Large quantities of microplastics
are thought to be emitted to
freshwater environments via wastewater treatment plants (WWTPs). To
evaluate the occurrence of microplastics in Korean WWTPs, a nationwide
study was conducted for the first time in 50 representative WWTPs
with large treatment capacities. Grab sampling and laboratory filtration
were used for influents, whereas in situ filtration using a custom-made
sampling device was used for effluents. The filtrates were pretreated
using wet peroxidation and density separation prior to the identification
of microplastics with a dissection microscope and Fourier-transform
infrared spectroscopy. Pooled analyses of the microplastics revealed
that they were predominantly fragment-shaped, and thermoplastics and
synthetic fibers were the dominant microplastic materials in WWTPs.
The concentration ranged from 10 to 470 L–1 in influents
and 0.004 to 0.51 L–1 in effluents. The removal
efficiency of microplastics during wastewater treatment was calculated
to be 98.7–99.99% in 31 WWTPs. Additionally, WWTPs using advanced
phosphorus removal processes exhibited higher removal efficiency than
those not implementing such processes. Power-law distribution was
successful in describing microplastic particle sizes down to 100 μm,
although it was not applicable for smaller particles. This comprehensive
monitoring study provides information on the current level and characteristics
of microplastics in WWTPs in Korea.
Oxidative stress was evaluated for anthracene (Ant) and alkyl-Ants (9-methylanthracene [9-MA] and 9,10-dimethylanthracene [9,10-DMA]) in Caenorhabditis elegans to compare changes in toxicity due to the degree of alkylation. Worms were exposed at 1) the same external exposure concentration and 2) the maximum water-soluble concentration. Formation of reactive oxygen species, superoxide dismutase activity, total glutathione concentration, and lipid peroxidation were determined under constant exposure conditions using passive dosing. The expression of oxidative stress-related genes (daf-2, sir-2.1, daf-16, sod-1, sod-2, sod-3 and cytochrome 35A/C family genes) was also investigated to identify and compare changes in the genetic responses of C. elegans exposed to Ant and alkyl-Ant. At the same external concentration, 9,10-DMA induced the greatest oxidative stress, as evidenced by all indicators, except for lipid peroxidation, followed by 9-MA and Ant. Interestingly, 9,10-DMA led to greater oxidative stress than 9-MA and Ant when worms were exposed to the maximum water-soluble concentration, although the maximum water-soluble concentration of 9,10-DMA is the lowest. Increased oxidative stress by alkyl-Ants would be attributed to higher lipid-water partition coefficient and the π electron density in aromatic rings by alkyl substitution, although this supposition requires further confirmation.
The inhalation of naphthalene used as deodorant balls in public toilets could be an important cancer risk factor. The atmospheric concentration of naphthalene in public toilets (
C
in
) was estimated both by a polyurethane foam passive air sampler (PUF-PAS) deployed in nine public toilets in Seoul, Korea and by a steady-state indoor air quality model, including emission estimation using Monte-Carlo simulation. Based on the estimated
C
in
, cancer risk was also assessed for cleaning workers and the general population. The steady-state
C
in
estimated using the estimated emission rate, which assumed that air exchange was the only process by which naphthalene was removed, was much greater than the
C
in
value measured using PUF-PAS in nine public toilets, implying the importance of other removal processes, such as sorption to walls and the garments of visitors, as well as decreased emission rate owing to wetting of the naphthalene ball surface. The 95 percentile values of cancer risk for workers based on the estimation by PUF-PAS was 1.6×10
–6
, whereas those for the general public were lower than 1×10
–6
. The results suggested that naphthalene deodorant balls in public toilets may be an important cancer risk factor especially for the cleaning workers.
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