In March, two reporters for The Oregonian/OregonLive bought 10 extracts from three recreational marijuana stores in Portland. The following month, we bought an additional five extracts from three more stores.

Why extracts? Sold as oils or solids known as wax and shatter, extracts are susceptible to contamination because pesticides tend to concentrate during production. The manufacturing process involves extracting tetrahydrocannabinol, or THC, and other cannabinoids from the plant's leaves and flowers.

Extracts also are increasingly popular products often consumed with portable vaporizer pens. While dried marijuana flowers typically contain 10 to 25 percent THC, marijuana concentrates can have up to 80 percent THC, the psychoactive component that gives consumers a high.

Getting marijuana to market: The state requires that every batch of marijuana extracts and a third of flowers headed to recreational stores be tested for the presence of 59 pesticides and for potency. Producers and processors determine the size of a batch - typically 2 pounds for extract producers; larger batches mean more test samples.

The state, for example, requires a dozen test samples from a 2-pound batch of cannabis extract. A 10-pound batch translates into 20 test samples. All must come back clean before the whole batch can move into the market. One contaminated sample and the batch gets retested.

The state recently introduced a rule that allows processors to remove contaminants from tainted extracts as long as all marijuana used to make the extract passed pesticide testing. New rules also allow the state to consider removing contaminants from flowers tainted with two pesticides known to pose a low risk to human health. Generally, those compounds dissipate with time and exposure.

Once the batch passes, the product can move into the retail market. Extracts sell in individual half-gram or 1-gram packages, so a 2-pound batch would yield 900 to 1,800 packages.

Test results: The Oregonian/OregonLive requested - and received - the original lab reports for each extract from the shops. These detailed reports are provided to stores by growers and processors to show that their products have met the state testing requirements. Product labels list the lab and the test date.

Round one tests: We delivered 10 extracts in their original, unopened packaging to ChemHistory, a state-accredited marijuana lab in Milwaukie. ChemHistory technicians, wearing gloves, split the 1-gram products into two samples. They put about a half-gram of each extract into containers that we then delivered to Pacific Agricultural Laboratory in Sherwood.

Why Pacific Agricultural Laboratory and ChemHistory? We picked Pacific Agricultural Laboratory because it specializes in pesticide residue analysis in water, soil, and plant tissues, like fruits and vegetables. The company tests crops for producers, packers and exporters who often must demonstrate to grocery chains and foreign countries that their goods meet residual pesticide standards. The lab is not accredited to test cannabis but holds an internationally recognized accreditation to test for pesticide residue. ChemHistory is one of eight marijuana labs that is state-accredited to test for pesticides.

Results: Both labs independently found pesticides in three of the extracts at levels that exceed what the state allows. The remaining seven extracts met state pesticide standards, both labs found.

Round two tests: In April, we decided to see how the failed three extracts would fare in another round of tests so we found products marketed under the same brand names and strains with the same batch information as the initial purchase. We also bought two additional extracts from marijuana companies that were included in the first round. We bought the extracts at licensed marijuana stores in Portland and this time commissioned only Pacific Agricultural Laboratory to perform the tests.

Results: Pacific Agricultural Laboratory's analysis found four of the five extracts met state pesticide standards. The lab detected multiple pesticides on one of the extracts that failed the first round. The two other extracts that had failed in the first round were among those that passed this time.

Cost: We paid ChemHistory $1,500 to analyze the extracts in the first round. We paid a total of $2,120 for Pacific Agricultural Laboratory to test the extracts in both rounds.

Expert opinion: We consulted with Vincent Remcho, an Oregon State University chemistry professor. Remcho is an expert in analytical chemistry. We described to him how we bought the products, transported them in their original packaging to a lab and watched while the lab split each extract into two samples and then transported those portions to the second lab.

"What you have described to me is a pretty standard procedure when you want a sample to be analyzed by multiple laboratories," he said.

During the first round of testing, Pacific Agricultural Laboratory didn't test the extracts immediately; they waited until ChemHistory was finished with its work.

We asked Remcho to review Pacific Agricultural Laboratory's description of its storage methods for the products. He characterized their protocol as "a thorough description of standard, proper procedure."

-- Noelle Crombie

503-276-7184; @noellecrombie