.1 to 10 mL Class A pipettes or calibrated mechanical pipettors.
  5. 5.5 ED-XRF
  6. 5.6 ICP-OES Instrument
  7. 5.7 Microwave oven,
    1. 5.7.1 Laboratory grade variable power microwave.
    2. 5.7.2 Teflon Microwave Digestive Vessels equipped with pressure relief valves and Advanced Composite sleeve assemblies. Included in each set of vessels must be a pressure and temperature control vessel.

6. Sample Collection, Preservation and Handling

  1. 6.1 Collect samples in original product containers.
  2. 6.2 Bulk samples can be collected in plastic or glass bottles or plastic bags.
  3. 6.3 No preservation is required.
  4. 6.4 The minimum quantity required to analyze one sample is 0.001 g. Smaller sample sizes will require appropriate changes in the post-digestion dilutions.

7. Procedure

  1. 7.1 Unless otherwise specified in this method, clean all glassware as per good laboratory practices.
    1. 7.2 Samples must be dry. In the event that a sample is wet, air or oven dry the sample. The percent moisture is not relevant to this method.
    2. 7.3 Record weights of all components and subsamples.
    3. 7.4 Wheel weights for vehicles come in five common types: adhesive, usually available in strips; quick tab (clip) weights with a hook and plastic coated; spoke crescent; inserts; and, hub weights.
      1. 7.4.1 The hook on the quick tab weights is a less pliable metal such as steel. The two metals parts need to be separated, each analyzed, and the %Pb determined from the combined weight. Note that the hook extends into the lead weight internally which may be difficult to extract.
      2. Two methods to separate the components of the sample are to:
        1. Use wire cutters and other tools to disassemble the sample into its components; or,
        2. Heat the sample in a thick walled aluminium dish over a blast burner. The melting point of lead is around 360 °C while the aluminium is around 1100 °C.

Be careful not to get the dish too close to the flame as the aluminium may deteriorate, watch for discolouration of the aluminium. The lead will melt in about one minute at a height of six centimetres above the flame.

While the lead is molten remove any solid pieces with a short set of tongs or tweezers. Once cooled the remaining lead adhering to the other metals is easy to remove.

CAUTION: This part of the procedure must be done in a fumehood.

NOTE: Combustible material either inside or coating the sample may ignite. Remove combustible material if possible, noting the weights. In most cases the amount of combustible material is minimal and difficult to remove. Proceed with the heating and allow combustible material to burn out if it ignites before proceeding further with the heating.

    1. 7.4.2 Adhesives, bolts, paint, plastic coatings and other parts that may be part of the sample are considered part of the sample and must be estimated to obtain the true lead concentration.
  1. 7.5 Screening using ED-XRF
    1. 7.5.1 CAUTION: X-Rays can cause temporary or permanent damage to the eyes. Do not open or leave open the lid of the Quant-X instrument when the X-rays are being used. Do not disconnect or bypass the safety mechanisms incorporated in the instrument.
    2. 7.5.2 Analyze the sample using as per the procedure of analysis for ED-XRF.
    3. 7.5.3 For the materials applicable to this method as noted in the introduction ED-XRF is reliable for testing samples or subsamples for lead.
      1. 7.5.4 Use the results from this test to determine the next course of action as follows:
        1. Where no lead is indicated, no further testing is required;
        2. For trace counts, follow the digestion procedure in section 7.6 though use a 1:20 dilution after the digestion process if using 0.5 g sample; or,
        3. For substantial counts continue with the procedure as described in section 7.6.
    4. 7.6 Digestion Procedure
      1. 7.6.1 Weigh 0.05 to 0.5 g of sample into a Class A 50 mL digestion tube (see section 6.2.1) using an analytical balance (see section 6.1).
        1. For samples greater than 0.5 g, use pliers, cutters, knifes or razor blades to shave off subsamples from the bulk material, a number of smaller particles rather than one large artefact is better.
        2. Samples less than 0.05 g can be determined though dilutions must be adjusted to a minimum of 0.5 mg/L Pb for analysis by ICP-OES, if Pb is present.
      2. 7.6.2 Add 40 mL reagent water to each tube.
      3. 7.6.3 Add 10 mL nitric acid (see section 5.1) to each tube.
      4. 7.6.4 Place the tubes in the digestion unit (see section 6.2) that is preheated to 95 °C. Digest for one hour. Note: Pb samples will digest in this timeframe and temperature. Total digestion is not required. Lead-free, harder metals in blocks, or non-metal material may not digest.
      5. 7.6.5 Remove tubes from heater; allow to cool to room temperature; and fill to 50 mL with reagent water. Cap and shake well.
      6. 7.6.6 Dilute samples, by serial dilution if necessary, such that the lead concentration is equal to or less than 10 mg/L and greater than 0.05 mg/L. Assume the material is 100% lead which requires a 1:1000 dilution to obtain 10 mg/L with 0.5 g sample. Dilutions after digestion of more than 200 times must be made up in 0.2% HNO3.
      7. 7.6.7 Analyze the diluted samples by ICP-OES.
        1. The nitric acid concentration of the dilutions will determine the standards to use, for samples between 2% and 10% nitric acid use the 10% nitric acid standards. For nitric acid solutions less than 2% use 0.2% standard solutions.
      8. 7.6.8 If Pb is present, is less than the 0.1% threshold and not all of the metallic material of the sample dissolved before the ICP-OES analysis, then use microwave digestion to digest a separate sample/subsample with the following specifications:
        1. The laboratory using the microwave digestion process must complete the validation of the method using EPA method 3051a or an equivalent method.
        2. Use 5 mL HNO3 and 10 mL H2O.
        3. Use no more than 0.5 g sample, less if organic materials adhere to the sample.
        4. Depending on the microwave the ramp and hold times of the process may be different than that noted in EPA method 3051a.
        5. Freezing and sieving are not required.
        6. Use a solid Pb CRM or lab-designated RM for the accuracy QC.

8. Calculations and Reporting

  1. 8.1 Calculation of metal concentration in solid sample

Concentration Pb in sample (%) = (A (mg/L) ×0,05 L ×DilFac ×100)/(mass (g)×1000 mg/g)

where A = Pb concentration as determined by the ICP in mg/L.

  1. 8.2 Where a sample is composed of multiple components, each is analyzed and the following formula is used to determine the final lead concentration of the sample:

Concentration Pb in sample (%) = (∑_1^n▒〖(% 〖Pb〗_n ×〖 mass component〗_n (g))〗)/(mass total sample (g))

  1. 8.3 Report results in % lead, dry weight.

9. Quality Assurance / Quality Control

  1. 9.1 Analyze at least 10% of the samples as Laboratory duplicates, with a minimum of one duplicate per batch.
  2. 9.2 Prepare and analyze Laboratory Fortified Samples on a 10% basis, using 20 mL of a 10,000 mg/L Pb certified material. Alternately, adding an equivalent amount of a known solid material (preferably CRM, or lab-designated RM) can be used to fortify the sample. Recoveries must be within 90 – 110 % of the true value.
  3. 9.3 Analysis by ICP-OES:
    1. 9.3.1 An Instrument Performance Check and Instrument Performance Blank must be done after calibration and before any samples or QC’s, after every ten samples and at the end of a run.
    2. 9.3.2 A NIST traceable calibration reference sample must be done after calibration and before any samples.
  4. 9.4 Analyze a method blank with each batch and dilute the blank at least 50:1. Results for all blanks must be less than the MRL.

10. References

10.1 US EPA Method 3051a, Rev 1, Feb 2007, Microwave Assisted Acid Digestion Of Sediments, Sludges, Soils, And Oils

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