The use of microplastics as a reliable chronological marker of the Anthropocene onset in Southeastern South America

Links between international market trends, agricultural intensification and extreme sedimentation rates in a transboundary South American coastal lagoon

In response to global food demand, crop cultivation in the South American Pampa Biome rapidly expanded, intensifying erosion linked to land-use change and mechanisation. In Uruguay and SE Brazil, the most significant expansion occurred after 2000. This study examines the economic, environmental, and productive changes in an agricultural basin over the past two decades, focusing on the expansion of the primary sector of the economy, particularly soybean cultivation. It also investigates the cause of not only maximum but also abnormally extreme sedimentation rates (SR) observed between 2005 and 2009 CE. Findings indicate that SR trends reflect land-use changes in the basin. A notable shift occurred in the 1980s after the lagoon was converted to a freshwater system, leading to a twofold increase in SR. The peak in SR observed in core MIR2 (i.e., 400 % increase) was recorded around 2005-2009 CE, alongside a 2000 % increase in terrestrial palynomorphs (pollen, spores, and other organic-walled microfossils from terrestrial sources) in core MIR4. For this period, changes in sediment grain size distribution appear to resemble drastic shifts in land cover. This coincided with the approval of glyphosate-resistant seeds (2005/2006 harvest) and a rise in soybean prices post-2006. The extreme sedimentation rate likely resulted from soybean expansion and intensified unsustainable practices like ploughing, which increased the export of fine terrestrial material. Our findings highlight how both land-use changes and climate variability (particularly extreme precipitation events) contributed to the observed SR anomalies, thus suggesting a reinforcing interaction between agricultural expansion and hydrological extremes.

Profiling microplastics in a forgotten river system in Southern Africa

Microplastics have been studied in rivers worldwide with far-reaching implications for aquatic ecosystems. What is less understood is how microplastics distribute through rivers, as microplastics do not distribute ubiquitously through a river system. This study described the microplastic profile of the Nyl, Mogalakwena and Limpopo Rivers in South Africa. The study aimed to determine the driving environmental factors of microplastic distribution in a river system over multiple seasons. The study discovered relationships between flow and microplastics in sediment. This relationship allowed microplastics to have significantly (p < 0.05) different distributions over seasons. Seasons with reduced flow had higher mean microplastic abundances in water (1436 ± 4492 particles.m-3) and sediment (1710 ± 4951 particles.kg-1dw), which decreased in both water (59 ± 46 particles.m-3) and sediment (17 ± 11 particles.kg-1dw) during the high flow season. Although microplastic abundances decreased with increased flow, a more homogenous distribution was detected through the entire system in the high flow period. The results suggest that microplastics could become trapped and increase significantly during reduced flow but become more evenly distributed during high flow seasons. The microplastics had also become bioavailable, being found in benthic macroinvertebrates in the river system at varying concentrations with a mean of 29 ± 33 particles.g-1ww, which could not be related to environmental matrices. Significant differences (p < 0.05) were determined between microplastic polymers found in water compared to sediment in all seasons. The study is the first in this transboundary river system, which impacts multiple African nations and a RAMSAR accredited wetland of international importance.

Coastal populations and river discharges as sources of microplastic pollution of the Ciénaga Grande de Santa Marta, Colombian Caribbean

The large-scale production of plastic began in the 1950s, leading to a significant global increase and has become one of the world's major problems since its disintegration generates small particles of microplastics (MPs), considered pollutants of emerging concern, which are commonly found in most ecosystems. In Colombia, research on microplastics (MPs) in coastal ecosystems is still in its early stages. This study seeks to advance understanding of MPs contamination in surface waters of the Ciénaga Grande de Santa Marta (CGSM), the most significant coastal lagoon in the Colombian Caribbean, which has been designated both a Biosphere Reserve and a Ramsar site of international importance. The study focuses on examining the relationship between MP pollution and two primary sources: coastal populations and discharges from tributary rivers into the lagoon system. Water samples were collected at 33 stations during the dry season (March 2021) and rainy season (May 2021), and MPs were identified and quantified by microscopy. The effect of the distance from river mouths (km) and populated zones (km) on the abundance of MPs was evaluated by applying a Generalized Additive Model (GAM) in R. The study revealed that the abundance of MPs was significantly influenced by proximity to pollution sources, with higher concentrations observed closer to river mouths and coastal settlements during both dry and rainy seasons. The seasonal composition of MP in the two studied zones reveals a consistent prevalence of filaments during the seasons, indicating the persistent influence of various sources of contamination. The findings show that inadequate waste management practices and the lack of proper infrastructure for waste disposal are key factors contributing to microplastic pollution in the area. The study provides critical insights for addressing deficiencies in waste management while promoting active community engagement to preserve the ecological and socioeconomic value of this vital lagoon complex. The CGSM is not only a key coastal ecosystem in Colombia but also supports diverse livelihoods and cultural heritage, emphasizing the importance of sustainable management.

