Apparently someone is trying to demonize sheet mulching in local #permaculture circles based on a study of chicken bedding which found that shredded cardboard had more than double the measured PFAS compared to wood chips.
unrelated use case aside (and ignoring the use of high PFAS cardboard rather than shipping boxes), by volume, with sheet mulching, you would do a layer of cardboard and 3" of wood chips to have the same effect as about 12" of woodchips alone.
So even if a layer of cardboard were 15 µg and 3" of chips were 6µg, you'd be looking at 21µg for sheetmulched vs. 24µg for chips.
But the figures are by weight. woodchips are 23.72 lbs per sq ft. cardboard is .026 lbs per sq ft.
