Oxidative stress can be used to evaluate not only adverse
health effects but also adverse ecological effects, but limited research
uses eco-toxicological assay to assess the risks posed by particle matters
to non-human biomes. One important reason might be that the concentration of
toxic components of atmospheric particles is far below the high detection
limit of eco-toxic measurement. To solve the rapid detection problem, we
extended a versatile aerosol concentration enrichment system (VACES) for
ecotoxicity aerosol measurement and firstly used VACES to provide a
comparison of ecotoxicity between non-concentrated and concentrated aerosols
in ambient air. In this study, the total concentration (number or mass), the
concentration of chemical components and the ecotoxicity were all increased
by approximately 7 to 10 times in VACES, making the detection of ecotoxicity
above the baseline. The comparison of ecotoxicity data and PM
Currently, most toxicological studies focus on discovering the relationship between particulate matter and the morbidity or mortality of organisms (e.g., Vincent et al., 2001; Cox et al., 2016; Miri et al., 2018) or on exploring toxic mechanisms by exposure experiments (e.g., Magnani et al., 2016; Huang et al., 2017; Rychlik et al., 2019). However, the measurement of ecotoxicity data is rarely available because of technical limitations. For instance, it requires a long detection time due to animal and plant reproduction or cell cultivation (National Research Council, 2006), but the concentration and chemical composition of particulate matter in the atmosphere continue to change over time, especially during severe pollution (Shang et al., 2018a, b). Thereby, a short analyzing time is quite important.
To solve this problem, photobacteria (e.g.,
In this respect, aerosol enrichment techniques have been developed and applied to increase aerosol concentrations to meet ecotoxicity detection limits. Among them, the versatile aerosol concentrator enrichment system (VACES) originally developed by Sioutas et al. (1999) is effectively used to concentrate ambient particles. Since then, it has been widely used for laboratory and field measurements of particulate matter (De Vizcaya-Ruiz et al., 2006; Steenhof et al., 2011; Plummer et al., 2012; Loxham et al., 2013) because the physical and chemical properties do not change after becoming concentrated (Kim et al., 2001a, b; Wang et al., 2013). It has also been extended to combine various chemical and physical analyses of particulate matter (e.g., gases, water-soluble ions, heavy metals, polycyclic aromatic hydrocarbons, cloud condensation nuclei, etc.) (Jung et al., 2010; Freney et al., 2006; Pakbin et al., 2011; Zhao et al., 2005; Dameto et al., 2019). In addition, VACES has been applied to determine the relationship between particulate matter and health effects based on exposure experiments (Klocke et al., 2017; Ljubimova et al., 2018). Nevertheless, although VACES was originally developed to provide technical support for ecotoxicity detection, there is no direct measurement data to show the change in ecotoxicity between ambient particles and VACES particles.
Therefore, according to the previous design, by optimizing technical parameters, we modified and further developed VACES to be integrated into the ecotoxicity measurements, verified the enrichment effect on physiochemical concentration and ecotoxicity in laboratory and field studies, and also investigated the relationship between ecotoxicity and particulate masses.
VACES used a saturation and condensation system to rapidly grow particles into supermicron droplets which were then concentrated by a virtual impactor (VI). A detailed description of the design of VACES is available in previous studies (e.g., Kim et al., 2001a, b). Briefly, when the airflow was sucked into a water tank filled with deionized water (defined as a saturator) with a U-shaped heating tube inside, the particles became supersaturated. A tube was fixed above the outlet of the saturator, and a copper tube coil was tightly wound on the outside to provide fast condensation conditions. A chiller (Bilon, China) filled with ethanol (80 %, Hushi, China) was cooled through the coil. The condensed aerosols were drawn up to a virtual impactor where particle concentration by size was concentrated to a desired level by changing the ratio of the major-to-minor air flow controlled by a mass flow controller (MFC; D08-4F, Sevenstar, China).
Setup for performance test and field sample collection.
