Which material in electronic devices poses an environmental hazard?

Mercury, commonly found in older LCD displays, fluorescent backlights, and some batteries, is a toxic heavy metal that poses significant environmental and health hazards if electronic waste is not disposed of properly. It can contaminate soil and water supplies, harming both humans and wildlife.

Option B: Plastic is generally not toxic in the same way, though it contributes to waste.

Option C: Aluminum is recyclable and not considered highly hazardous.

Option D: Gold is valuable and recyclable, not an environmental hazard.

Therefore, the hazardous material in electronic devices is mercury in displays.