Perchlorate?

Doesn't sound all that inviting for life on Mars - perchlorates are used in fireworks and related purposes (which may be why they are also worried about inadvertent contamination, maybe from rockets):

Within the last month, two samples have been analyzed by the Wet Chemistry Lab of the spacecraft's Microscopy, Electrochemistry, and Conductivity Analyzer, or MECA, suggesting one of the soil constituents may be perchlorate, a highly oxidizing substance. The Phoenix team has been waiting for complementary results from the Thermal and Evolved-Gas Analyzer, or TEGA, which also is capable of detecting perchlorate. TEGA is a series of ovens and analyzers that "sniff" vapors released from substances in a sample.