FALLON, Nev. (AP) - A small mercury spill caused a scare at a northern Nevada high school where more than 600 people temporarily were locked down Tuesday but initial tests showed there was little contamination and no immediate health hazard, state environmental officials said.An estimated 500 students, 71 teachers and 25 others who had been held for several hours at Churchill County High School in Fallon were released about 7 p.m., said Dante Pistone, a spokesman for the Nevada Division of Environmental Protection."There is no danger at this point," he told The Associated Press. "The initial sweep indicated that the …