Exposure to widely used insecticides decreases sperm concentration, study finds
Ali Alotbi
Link to Paper: https://ehp.niehs.nih.gov/doi/10.1289/EHP12678
Link to Article: https://www.theguardian.com/environment/2023/nov/24/insecticides-decrease-sperm-concentration-study-finds
Over the
last century, human sperm concentrations have been shown to have significantly
decreased across a wide range of populations studied, and prospects of further
decline threatens male fertility. In addition to fertility issues, low sperm
concentration is also linked to reduced male health, including higher rates of cancer
and mortality. Reproductive toxicants (environmental pollutants that negatively
impact reproductive health) are everywhere in the environment but are usually
not observed until their adverse effects have already impacted people.
Pesticides are known to have disruptive effects on the endocrine and reproductive
systems yet are still widely used and applied. People are therefore exposed to
these reproductive toxicants via occupational and environmental exposure. Although
these pesticides are meant to kill pests, they often cause acute (short term)
and chronic (long term) effects in off-target organisms, such as the thinning
of bird eggshells with DDT, and reduced reproductive health in humans with
organophosphate (OPs) and N-Methyl Carbamate (NMCs) pesticides. OPs and
NMCs are acetylcholinesterase inhibitors and therefore prevent the degradation
of neurotransmitters such as acetylcholine, resulting in the continuous reopening
of sodium channels of neurons, disrupting normal neural impulse transmission. While
the mechanism of male reproductive damage caused by these insecticides is not
well-understood, it is known that they interfere with hormone receptors and cause
oxidative damage to cells in the testes. Additionally, neurotransmitter levels
may be altered which can disrupt the release of gonadotropins that directly
influence sperm production.
A recent article
published in The Guardian written by Tom Perkins on November 24, 2023, discusses
a paper recently published that looks at the association between OP and NMC
exposure and reduced human sperm concentration.
The scientific
paper itself is a meta-analysis looking to find the association between chronic
OP/NMC insecticide exposure and sperm concentration in human adult males ages
18 and up. Meta-analyses on how insecticides impact sperm are rare, so this is
a valuable study. The paper focused on 2 insecticides: organophosphates (OPs)
and N-Methyl Carbamates (NMCs). OPs and NMCs are less environmentally
persistent than organochlorine pesticides and have therefore seen increased use
over the last few decades. Beginning in November 2020, the team collected papers
from 3 online science databases (PubMed, Scopus, and Web of Science), 2
governmental databases (NIOSHTIC-2 and Science.gov), and 5 nongovernmental
databases. Papers of any language and published through August 11, 2022 were
examined and then bias for each paper was evaluated by a three-level,
multivariate random-effect meta-analysis model with cluster-robust variance
estimation. Studies on exposure before childhood and acute exposure events
(chemical warfare, industrial accidents) were excluded from the meta-analysis. The
meta-analysis revealed that across 20 studies, 21 study populations (North
America, South America, Asia, and Europe), and 1,774 adult men studied, sperm
concentration decreased by 30% in men who had greater exposure to OPs and NMCs relative
to those who had less exposure to these insecticides. At the 95% confidence
interval, this number ranges from 49% to 10% decrease. The researchers checked
for bias, insecticide class, exposure setting (occupational or environmental),
and recruitment setting (where they recruited people to be sampled, i.e.,
general population or infertility clinic) and found a trend where reduced sperm
concentrations were observed in men exposed to insecticides across the board. 60%
of studies they examined focused only on OP insecticides. Most of the studies
(72%) looked at occupational exposure as opposed to environmental exposure
(28%). 44% of the studies accounted for abstinence time of the men they sampled
from. Most studies (68%) accounted for coexposure to other chemicals. The authors
discuss that OP insecticides may present a greater risk to sperm concentration
than NMCs, but this could be due to the increased proportion of studies that
only examine OPs. Something I found interesting was that the authors say that
the body of evidence is of moderate quality and that there is sufficient evidence
of an association between higher adult OP and NMC exposure and lower sperm
concentration. In other words, although more studies “can be beneficial to fill
data gaps,” the evidence shows this association, and the authors recommend that
action be taken now to reduce OP and NMC insecticide exposure to prevent
further male reproductive harm.
Within the
scientific paper, a call to action is given twice: once at the very beginning
of the paper at end of the Discussion section, and again at the last sentence
of the Conclusion section at the very end of the paper. The Guardian article uses
correspondence with Melissa Perry, a coauthor of the meta-analysis, to
strengthen this call to action which I think is a good move. I believe that papers
with such big implications need to be discussed between authors and media
publishers so that they can get things right and capture the emotion and the science
simultaneously. The Guardian article correctly describes the meta-analysis by
including the number of people studied and stating that papers from the last 50
years were reviewed. It even does a great job of qualifying key results of the
meta-analysis! For example, the article states that while the strongest associations
have been made between occupational exposure to insecticide and reduced sperm, this
may be because there are fewer studies on alternate exposure settings. The
article also doesn’t try to over-sensationalize the role that insecticides may
play in male infertility, stating that insecticides may represent a piece of
the puzzle in understanding the decline in human sperm concentration over the last
century. The article also discusses OPs and NMCs mechanism of action and even
an EPA announcement from this year that will accelerate OP regulations.
The
Guardian article does not include a link to the paper, so I had to search for
it myself. Although this was a very quick search and the paper was easy to find
and is open-access, I think it would have been nice for the link to be included
in the article itself. Additionally, the article also includes statements that
link organophosphates to ADHD and autism but does not include the sources that support
this claim as this is not discussed in the paper. The article also does not
discuss the many statistical tools the researchers used, but I think this is
fine because those tools can be pretty esoteric and not readily understood by
the general public who may not have deep understanding of a large variety of
statistical formulae.
Overall, I
believe the article does a fantastic job of summarizing the key findings of the
meta-analysis and making them digestible for the public. It also includes more
information about the insecticides of interest, discussing their mechanisms of
action and even looming regulations by the EPA. However, my main critique of
the article is that it doesn’t link all its sources or even the main paper it
is discussing, though it does include enough information to readily search up
the article. Therefore, I’d rate it a 9/10!
One thing I liked about the scientific article was how they went into detail about the meta-analysis and how they had a specific method of cross-analyzing so many studies. There is a strong correlation between insecticide exposure and decreased sperm count but the article mentions that this doesn't necessarily indicate a causal relationship. This is definitely a good place to start, though! Do you think there are any other factors that should have been considered?
ReplyDeleteI agree! I believe their meta-analysis was quite extensive and it was really cool to learn just how much work and statistical analysis goes into that process. I think future work could perhaps examine diet of the men tested and account for abstinence. I'm aware that certain foods can boost sperm production and testosterone such as ginger, leafy greens, and legumes, so I think it could be interesting to compare men who were exposed to insecticides and men who have a diet deficient in these foods. It would be hard to do this with the same groups of men from the original studies because it may be hard to verify their diets from that long ago, but it would have been interesting if that was also considered at the time.
DeleteI think it is very interesting an observational study was reported on, as opposed to an experimental study since observational studies cannot determine causation just correlation. I like how the research specifically said it cannot say for sure it is a casual relationship, but I wish the article made it a bit more clear other than a quick probably. As a call to action it is effective but it is interesting that the PI's quotes in the paper make it seem that pesticides are definitely impacting fertility and are the main problem, which is not necessarily able to be proved or the tone the actual research came across with.
ReplyDeleteI completely agree. This was initially something that struck me as being a drawback about the article (and I still think it could be a negative), but then I thought that a scientific journal might not be the right place to have such strong calls to action. Public media may be a better place for researchers to give stronger calls to action as it may have a greater chance of being seen by someone involved in politics who can enact regulations necessary to bring about that change. Of course, one could argue that it may be irresponsible for a researcher to have a mild-toned paper and then very strong calls to action in an article that the public will read as this could be seen as oversensationalizing. It's definitely interesting!
DeleteI agree that this article does a fantastic job of relaying the important information found in the article in such a short time. I'm surprised, though, that there is no link or mention of the title of the article to which they're referring. I've noticed that's a recurring theme in some scientific news articles, and I'm curious if there is some administrative red tape preventing the author from linking directly to the study. Going so far as to have correspondence with the co-author of the study seems like it would be enough of a green light to go ahead and mention the paper directly.
ReplyDeleteI agree. I noticed that some of the links actually included in the article referencing previous information are just links to other articles from The Guardian instead of the primary sources themselves. This made me suspect some kind of administrative red tape as well, but then they include links directly to the EPA announcement! I agree that correspondence with one of the authors should have been enough for the writer to directly link the paper. I'd be interested to hear if anyone knows why this may be done in scientific news articles.
DeleteI understand why the researchers decided to do a review on those measuring sperm count in adult males pre-exposed to these pesticides and report the correlation. Trying to provide more solid evidence as to these pesticides "causing," sperm depletion would most likely involve extensive animal studies. Many pollutants and pesticides in addition to those discussed in this research article have been shown to cause cancer or block endocrine receptors. It is likely they all play some role in the decrease in sperm count over the last century and should be limited in terms of the amounts we are exposed to. I think this news article is one of the better ones we have seen in class so far. My biggest qualm is just with the fact they mentioned one of the chemicals discussed being associated with autism and ADHD and then did not site any sources.
ReplyDeleteI agree! I think it's important for science communication (whether a news article or a primary paper itself) to cite sources. Not citing sources in public media could have many consequences, but the two that come to mind for me right now is that 1)People can assume someone is completely making something up and therefore not believe it even if it's true, and 2)People can read something they saw online, take it as fact, and go on disseminating that information even though it may be false. I believe citing sources in public media is important to limit those two things.
