David Hostler learned the troubling news when he journeyed more than 3,000 miles from his Hoopa Valley reservation, California's largest, to dig through troves of tribal artifacts on display and in storage at Harvard University.
Arriving at the Ivy League school's Peabody Museum of Archaeology and Ethnology, which owns the largest collection of American Indian remains outside the Smithsonian, officials suggested he don a pair of gloves and a dust mask before sifting through the collection.
''That's when I found out some of the artifacts had been contaminated,'' said Hostler, a director of the Hoopa museum and a ceremonial leader of the tribe, which has 4,000 members and an 89,000-acre reservation about 40 miles outside the northern California coastal city of Eureka.
Two years later, Hostler and fellow Indians across the United States remain unsettled by the notion that human remains and sacred objects being returned to them under the Native American Graves Protection and Repatriation Act, or NAGPRA, may be poisoned with heavy metals and pesticides that were used as preservatives.
On Friday, representatives of California's 110 tribes began arriving at San Francisco State University for a three-day workshop aimed at raising awareness of the potential health risks that scientists consider especially acute because many of the artifacts - steeped in spiritual significance - have been or will be returned to their traditional use.
''For people who are only hearing about this for the first time, it's only human to be scared and angry,'' said Lee Davis, an anthropology professor at SFSU and consultant for the Hoopa tribe.
Pesticides and other toxins, including mercury and arsenic, have been routinely used on all kinds of artifacts to preserve them and keep insects away, with the idea that the objects would only be displayed under glass.
But that changed when the repatriation act, passed in 1990, required museums to return headdresses and other regalia to their rightful tribal owners.
It is unclear how widespread the contamination may be, since most of the evidence is anecdotal and no official empirical studies have been conducted to determine whether mercury, arsenic, DDT and other toxins used as pesticides or preservatives persist in harmful levels.
SFSU on Friday released preliminary findings of a study showing traces of mercury in a handful of items that have found their way back to the Hoopa tribe. There were also low levels of pesticides on some samples, including DDT and naphthalene, an active ingredient in mothballs.
But Peter Palmer, a chemical analyst who led the study, questioned whether the results were reliable, saying he was ''not sure how they would hold up in a court of law.''
He and other researchers noted how they are impeded by financial constraints and limited in the types of testing they can do since a lot of the cultural material must remain intact, and removing toxins could be destructive.
''There are no easy answers - a lot of uncertainties,'' Palmer told a large group of other scientists, Indian leaders and observers during one of Friday's sessions, calling the study a ''best effort'' by students. ''At least we've done this much.''
Palmer and other scientists agree more in-depth studies are needed. On Sunday, organizers plan to start drawing up a cohesive plan to address the issues raised at the workshop.
''The ramifications are complex,'' said Jeff Fentress, coordinator of SFSU's artifact testing lab. ''Where did all these contaminants come from? What other contaminants are there? What exposure have we all had all these years? And last, what do we do about it?''
For the tribes, the waiting could mean sacrificing tradition.
''Repatriation is important for preserving our culture and educating our youth, and carrying on our religion as it always was,'' Hostler said. ''At this time, hopefully we'll find solutions on how to get the poisons out.''