Accelerating microplastic contamination in 210Pb dated sediment cores from an urbanized coastal lagoon (NW Mexico) since the 1990s

The ubiquity of microplastics (MP) across all ecosystems raises concerns about their potential harm to the environment and living organisms. Sediments are a MP sink, reflecting long-term accumulation and historical anthropogenic impacts. Three 210Pb-dated sediment cores were used to understand the temporal variations of MP abundances (particles kg-1) and fluxes (particles m-2 year-1) within the past century in Estero de Urías Lagoon, an urbanized coastal lagoon in the Mexican Pacific. MP particles, extracted from sediments by density separation (saturated NaCl solution) were counted using a stereomicroscope, under visible and ultraviolet light on Nile red (NR) stained filters. The polymer composition was determined in ∼10 % of the suspected MP particles using Fourier Transform Infrared spectrometry. Fibers (66 to 89 % of the total particles) predominated over fragments (11 to 34 %). Before 1950, no MP particles were detected. Polyethylene terephthalate (PET) was the prevalent synthetic polymer (up to 50 % of the particles), while semisynthetic cellulosic fibers were predominant, underscoring the broader scope of anthropogenic contamination. Suspected MP abundances (NR stained filters) were highest in the core collected at the innermost area, which was attributed to the lagoon's hydrodynamics, since current velocities decrease from the proximal to the distal area to the sea. From the regression between MP fluxes and time elapsed since sediments deposited, the cores showed consistent accelerated increases of MP burial since mid-20th century, most likely because of the increasing availability of plastic products and population growth, with the consequent increment in plastic waste and wastewater releases. Our findings emphasize the growing MP pollution challenges at EUL, which may directly impact subsistence fishing and shrimp aquaculture activities, threatening local livelihoods and food sources; and also highlight the need for improved waste management and pollution control strategies in rapidly industrializing regions, to protect both aquatic ecosystems and human populations dependent on fishing products.

The effect of fluvial avulsion on the Holocene chronostratigraphic record and the agricultural signal of the world's largest coastal lagoonal system

This study identified the occurrence of Holocene chronology hiatuses in the sedimentary record of the Patos-Mirim system caused by river avulsion processes, as well as evidence of sharp anthropogenic changes in the surrounding region of the lagoon water bodies. The presence of chronology hiatuses demonstrates the importance of considering the disturbance effect of paleo-drainage processes on the paleoenvironmental resolution and expression of the sedimentary record of such coastal plains. Anthropogenic activities especially those related to agriculture and forestry have increased significantly during the great acceleration, resulting in modifications of both the landscape and the environmental conditions of the lagoon bodies. Such impacts were clearly reflected in the sedimentary record where abrupt changes in palynological trends, sedimentary DNA, isotopic and granulometric analyses were inferred. The climatic conditions combined with regressive sea level can explain the chronology hiatuses. Pollen analyses demonstrated changes in the landscape, particularly indicated by the shift from Cyperaceae to Poaceae dominance after the 1960 CE. Therefore, all proxies together demonstrate the modification in the landscape and changes in the environment, clearly influenced by anthropogenic action from unsustainable agricultural practices.

