So what is sludge, really? A stinking, sticky, dark-grey to black paste, it’s everything homeowners, hospitals and industries put down their toilets and drains. Every material-turned-waste that our society produces (including prescription drugs and the sweepings of slaughterhouses), and that wastewater treatment plants are capable of removing from sewage, becomes sludge. The end product is a concentrated mass of heavy metals and carcinogenic, teratogenic, and hormone-disrupting chemicals, replete with antibiotic-resistant bacteria. There are some 80,000 to 90,000 industrial chemicals, including a host of dioxin-like deadly substances, which are allowed to be present in sludge under current EPA rules. What’s worse, there’s no way of knowing which toxic chemicals and heavy metals are entering the wastewater stream at any given time or in what concentrations. Sludge is always an unknown quantity, and therefore, assessing whether sludge is safe to use for growing food, is — in practice — impossible.

Farmers who care about what they grow know this, and — despite the best efforts of government and the sludge industry — growing food in sewage sludge is prohibited under the federal organic regulations. Still, sludge is still widely used as a cheap alternative to fertilizer, and unless you’re buying organic produce, it’s impossible to know if the food you eat was grown in it.