Late last week, non-profit environmental watchdog group As You Sow issued a press release indicating its intention to file suit against the makers of Soylent, the meal replacement product engineered by Silicon Valley entrepreneur Rob Rhinehart. As You Sow states that two separately tested samples of Soylent’s latest 1.5 formula contained "12 to 25 times" the amount of lead allowed under the "safe harbor for reproductive health" provisions of the state of California’s Safe Drinking Water and Toxic Enforcement Act of 1986 (commonly called "Proposition 65"). As You Sow also says it found cadmium levels at least four times higher than the safe harbor for reproductive health levels.

Soylent already displays a Proposition 65 notice on its web site—according to the information there, consuming a full day’s worth of Soylent 1.5 would indeed exceed both the Maximum Allowable Dose Levels (MADLs) and No Significant Risk Levels (NSRLs) for lead and cadmium.

California’s Proposition 65 guidelines for heavy metals are more strict than those used internationally by the World Health Organization. The MADL and NSRL numbers for lead and cadmium aren’t indicators of immediate harm; rather, they are limits below which no harm has been observed.

For example, the cadmium MADL is 4.1 μg per day and was computed by taking the lowest dosage level of cadmium that resulted in adverse reproductive effects in rats, dividing that level by 10, and then dividing that level by 1000. Going by Soylent’s numbers of (85.39μg of cadmium in a full four-serving bag of Soylent 1.5), that results in a number that exceeds the MADL but is still far below any level of observed effect. Similarly, the NSRL for lead is 15μg per day, and Soylent’s data shows 24.95μg in a four-serving bag.

The press release from As You Sow seems to indicate that the levels of lead and cadmium found were higher than Soylent’s published numbers, though it contains no specific measurements. Ars contacted As You Sow with questions and a request for comment, but the organization had not responded as of press time.

It is possible to say that, per the state of California’s Proposition 65 guidelines, Soylent requires extra labeling. The overriding question of "Is this dangerous?" is more difficult to answer. The levels here are for reproductive toxicity, which are much tighter than levels for poisoning or carcinogenic effects.

As You Sow has raised similar lead and cadmium allegations against other companies, most recently in February against a half-dozen chocolate makers including Ghirardelli, Godiva, Hershey, Lindt & Sprungli, Mondelez, and Earth Cicrle Organics.

Ars contacted Soylent for comment, and the company responded with this statement: