DDT's toxic legacy can harm granddaughters of women exposed
Esmé Frattarelli
Scientific article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8338759/#R13
News article: https://www.latimes.com/environment/story/2021-04-14/toxic-legacy-of-ddt-can-harm-granddaughters-of-women-exposed
Persistent organic pollutants (POPs) were extremely wide-spread in the mid 20th century and continue to negatively impact those who have been exposed to them; including exposure in ovum. Dichlorodiphenyltrichloroethane (DDT) is an organic compound which was previously used as an insecticide. DDT was banned in 1972 but persists in the environment and continues to be present in food. This study focuses on the correlation between obesity and DDT exposure. In commercial DDT, the active insecticide was p,p’-DDT but was also made of the low level contaminant o,p’-DDT; the former being the primary form and the slowest to metabolize. The primary metabolite of p,p’-DDT is p,p’-DDE and lasts significantly longer in the environment and continues to impact our food supply.
The study follows three generations of women: grandmothers (F0), their daughters (F1) and their granddaughters (F2). Perinatal serum samples were collected from F0 between 1959 and 1967 during active use of DDT. Daughters (F1) self-reported their height, weight, and age of menarche during a telephone interview. Granddaughters (F2) on the other hand, were measured during a home visit and data were collected about the woman’s height, weight, waist circumference, and age at menarche. I was surprised that data collections were not the same for generations F1 and F2, especially because F1 was asked to self-report data. Weight is a topic that many people are sensitive about so I imagine that not every participant was truthful with the numbers provided which could cause inaccuracies with the BMI calculations.
From the collected data, the study found that daughters (F1) who has been exposed to o,p’-DDT had an increased risk of breast cancer and breast cancer risk factors including obesity. F1 obesity was significantly positively correlated with F2 obesity but not with F2 early menarche. Comparing F2 obesity to F0 o,p’-DDT exposure, the study found that granddaughters had a 2-fold greater risk for obesity when grandmothers o,p’-DDT levels were in tertile 3 compared to tertile 1. Interestingly, when grandmothers were obese/overweight, the risk of obesity in F2 was significantly lower which can be attributed to the fact that DDT and DDE are lipophilic so it is believed that excess body fat diluted the exposure to F1.
In my opinion, the main weakness of this study is that the participants have too many unknown variables. Obesity, early menarche, and breast cancer are all positively correlated with DDT/DDE exposure but the paper points out that these traits also tend to be genetic as well; specifically, that obesity tends to increase in subsequent generations and menarche age tends to decrease. The data that I found most interesting was that although obesity can be genetic, overweight grandmothers were less likely to have obese granddaughters because excess fat helped protect the baby from the harsh chemical by limiting exposure.
The LA Times article explains the overall idea of the research study and I think it does a good job of providing context about DDT. However, I think it gets off track in a few spots and discusses issues that are not directly related to DDT. For example, there is a quote from Blumberg about how obesity affects 42% of Americans which may be true but it is a statistic independent of this research study and exposure to this chemical. I also notices a misrepresentation about the size of the study when the author said that it is a multigenerational study that followed 15,000 women. Although the original group was large, the study could not get data from 3 generations of everyone who participated in the 1960s. Part of the research paper explains how some people were excluded due to incarceration, mental health, participation in another study, or refusal. Because of that, only about 1200 daughters participated and 1100 granddaughters.
Overall, I would give the media article a 7/10. The majority of the information was correct but it was vague and didn't mention the weaknesses of the article (weaknesses that I think are pretty significant). This article seemed to attribute many negative health effects like cancer and obesity, to the use of DDT without considering all of the external factors. Additionally, the differentiation between the types of DDT was not included which is odd to me because the research shows that different isoforms have different biological activities and the metabolites (DDE) are acquired independently of DDT exposure. I think that the most important issue of this study is the fact that chemical exposures can be passed down for generations and the LA times article does a good job of explaining the significance of that but it would have benefitted from the discussion of the present-day DDT metabolites. Without that part of the discussion, it is hard to make sense of the fact that DDT/DDE is still present in our food since the author only really discussed how it is passed down during development.
