Environment Minister Gabrielle Upton has refused to explain her claim that NSW cannot ban the use of toxic firefighting chemicals, despite it appearing to contradict the advice of the federal government and two other states that have already put bans in force.

In Parliament, Ms Upton was grilled by Labor over why NSW had failed to ban the use of per- and poly-fluoroalkyl chemicals [PFAS], which have contaminated at least 90 communities across the country as a result of their use in fire retardants for decades.

Environment Minister Gabrielle Upton says NSW can't ban PFAS chemicals.

"The member for Port Stephens knows that this government cannot ban PFAS," she responded.

"The responsibility for that lies directly at the feet of the federal government and the things it has done."