Automated analysis of microplastics based on vibrational spectroscopy: are we measuring the same metrics?

The traditional manual analysis of microplastics has been criticized for its labor-intensive, inaccurate identification of small microplastics, and the lack of uniformity. There are already three automated analysis strategies for microplastics based on vibrational spectroscopy: laser direct infrared (LDIR)-based particle analysis, Raman-based particle analysis, and focal plane array-Fourier transform infrared (FPA-FTIR) imaging. We compared their performances in terms of quantification, detection limit, size measurement, and material identification accuracy and speed by analyzing the same standard and environmental samples. LDIR-based particle analysis provides the fastest analysis speed, but potentially questionable material identification and quantification results. The number of particles smaller than 60 µm recognized by LDIR-based particle analysis is much less than that recognized by Raman-based particle analysis. Misidentification could occur due to the narrow tuning range from 1800 to 975 cm-1 and dispersive artifact distortion of infrared spectra collected in reflection mode. Raman-based particle analysis has a submicrometer detection limit but should be cautiously used in the automated analysis of microplastics in environmental samples because of the strong fluorescence interference. FPA-FTIR imaging provides relatively reliable quantification and material identification for microplastics in environmental samples greater than 20 µm but might provide an imprecise description of the particle shapes. Optical photothermal infrared (O-PTIR) spectroscopy can detect submicron-sized environmental microplastics (0.5-5 µm) intermingled with a substantial amount of biological matrix; the resulting spectra are searchable in infrared databases without the influence of fluorescence interference, but the process would need to be fully automated.

Geochemical markers of the Anthropocene: Perspectives from temporal trends in pollutants.

Determining stratigraphic markers of the Anthropocene is important for demarcating Global Stratotype Section and Point (GSSP). Heavy metals and persistent organic pollutants (POPs) are candidate geochemical markers of the Anthropocene, but no study has comprehensively evaluated temporal trends in these pollutants in sediment cores globally. 454 data points for 8 heavy metals and 8 POPs were compiled to reconstruct their temporal trends and evaluate their global consistency. The heavy metals did not increase rapidly in the 20th century, and their temporal trends were locally but not globally consistent, which are not suitable geochemical markers of the Anthropocene. POPs rapidly increased beginning in the mid-20th century but have declined in the past decade, and these data are more consistent globally. The time of the peak concentration and period of rapid increase for polychlorinated biphenyls (PCBs) occur near the boundary of the Anthropocene and are consistent globally. Forty-five percent of the studies evaluated used only 210Pb chronology for dating, which creates definite uncertainty in the analysis. In GSSP candidate sections, PCBs could be considered candidate markers of the Anthropocene.

Raman spectra and surface changes of microplastics weathered under natural environments.

Raman spectroscopy can be used to effectively analyze submicron- to microsized microplastics, but Raman spectra of weathered microplastics commonly show deviations from those of unweathered microplastics and are often affected by fluorescence. However, studies of weathering-induced surface changes in microplastics have been limited to laboratory simulations. To systematically study Raman spectra and surface changes of microplastics weathered under natural environments, we collected microplastics from sediments around waste plastics processing and recycling industries in Laizhou City, Shandong Province, East China. Raman spectra of weathered microplastics differ greatly from standard spectra of unweathered plastic material. Peaks in the Raman spectra of weathered microplastics are weakened and even invisible. A preliminary Raman database of weathered microplastics (RDWP) including 124 Raman spectra of weathered microplastics was built to accurately identify microplastics in natural environments, and it is open to all users. FTIR spectroscopy revealed the presence of oxygen-containing functional groups and CC bonds related to oxidation and chain scission. SEM showed that weathered microplastics had rough surfaces and that PP was more easily fractured than PE. Complementary C and O elemental maps suggested that the O/C ratio is a potential indicator of oxidation degree. EDS revealed titanium on PET and PVC surfaces, which is related to titanium dioxide typically used as a light-blocking aid. Our data document that Raman spectroscopy has great potential in the identification of naturally weathered microplastics and that combined spectral and elemental analyses can be useful in deciphering the degradation processes of microplastics under natural conditions. CAPSULE: Raman spectra of weathered microplastics differ greatly from standard spectra. A Raman database of weathered microplastics is established. Surface changes of weathered microplastics were systematically studied.

The rapid increases in microplastics in urban lake sediments.

Microplastics have received widespread attention as an emerging global pollutant. However, the research on the abundance and characteristics of microplastics entering the environment throughout history has been limited. Meanwhile, the determination of the start of the Anthropocene is important because humans have become a vital force affecting the environment and Earth surface processes. It is unclear whether the plastic can be used as an artefact to indicate the start of the Anthropocene. In this study, combined with 137Cs, 210Pb, and spherical carbonaceous particles (SCP) high-resolution chronology, a microplastics-time curve was established by using the sedimentary record from an urban lake in Wuhan city. The microplastic abundance increased from 741 items·kg-1 to 7707 items·kg-1 over the past 60 years. The microplastics were mainly fibres and composed of polyester and rayon polymers, which indicated that the microplastics most likely originated from textiles. The surfaces of the older microplastics were rough and weathered with many absorbed elements. Microplastics are similar to fossils belonging to the Anthropocene, and may be used as an indicator. The comparison of microplastic-time curves in different records on a global scale will be necessary in the future.

[Alleviation Effects of Exogenous Melatonin on Ni Toxicity in Rice Seedings].

