There
are many ways for putting toxic mercury into the environment to cause
pollution. The most common ways are releasing gaseous mercury into the
atmosphere and dump waste into water. When microbes in the seawater absorb
mercury, they convert it into a powerful neurotoxin called “methylmercury”,
which can be transferred among predators, until it reaches the top of the food
chain - human. That’s why scientists pay very close attention to this issue.
A recent article in The Washington Post discusses a new study published in Proceedings of the National Academy of Sciences, which suggests that
the water in coastal areas can be contaminated by mercury from the fur of seals
coming from the ocean. The article describes the results of the research done
by Cossaboon and his team at Año Nuevo – the area that elephant
seals reside. The research shows that the seawater at Año Nuevo has
an eight times higher level of methylmercury than that of other sites along the
California coast, and there is a peak during the elephant seal molting season. Researchers
then tested the molted fur, and found mercury in it. Giving the fact that
elephant seals don’t eat at the coast, it’s reasonable to assume that they
carry the mercury all way from the ocean. However, because there have been no
obvious signs of other marine organisms being damaged, and Año Nuevo is not
used for fishing, it’s still unclear how much impact the mercury in this area have
on human.
Nearshore seawater sampling locations. (A)
Locations of Año Nuevo and comparison sites along the Central California coast.
(B) Detailed map showing the sampling stations at the south end of the Año
Nuevo mainland breeding rookery during the 2012 Northern elephant seal molting
season (M1–M6) and 2013 breeding season (B1–B6), as well as the Cove Beach Año
Nuevo State Reserve sampling site.
MeHg and HgT in nearshore unfiltered
seawater samples. (A) MeHg concentrations for the Año Nuevo mainland rookery
during the 2012 molting season (M1–M6), 2013 breeding season (B1–B6), and
Central California comparison sites. (B) HgT concentrations for the rookery
during the 2012 molting season, 2013 breeding season, and Central California
comparison sites. Error bars (±1 SD) indicate the sample was analyzed at least
three times. HgT for B5 (1,650 pM) was considered contaminated and is not
graphed.
The
study measured the concentration of total Hg (HgT) and methylmercury (MeHg) at Año Nuevo
and nearby shores that don’t have great marine mammal populations,
respectively. Data showed that the concentrations of HgT at Año Nuevo (3.1~34.0
pM ) and nearby shores (9.2~41.7 pM) had no distinct difference. On the
contrary, the MeHg level had an obvious increase at Año Nuevo during molting
season (0.28~9.5 pM) compared to that of breeding season (0.39~0.83 pM) and
that of nearby shores (0.16~0.41 pM). Scientists then tested the molted fur
samples from Northern elephant seals and found that they contained a high level
of HgT concentrations, >80% of which are presumed to be MeHg. The results
indicate a strong relationship between the increasing concentration of MeHg at Año
Nuevo and the molted fur of Northern elephant seals.
One big concern
for scientists is that along the shoreline of the U.S. Pacific Coast reside
hundreds of thousands of seals and sea lions, all of which have the potential
to increase the MeHg concentration in the seawater. So it’s important to
understand the mercury cycling in the ocean and its effect on human.
I thought the Washington Post article summarized the issue efficiently without over-hyping the topic. However, I am surprised they didn't explicitly address biomagnification - a common problem associated with mercury. When mercury reaches the ocean, it is consumed by small fish. Then large fish become contaminated by consuming the small fish. As mercury is a persistent chemical, and large fish consume many small fish over the course of time, mercury concentration within large fish increases dramatically.
ReplyDeleteYes, I agree with you that this article is objective. As for the biomagnification, it's an important issue, but not what they mainly wanted to discuss. I think that's why they didn't mention it.
DeleteHan, I agree that the WP article presented the study in a generally unbiased manner and did not over-hype its findings. I also found that they followed the same general tone as the study. I was impressed by the fact that they explicitly pointed out the research's major limitation. However, I do agree that they could have quantified the findings further and also could have clarified the conversion of inorganic Hg into MeHg and its bio-magnification up the food chain.
ReplyDeleteI also appreciate that they pointed out the limitation. Besides, I do agree that they could give more background information since it's a really complicated issue.
DeleteI think this is a great article, it's informative and very intriguing. I think the author should have expanded more on mercury's effects, particularly on how they affect the seals and sea lions. As the author mentioned, seals and sea lions eat contaminated fish on shore, and eventually the mercury is excreted into the ocean through their fur, but what effect does mercury have while it is inside their bodies? I think the author could have strengthened this article by answering this question, and describing more about the specifics of mercury poisoning in the species involved.
ReplyDeleteThat's true. They mentioned that Hg and MeHg have adverse health effects on human and marine organisms, but didn't go deeper. Although this study is mainly about mercury cycling, I think the author could have put some background knowledge into the article.
DeleteThese were very interesting articles. This topic of mercury contamination and how biomagnification occurs has a lot of potential for future research, specially when the process of Hg getting into the animal's fur is not yet understood. As mentioned before, maybe a bit more background of mercury's toxicity would have been helpful sense it only mentions methylmercury being a nerotoxin but it never tells you what it does AS a neurotoxin. Also, a question I would like to be answered in the future is why is it so toxic to human but other mammals have a way of excreting the mercury through varies ways ( at least two are mentioned in the paper).
ReplyDeleteYes, both the article and the study should have discussed what exact effects do Hg and MeHg have on human health. After all, that's what people most care about. I also agree that more studies should be done to discover how marine mammals excrete mercury. According to this study, it seems different mammals have different ways of excreting mercury.
DeleteIf mercury concentrations are highest in productive marine ecosystems, I would expect these concentrations to fluctuate throughout the year when you have more/less activity in the ecosystem (more or fewer organisms). I wonder how long it takes for the concentrations of MeHg to dilute back to safe levels as well.
ReplyDelete