The discovery that scores of students had been exposed to mercury during their morning bus ride prompted lockdowns at a high school and two primary schools in Pacific Beach and Bay Park today, authorities reported.

Staff members at Mission Bay High School learned in the late morning that one of their students had brought a 35 mm film canister containing a small amount of the silvery element to school and had been showing it to his classmates, according to the San Diego Fire-Rescue Department.

"Some kids were scared and called their parents," said one witness.

"It was really bad, I had to hold my pee for an hour and a half and I was crying because they wouldn't let me go out," said Yajaira Ramirez, an 11th grader.

There were no reports that anyone had suffered any ill effects from exposure to the substance, SDFRD spokesman Maurice Luque said.

Administrators directed teachers to keep all students in their classrooms to prevent the spread of any contamination. About an hour later, similar directives were issued at nearby Toler and Bay Park elementary schools, some of whose students had come to school aboard the same bus as the teen carrying the mercury.

Hazardous-materials personnel screened about 150 students and staffers for contamination, finding high levels of the metal on the clothing of several, including the bus driver, said Linda Zintz, a spokeswoman for San Diego Unified School District. Those youngsters and employees underwent decontamination procedures, she said.

"No one has shown any (illness) symptoms at this point,'' Zintz said in the late afternoon.

The boy who brought the mercury to school apparently did so with no malicious intent but Mission Bay High School's principal say there will be consequences.

"Obviously it was a huge distraction and disruption to the learning environment," said Fred Hilgers, Principal. "We have to hold him accountable so he knows that what he did was serious but I believe after talking to him, he understands, he was pretty upset about the whole experience."