BOULDER, Colo. (AP) — A Boulder, Colo., laboratory says new tests show that more people were exposed to plutonium than originally thought after a June spill there.

No one who was exposed is expected to have significant health effects.

The National Institute of Standards and Technology said Thursday that about half the 29 people who have been tested showed signs of exposure. The specific number wasn't released.

NIST has not said how many people tested positive originally. The lab says results for six more employees are expected in about a month.

A vial cracked June 9, spilling about one-fourth of a gram of powder containing plutonium.

The lab promised to tighten procedures after an internal review found a "casual and informal research environment."