The experiments referring to VACES including laboratory and field
performance tests, discontinuous and continuous sample collections, and their
measurements. In the laboratory performance test, air flow passed through the
atomizer, VACES (saturator-condensation tube-virtual impactor), Nafion
tubing, DMA and CPC successively. For the two field performance tests, in the
first one, air flow passed through VACES, Nafion tubing, DMA and CPC
successively, and in the second, one air flow passed through the aerosol filter,
VACES, Nafion tubing, DMA and CPC successively. During the discontinuous sample
collection, particles followed the flow line of VACES to the biosampler. For the continuous sample collection, particles were collected from the PM
Sampling was conducted for several experiments, including a laboratory
performance test, a field performance test, discontinuous sample collection
and continuous sample collection. The performance test in this study used
the enrichment factor (EF) defined as the ratio of concentrated (VACES) to
non-concentrated (ambient) particle concentration and the enrichment
efficiency (EE) defined as the ratio of the concentrated concentration to 10 times the non-concentrated concentration as a standard. The closer the
EF and EE are to 10 % and 100 %, respectively, the better the enrichment
effect of VACES. The instrument operating parameters (major air flow, minor
air flow, condensation temperature and saturation temperature) were defined
as the optimal parameters when the best enrichment effect was obtained. In
the laboratory performance test, an atomizer (model 9302, TSI, USA) was used
to atomize polystyrene latex (PSL; Thermo Fisher Scientific, USA) to produce
200, 300, 500 and 700 nm particles, respectively (Fig. 1). In one case, after drying the generated PSL particles (Nafion tube, MD-700,
Perma Pure, USA), we set the corresponding voltage through a differential
mobility analyzer (DMA; model 3081, TSI, USA) for screening, and then they
entered the condensation particle counter (CPC; model 3775, TSI, USA) at a
flow rate of 0.3 L min
In the performance test, we determined the optimal parameters (as defined
above) of VACES. Then, we successively carried out discontinuous and
continuous VACES particle collection on the sixth floor of the Environmental
Science and Engineering Department of Fudan University in Shanghai. We
opened the inlet to the ambient air, in which particles were sucked into the
saturator at a major flow rate and increased in concentration at a minor
flow rate (Kim et al., 2001a). VACES particles were collected in 5 mL of
deionized water through a biosampler (SKC, USA) for 30 min and 1 h. In
order to study the physiochemical and ecotoxicity differences between VACES
particles and environmental particles, we switched the inlet of the
biosampler to ambient air after VACES particles were collected; that is to say, 30 min (1 h) VACES samples then 30 min (1 h) environmental samples. From
23 October to 11 December 2019, we obtained a total of 10
sets of 30 min samples and 10 sets of 1 h samples. Therefore, due to
time discontinuity, sampling was defined as a discontinuous collection. In
contrast, in the continuous sample collection process, we added a PM
All samples were filtered using 0.22
The optimization of VACES is to achieve 10-fold enrichment of ambient aerosol
concentration mainly through modulating temperatures of the saturator and
chiller, the major air flow, the minor air flow, and their flow ratio. By
switching air pathways between ambient and VACES and comparing their number
and mass concentrations observed in a scanning mobility particle sizer (SMPS;
DMA
Enrichment efficiency of ambient aerosols in VACES at different size ranges.
For the laboratory performance test, the number concentrations of VACES and
ambient PSL particles were alternatively measured six times in parallel. The
EF calibration line was plotted by the number concentration in four sizes of
VACES particles against ambient particles. It showed a quite high
correlation coefficient (
Calibration of enrichment factor of VACES system using polystyrene latex (PSL) aerosol reagent 200–700 nm in size. Error bars are the standard deviation of six parallel measurements.
Particle
Similarly, we measured the number and mass concentrations of particulate
matter in the field performance test. When the concentration coordinate value of
VACES was set to 10 times that of ambient air, the two curves almost
coincided for particle size greater than 25 nm (Fig. 3a and b), indicating
that the EE was close to 100 %. In addition, the investigation of
particle formation in VACES showed that the maximum of newly formed
particles in size was only
The study evaluated the ecotoxicity by the light inhibition rate of
photobacteria; the higher the value is, the higher the ecotoxicity is. The light
inhibition rate was calculated by multiplying by 100 the ratio of the
changes in fluorescence intensity (between treated and untreated medium) to
the intensity of untreated medium. The untreated medium meant only bacteria in medium, and treated medium corresponded to a sample adding in
bacteria medium. Discontinuous sampling was operated under PM
Comparison of light inhibition rate and ratio of ambient
and VACES particles with ambient PM
Comparison of light inhibition rate between ambient and
VACES particles based on continuous sampling of VACES and ambient particles. VACES
samples were collected hourly and ambient filter samples were collected
every 8 h. The PM
Enrichment factors of chemical compositions and light
inhibition of PM
The change in EF was roughly the reversal of the trend of the light inhibition
rate of the ambient and VACES particles (Fig. 4). The main reason was that
the increase in the light inhibition rate of VACES particles was lower than
that of the ambient particles at high PM
To achieve detection limits for atmospheric particulate ecotoxicity, a
versatile aerosol concentration enrichment system (VACES) was extended to be
integrated with ecotoxicity measurements. The VACES was developed to increase
particle concentrations by about 7–10 times under the conditions of chiller
temperature (
Data are available by contacting the corresponding author.
XS and JC designed the experiments. XS performed the experiment, analyzed the data and wrote the paper. XZ, HK, LL, GS and XY assisted with bio-toxicity and enrichment experiments. GW and HX helped by providing suggestions in paper revisions.
The authors declare that they have no conflict of interest.
This work was funded by National Natural Science Foundation of China (grant nos. 21527814, 91843301, 91743202, 22006021).
This research has been supported by the National Natural Science Foundation of China (grant nos. 21527814, 91843301, 91743202, and 22006021).
This paper was edited by Paolo Laj and reviewed by two anonymous referees.