Mercury in the Environment
Sarah provided you with an overview of how mercury affects biota. Here is a good USGS article that provides you with a review of the points that Sarah made.
Here is a question to test your understanding of some of these issues: Would you expect mercury to have a bigger impact on loons or on chickadees? Why?
-- Bill
Here is a question to test your understanding of some of these issues: Would you expect mercury to have a bigger impact on loons or on chickadees? Why?
-- Bill
11 Comments:
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By Zen Buraceski, At January 8, 2007 7:43 PM
It seems like the mercury would affect loons more because they eat fish quite a bit. I don't know about chickadees, but I assume they don't because they're not very big birds.
By Kaitlin Stenberg, At January 9, 2007 7:28 PM
Loons live off the water. They live in and around it. The piece we were asked to read told us that the loons diet is mostly fish and fish have high levels of mercury so the loons would have a higher level. Chickadees are located in more forest areas. I would guess that they do not eat fish taking them from that risk group. This is just my guess.
By Ian Macomber, At January 9, 2007 7:39 PM
It seems to me that loons would suffer a considerable amount since they expel mercury from their bodies by means of their eggs. I don't know if this is the case with chickadees. Since the dose makes the poison, I would say that loons in their embryonic stages are at a far greater risk to fatal levels of mercury than adult chickadees. Further, according to the article you referred us to, organisms in their embryonic state are much more sensitive to mercury levels than adults. This would mean that the loon population could be majorly affected if a whole generation of chicks was poisoned by mercury.
Kate also makes a great point. Where loons make fish the staple in their diet, they seem to be at a much larger risk for mercury poisoning than chickadees.
By Natalie Jimenez, At January 9, 2007 7:40 PM
I would think that mercury would affect the loons more than the chikadees because they spend time in the water and because they eat fish which contain mercury. Chikadees may pick up some dry particles in the air but it is probably washed off in a rainstorm and then some from the rain might stay on the chikadee but loons actually spend time in water and don't just get caught in storms. The fact that loons eat fish also adds mercury that they would collect in their bodies.
By Ashley Chenevert, At January 9, 2007 7:41 PM
Loons seem as though they would have a exposure to mercury seeing as how they live on the water, and also since loons ingest two pounds of fish a day, the likelihood of ingesting a high amount of mercury is very likely. Since Chickadees do not live on the water and also eat mainly insects, they should have less exposure to mercury.
By Andrea Jarrett, At January 9, 2007 7:50 PM
Sarah told us earlier that loons get rid of mercury through their eggs, so it seems like loons would be more susceptible to higher mercury levels from early development. After they hatch, loons spend most of their time in the water, where most of the mercury ends up. They live in it, and eat fish, which also contain high levels of mercury. Chickadees are smaller and live in the forested areas, so they would be less affected by the mercury.
By Courtney Keen, At January 9, 2007 8:01 PM
These are good ideas, definitely headed in the right direction.
Chickadees eat seeds.
What do we know about mercury that would make us think that seeds would have less mercury than fish? (The answer isn't just that fish have a lot of mercury. Think about the reason WHY. Why would a seed eater be less likely to be exposed to a lot of mercury?)
This is great stuff -- headed in the right direction.
-- Bill
By Bill Zoellick, At January 9, 2007 8:05 PM
Here's another surprise from mother nature, and something that scientists are actively researching right now. They've actually found that a bird that lives higher up in watersheds and that's not dependent on fish as part of the diet has more mercury in it than previously suspected. Here's an article from Audubon summarizing the study:
http://magazine.audubon.org/fieldnotes/fieldnotes0505.html
By Sarah Nelson, At January 9, 2007 8:16 PM
I read that article Sarah posted. I looked up the diet of the thrush in question http://en.wikipedia.org/wiki/Bicknell%27s_thrush and found that they are insectivores, but they also eat fruit. I hypothesis that chickadees might take up mercury that exists on the surface of the seed, but I would say the reason why mercury is less of a threat to them compared to loons would be because the chemical has bioaccumulated in fish, the main diet of the loon, while seeds are produced by trees or other plants which, as far as we know, do not take up mercury in excess from the environment.
The problem with my hypothesis is that this particular thrush mentioned in Sarah's article eats insects and fruit (not fish) but has been found to definitely harbor mercury in its veins. Why this is...I don't know right now.
By Natalie Jimenez, At January 11, 2007 7:46 PM
Thanks go to Sarah and Natalie for making this question more interesting than I had intended.
Natalie has her hands around the issue that I had in mind, which is bioaccumulation. Animals like loons (or non-vegetarian humans) that eat higher on the food chain are, in general, more likely to suffer from the effects of mercury.
As Natalie points out, the thrush's including insects as a good part of its diet mean that it is very probably at higher risk of bioaccumulation than a bird that is strictly a seed eater.
But, in fact (and Sarah's comment points this out) there is always the possibility of special interactions that can make a particular species more or less sensitive, regardless of where it is on the food chain. Certinaly, the environment it lives in is one such factor. Another could be some particularly devastating effect of the toxic chemical. The way that DDT makes egg shells thinner and much more likely to break is a good example.
-- Bill
By Bill Zoellick, At January 11, 2007 9:19 PM
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