The alleviation effect of exogenous melatonin (MT) on Ni toxicity in rice seedings was investigated. The results showed that low concentration of Ni stress (10, 50 µmol·L-1) had little effect on the growth of root of rice seedings, while higher concentration of Ni stress (100-1000 µmol·L-1) significantly inhibited the growth of rice root. Compared with the control treatment, the addition of 100 and 1000 µmol·L-1 Ni would decrease the total length and surface area of root by 63.3%-98.0% and 56.9%-96.3%, respectively. The results showed that addition of exogenous melatonin had a positive effect on the growth of rice seedings under Ni stress. This kind of positive effect was even more obvious in the root of rice seedings. The total length of rice root decreased by 58.4%-83.8% at Ni concentration of 100 µmol·L-1, whereas it decreased by only 8.7%-29.1% when 100 µmol·L-1 Ni and 10 µmol·L-1 MT were added, compared with the control treatment. The addition of exogenous melatonin had significant alleviation effects on oxidative stress in rice seedings caused by Ni. Compared with the 100 µmol·L-1Ni treatment, addition of 10 µmol·L-1 exogenous MT could significantly decrease the production rate of O2-· by 43.2%-50.2% and the relative electrolytic leakage by 25.7%-31.6%, whereas increase the activities of CAT by 21.9%-33.7% and the soluble protein content by 82.6%-84.6%. The results suggested that application of exogenous melatonin could effectively alleviate the toxic effects of Ni on rice seedings.

[Phenols pollutants in soil and shallow groundwater of a retired refinery site].

To study the distribution of phenol compounds in a retired refinery site, 21 soil sampling sites and 8 shallow groundwater wells were investigated. The results showed, shallow unconfined groundwater of the site was in a serious pollution situation and the phenols concentration was much higher than quality standard for ground water. Confined water sample was slightly contaminated by phenols and the total quality was good. Approximately half of the area was heavily polluted by phenol compounds. According to the retired refinery layout, the phenols pollution distribution in shallow groundwater and soil exhibited the regional similarity. The highly contaminated area was production workshop, oil tank and plant storage. Horizontal diffusion of pollutants was not serious. Vertical diffusion of pollutants was different, and a site with pollutant diffusion was deeper than ten meters. The 2-chlorophenol, 2-nitrophenol, 2,4-xylenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol, 2,4-dinitrophenol and 2-methyl-4,6-dinitrophenol in typical soils were analyzed by GC/MS. It showed that concentrations of seven phenol compounds were 0.01-232.96 mg x kg(-1), and the concentrations of 2,4-dinitrophenol and 2-methyl-4,6-dinitrophenol were high.

Cr-(III)-organic compounds treatment causes genotoxicity and changes in DNA and protein level in Saccharomyces cerevisiae.

Natural Cr-(III)-organic species are being known as the part of natural biogeochemical cycle of chromium, but unfortunately, their mechanism of toxicity as well as genotoxic potentiality is still unknown. To evaluate the characteristic toxic effect exerted by natural Cr-(III)-organic species on the cellular macromolecules, changes in DNA and protein level was observed. Besides, Comet assay was applied to measure genotoxic potentiality of Cr-(III)-organic species in the target organism Saccharomyces cerevisiae exposed to Cr-(III)-citrate and Cr-(III)-histidine. It has been observed that both of the Cr-(III)-organic compounds are responsible for diminution in macromolecules concentration. Cr-(III)-citrate showed ladder pattern of DNA fragmentation in support of apoptosis. Two new protein bands appeared in protein profile of the Saccharomyces cerevisiae treated with Cr-(III)-organic compounds. Thus it supports the possibility of the synthesis of stress proteins. Comet assay proved positive correlation between Cr-(III)-organic compounds' concentration and DNA damage. The Cr-(III)-citrate causes DNA damage at the concentrations ranging from 50 to 150 mg L(-1), whereas the DNA damaging capacity of Cr-(III)-histidine was found insignificant, except at highest concentration (150 mg L(-1)). These results can throw light on the mechanism of the toxic effect as well as genotoxicity exerted by natural Cr-(III)-organic species.

Isolation and identification of profenofos degrading bacteria

An enrichment culture technique was used to isolate bacterial strains responsible for the biodegradation of profenofos in a soil from Hubei province of central China. Two pure bacterial cultures, named W and Y, were isolated and subsequently characterized by sequencing of 16S rRNA genes and biochemical tests. Isolate W showed 96 percent similarity to the 16S rRNA gene of a Pseudomonas putida unlike Y which showed 99 percent similarity to the 16S rRNA gene of Burkholderia gladioli. Both strains grew well at pH 5.5-7.2 with a broad temperature profile ranging from 28º to 36 ºC. Bioremediation of profenofos-contaminated soil was examined using soil treated with 200 ug g-1; profenofos resulted in a higher degradation rate than control soils without inoculation. In a mineral salt medium (FTW) reduction in profenofos concentration was 90 percent within 96 hours of incubation. A literature survey revealed that no data is available regarding the role of Burkholderia gladioli on pesticide biodegradation as well as on profenofos.

Isolation and identification of Profenofos degrading bacteria.

An enrichment culture technique was used to isolate bacterial strains responsible for the biodegradation of profenofos in a soil from Hubei province of central China. Two pure bacterial cultures, named W and Y, were isolated and subsequently characterized by sequencing of 16S rRNA genes and biochemical tests. Isolate W showed 96% similarity to the 16S rRNA gene of a Pseudomonas putida unlike Y which showed 99% similarity to the 16S rRNA gene of Burkholderia gladioli. Both strains grew well at pH 5.5-7.2 with a broad temperature profile ranging from 28° to 36 °C. Bioremediation of profenofos-contaminated soil was examined using soil treated with 200 ug g(-1); profenofos resulted in a higher degradation rate than control soils without inoculation. In a mineral salt medium (FTW) reduction in profenofos concentration was 90% within 96 hours of incubation. A literature survey revealed that no data is available regarding the role of Burkholderia gladioli on pesticide biodegradation as well as on profenofos.