New study of European rivers shows substantial variation in how quickly commercial chemicals biodegrade
By: Teresa Billecke
Peer-Reviewed Article: https://pubs.acs.org/doi/10.1021/acs.est.4c07410
Background:
Bodies of freshwater have means of degrading chemicals found in pollutants through natural means, and their capacity for this biodegradation is influenced by several different factors such as bacteria found in the water, the concentration of the pollutant, and environmental factors like pH and sediment properties, among others (1). Understanding biodegradation can provide additional and important information about the environmental harm and persistence of different pollutants, as the European Union (EU) has regulation concerning chemical pollutants called REACH (registration, evaluation, authorization, and restriction of chemicals) by considering risks to human health and the environment (2).
Peer-Reviewed Article:
Many pollutants are dumped into freshwater bodies around the globe regularly, but these bodies of water are often able to facilitate chemical reactions that degrade some of these chemicals (1). Different environmental factors can contribute to the rate of this biodegradation, and this paper looked at ten such factors: longitude, latitude, total cell counts, total organic carbon, electrical conductivity, dissolved oxygen, pH, temperature, and sand and clay content in the soil (1). Other factors can influence the bacterial community composition, such as additional contaminants from human activity (1).
This paper looked at 18 freshwater rivers in five different European countries: Sweden, Germany, Switzerland, Spain, and Greece. They also looked at 97 different chemical compounds, and “All but two of the compounds showed significant spatial variability in rate constants across European rivers,” which means that 95 out of 97 compounds were found to be degraded in at least one of the studied rivers (1). Some of these compounds can be found in “agrochemicals, pharmaceuticals, cosmetics, food additives, and industrial chemicals,” and the two compounds that did not degrade were C12 Isethionate, which is found in liquid soaps, and hydrochlorothiazide, a medicine (3).
Figure 1: Map of the studied rivers, along with the biodegradation rates found in each country.
The three environmental factors that contributed the most to the different biodegradation rates, as shown in Figure 2B, are “The longitude, total organic carbon, and clay content of sediment” (1). Seasonality was also found to impact biodegradation in a previous research article by the same author through seasonal variations in pH that impact bioavailability or cell density (4).
Figure 2B: Shows the significance of the different factors, with longitude, total organic carbon, and clay content being the most influential on biodegradation rates. (Figure 2A is a redundancy analysis scatterplot.)
Additionally, the different compounds were found to degrade at different rates. The fast compounds had a smaller spatial variability, while the slow compounds had much larger spatial variability, and the remaining compounds that did not fit into these two categories also tended to have larger spatial variability (1). The researchers used a protocol called OECD 309 to measure the rate of biodegradation of these various pollutants at low concentration in aerobic natural water (5).
There are still additional questions that this paper did not discuss, such as different types of bodies of water like lakes and wetlands, for example. The paper also focused on the relative rates of biodegradation and did not provide much information about the chemistry of degradation or provide any calculations or estimates about the amounts of pollutants degraded in these various rivers.
News Article:
The news article “New study of European rivers shows substantial variation in how quickly commercial chemicals biodegrade” did a great job summarizing the findings from the peer-reviewed paper, including some background, the research parameters such as the countries and environmental factors considered, some of the statistical analysis utilized, and information about the fast vs slow biodegradation (3). They even included information about EU REACH Regulation and the test used in the paper, OECD 309, and discussed some shortcomings of the paper as well as future directions. Some such shortcomings are that “currently there is no clear and direct link between these geographical and environmental properties and biodegradation rates. Further research could aim to improve the understanding of the drivers of spatial variability, particularly connecting data from molecular microbiology with the biodegradation rates of chemicals” (3).
Review:
I would give this article an overall score of 8.5/10 because everything was very clearly described and had a lot of detail without being too complex. I took off some points because I would have liked for them to bring in some other sources and perhaps include some quotes from the original authors, and it would have been nice if they briefly mentioned the previous paper written by these authors, “Influence of Season on Biodegradation Rates in Rivers.” It also would have been informative if they discussed how this research could contribute to legislative work being done to prevent pollution, such as how REACH could use this information. Overall, the article did a great job summarizing the research paper.
Sources:
[1] Tian, R., Posselt, M., Fenner, K., & McLachlan, M. S. (2024). Variability of Biodegradation Rates of Commercial Chemicals in Rivers in Different Regions of Europe. Environmental Science & Technology, 58(45), 20201–20210. https://doi.org/10.1021/acs.est.4c07410
[2] https://environment.ec.europa.eu/topics/chemicals/reach-regulation_en
[3] “Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by SCU, The University of the West of England, Bristol. https://environment.ec.europa.eu/news/new-study-european-rivers-shows-substantial-variation-how-quickly-commercial-chemicals-biodegrade-2025-05-15_en
[4] Tian, R., Posselt, M., Miaz, L. T., Fenner, K., & McLachlan, M. S. (2024). Influence of Season on Biodegradation Rates in Rivers. Environmental Science & Technology, 58(16), 7144–7153. https://doi.org/10.1021/acs.est.3c10541
[5] OECD (2004), Test No. 309: Aerobic Mineralisation in Surface Water – Simulation Biodegradation Test, OECD Guidelines for the Testing of Chemicals, Section 3, OECD Publishing, Paris, https://doi.org/10.1787/9789264070547-en.
