In ancient times as well as sometimes today, fishing sinkers consisted of materials found ordinarily in the natural environment, such as stones, rocks, or bone. Later, lead became the material of choice for sinkers due to its low cost, ease of production and casting, chemical inertness (resistance to corrosion), and density. However, lead is known to cause lead poisoning and enter the environment as a result of the inevitable occasional loss of fishing sinkers during routine fishing. Thus, most lead-based fishing sinkers have been outlawed in the United Kingdom (under 1 oz weight), Canada, and some states in the United States. Lead based fishing sinkers are banned in all of US and Canadian National Parks. These bans have motivated the use of various other materials in sinkers.