Six Hazardous Substances Restricted by the EU RoHS Directive

The European Union’s Restriction of Hazardous Substances (RoHS) directive strictly limits the use of specific toxic materials in commercial electrical and electronic equipment to protect human health and the environment. Adopted in 2003, the original legislation targeted six primary hazardous materials commonly used in manufacturing. These six restricted substances are lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB), and polybrominated diphenyl ethers (PBDE). This article provides a direct breakdown of each of these six substances, their uses in electronics, and the maximum concentration levels allowed under EU law.

1. Lead (Pb)

Lead was widely used in electronics for soldering printed circuit boards, inside glass for cathode-ray tubes, and in battery production. Because lead is a cumulative neurotoxin that causes severe damage to the brain, nervous system, and kidneys, the RoHS directive limits its maximum concentration to 0.1% (1,000 parts per million) by weight of homogeneous material. Manufacturers now primarily use lead-free solders made of tin, silver, and copper.

2. Mercury (Hg)

Mercury was commonly utilized in thermostats, sensors, relays, switches, and fluorescent lamps used for backlighting displays. Mercury exposure is highly dangerous, leading to severe neurological and behavioral disorders. Under the RoHS directive, mercury is restricted to a maximum concentration of 0.1% (1,000 ppm) by weight.

3. Cadmium (Cd)

Cadmium was frequently used in rechargeable nickel-cadmium (NiCd) batteries, electroplating to prevent corrosion, switches, and pigment stabilizers for plastics. It is a known human carcinogen that causes extreme damage to the lungs and kidneys. Because of its exceptionally high toxicity, cadmium has the strictest limit of the original six substances, capped at a maximum concentration of 0.01% (100 ppm) by weight.

4. Hexavalent Chromium (Cr VI)

Hexavalent chromium was used in the electronics industry primarily for corrosion protection in metal coatings, such as zinc-plated screws and chassis parts. It is highly toxic, carcinogenic, and causes severe skin, eye, and respiratory irritation. RoHS restricts hexavalent chromium to a maximum concentration of 0.1% (1,000 ppm) by weight. Trivalent chromium is now used as a safer alternative for metal finishing.

5. Polybrominated Biphenyls (PBB)

Polybrominated biphenyls are a class of brominated flame retardants that were added to plastics used in computer monitors, television casings, and circuit boards to reduce flammability. PBBs are persistent organic pollutants that accumulate in the food chain and disrupt the endocrine system. The RoHS directive limits PBBs to a maximum concentration of 0.1% (1,000 ppm) by weight.

6. Polybrominated Diphenyl Ethers (PBDE)

Like PBBs, polybrominated diphenyl ethers are brominated flame retardants used in plastic enclosures, cables, and printed wiring boards. PBDEs easily leach out of plastics into the environment, where they bioaccumulate and cause neurodevelopmental and thyroid toxicity in humans. RoHS restricts the use of PBDEs in commercial electronics to a maximum concentration of 0.1% (1,000 ppm) by weight.

Compliance and Homogeneous Materials

The percentage limits set by the RoHS directive do not apply to the total weight of the finished electronic product. Instead, they apply to each "homogeneous material" within the device—meaning any single substance that cannot be mechanically disjointed into different materials, such as the plastic coating on a wire or the ceramic body of a capacitor. While the directive has since been updated (such as RoHS 3) to include four additional phthalates, these original six substances remain the foundation of global electronics compliance.