Study provides safe consumption levels for wapato

By Nicole Montesano

Smoke Signals staff writer

A three-year study of wapato harvested at Wapato Lake and at two locations on the Tualatin River has revealed that the tuber doesn’t appear to store concerning amounts of pesticides but does contain copper at some sites. Researchers have also now calculated safe daily consumption rates over a lifetime, working with the Oregon Health Authority.

They announced their findings Tuesday, Sept. 22, at the Tribe’s Ancestral Homelands: Land Stewardship, Land Tending & Cultural Gathering held at Chachalu Tribal Museum & Cultural Center gym. The evening included a meal of chili and salad, information tables about cultural gathering and Tribal stewardship, and a presentation by the U.S. Fish & Wildlife Service on the testing results from the Tualatin and Ridgefield national wildlife refuges.

Tribal Cultural Policy Analyst Greg Archuleta worked on the study and gave a brief overview of the stewardship work the Tribe is doing with various local government partners around the state, including the Metro regional government office, to cultivate and preserve First Foods.

The U.S. Fish & Wildlife Service, Archuleta said, “is one of our biggest partners,” and oversees the area of Wapato Lake, once the home of a large Kalapuyan village. For eons, Wapato Lake, filled by the Tualatin River, was a prime source for the nutritious tubers. But after settlement, farmers pumped the water out every summer for irrigation and planted onions and potatoes in the rich soil of the area. Not until 2024 was the lake allowed to remain filled.

“We’ve been transplanting wapato there,” Archuleta said, noting that there were also remnant populations still hanging on. “Over two years, we planted over 20,000 tubers there.

However, given the herbicides and other substances used on farmland, “The big question is, are they safe for consumption?” he said.

Three years ago, the Tribe partnered with Dr. Robin Van Meter, an environmental contaminants specialist and Jeremy Buck, both of the US Fish and Wildlife Service, to design a study to answer those questions. Each year, Fish & Wildlife staff and dozens of Tribal volunteers waded into the muck to locate and harvest the tubers for laboratory examination and to take soil samples. The samples were tested for heavy metals, glyphosate, certain types of herbicides, DDT and other legacy pesticides, meaning those that persist in the environment for years and sometimes decades.

The work was sometimes arduous.

“At some sites, there was so much ground cover that it required a lot of labor just to clear down to the soil, so we’d go out there with rakes and other tools,” Van Meter said. “Once I literally got sucked in up to my hips and it took several people to pull me out.”

DDT, an insecticide that was banned in 1972, and several other insecticides were detected in the soil, particularly in Wapato Lake, but the study determined that wapato does not appear to take up and store pesticides. The tubers at some sites, however, did contain copper and zinc, although not at high levels. With that information in hand, Van Meter said, she reached out to the Oregon Health Authority to help her calculate safe consumption rates.

The rates change slightly for each sampled site, depending on the amounts of copper and zinc found, however, the daily serving limits are generous, at least for those not depending on wapato as a winter staple.

Van Meter said that an adult woman, according to the guidelines drawn up, could consume nearly a pound to a pound and a half a day, depending on her size – from Wapato Lake, for life, without incurring issues, they said. For an adult man, the amount would be slightly more than a pound to slightly more than a pound and a half. A pound is 16 ounces.

For the Oleson Area of the Tualatin River, the amount is slightly lower; 10 to 17.98 ounces daily for women. The limits for adult men at the Oleson Area are 12 to 20 ounces daily. 

At Chicken Creek, the limits are 19 ounces to two pounds for women, and 24 ounces to 2.44 pounds for men.

For children ages 9 to 13, the limits are roughly 9 to 14 ounces at Wapato Lake; 6.7 to 10.5 ounces at the Oleson Area, and 12.6 to 20 ounces for wapato from Chicken Creek.

To obtain the full list, email Archuleta at greg.archuleta@grandronde.org.