Because of its durability and resistance to decay, insects, mold, and water damage, pressure-treated wood is commonly used in the construction industry for things like fence posts, decking, pilings, docks, and railroad ties. However, what makes it withstand the elements can also make it toxic to humans and the environment. Harmful chemicals such as arsenic and copper are infused into the wood, and can contaminate soil, surface water, and groundwater when handled or disposed of improperly. These chemicals can also produce toxic gases after reacting with other materials in landfills.