Chemical field tests—those inexpensive test kits used to detect illegal drugs—have become a staple in the fight against drug crimes. These tests work when officers drop an unknown substance into a pouch of chemicals, and the telltale color changes identifies the presence of any controlled substance.
These tests are oft-used when making roadside DWI and drug arrests, and, over the years, said tests have been considered to be legitimate tools to ascertain the presence of illicit drugs and to warrant an arrest. However, there is ample evidence that these tests are highly unreliable and vulnerable to error, especially when legal substances produce the same color changes as do illicit substances.
A brief history of chemical field tests
In 1973, Drug Enforcement Agency (DEA) chemist L. J. Scott, Jr. was working on creating a chemical mixture that could identify the presence of cocaine since, at that time, cocaine trafficking, sales, and usage was exploding. Of course, price was a consideration.
Initially, Scott discovered a pink liquid known as cobalt thiocynate that turns blue when it comes in contact with cocaine. However, it also turns blue when it comes in contact with other, perfectly legal, substances. In fact, there are over 80 different compounds that could yield a false-positive—including methadone.
After further experimentation, Scott’s final test was three-fold: cobalt thiocyanate to turn the liquid blue, hydrochloric acid to turn the solution pink again, and chloroform which causes separation of the solution into a pink (top) layer and a blue (bottom) one in the presence of cocaine. Scott ultimately declared that his test was highly sensitive and specific and nearly impossible to misinterpret. Thus, police departments responded in droves, purchasing thousands of them.
In 1974, a National Bureau of Standards study cautioned using these tests as sole evidence for identifying a drug. Then, in 1978, the US Department of Justice (DOJ) determined that field tests should not be used for evidentiary purposes, thus resulting in the inadmissibility of these tests at trial in nearly every jurisdiction. The DOJ urged prosecutors to present a confirmatory test using more reliable methods.
In 1975, Duquesne University-Pittsburgh toxicologists documented several false-positives in these tests and also highlighted the possibility of officers sustaining injuries when opening the acid-filled vials.
Police arrest 1.2 million people each year on drug possession charges based on these $2 tests which have remained largely unchanged since the 1970s and which have been proven to be unreliable. Nevertheless, many jurisdictions across the country. continue to use these field tests to secure guilty pleas. For example, in 2015, the Las Vegas Metropolitan Police Department made 5,000 drug arrests and secured 4,600 convictions based on field test results.
Additionally, according to a 2016 ProPublica investigation, these test kits were central to dozens of wrongful convictions in Houston by either officers misrepresenting the tests’ results or by the tests’ false-positive results. Since 2014, the Harris County District Attorney’s Office has been working hard to rectify the wrongful convictions and no longer accepts guilty pleas for drug possession unless a crime lab verifies the results of a field test. The state of Texas also created a commission in 2015 to research wrongful convictions based on faulty drug tests and to prevent future occurrences.
The demand for these tests continues to be strong, and at least nine different companies manufacture and sell them. In 2000, the DOJ issued guidelines requiring these test kits to contain warning labels including statements recommending comprehensive training as well as a disclaimer that the reagents can provide both false-positive and false-negative results. However, several companies fail to present these warnings on their labels.
With the growing recognition of the fallibility of these tests, many departments now require that any positive findings are confirmed by a crime lab, and the results of field tests alone are prohibited from being the sole evidence in a trial in many states.