Abstract: A method and apparatus for rapidly detecting toxicants via the use of a ft CO.sub.2 sensing cell and a second reference CO.sub.2 sensing cell, with each sensing cell including a first chamber and a second chamber, separated by a CO.sub.2 permeable membrane, and a pH sensor disposed in each of the second chambers. The method includes the step of placing distilled water in the first chamber of each cell, and allowing its dissolved CO.sub.2 to become equilibrated with the water in the second chamber, from which it is separated by the CO.sub.2 permeable membrane. Next, exact amounts of a microorganism and sugar are added to small dishes in the first chambers along with control vegetation for one dish and vegetation to be tested to the other dish. Then the first chambers are completely filled with distilled water and the dishes are agitated to facilitate a solution of microorganisms and sugar.