(a) Grounds. The Administrator may revoke or modify the terms or conditions of a specific, quarantine, or public health exemption if he determines one of the following:

(1) An emergency no longer exists;

(2) Use of the pesticide under the exemption may cause unreasonable adverse effects on the environment;

(3) The pesticide authorized under the exemption is not effective at controlling the pest or conditions causing the emergency; or

(4) The terms and conditions established by the exemption and these regulations are not being complied with.

(b) Implementation. The revocation or modification becomes effective as soon as the Administrator notifies the State or Federal agency which submitted the application. Upon notification, the applicant is required immediately to take all necessary steps to assure that further use complies with the terms and conditions of any modification or, if the exemption has been revoked, to stop further use.