No abstract

The interaction of ozone and water vapor with spark discharge soot particles coated with the five-ring polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) has been investigated in aerosol flow tube experiments at ambient temperature and pressure (296 K, 1 atm). The investigated range of ozone volume mixing ratio (VMR) and relative humidity (RH) was 0-1 ppm and 0-25%, respectively. The observed gas-phase ozone losses and pseudo-first-order BaP decay rate coefficients exhibited Langmuir-type dependencies on gas-phase ozone concentration and were reduced in the presence of water vapor, which indicates rapid, reversible and competitive adsorption of O 3 and H 2 O on the particles followed by a slower surface reaction between adsorbed O 3 and BaP. At low ozone VMR and RH, the half-life of surface BaP molecules was found to be shorter than previously reported (∼ 5 min at 30 ppb O 3 under dry conditions). At higher RH and for multilayer BaP surface coverage, however, a strong increase of BaP half-life was observed and can be attributed to competitive H 2 O adsorption and to surface/bulk shielding effects, respectively. From four independent sets of ozone loss and BaP decay measurement data the following parameters have been derived: O 3 and H 2 O Langmuir adsorption equilibrium constants K O 3 ) (2.8 ( 0.2) × 10 -13 cm 3 and K H 2 O ) (2.1 ( 0.4) × 10 -17 cm 3 , maximum pseudo-first-order BaP decay rate coefficient k 1,4 ) (0.015 ( 0.001) s -1 , adsorption site surface concentration [SS] S ) (5.7 ( 1.7) × 10 14 cm -2 . On the basis of these values, a second-order BaP-O 3 surface reaction rate coefficient k 2,s ) (2.6 ( 0.8) × 10 -17 cm 2 s -1 can be calculated, and estimates for the mean surface residence times and adsorption enthalpies of O 3 and H 2 O have been derived: τ O 3 ≈ 5-18 s; τ H 2 O ≈ 3 ms, ∆H ads,O 3 ≈ -(80-90) kJ mol -1 , ∆H ads,H 2 O ≈ -50 kJ mol -1 . The results and their atmospheric implications are discussed in view of related studies.

Although plastic debris is constantly accumulating in aquatic environments, the impact on aquatic ecosystems is not yet fully understood. A first important step to assess the consequences of plastic debris in aquatic ecosystems is the establishment of a reliable, verified, and standardized method to quantify the amount of plastic particles in the environment. We improved the density separation approach by the construction of the so called Munich Plastic Sediment Separator (MPSS). It enables a reliable separation of different ecologically relevant size classes of plastic particles from sediment samples. A ZnCl 2 -solution (1.6-1.7 kg/L) as separation fluid allows for an extraction of plastic particles ranging from large fragments to small microplastic particles (S-MPP, <1 mm). Subsequent identification and quantification of the particles with spatial resolution down to 1 µm can be performed using Raman microspectroscopy. Our study is the first providing validated recovery rates of 100% for large microplastic particles (L-MPP, 1-5 mm) and 95.5% for S-MPP. The recovery rate for S-MPP, using the MPSS, was significantly higher than the value obtained by application of classical density separation setup (39.8%). Moreover, our recovery rates were significantly higher than those based on froth flotation (55.0% for L-MPP) commonly used in recycling industries. Hence, our improved method can be used for a reliable and time-efficient separation, identification and quantification of plastic fragments down to S-MPP. This will help foster studies quantifying the increasing contamination of aquatic environments with microplastic particles, which is a crucial prerequisite for future risk assessment and management strategies.

The contamination of marine and freshwater ecosystems with plastic, and especially with microplastic (MP), is a global ecological problem of increasing scientific concern. This has stimulated a great deal of research on the occurrence of MP, interaction of MP with chemical pollutants, the uptake of MP by aquatic organisms, and the resulting (negative) impact of MP. Herein, we review the major issues of MP in aquatic environments, with the principal aims 1) to characterize the methods applied for MP analysis (including sampling, processing, identification and quantification), indicate the most reliable techniques, and discuss the required further improvements; 2) to estimate the abundance of MP in marine/freshwater ecosystems and clarify the problems that hamper the comparability of such results; and 3) to summarize the existing literature on the uptake of MP by living organisms. Finally, we identify knowledge gaps, suggest possible strategies to assess environmental risks arising from MP, and discuss prospects to minimize MP abundance in aquatic ecosystems.