Human activity doubles microplastic pollution in urban lakes compared to remote ones

A Global Review of Lake Contamination

Microplastics are an persistent form of pollution threatening the health of global lake ecosystems. A new review by researchers at the Chinese Research Academy of Environmental Sciences synthesizes current knowledge on the sources, distribution, and environmental effects of these tiny plastic particles. The study, led by author Ting Pan, analyzed data from 89 lakes worldwide to identify key factors influencing contamination levels and to outline the risks to aquatic life. The findings confirm that human activities are the principal drivers of microplastic pollution in these essential freshwater bodies.

The Urban Connection

The research establishes a clear relationship between human populations and the quantity of microplastics found in lakes. The analysis showed that the abundance of microplastics is positively correlated with surrounding population density and negatively correlated with the distance from populated areas. On average, urban lakes contain twice the concentration of microplastics 4078 particles per cubic meter compared to remote lakes 1302 particles per cubic meter. Major sources in urban settings include wastewater treatment plants, landfill runoff, and industrial manufacturing, which introduce plastic microbeads from personal care products and household supplies.

Widespread Pollution Beyond City Limits

Microplastic pollution is not confined to urban centers. In suburban and rural areas, sources include waste from fishing activities, such as aged nets and lines, and agricultural films. The review also documents the presence of microplastics in remote and high-altitude alpine lakes, far from direct industrial or domestic sources. In these pristine environments, particles arrive through atmospheric transport via wind and precipitation. Human tourism, including hiking and climbing, also contributes to pollution as microfibers are shed from clothing and equipment. This demonstrates the extensive reach of microplastic contamination.

Where Microplastics Accumulate

The study examined how microplastics are distributed across different parts of the lake environment. While water contains a wide variety of particle shapes and sizes, sediments act as a sink for larger and denser fragments. The review reports that fragments and particles between 1 and 5 millimeters are more likely to settle at the bottom of lakes. In contrast, lighter forms like fibers, which account for a large portion of microplastics, are more mobile and can be found throughout the water column and even transported upward into ice.

A Chilling Discovery in Lake Ice

A significant finding from the review relates to the behavior of microplastics in seasonally frozen lakes. Lake ice caps can adsorb microplastics from both the water below and the air above during freezing. This process leads to much higher concentrations of microplastics in the surface and bottom layers of ice—sometimes 10 to 100 times higher than in the lake water itself. When this ice melts, it releases a concentrated dose of plastic particles back into the ecosystem, presenting a seasonal shock to the environment.

The Ecological Toll on Aquatic Life

Microplastics present a direct threat to lake organisms. The review details how these particles can inhibit the growth of aquatic plants like algae by blocking sunlight needed for photosynthesis. Aquatic animals often mistake colored microplastics for food, leading to ingestion. Once inside an organism, microplastics can cause intestinal damage, disrupt energy metabolism, and induce physiological stress in organs like the liver. In some cases, high concentrations of these particles can be lethal to aquatic life.

A Carrier for Other Pollutants

Beyond their physical effects, microplastics act as vectors for other harmful substances. Their surfaces can adsorb pollutants such as heavy metals, organic chemicals, and even antibiotics from the surrounding water. When aquatic organisms ingest these plastic particles, they are also exposed to a concentrated dose of these attached toxins. This combined pollution complicates the environmental risks and introduces another pathway for dangerous substances to enter the food chain, potentially affecting human health through consumption of contaminated fish.

Corresponding Author:

Haiqing Liao or Fang Yang

Original Source:

https://doi.org/10.1007/s44246-023-00057-1

Contributions:

Ting Pan collected and analyzed the data and wrote the manuscript; Haiqing Liao and Fang Yang analyzed and modified the manuscript; Fuhong Sun and Youjun Guo improved the language of the manuscript; Hao Yang, Dongxia Feng, Xingxuan Zhou and Qianqian Wang analyzed the data. All authors have read and agreed to the published version of the manuscript.