ppm

The residents wanted to grow food, he said, but the soil had lead levels around 112 ppm, well over the state limit.

But other burned homes in the same communities had lead levels far lower, between 23 and 40 ppm.

Acceptable lead levels vary by state and the federal limit recently decreased from 400 ppm to 200 ppm because of increasing evidence that lead in any amount is harmful to humans.

High zinc levels aren’t considered toxic to humans until they reach about 23,000 ppm, Wallace said.

When they tested their soil again in June 2024, they were thrilled to see the lead levels had dropped to 37 ppm, Davis said, making them feel safe enough to add soil and compost to deep raised beds on the property to grow food.