食物链的文章是这篇嘛？今天正好有空在家搜索了一下： Biomagnification means that the level of atoxin in animals' tissues rises as one moves up the food chain. For instance,as larvae eat algae, fish eat the larvae, and bigger fish eat smaller fish, thetoxin present in the algae becomes increasingly concentrated; top predatorslike swordfish and polar bears end up with the highest doses in their tissues.This can happen with stable, fatsoluble chemicals that aren't easily excretedin urine or feces. Biomagnification was first studied in the late 1960s inaquatic food webs, explains Frank Gobas, professor at Simon Fraser Universityand leader of the study. To screen chemicals, scientists began using a propertyknown as Kow, which indicates how readily a chemical dissolves in watercompared with fat and thus predicts how easily it will move from a fish's bloodlipids into water through its gills. Low-Kow, or more watersoluble, chemicalsdon't build up in the fish food chain and were assumed to be safe. Environmental chemists realized, however, that this assumption might not holdin food chains involving mammals and birds because their lungs are in contactwith air, not water. This means that many chemicals that are relatively solublein water and therefore don't accumulate in fish might remain in the tissues ofland animals if they aren't volatile enough to easily move from the lungs intothe air (predicted by a property called Koa). Supporting this idea, someorganic chemicals that don't biomagnify in fish appeared to be doing so inother wildlife and humans. To explore this hypothesis, Gobas andgraduate student Barry Kelly and colleagues collected plant and animal tissuesamples— from lichens to beluga whales killed in Inuit hunts—in the Arctic,where, because of weather patterns and cold temperatures, organic pollutantlevels are high. They tested the samples not only for known POPs but also forseveral chemicals with a low Kow but high Koa, which suggested they mightbiomagnify in air-breathing animals. The measured levels of contaminants forvarious animals in aquatic and land food webs were similar to those predictedfrom a bioaccu- mulation model incorporating Koa and Kow, suggesting the modelwas correct. Chemicals with low Kow and high Koa stood out as potentiallyrisky. -- by 会员 XYXB (2010/4/2 23:24:45)
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