Hi Esmé, I thought the studies' premise was extremely interesting, but as you pointed out they didn't consider outside influences on cancer and obesity, such as diet. I believe the study's authors felt it would become too complex if they included all these other factors in their experimental setup which may be why they weren't factored in. However, how significantly would the study's results be impacted if they could take them into account?
ReplyDeleteI agree! It would have gotten too complicated if the study had to consider every factor. Since the main cause of obesity is consuming more calories than you expend, I think the person's caloric intake would have been useful in narrowing the focus of the study to get more precise numbers. The media article included an interview with one of the granddaughters from this study who said that she eats a balanced diet and exercises regularly but still has a hard time with her weight. In that case, I think she was a great example of the effects of her grandmother being exposed to DDT.
DeleteSo to answer your question, I imagine that the overall findings of the study would still show a correlation between DDT exposure and obesity in future generations but I wonder if it would still be a 2-3 fold increase in risk without looking at habits and lifestyle.
This scientific/news article blog post is interesting, because it seems like there are more issues with the scientific paper than the news article. I am surprised that the scientific article didn't attempt to get control groups for the data. I feel this would help to control for other factors such as genetics. I do understand that this could be difficult for the authors to do, though, considering the massive, widespread use of DDT during that era. It would be interesting to see, though, if communities that had minimal DDT exposure showed some of the same trends. If so, this could be a case of correlation rather than causation.
ReplyDeleteI thought the same thing! Since we know that it accumulates in adipose tissue, I thought it was interesting that there may be a connection between fat storage and DDT exposure but this research definitely focused on correlation instead of causation. Some other studies found that serum DDT/DDE may lower circulating thyroid hormone and resting metabolic rate which could offer an explanation for the weight gain (but these were over 5 years ago and the test subjects were rats).
DeletePopulation studies are always hard to look because of these outside factors and this one with the lack of control makes it even harder. I agree that it would be a lot stronger if outside factors were considered more in the study. It's also interesting when you go from article to study how the discussion of the metabolites such as DDE is no longer present. This is a clear simiplication for the public that probably wasn't necessary
ReplyDeleteI agree that it probably isn't necessary for the media article to get into too much detail about DDE but I think it would have been beneficial for them to mention why people are still being exposed to this pesticide (because of the metabolites that persist in the body and environment longer than DDT). It's important to note that there are multiple ways to be exposed to this chemical today, even after DDT has been banned.
DeleteThis study uncovers a fascinating intergenerational connection between DDT exposure and obesity. It reveals that daughters exposed to o,p’-DDT had a higher risk of breast cancer and obesity, with an unexpected twist: when grandmothers were overweight or obese, the risk of obesity in their granddaughters decreased significantly, suggesting a potential protective role of excess body fat. However, the study's weakness lies in the numerous unknown variables, as obesity and early menarche have genetic components, complicating causation interpretation. The media article, while generally accurate, lacks depth in addressing study limitations and essential details, such as DDT isoform distinctions and the persistent presence of DDT/DDE in our food beyond developmental transmission. How might advancements in epigenetic research enhance our understanding of the interplay between environmental exposures like DDT and genetic factors, providing new insights into the mechanisms underlying multigenerational health impacts?
ReplyDeleteThats a really interesting question! The research paper mentions other studies, specifically studies that looked at the relationship between DDT and breast cancer. Those studies found that DDT may actually alter methylation patterns of certain genes and turn on breast cancer genes. So it's possible that DDT is altering other genes (impacting obesity, age at menarche, etc.) so the traits being passed down may have been altered by ancestral exposure to chemicals. I think there's a lot more research to be done about the long-term effects of chemicals. Genetic sequencing seems like a good way of tracking exposure and gaining information on how they work (which would also help us treat the problems they cause).
DeleteI understand that it would probably be very hard to find a control for this type of study since DDT was very widespread, but it is shocking to me that there wasn't a control. I also agree that it would have made the article a bit complex if they included other factors such as diet and exercise, but in order to get more accurate findings, it would really strengthen their research. I do wonder if the relationship is actually quite as strong as it appears or if these unaccounted factors inflate it to a degree.