DeleteHi Ali, this is a fascinating scientific paper (and well-relayed article) that I'm certain opens a can of worms when we consider the impacts OP's and NMC's has on future generations. Perhaps this is a bit far-fetched, but were you able to find any research showing negative health impacts on children of males exposed to endocrine disrupting insecticides with low sperm production? We've certainly become more aware of generational effects via heavy metal exposure over the years, and it seems like this proves to be a wild-card as evidenced by cited research showing insecticides impacting neurodevelopment during pregnancy.
ReplyDeleteThanks for the question! I did some more research and I found a source (https://pubmed.ncbi.nlm.nih.gov/18032334/) that discusses adult pesticide exposure and its effects. Some of these effects on the babies of these people include birth defects, fetal growth retardation (the fetus is not growing at the rate it's supposed to), and possibly childhood leukemia. I agree that it will be important to monitor future generations to see how they're impacted.
DeleteI was very impressed with the faithful report from the news article's perspective. Perkins does a good job echoing the study's positions, and avoided the generalizations that one might expect. The Guardian article explains that there was a correlation found between OP/NMC pesticide exposure and lower sperm counts while informing the reader that the study was a meta-analysis rather than experimental in nature. Additionally Perkins echoes the study's call to action, highlighting how this research provides reason for further study into the public health issue rather than conclusive data on the exact cause of the issue. Overall I was very impressed with the brevity and accuracy of the news report from the Guardian!
ReplyDeleteI was impressed as well! There are certainly more studies that need to be done to collect more conclusive data. I think that future studies should account for alternate routes of exposure, diet, and abstinence of the men they sample from. I was also happy with the brevity of the article and simultaneous communication of the key points of the study and extra information (mechanisms of action & EPA regulations) related to these pesticides!
DeleteI agree this article does an amazing job of conveying the ideas presented from the scientific article in a way that accurately describes the research presented as stays true to the research. I throughly enjoyed reading the scientific article as its research goes into great depth. I was honestly surprised to see a Guardian article that actually stays completely faithful to the scientific research presented, they often tend to miscue the research presented in scientific articles to fit their own agenda and message, honestly Kudos to Perkins for doing such a good job presenting the research from the scientific article. The only thing that still sticks out to me from the article is the mention between the link of chemicals discussed in the article to Adhd and autisim when that is not stated anywhere in the scientific research, do you have any outside sources for where they got this idea?
ReplyDeleteHi Ali, I absolutely agree with you that the article does a nice job communicating the key aspects of the scientific article as well as integrating the quotes from Perry into the piece. Similarly, I can see how the way this article could incorporate the paper is very different as it is a meta-analysis instead of a single experimental paper; though, I would have liked to have seen a little more about (in/ex)clusion criteria in the article, as "this meta-analysis..." is something that may prompt more questions than answers, specially about the integrity of the analysis (i.e. the meta-analysis may be perfectly integral, but the lack of communication in the article about this may inadvertently sway the audience away from this piece).
ReplyDeleteThis might be the best Perkins article we have read in this blog so far, we've seen that he has a track record of making minor yet significant errors. Although the article was very short, like others have mentioned it conveyed the findings well and with a good sense of urgency. I think that in the spirit of the 'call to actions' mentioned by Ali, I feel like a mention of Europe's stricter bans on pesticides might be helpful in making stricter bans in the US feel like common sense.
ReplyDeleteI think this article does a very good job of getting the original study's key points across to the audience in a concise manner. Although the news article doesn't include the link to the scientific paper, it does not detract from how well the author cited statistics from the paper. I was also pleased with how the author included direct quotes from Melissa Perry. I also agree that a lack of discussion on the statistical tools used is not much of a problem--and my actually be to the article's benefit if the goal was to make more people aware of the issue. However, I wish the article also discussed Perry et al.,'s suggestions at where the meta-analysis can be improved, and on which insecticides should be emphasized.
ReplyDeleteThe article does a good job summarizing the study's key findings for the public. However, it could improve its credibility by including a direct link to the scientific paper discussed, making it easier for readers to delve deeper into the research. Additionally, while the article explains insecticide mechanisms well, it lacks sources for claims about organophosphates' potential links to conditions like ADHD and autism. Overall, however, I agree with your rating. Maybe a little low an 8/10.
ReplyDeleteI really enjoyed this article and I liked how it ties in ideas from what we are learning to broader impacts. In terms of the news article itself, I think the author does a quite nice job at summerizing all the main points the paper makes. It does skip over all methods as you mentioned. I think it would of been nice if they included the data about where they surveyed these men from as you can get an idea that this is not a regional problem but a worldwide problem. I think if the author included a more call to action to at some point during the article that would be been nice. But overall I agree with your analysis and I would give it a 8/10.
ReplyDelete