*Q4.关于bear的说法正确的是? 选了其身上的毒素是从algea中积累的。 (本月710狗主 Q48，V38) 4.疑似原文： Biomagnificationmeans that the level of toxin in animals' tissues rises as one moves up thefood chain. For instance, as larvae eat algae, fish eat the larvae, and biggerfish eat smaller fish, the toxin present in the algae becomes increasinglyconcentrated; top predators like swordfish and polar bears end up with thehighest doses in their tissues. This can happen with stable, fat-solublechemicals that aren't easily excreted in urine or feces. Biomagnification wasfirst studied in the late 1960s in aquatic food webs, explains Frank Gobas,professor at Simon Fraser University and leader of the study. To screenchemicals, scientists began using a property known as Kow, which indicates howreadily a chemical dissolves in water compared with fat and thus predicts howeasily it will move from a fish's blood lipids into water through its gills.Low-Kow, or more water soluble, chemicals don't build up in the fish food chainand were assumed to be safe.
Environmentalchemists realized, however, that this assumption might not hold in food chainsinvolving mammals and birds because their lungs are in contact with air, notwater. This means that many chemicals that are relatively soluble in water andtherefore don't accumulate in fish might remain in the tissues of land animalsif they aren't volatile enough to easily move from the lungs into the air(predicted by a property called Koa). Supporting this idea, some organicchemicals that don't biomagnify in fish appeared to be doing so in otherwildlife and humans.
Toexplore this hypothesis, Gobas and graduate student Barry Kelly and colleaguescollected plant and animal tissue samples— from lichens to beluga whales killedin Inuit hunts—in the Arctic, where, because of weather patterns and coldtemperatures, organic pollutant levels are high. They tested the samples not onlyfor known POPs but also for several chemicals with a low Kow but high Koa,which suggested they might biomagnify in air-breathing animals. The measuredlevels of contaminants for various animals in aquatic and land food webs weresimilar to those predicted from a bioaccumulation model incorporating Koa andKow, suggesting the model was correct. Chemicals with low Kow and high Koastood out as potentially risky.
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发表于 2012-11-23 23:15:21
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