ReplyDeleteI completely agree! Although there wasn't a specific control group, the data were being compared to the standards of the World Health Organization in terms of BMI and age at menarche. I wonder if they were trying to use "normal" BMI and age at menarche as their unofficial control control group.
DeleteThe topic of this article is very interesting, it makes me wonder what other chemicals could be affecting us right now even if we weren't exposed to them directly, but rather by proxy through our parents. It does take away some of the power of the study's results knowing that not any significant attempt to control for lifestyle or other factors affecting negative health effects, and I think the media article should have addressed this more explicitly just to be sure that they're not giving undue authority to the results of the study. I also found it really interesting that obesity in offspring was less common for grandmothers who were obese due to the effect of body fat sort of shielding the chemicals, and I liked that you included this fact in your summary.
ReplyDeleteI wondered about other chemicals too, I'm sure they impact our health more than we realize. I agree that the media article should have addressed the lack of a control group, that seems to be a problem with a lot of the media articles- they leave out some pretty important details in order to get the readers' attention.
DeleteI find it interesting that that the scientific paper did not really consider other factors affecting the health of these women because that feels like something they should very obviously do. Additionally, I think the news article should point this out, as you mentioned. It seems maybe dramatic to not do so and could cause readers to to take the findings of the study more seriously than maybe they ought to.
ReplyDeleteI agree! The media article says that scientists have "confirmed for the first time" that grandmothers exposed to DDT causes negative health impacts in their granddaughters. The way it's worded makes it sound more definitive than it is, they should've said that it is correlated instead of caused.
DeleteI agree that self-reporting could be a source of potential uncertainty as people may not have given 100% accurate information about themselves at the time of the phone interview. Nonetheless, I am always impressed by multigenerational studies, especially in humans, because it takes so long to get information and see trends. I think it's interesting here that the excess bodyfat potentially limited the daughters' exposure to DDT. I agree that there are a lot of unknown variables that could be at play. What would you suggest be done to collect better/more sound data?
ReplyDeleteAlthough I do agree that the news article sometimes strayed away from the main discussion in the scientific paper, I do believe that if either was lacking, it was the scientific paper. This is because the article had several shortcomings, as you mentioned, such as that the main point being tested was to see the affect of DDT as it is passed down through the generations. Also, since much was self-reported, inconsistencies in the data likely came about, especially when it came to BMI calculations. If these are deemed unlikely to be true and there is a clear reason why they likely aren't true, it shouldn't have been reported.
ReplyDeleteI am a bit confused on how the perinatal serum samples were used to study DDT in the grandmothers' bodies. Maybe it's just a lack of understanding of what perinatal serum is, but when I looked it up the results showed that it's a simple blood test to scan for genetic disorders. I know you can get a lipid panel done from a blood test which can show things like triglyceride levels so did they do something similar to determine DDT levels in the fat?
ReplyDeleteThough the news article describes the scientific study in a thorough way and discusses the legacy impact of environmental pollutants, I agree with you that the news article is lacking the explanation for confounding factors that might also have led to early menarche and adult obesity. I wonder if there are specific methods to separately quantify the effect of DDT, like chemical tracers and genetic techniques?
ReplyDeleteBoth the news and scientific article did a good job of conveying the long standing impact of DDT, however the article strays off focus at the end of it's length with an odd inclusion of BPAs and PFAS, which are not an aspect of the research article. A few other comments have mentioned the lack of control group availability in the study. While from an experimental perspective this is unfortunate, I believe the more substantial take-away is the difficulty in sourcing a control group given the prevalence of DDT/DDE exposure for the US population. Additionally, this highlights the importance of caution from the public when pesticides are presented as 'harmless' and the duty of the scientific community to be diligent in safety evaluations prior to deployment of new substances.
ReplyDeleteThis was a very interesting topic and paper to read and choose! I love the idea of this paper but the bringing to life seems quite difficult as we see. I believe one main pitfall of this study is the fail of a control group. I do believe that it is rather too difficult to account for all the aspects that influence a persons health as it relates to these studys as one has to take in to account human nature. I think the news article does a decent job at relating all the information given in the article but seems to include other 'unnecessary' information. I like your analysis of these but I wonder what would you try or consider when conducting a study on this scale to get more emperical data?
ReplyDelete