Hi Teresa! Your blog post was very interesting to read. I think the title of the article did a good job of summarizing the main point of the study. I also liked how the news article included sufficient information to make it well-rounded, such as information about EU REACH Regulation and the shortcomings in the research paper. I agree that having interviews with the authors of the study can increase the credibility, and connecting the research paper to legislative work can be effective for readers. Do you know how the researchers decided on the specific 97 chemicals that they chose? Also, it said that longitude was an important factor that showed variation in biodegradation rates. Was there a variation in specific environmental factors that the varying longitudes led to?
ReplyDeleteThank you for your comment, Kristen! In the paper, it says that they prepared 129 test compounds for the biodegradation experiments, which they had also used in their previous study, and most of them could be found in waste water and surface water. They wanted to include chemicals from multiple sources, such as pharmaceuticals, cosmetics, and food additives, and also have a variety of different molecular structures such as thioethers and amines, among others. I was trying to find how they narrowed their sample from 129 to 97 chemicals, but they didn't specify this beyond saying, "Out of 129 spiked compounds, 97 were quantified." I also checked the Supporting Information document and wasn't able to find anything. As for the question of longitude, I was very curious about that myself, but unfortunately they said that there is no clear link between longitude (along with the other studied geographical and environmental factors) and the biodegradation rate constants, and they said that more research would have to be done. Thank you for your questions!
DeleteGreat Job Teresa, I would agree with your assessment of an 8.5/10 I felt that the article summarized nicely but would have been better if it had added quotes or gone beyond just the peer reviewed article. I also thought you made a great point mentioning how the article could have gone further by connecting the findings to environmental legislation.The understanding of how research can influence policy is very important for creating future change. I have two questions for you: how do you think the inclusion of other types of water bodies, such as lakes or wetlands, change the overall findings about biodegradation rates? And do you think highlighting the environmental and health implications of slow-degrading pollutants could make the research more relatable or urgent for the public in terms of the public pressure to make policy changes?
ReplyDeleteHi Theresa! This is a very interesting subject. I am very curious if the peer review article touched on how the chemicals ended up in the lakes in the first place. Also, how does the the seasonality affect impact biodegradation? Which seasons does biodegradation occur more in? I agree with you 8.5/10 assessment of the news article because it seemed packed with information about the peer-reviewed article. I liked that it was able to explain the identities of a few complex chemicals very easily as well as the factors that contribute to biodegradation.
DeleteThank you for your comment, Sarea! I'm very curious for research to include other kinds of wetlands for a couple or reasons. One of which is that rivers, more than lakes and wetlands, have rapidly moving water, so I would be curious to see how that could impact biodegradation rates, if it does so. Different types of water bodies could potentially allow for different kinds of chemical reactions, which could be useful to know. I also think it would be useful to know because different communities around the world rely on different sources of water, particularly freshwater, so I think it would be more applicable to a wider group of people to have this additional research. For example, biodegradation in lakes could potentially be more useful here in Michigan. For your second question, I hope that the public can understand that because biodegradation rates vary, it can be dangerous to assume it's safe to dump chemicals everywhere. Hopefully, this would lead to people pushing for research to be done on each specific body of water with each chemical, as well as a push for policy changes, but I'm not sure how much traction this is really likely to gain. Thank you for your questions!
DeleteThank you for your comment, Lanna! Unfortunately, the research did not discuss much how the chemicals end up in the rivers beyond saying that there are many thousands of substances in commerce, and that many of them end up in the environment. They do look at pristine and contaminated water from downstream of wastewater treatment plants, but rather than looking at the pollutants that could be in this contaminated water, they mostly use this to analyze the spatial variability in pristine and contaminated water. As for your question about seasonality, that research was from their previous paper that I did not look at in as much detail, but it was found that "Variations in pH and total bacterial cell count were not the major factors explaining the seasonality of biodegradation," even though pH does impact biodegradation rates. It may be influenced by bacterial community structure and functions, which vary by seasons. Most of the compounds were found to degrade the fastest in the spring or summer, but there were a couple that degraded faster in the fall or winter, which suggests that temperature is not a leading reason for degradation rate variability. I would, however, be curious to see why that is the case, and why certain compounds degrade faster in these different seasons. Thank you for your questions!
DeleteHi Teresa, thanks for sharing this article and for your analysis! I agree with your article rating of 8.5/10. Legislation is a really important component of preventing pollution and subsequent climate change, and I definitely think the article would have been meaningful to include. I would be interested to see research that included different types of bodies of water - how do you think this could be accomplished? Do you think it would it be easiest to just include additional environmental factors that are specific to different bodies of water, or separately define different types bodies of water based on consideration of multiple unique characteristics?
