In 1962, Rachel Carson wrote Silent Spring, warning the public of the dangers of pesticide pollutants to living things. While we have made strides in reducing pollution since, such as the banning of PCBs from commercial production in 1977, streams today are still in danger from different chemical cousins.
These “persistent organic pollutants” or POP’s comprise a big alphabet soup of chemical names (If you’re a chemist, these are PCDDs, (polychlorinated dibenzo-p-dioxins) PCDFs, (polychlorinated dibenzofurans), and dl-PCBs (dioxin-like polychlorinated biphenyls), and so forth), but the important thing to know is that these POPs are carcinogenic toxins that accumulate within bodies, and poison natural ecosystems (Pereira 2004).
While POPs can come from many places– burning fuel and waste, producing paper and herbicides, and entering streams from inadequate wastewater treatment– human activity is ultimately responsible. It is then our power now to learn about these chemicals and develop solutions for their removal.
This study by Urbaniak and colleagues in Poland advanced this understanding by examining the pollution threat in the Pilica River– a tributary to Poland’s longest Vistula river, surrounded mostly by agriculture. The researchers wanted to see how flow and wastewater plants are involved, and the potential power of cucumbers for removing toxins from sediments.
Dams that Protect the River
Rivers have been the centers of human civilization, but are also some of the biggest victims of pollution. Because they are the lowest points on the landscape, rivers will collect and carry everything that flows into it. Persistent organic pollutants, for example, bind to organic matter within streams, get transported down the river, and accumulate in sediments. But streams are more than a conveyer belt: their meandering and variation in speed means that these polluted sediments will end up more in some places than others.
When water slows, sediment drops. A big place where this can happen is in the reservoir for a dam. Water collects upstream, waiting to be used for energy or irrigation, and drops its polluted baggage along the way.
The researchers hypothesized that because these reservoirs make the polluted sediment settle to the bottom, that downstream of the dam there will be fewer pollutants. This turned out to be true! Dams, while having unfavorable impacts such as impeding migratory fish, in this case help protect the downstream ecosystem from pollutants.
The opposite dynamic is also true: when the rate of water flow speeds up with higher volume, that sediment, paired with extra inputs from rain, moves more pollutants. The researchers found that when the river has its seasonal flood, this higher flow of water means higher loads of pollutants– 46 percent higher, to be exact.
Wastewater treatment plants are under a lot of pressure to clean our dirty water– but some are not well-enough equipped for the job, letting these pollutants enter at will. Instead of measuring pollutants directly at the treatment plants, the researchers measured pollutants that entered the river– allowing them to better see the impact of the treatment process on the natural system. They found that the larger plants released the highest load of pollutants to the river; not surprising given the amount of water they process. However, the researchers also saw that the smallest plants put out a high concentration of pollutants for the volume of processed water, probably due to older technology that doesn’t work as efficiently. This is something that needs to change.
Pollution is clearly a problem; it’s persistent, dynamic nature makes it difficult to control. Having learned this, the researchers then looked for some garden-variety solutions: in this case, cucumbers.
By using sludge from wastewater treatment plants and polluted sediments as soil additions, the research team hoped to see if and how plants would grow. After all, these sediments and sludge can be high in nutrients that support plant life (just high in other undesirable things as well, like heavy metals).
It turned out that cucumbers were able to decrease the concentration of pollutants in the sediment-added soils by 64%, trapping the pollutants in the stems and leaves! This practice of using plants to decrease pollutants is called phytoremediation, and is a step in the right direction for addressing these big problems.
Learning the dynamics of a stream and developing simple, smart solutions will help us protect our waters and the living things that depend on it for their survival. From rivers in Poland to the streams near your backyard– let’s keep them loud with life.
Urbaniak, M., Kiedrzy, E., Wyrwicka, A., Zieli, M., & Mierzejewska, E. (2019). An ecohydrological approach to the river contamination by PCDDs , PCDFs and dl-PCBs – concentrations , distribution and removal using phytoremediation techniques. Nature, 9, 1–17. https://doi.org/10.1038/s41598-019-55973-3
Pereira, M. D. S. (2004). Polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF) and polychlorinated biphenyls (PCB): Main sources, environmental behaviour and risk to man and biota. Quimica Nova, 27(6), 934–943. https://doi.org/10.1590/S0100-40422004000600018
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