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Marine pollution from pyroplastics
Summary
Scientists discovered a new type of ocean plastic pollution called "pyroplastic", chunks of melted, burned plastic that wash up on beaches looking like ordinary rocks or pebbles. This disguise is concerning because these fragments can contain lead (sometimes at high levels) that may leach into sea life living on their surfaces, and because their rock-like appearance means they're likely being overlooked in beach cleanups and pollution surveys, meaning the true amount of plastic waste in our oceans is probably higher than we think.
Items of marine plastic litter are conventionally classified as primary or secondary, depending on whether they are distinct objects or angular fragments, respectively. "Pyroplastic" is an additional type of plastic litter that is described here, based on observations made on beached samples from south west England. Pyroplastics are derived from the informal or more organised burning of manufactured plastics and may be angular "plastiglomerates", comprising pieces of plastic debris within a matrix, or rounded plastic "pebbles", where agglomerated material has been weathered and smoothed into more brittle and neutrally-coloured geogenic-looking clasts. Beached pyroplastics are usually positively buoyant because of a polyethylene or polypropylene matrix, and exhibit a bimodal mass distribution attributed to the breakage of larger clasts (>20 mm) into smaller fragments (<5 mm). XRF analysis reveals variable quantities of Pb in the matrix (up to 7500 μg g-1), often in the presence of Cr, implying that material in many samples pre-dates restrictions on the use of lead chromate. Low concentrations of Br and Sb relative to pieces of manufactured plastics in the marine environment suggest that pyroplastics are not directly or indirectly derived from electronic plastic. Calcareous worm tubes on the surfaces of pyroplastics dense enough to be temporarily submerged in the circalittoral zone are enriched in Pb, suggesting that constituents within the matrix are partly bioavailable. Evading ready detection due to their striking visual similarity to geogenic material, pyroplastics may contribute to an underestimation of the stock of beached plastics in many cases.