Our Sewage Often Becomes Fertilizer. Problem Is, It’s Tainted With PFAS

The Deer Island Wastewater Treatment Plant is a pollution success story. Over the last several decades, it transformed Boston Harbor from a nationally embarrassing cesspool into a swimmable bay.

The treatment plant takes everything the people of Greater Boston send down their sinks, toilets, showers and washing machines — plus industrial waste — and treats it. The treated water is clean enough to let out into the ocean. The remaining sludge gets recycled into fertilizer that’s used in nearly 20 states.

But now that fertilizer is raising fresh concerns. That’s because wastewater treatment plants like Deer Island were not built to handle the toxic “forever chemicals” known as PFAS.

The treatment process concentrates PFAS chemicals in the sludge, and therefore in the fertilizer, leading environmentalists and public health advocates to call for an immediate end to its use. Others are not sure that a full ban on sludge-based fertilizer, or “biosolids,” is the answer. But there is widespread agreement that we have only begun to grasp the extent of the problem.

“I think we’re only starting to discover how important biosolids are as a source of PFAS contamination,” said Heidi Pickard, a Harvard doctoral student who is analyzing soil and corn from farms contaminated by sludge-based fertilizer.