The five-day biochemical oxygen demand, being the consumed by micro-organisms during oxidation of the water over a period of five days, expressed in units of oxygen consumed per milligrams of the substance
Ministry of Business, Innovation and Employment, Glossary of terms and acronyms, Wellington, New Zealand 2010. http://wwwsosh.govt.nz/resources/glossary-u.shtml, (Occupn Hlth and Sfty - Brit) {530}