Characterization of Inorganic Additives in and Photochemically Liberated from Consumer Plastics: Implications for Global and Local Biogeochemical Cycles

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.