ReplyDeleteThank you for your comment, Madison! I think it would be beneficial to perform a study on different bodies of water using the same parameters as this study in order to more effectively compare and contrast the biodegradation rates, as I believe all of the environmental factors they investigated here are also applicable to other bodies of water. Additional research that includes new factors that may be more specific to one type of body of water could be interesting and worth looking into. Thank you for your questions!
DeleteThanks, Teresa! It was really interesting to see all of the factors that influence biodegradation. I agree with your article rating as it seemed like a very informed author reporting on the paper and he seemed to mention all of the important details. I did think it was unfortunate that the paper itself did not give background on how the rivers chemically biodegrade the pollutants, and that they didnt study any lakes or other types of bodies of water, but rivers have a constant flow, and I assume that's why they were chosen to study this. It looked like total organic carbon was the largest influence on chemical biodegradation in the rivers under study. Is there a partcular reason why this might be, without knowing the specific chemical processes that cause the biodegradation? My guess is that the pollutant chemicals degrade more easily when there is more life in the rivers because the fish and other species in the river have biological processes that change the pH and chemical makeup of the water.
ReplyDeleteThe spatial variability of certain compounds definitely poses a significant challenge to policy making, as the compounds decay at much different rates in different locations. I think this would have also been interesting if done in rivers across the world, as while the authors cared about European legislation, it would have been informative to see how these same chemicals would decay in say the Mississippi, Amazon, or Nile river systems. I was also slightly confused on why they were highlighting longitude as being one of the three major environmental factors influencing different biodegradation rates. It didn't really seem like they explained what they thought the factors in the different longitudes were that was causing degradation rates to be different. In other parts of the world, longitude would likely not be a leading "factor", and so to me I feel like this isn't a very good explanation into the variation in degradation rates.
ReplyDeleteHi Teresa, I really enjoyed the analysis. I find it interesting that the research team decided to look into freshwater rivers over lakes. Personally, I'd always opt for analyzing lakes since they're easier to observe over long periods of time in case the research expands to a long-term observational study. I definitely think their and your point of looking into different bodies of water would be an amazing next step in research. To that point, I'm excited to see if salinity might also pay a factor in things. I also wonder, though, do you think plant life or animal life in and around any of the bodies of water would've also changed biodegradation speed? Especially considering the presence of fish could affect concentration of dissolved Oxygen, a factor that was studied.
ReplyDeleteThank you for your comment, Elizabeth! I agree that lakes would have been better for long-term studies, but I think they chose rivers because they wanted to be able to test water found both upstream and downstream of wastewater treatment plants, although they did not say so directly. They did not comment on how the rates differ between pristine vs contaminated water, but they did find that there was slightly more variability in the contaminated water. I am also curious to see the effect of salinity on biodegradation, and I hope that future research could illuminate this, but the paper said that they decided to focus on freshwater sources because REACH legislation prioritizes chemical persistence in freshwater bodies. They didn't discuss it much in this paper, but I would think that local plant and animal life would impact biodegradation speed because they mention the degradation rates being influenced by bacterial community composition, which would likely be related to local wildlife. Thank you for your questions!
DeleteThe news article starts off with this new research making classification of chemicals challenging. This seems especially troubling because it the EU and not just one country. There didn't seem to be any discussion about this other than just using it to introduce the research article. Was there anything you found about REACH that has changed in response to this article? I know this is still very new and these types of things progress slowly so it will probably be a while before anything changes. Do you have any ideas about how this could impact it, like varying the designation by country or being intentionally strict and if it is persistent in even one country it is classified as persistent?
ReplyDeleteI think for me this study really feels like it is missing out on some important conclusions or results in my opinion. The article and you mention that 95 of the 97 chemicals are statistically significant in AT LEAST one of the rivers; however, I think an analysis of which ones were found in all rivers or how prevalent they are throughout the region would be the more important conclusion to draw. Maybe this is the plan for this author in the future though, as you mentioned this peer-reviewed journal alreaady expands on their seasonal change in their previous research paper. Its definitely interesting to have the broad classifications though and it is very concerning that only two weren't significant enough to show up. I agree the article did a good job on the summary/explanation and it even mentions the second most critical expansion of this study that needs to be done now in that it should be expanded to lakes, wetlands, oceans, seas, etc.
ReplyDeleteGreat review! The research does a great job of addressing knowledge gap with spatial variability and freshwater biodegradation. I wonder if the authors would consider studying these rates across multiple seasons or years to analyze any fluctuations in their data. This is just a curiosity of mine to observe how the biodegradation rates may be affected by weather or time. I also wonder how these results could translate to global river systems that lie in different climates.
ReplyDeleteGreat job on your analysis! The research article showed that pH of the water influenced the biodegradation rates, but I’m curious if there was any information about how the pollutants might influence the pH of the water as well. While it makes sense that pH fluctuations would be associated with the ability to break down these chemicals, is it possible that the presence of some of these pollutants would actually decrease the biodegradation ability?
ReplyDelete