So, after a bit more than a year of the Friday Parasite, some of you are probably scratching your heads, saying “ok, the parasites are kinda cool, and definitely gross, but are they actually good for anything?” Funny you should ask. I recently ran across an interesting study in the July 2007 issue of Parasitology that describes how intestinal parasites in fish can assess heavy-metal pollution in the open ocean.
Using animals as heavy-metal test strips isn’t a new idea: scientists have assessed environmental pollution by measuring metal accumulation inside organisms like lichens, mosses, predatory insects and mussels. But all of these organisms live either on land or close to the shore. There was no easy way to test levels of heavy metals in the ocean, so there was no way of knowing how polluted it was out there.
In this study, a team of scientists led by Masoumeh Malek from the University of Tehran caught sharks in the Persian Gulf, dissected out their intestinal tapeworms, and tested both the worms and the shark tissues for cadmium and lead. The sharks had some heavy metals in their tissues, but the tapeworms had more. A lot more. Heavy metal levels in the worms were 278 to 455 times higher than in the sharks they lived in.
Sharks, as major predators, are eating fish that have already accumulated heavy metals through the food chain. By filtering the predigested fish goo in their intestines, their tapeworms accumulate even more of the metals. The more metals in the sharks’ environment, the more metals you’ll find in their tapeworms.
So we can use tapeworms to test environmental pollution. This particular study may have used sharks, but there's no reason to assume that other oceangoing fish can't be harvested for their parasites instead. (Sharks don't breed very quickly, and it's easy for them to get overfished.)
Source: Malek, M. et al. 2007. Parasites as heavy metal bioindicators in the shark Carcharhinus dussumieri from the Persian Gulf. Parasitology 134(7): 1053-1056.
(Parasitology is a subscription-only journal, but you can read a news article about the paper here.)
Comments