The role of analytical chemistry in the study of the Anthropocene

The recovery of aerosol-sized microplastics in highly refractory vegetal matrices for identification by automated Raman microspectroscopy

Ombrotrophic peatlands are fed uniquely by atmospheric inputs and therefore have much potential as temporal archives of atmospheric microplastic (MP) deposition, yet the recovery and detection of MP within an almost purely organic matrix is challenging. This study presents a novel peat digestion protocol using sodium hypochlorite (NaClO) as a reagent for biogenic matrix removal. NaClO is more efficient than hydrogen peroxide (H₂O₂). By using purged air-assisted digestion, NaClO (50 vol%) reached 99% matrix digestion compared with 28% and 75% by H₂O₂ (30 vol%) and Fenton's reagent, respectively. At a concentration of 50 vol% NaClO did however chemically disintegrate small amounts (<10 mass %) of polyethylene terephthalate (PET) and polyamide (PA) fragments in the millimeter size range. Observation of PA6 in natural peat samples, while not found in the procedural blanks, questions whether PA is fully disintegrated by NaClO. The protocol was applied to three commercial sphagnum moss test samples, in which MP particles in the range of 0.8-65.4 μm were detected by Raman microspectroscopy. The MP mass% was determined at 0.012% corresponding to 129 thousand MP particles/g, of which 62% were smaller than 5 μm and 80% were smaller than 10 μm, yet were accountable for only 0.4% (500 ng) and 3.2% (4 μg) of the total mass of MP, respectively. These findings underline the importance of the identification of particles Ø < 5 μm when investigating atmospheric MP deposition. The MP counts were corrected for MP recovery loss and procedural blank contamination. MP spike recovery following the full protocol was estimated at 60%. The protocol offers an efficient way of isolating and pre-concentrating most aerosol sized MPs in large quantities of refractory vegetal matrices and enables the automated μRaman scanning of thousands of particles at a spatial resolution on the order of 1 μm.

Temporal Archive of Atmospheric Microplastic Deposition Presented in Ombrotrophic Peat

Ombrotrophic peatland-fed solely from atmospheric deposition of nutrients and precipitation-provide unique archives of atmospheric pollution and have been used to illustrate trends and changes in atmospheric trace element composition from the recent decadal to the Holocene period. With the acknowledgment of atmosphere plastic pollution, analysis of ombrotrophic peat presents an opportunity to characterize the historical atmospheric microplastic pollution prevalence. Ombrotrophic peatland is often located in comparatively pristine mountainous and boreal areas, acting as sentinels of environmental change. In this paired site study, a Sphagnum ombrotrophic peat record is used for the first time to identify the trend of atmospheric microplastic pollution. This high altitude, remote location ombrotrophic peat archive pilot study identifies microplastic presence in the atmospheric pollution record, increasing from <5(±1) particles/m²/day in the 1960s to 178(±72) particles/m²/day in 2015-2020 in a trend similar to the European plastic production and waste management. Compared to this catchment's lake sediment archive, the ombrotrophic peat core appears to be effective in collecting and representing atmospheric microplastic deposition in this remote catchment, collecting microplastic particles that are predominantly ≤20 μm. This study suggests that peat records may be a useful tool in assessing the past quantities and trends of atmospheric microplastic.

A Multidisciplinary Approach for the Assessment of Origin, Fate and Ecotoxicity of Metal(loid)s from Legacy Coal Mine Tailings

Over the course of history, the development of human societies implied the exploitation of mineral resources which generated huge amounts of mining wastes leading to substantial environmental contamination by various metal(loid)s. This is especially the case of coal mine tailings which, subjected to weathering reactions, produce acid mine drainage (AMD), a recurring ecological issue related to current and past mining activities. In this study, we aimed to determine the origin, the fate and the ecotoxicity of metal(loid)s leached from a historical coal tailing heap to the Beuveroux river (Franche-Comté, France) using a combination of mineralogical, chemical and biological approaches. In the constitutive materials of the tailings, we identified galena, tetrahedrite and bournonite as metal-rich minerals and their weathering has led to massive contamination of the water and suspended particles of the river bordering the heap. The ecotoxicity of the AMD has been assessed using Chironomus riparius larvae encaged in the field during a one-month biomonitoring campaign. The larvae showed lethal and sub-lethal (growth and emergence inhibition and delay) impairments at the AMD tributary and near downstream stations. Metal bioaccumulation and subcellular fractionation in the larvae tissues revealed a strong bioavailability of, notably, As, Pb and Tl explaining the observed biological responses. Thus, more than 70 years after the end of mining operations, the coal tailings remain a chronic source of contamination and environmental risks in AMD effluent receiving waters.

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.

Trace metals as markers for historical anthropogenic contamination: Evidence from the Peshawar Basin, Pakistan

Trace element concentrations in the youngest Holocene sedimentary archives, historical mining, and archaeological sites are reliable indicators for historical anthropogenic contamination. The Pleistocene-Holocene strata and the overlying archaeological sites of the Peshawar Basin, NW Pakistan provide sedimentary archives to explore historical anthropogenic controls on the distributions of trace elements. The basin with 2500 y of human civilization was sampled using archaeological trenches at Gor Khuttree and Hund, and six sections of youngest Pleistocene-Holocene strata along river banks. Geochemical analysis of high-resolution samples were conducted for both the lacustrine-floodplain sediments and archaeological sites. Results from various horizons of the archaeological sites provide signals for anthropogenic control on the distribution of As, Zn, Cu, Mo, Pb, Hg, Ag, and Au during the Meghalayan Stage of Holocene that gain progressive strength since the 18th century. The geochemical proxies negate direct mining of Cu-Pb and Zn in the area. The consistent, anthropogenic Ag and Au contribution to the system throughout the basin's archaeological history is a significant finding. When correlated against the anthropogenic mercury contamination, it appears that Hund was a major silver-gold panning site throughout its known history whereas Gor Khuttree was the major silver-gold processing center. The Peshawar Basin anthropogenic signals contribute to widespread European early Anthropocene signals at around 2000 BP related to the Greek and Roman mining. Signals during the Hindu Shahi period correlate well with the Medieval period mining and smelting peak signals observed in Europe and China. Hg, Ag, and Au concentrations in the area since the start of the 19th century CE correlates to the start of industrialisation. During the mid-20th century, these geochemical signals from the Gor Khuttree reflect anthropogenic contributions to the local system and correlate to the suggested base of a formalised Anthropocene.

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.

Airborne Magnetic Technoparticles in Soils as a Record of Anthropocene

Airborne magnetic particles in soils were studied in sites located in various distances to industrial plants. Chemical and mineral composition of soil samples were analysed. The highest values of the Pollution Load Index (PLI) calculated for several elements were noted for sites relatively distant from industrial plants. Soil samples exposed for the deposition of airborne particles were examined by means of magnetization versus an external applied magnetic field as well as 57Fe Mössbauer spectroscopy measurements showing a lack of correlation of the magnetic properties with total Fe content, which points toward a strong impact of the industrial activities. Magnetic fraction was extracted and studied using scanning electron microscopy with energy dispersive spectrometry. Two types of spherical particles were noted. Massive ones occurring in all sites and particles with a complex internal structure more abundant in sites situated closer to industrial plants. The presence of spherical magnetic particles formed in high temperature processes indicate their relatively long range transport in the atmosphere. Broad distribution, characteristic and easy for identification spherical form of these magnetic technoparticles, suggest that one can consider them as a record of the Anthropocene. Accumulation of such technoparticles is related to rapid industrialization in the post-World War II period.