Environmental', 'Pyrithiobac is a post-emergence herbicide to control broad-leaved weeds in cotton an other crops. It has a high aqueous solubility, is semi-volatile and, based on its chemical properties, it is very mobile and has high potential to leach to groundwater. As of Reg. (EC) No 1107/2009 pyrithiobac sodium is not approved for use as plant protection product in the European Union (EU). A default maximum residue levels (MRL) of 0.01 mg/kg has been set according to Art 18(1)(b) Reg 396/2005. The certified reference material (CRM) is intended to be used as a calibrant for chromatography and other analytical techniques.