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Characterization of Inorganic Additives in and Photochemically Liberated from Consumer Plastics: Implications for Global and Local Biogeochemical Cycles
Summary
X-ray fluorescence and mass spectrometry analysis of up to 80 consumer plastic items found they contain approximately 8% inorganic additives by mass, with calcium, titanium, and aluminum most abundant. Sunlight exposure readily released most elements from plastics, and mass balance calculations suggest plastic pollution could contribute 13% of global natural riverine antimony flux and 4% for zinc by 2060.
The composition and environmental impacts of inorganic additives in consumer plastics have received little attention within the plastic pollution discipline relative to organic additives. In this work, X-ray florescence spectroscopy, loss-on-ignition, and inductively coupled plasma mass spectrometry were used to qualitatively and quantitatively characterize inorganic additives from up to 80 consumer plastic items. On average, consumer plastic goods contained ∼8% inorganic additives by mass. Concentrations of each element often varied by orders of magnitude. The most common elements detected were from the alkali metal, alkaline earth metal, and first-row transition metal groups, with Ca, Ti, and Al being most abundant. The diversity and abundance of inorganic additives was notably higher in consumer-grade plastics than in standard plastics routinely used to assess the fate and impacts of plastic pollution. Sunlight exposure readily liberated most elements from consumer plastics, typically in the <10 and <1 μm fractions. However, the relative percent of photochemical liberation varied considerably across element and plastic articles, suggesting that formulation is a key control of their liberation from consumer plastics. Compared to average upper continental crust concentrations, Sb and Zn were most enriched, with median enrichment factors of 2 and 1 orders of magnitude, respectfully. Mass balance calculations indicate that plastic pollution may represent a substantial proportion of natural riverine elemental fluxes, particularly for Sb and Zn, which could reach ∼13% and ∼4% of the global natural riverine fluxes by 2060, respectively. Localized impacts in many small, highly polluted rivers could be even larger. However, such impacts are highly dependent on the riverine plastic loading rate to the ocean. Overall, these findings highlight the need for increased consideration of inorganic additives when assessing the fate and impacts of consumer plastics leaking into the environment.