Abstract
The presence of microplastic (MP) particles in aquatic environments raised concern about possible enrichment of organic and inorganic pollutants due to their specific surface and chemical properties. In particular the role of metals within this context is still poorly understood. Therefore, the aim of this work was to develop a fully validated acid digestion protocol for metal analysis in different polymers, which is a prerequisite to study such interactions. The proposed digestion protocol was validated using six different certified reference materials in the microplastic size range consisting of polyethylene, polypropylene, acrylonitrile butadiene styrene and polyvinyl chloride. As ICP-MS/MS enabled time-efficient, sensitive and robust analysis of 56 metals in one measurement, the method was suitable to provide mass fractions for a multitude of other elements beside the certified ones (As, Cd, Cr, Hg, Pb, Sb, Sn and Zn). Three different microwaves, different acid mixtures as well as different temperatures in combination with different hold times were tested for optimization purposes. With the exception of Cr in acrylonitrile butadiene styrene, recovery rates obtained using the optimized protocol for all six certified reference materials fell within a range from 95.9% ± 2.7% to 112% ± 7%. Subsequent optimization further enhanced both precision and recoveries ranging from 103% ± 5% to 107 ± 4% (U; k = 2 (n = 3)) for all certified metals (incl. Cr) in acrylonitrile butadiene styrene. The results clearly show the analytical challenges that come along with metal analysis in chemically resistant plastics. Addressing specific analysis tools for different sorption scenarios and processes as well as the underlying kinetics was beyond this study's scope. However, the future application of the two recommended thoroughly validated total acid digestion protocols as a first step in the direction of harmonization of metal analysis in/on MP will enhance the significance and comparability of the generated data. It will contribute to a better understanding of the role of MP as vector for trace metals in the environment.
Highlights
Anthropogenic litter, especially highly persistent plastic litter, has become a global problem [1,2,3]
This study presents the development of a new, validated microwave-assisted acid digestion (MWAD) approach for metal analysis in the most important polymeric matrices on the market using five certified reference material (CRM) from different international and national metrology and research institutes, and one certified quality control standard from a chemical
The aim of this study is to provide a thoroughly validated polymer-specific MWAD protocol for metal analysis in MP for a better understanding of the interactions between MP sampled in different environments and metal contaminants
Summary
Anthropogenic litter, especially highly persistent plastic litter, has become a global problem [1,2,3]. Numerous studies have examined in particular the sorption of hydrophobic organic chemicals, such as polycyclic aromatic hydrocarbons, dioxins, phthalates and polychlorinated biphenyls to MP [8,9,10,11] and their further transfer to organisms via MP [12,13,14,15]. The toxicity of heavy metals such as As, Cd, Cr, Hg, Pb, Sb, Sn present in the marine environment is well studied and documented [16,17,18]. In contrast to the MP-mediated transport of organic contaminants, the analogous transport of metals and the related adsorption and desorption processes remain poorly understood.
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