With a better understanding of how the nervous system works, Lauren was ready to meet again with Carl. After reviewing the anatomy and physiology, Carl said, “As you’ve probably guessed, the hunch I had was that a neurotoxin is poisoning the animals. Because the animals are found in different habitats and occupy different places on the food chain, I’m guessing the neurotoxin is found in something that is common to all of them—their water source.”
“But yesterday you said that it’s probably not something that’s seeping in nor something someone deliberately put there,” Lauren said.
“Right, I think it’s a neurotoxin that is being produced in the water by microorganisms—cyanobacteria to be exact. Cyanobacteria blooms can occur in any kind of water, but can especially be found in stagnant water, and can appear as a surface film at one end of a lake or pond. The cyanos produce toxic metabolic byproducts, including some powerful neurotoxins. I noticed a surface film at Bill’s pond yesterday. It hasn’t rained in a while and the air’s been pretty still, so the film of cyanos has had time to accumulate.”
“OK, so how do these neurotoxins work?” asked Lauren.
“One kind of neurotoxin is called Anatoxin-A,” replied Carl. “It works by mimicking acetylcholine, but the body’s natural acetylcholinesterase can’t break it down. So what would that cause, Lauren?”
Lauren thought for a moment and then responded.
“Excellent,” Carl said. “Another kind of neurotoxin is Saxitoxin, which acts by blocking the voltage-dependent sodium channel. And what would that cause, Lauren?”
Again Lauren answered.
“Excellent again,” said Carl.
Then Lauren asked, “So how do you know for sure it’s either one of those, and if it is, which one is it and what can you do about it?”
“We took water samples,” Carl said, “so we can look for the presence of the cyanobacteria in the water, and we can use high performance liquid chromatography to look for either of the suspected toxins. Since we know exactly what we’re looking for, we’ll know if it’s there or not. Finally, we can test the stomach contents of at least the recent kills for presence of the toxins. As for what can be done, Bill can fence the area off to keep animals from drinking from the pond. We can come out and test the water samples whenever the weather gets like this, and if it’s a recurring problem, Bill can add an algaecide to kill the cyanobacteria. For right now, it’s supposed to cool down and rain for a couple of days, so that will take care of the problem, at least for the next week or so.”
Originally published at http://www.sciencecases.org/hot_august/hot_august3.asp
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