Chromium exists in nature in various valence states, with trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)) being the most common. Hexavalent chromium is the toxic form of chromium, typically formed during industrial processes (such as electroplating, welding, chromate treatment) rather than occurring naturally.

Toxicity of Hexavalent Chromium:

•Highly Toxic and Carcinogenic: Cr(VI) is a confirmed human carcinogen; inhalation can lead to lung cancer.

•Sensitizing: Skin contact can cause allergic contact dermatitis and ulcers.

•Environmental Hazard: Cr(VI) compounds are not easily degradable, can persist and accumulate in the environment and living organisms, posing long-term risks to aquatic and terrestrial ecosystems.

Regulatory Limit under the EU RoHS Directive:The maximum allowable concentration limit for hexavalent chromium is 0.1% (1000 ppm) by weight in any homogeneous material. The purpose of restricting Cr(VI) is to protect workers on production lines, personnel handling electronic waste recycling, and to reduce environmental pollution from e-waste.

Historical Applications and High-Risk Materials in E&E Products:Due to its excellent anti-corrosion and wear-resistant properties, Cr(VI) was widely used in electrical and electronic products. High-risk materials include:

1.Metal Coatings/Platings: This was the most common application. To enhance corrosion resistance, many metal components (e.g., screws, brackets, casings, connectors) underwent "chromium plating" or "zinc chromate conversion coating." Traditional chromate conversion coatings (e.g., yellow, iridescent, or black passivation layers on galvanized steel) contained hexavalent chromium.

•Alternatives: Trivalent chromate conversion coatings or more environmentally friendly chromium-free passivation (e.g., zirconium-based, titanium-based, silicon-based passivation) are now commonly used to replace Cr(VI) passivation. Trivalent chromium is far less toxic than hexavalent chromium and is currently considered a safe alternative.

2.Pigments and Dyes: Some older plastics or paints might have used pigments containing Cr(VI) (e.g., chrome yellow, chrome orange) as colorants.

3.Anti-Corrosion Coatings: In some older electronic equipment, primers or coatings containing Cr(VI) might have been used for rust prevention.

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