Pollution is Not Just "Evil" — "Traces of Humanity" Unravel Earth's Mysteries

Pollution is Not Just "Evil" — "Traces of Humanity" Unravel Earth's Mysteries

Pollution is Not Just Something to "Erase"—The "Fingerprint of Human Activity" Seen by Science

"Pollution is rampant. So, we might as well make use of it." These are strong words. Before reading, it might sound like defiance or provocation. However, this phrase does not suggest a positive attitude towards pollution; rather, it reflects a realistic and somewhat bitter research stance of interpreting anthropogenic substances that have already spread worldwide as "evidence."


Chemical substances and particles left in the environment are not merely waste. Their concentration, isotope ratios, particle types, and spatial distribution encode "sources," "timing," "transport routes," and "residence time." In other words, pollution is a "log" that the Earth has preserved. Of course, just because it's a log doesn't mean the harm disappears. However, if we can't read the log, countermeasures become guesswork. Scientists continue the paradoxical task of "reading pollution to reduce pollution."


1) Lead Imprinted in Ice—Unearthing the "Chronicle" of Industry and Policy

A representative example of anthropogenic substances functioning as a "record of history" is lead (Pb) pollution found in ice core samples. Ice accumulates like tree rings, encapsulating past atmospheric components. The lead contained within reflects the impacts of mining, smelting, coal combustion, and (formerly) leaded gasoline.


For instance, records from Greenland reveal fluctuations in lead emissions over time, providing concrete evidence of how human activities have altered the chemical composition of the atmosphere. Some studies have even estimated lead pollution dating back to ancient mining activities, while for the modern era, efforts are underway to "fingerprint" changes in emission sources using isotope ratios.

 
The important point here is that science doesn't just stop at saying "this is how it was in the past." Changes in policy and industrial structure, such as the introduction of regulations and fuel transitions, appear as "results" in the ice records. In other words, pollutants can also serve as a measure to verify whether countermeasures have been effective.


2) "Leftovers" from Nuclear Tests Determine the Age of Sediments

Another powerful timestamp is **radioactive nuclides from nuclear tests and accidents (e.g., ^137Cs)**. Atmospheric nuclear tests from the 1950s to the 1980s widely deposited radioactive nuclides on the surface and in water bodies. These serve as markers in sediment cores to estimate "this depth corresponds to this era."

 
Ironically, global pollution events have helped read high-precision records of the "last few decades to a century" in lakes, coasts, and seabeds. Knowing the sedimentation rate allows for a chronological discussion of when and at what rate eutrophication, heavy metals, and microplastics have increased.


3) CFCs and Tritium—Anthropogenic Tracers to Measure the "Age" of Groundwater

Surface pollution is visible, but the world of groundwater is less so. Here, tracers like **CFCs (chlorofluorocarbons) and tritium (^3H)** are used. CFCs surged in the 20th century and then declined due to regulations. By measuring the concentration of CFCs dissolved in groundwater, one can estimate when the water was "recharged" from the surface to the underground.

 
Similarly, tritium, with its concentration spikes associated with atmospheric nuclear tests, is used for "time alignment." The USGS organizes background information such as peaks in tritium input from nuclear tests.


What is the benefit of knowing the age of groundwater? For example, it allows for the estimation of whether pollution like nitrates, pesticides, and PFAS originates from "land use decades ago." This means that the causes can be reinterpreted as the impact of past decision-making rather than solely blaming current actions. The time axis of countermeasures (the delay until effects are seen) can also be estimated. Groundwater, because it "acts with a delay," makes age information directly relevant to policy.


4) PFAS—Visualizing Ocean Currents with "Forever Chemicals"

PFAS (per- and polyfluoroalkyl substances) are notorious for being "difficult to break down" and "easy to spread." However, their "stubbornness" has, conversely, drawn attention as a chemical tracer for tracking ocean circulation.


In the 2000s, it was noted that the distribution of PFAS (such as PFOA/PFOS) aligns with major ocean currents and deep circulation patterns, suggesting they could serve as a "new chemical tracer" for studying ocean transport.


Here lies a scientific pragmatism. PFAS should be reduced. However, since they already exist, by thoroughly measuring their distribution and understanding their movement, we can identify where they "accumulate" and where they might be re-released. In fact, there are reports suggesting a cycle of returning from the sea to the atmosphere and coasts, and the possibility that the sea, once thought to be the "end point" of pollution, might again affect the land is being discussed.


5) Microplastics—Strata of the "Plastic Age" Left in Sediments

Microplastics are also emblematic pollution of the modern age. In the research community, there is ongoing debate about whether microplastics in sediments could serve as a stratigraphic marker of the Anthropocene.

 
By dating sediment cores and examining the quantity and types of microplastics in each layer, the expansion of plastic use in society and changes in materials appear as "layers." Furthermore, microplastics have been detected in deep-sea sediments, indicating that surface consumption activities reach the depths of the ocean.


However, there are many caveats. Since microplastics can be contaminated, moved, or degraded, it is not always straightforward to say "deeper equals older." This is why recent consensus suggests the need for careful interpretation by combining them with independent age indicators like ^210Pb or ^137Cs.


6) "Using" is Not an Excuse—Ethical and Environmental Justice Issues

After reading this far, one might be tempted to think, "If pollution can be used, then it's not all bad." However, what scientists mean by "use" is not a shift in value judgment.


Rather, it is an attitude of extracting maximum information to reduce harm in the face of the reality that pollution has spread extensively. Lead, PFAS, and microplastics raise concerns about health and ecological impacts. Research use does not lead to "it's okay to keep polluting."


Furthermore, the perspective of environmental justice cannot be overlooked. Pollution does not fall equally on everyone. Structural factors such as industrial location, income, social vulnerability, and indigenous communities lead to unequal burdens. Therefore, research on "reading pollution" is useful not just when it satisfies academic curiosity but when it is linked to visualizing responsibility and inequity.


7) Reactions on Social Media (Due to the "Provocative Title" That Easily Splits Opinions)

This theme tends to split opinions on social media. Reactions generally fall into the following types:

  • "Sounds Like Defiance" Group: From just the title, it feels like endorsing or promoting pollution, leading to backlash.

  • "Realistic and Ironic Expression" Group: Interprets it as meaning "using data" for damage reduction and monitoring, assuming the widespread pollution.

  • "Difficulty of Science Communication" Group: Concerns that attention-grabbing headlines might lead to misunderstandings.

  • "Should Connect to Regulation and Corporate Responsibility" Group: Argues that the discussion should not end with research but connect to emission source countermeasures, regulations, and compensation.


In fact, this article is featured as a new release on the Eos page of the AGU, indicating that it is a topic of high interest within the academic community.


Conclusion: Reading Pollution as a "Record" is to Stop Pollution

Pollution is an irreparable scar. But at the same time, it is also a trace that tells the story of the "recent events" of the Earth and society.
Lead has imprinted changes in industry and policy, radioactive nuclides serve as chronological markers, CFCs and tritium mark the time of groundwater, PFAS trace ocean currents, and microplastics mark the strata of consumer society.


Therefore, what science must do is clear.
Thoroughly read these traces, visualize responsibility, measure the effectiveness of countermeasures, and reduce the next pollution.
"Using" is not to coexist with pollution but a bitter yet powerful means to end pollution.


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