Environment change recorded by lake sediment magnetism in the Songnen Plain, northeastern China

Stratigraphic determination of the Anthropocene, the "Great Acceleration", requires more key globally synchronous stratigraphic markers which reflect the significant human impacts on Earth. Lacustrine sediment magnetic characteristics are of considerable importance in Anthropocene studies because they respond sensitively to environmental changes. There are many shallow lakes in the Songnen Plain (SNP) in northeast China, which are conducive to obtaining Anthropocene sedimentary records. This study explored magnetic materials in lacustrine sediment responses to environmental evolution impact by human activities on the SNP by measuring magnetic parameters in dated sediment cores from 5 shallow lakes in the SNP, northeast China. The results revealed that detrital magnetite and hematite dominated the magnetic minerals in lake sediments. The persistently low value of magnetic susceptibility might be caused by the low content of natural ferrimagnetic minerals in Quaternary fluvial deposits and humus-rich black soil in the catchment, and the loss of magnetic materials during the transport process. In Lake Longjiangpao (LJP), the magnetic concentrations significantly responded to regional precipitation, whereas in the other 4 lakes in the center of the plain, the parameters tended to reflect complex human activities. However, the isothermal remanent magnetization ratio (S-300), which is indicative of the ratio of hematite to magnetite, exhibited relatively consistent variations in the 5 studied lakes. After 1950, the "Great Acceleration", the increase of S-300 indicated a relative proportion of magnetite in sediments, and was positively correlated with the growth of human-activity proxies (Gross Domestic Product (GDP) and population). Thus, this proxy can be regarded as a useful indicator of the beginning of the Anthropocene in the studied region. This study provides new insights into the estimation of local human activities in history and possible evidence for the global definition of the Anthropocene.

Microplastic in clams: An extensive spatial assessment in south Brazil

Microplastic pollution is becoming a continuously growing environmental concern, while bivalve mollusks are particularly vulnerable due to their sessile habits and feeding through water filtration processes. Microplastic incidence in soft tissues of the clam Amarilladesma mactroides was assessed along unconsolidated substrates distributed in extensive coastal regions of southern Brazil. Influence of urbanization levels, distance to rivers and local hydrodynamics on microplastic accumulation by the clam was tested. The average concentration of microplastics was high (3.09 ± 2.11 particles.g-1), considering 16 sampled sites. Particles were mainly composed by polyamide, polyethylene and polyethylene terephthalate, while were mainly smaller, fibrous and colorless. High urbanization and closer proximity to rivers insured higher contamination, which is a trend observed globally. No influence of coastal hydrodynamics was seen. Considering obtained findings, A. mactroides presents good potential to be used as a valuable tool to assess microplastic contamination in unconsolidated substrates of beach areas.

Downward migrating microplastics in lake sediments are a tricky indicator for the onset of the Anthropocene

Plastics are a recent particulate material in Earth's history. Because of plastics persistence and wide-range presence, it has a great potential of being a global age marker and correlation tool between sedimentary profiles. In this research, we query whether microplastics can be considered among the array of proxies to delimit the Anthropocene Epoch (starting from the year 1950 and above). We present a study of microplastics deposition history inferred from sediment profiles of lakes in northeastern Europe. The sediments were dated with independent proxies from the present back to the first half of the 18th century. Regardless of the sediment layer age, microplastic particles were found throughout the cores in all sites. Depending on particles' aspect ratio, less elongated particles were found deeper, while more elongated particles and fibers have reduced mobility. We conclude that interpretation of microplastics distribution in the studied sediment profiles is ambiguous and does not strictly indicate the beginning of the Anthropocene Epoch.

Decoding plastic pollution in the geological record: A baseline study on the Caribbean Coast of Colombia, north South America

This study presents the first report of plastics in the geological record (rocks and formations composed of plastics) along the central Caribbean Coast of Colombia, northern coast of South America. These novel records of pollution include two rock types (plastiglomerates and quartz plastisandstones), two altered plastic types (pyroplastics and plasticrusts), two soil types (plasticlasts and anthrosols), and a series of artifacts (fossils) found near human settlements. All of them were analyzed using Fourier Transform Infrared (FTIR) spectroscopy. Polyester, high-density polyethylene, and copolymers of alkyl acrylates or methacrylates were identified as the principal polymers forming these rocks. This research provides new insights into the petrology of these emerging new forms of pollution, for which humans are primarily responsible for their generation and distribution. Similarly, the results presented emphasize that plastics are generating a deluge of pollutants in terms of variety and volume, overwhelming natural environments globally. Controlling or even eliminating their use has become one of the most significant challenges of the 21st Century.