The Marijuana Arrest Research Project released a report Thursday detailing the arrest figures, based on data from the FBI. It comes as voters consider Initiative 502, which would legalize and tax pot sales at state-sanctioned stores for those over 21 under state law.
One of the study's authors is Harry Levine, a sociologist at Queens College in New York. He said it was impossible to figure out how many of the 240,000 might also have been arrested for other charges, such as assault, because of the way Washington state data are reported to the FBI.
But based on other studies of states that do separate such data, the researchers believe the overwhelming majority of the arrests were for simple misdemeanor possession alone.
"The scale of the marijuana arrest operation in the U.S. is really substantial," Levine said.
Those arrested are "overwhelmingly young people," he added. "And the most serious complication of these arrests is not the night in jail but the criminal record that results," which can create problems ranging from renting an apartment to landing a job.
The report said 79 percent of those arrested were 34 or younger, and most of those arrested were white, although minorities were arrested at a higher rate than whites based on their population. From 2001 to 2010, blacks, Latinos and Native Americans made up one-quarter of the arrests but just 14 percent of the population.
The study is at least the second recent look at marijuana arrests here. In August, a report by the state chapter of the American Civil Liberties Union estimated that enforcing marijuana laws cost Washington more than $211 million over the past decade. That estimate was based on data from the Washington Association of Sheriffs and Police Chiefs, court filings and other sources, and included costs from arrests, prosecution, public defense, jail and supervision.
The Marijuana Arrest Research Project is a New York-based, grant-funded group that researches pot arrest data for the Drug Policy Alliance, the American Civil Liberties Union and other organizations that advocate drug policy reform. It has performed similar studies in California and New York.
The study found the number of pot possession arrests has risen dramatically, from 4,000 in 1986 to 11,000 in 2010, the last year covered by the report. Echoing the findings of the ACLU of Washington, it estimated the arrests cost the state $200 million to $300 million over the past decade.
The most arrests were in the most populous county, King, which had 65,483. Pierce had 25,087; Spokane 22,716; Snohomish, 18,307; and Benton, 10,009.
Whitman County, home of Washington State University, had 474 arrests per 100,000 residents from 2001 to 2010, and Kittitas had 492. By contrast, King had 204.
The societal costs of prohibition, and the effects on those arrested, are two of the main reasons cited by proponents of Initiative 502, including three former federal law enforcement officials who participated in a television ad campaign that began Thursday.
But some others in law enforcement argue I-502 would increase marijuana access for teens, who are considered more susceptible to addiction.
If I-502 passes, marijuana would remain illegal under federal law.