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5. Cr(VI) in paint and coatings

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Cr(VI) compounds have been used in paint and coatings for decades due to their corrosion-inhibiting properties and use as pigments. Although these compounds have in many cases been replaced by alternatives, they remain present in existing paint layers and industrial applications. This brings health and environmental risks and requires careful management during maintenance and removal work.

Why is Cr(VI) used in paint and coatings? #

Cr(VI) compounds offer properties that remain difficult to replace in certain applications:

  • Corrosion protection: Cr(VI) prevents rust formation and extends the service life of metal structures. What makes Cr(VI) distinct is that it offers active protection, in contrast to passive barrier coatings. Cr(VI)-containing primers, such as strontium chromate, partially dissolve when corrosion damage occurs and form a protective layer that shields the underlying metal and prevents further corrosion. This process, known as cathodic protection, causes Cr(VI) to react with corrosion products and prevents further attack of the substrate. This maintains coating adhesion, which is particularly important with aluminium, where corrosion can otherwise rapidly lead to delamination of the paint layer.
  • Pigment function: Lead chromate and zinc chromate are used as yellow, red, and sometimes green colour pigments. When Cr(VI) compounds are used as pigments, the risks can be higher: concentrations are often considerably greater than in other Cr(VI)-containing applications, and the Cr(VI)-bearing paint layer is typically on the outside of the coating system, meaning direct exposure occurs when sanding or removing the coating. By contrast, some multi-layer paint systems contain Cr(VI) only in the primer, so sanding only the topcoat often results in no direct Cr(VI) exposure.
  • Adhesion: Strontium chromate improves the adhesion of coatings to metal surfaces, particularly in the aerospace and automotive industries. This is especially important with aluminium, which is susceptible to corrosion that can reduce coating adhesion. Strontium chromate prevents this corrosion and ensures durable adhesion of the paint or coating layer.

Where is Cr(VI)-containing paint used? #

Cr(VI)-containing paint and coatings are found in various sectors:

  • Infrastructure: Bridges, viaducts, and other steel structures.
  • Aerospace: Aircraft and helicopters, where strontium chromate is used as a primer.
  • Automotive: Rust-inhibiting primers on chassis and bodywork.
  • Shipbuilding: Protective coatings for marine applications.
  • Industrial installations: Storage tanks, pipelines, and other metal structures.
  • Residential construction: In 10–15 % of analyses, Cr(VI) is found to have been applied to wood as well.

How much Cr(VI) is present in existing coatings? #

SEEF analyses show that 42 % of existing coatings contain Cr(VI), with concentrations varying considerably:

  • Low concentrations: 10–100 ppm
  • Moderate concentrations: 100–1,000 ppm
  • High concentrations: 1,000–5,000 ppm
  • Very high concentrations: above 5,000 ppm

A Cr(VI) analysis is therefore necessary before any removal or treatment of coatings.

Risks during treatment and removal of Cr(VI)-containing paint #

During operations such as sanding, grinding, or blasting of Cr(VI)-containing coatings, large quantities of Cr(VI) particles can be released:

  • Inhalation: Cr(VI) dust particles can penetrate deep into the lungs and are carcinogenic.
  • Skin contact: Water-soluble Cr(VI) compounds can be absorbed through the skin. In paint, water-soluble Cr(VI) compounds are generally not used.
  • Environmental contamination: Paint fragments containing Cr(VI) can enter the soil or watercourses.

Safe handling of Cr(VI)-containing paint #

To minimise exposure and dispersion, several control measures are available:

  • Technical measures: Use extraction systems, containment, and wet working methods to limit dust generation.
  • Organisational measures: Clear work procedures and training of personnel.
  • Personal protection: Use respiratory protection (P3 filters), gloves, and protective clothing.
  • Monitoring: Conduct air measurements to assess exposure.

How to detect Cr(VI) in paint and coatings #

SEEF offers several analytical methods to reliably identify Cr(VI):

  • Rapid screening with swab tests and other test methods: We advise against using rapid tests or test kits for paint and coatings, as these represent a difficult matrix to measure reliably. It is difficult to fully extract Cr(VI) from the coating without releasing metals such as zinc or aluminium, which can donate electrons and reduce Cr(VI) to Cr(III), affecting the results. The acid concentrations in rapid tests are also often insufficient to dissolve chemically resistant coatings such as epoxy coatings or chlorinated rubber paint. Laboratory analysis is therefore the only reliable method to establish the actual Cr(VI) concentration.
  • Laboratory analysis: Other conventional analytical methods, such as NEN 5617, NIOSH 7600, and ISO 15192, also encounter problems with matrix interference and semi-quantitative results in Cr(VI) analyses of coatings and air samples. SEEF’s patented method is the only reliable way to establish the actual Cr(VI) concentration. Our method consistently achieves a recovery of 80 % of the Cr(VI) originally present, regardless of the degree of matrix interference.

Conclusion #

Cr(VI)-containing paint and coatings remain a significant risk during maintenance and remediation work. Because Cr(VI) is still present in a large proportion of existing coatings, detection and control are essential. SEEF offers reliable analytical methods and advice for working safely with Cr(VI)-containing coatings.

Want to know more? #

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