Some materials provide a better alternative in an application dominated by products for which there are concerns about toxic constituents, intermediaries, or by-products. For example, form-release agents are a good alternative to products that contaminate water or soil. With the panoply of products made with polyvinyl chloride (PVC) and brominated flame retardants, some products are green simply because they provide an alternative. Examples of this are natural wall coverings, drain and vent piping, and roofing membranes. Some green products are free of hazards common to the product category; for example, LED lighting is inherently free of the mercury found in fluorescent lighting sources.