Polyclilorinated bipheuyls (PCBs), a group of chemicals, can also be found in some fish. These man-made chemicals were used in many industries until 1977, when they were banned. PCBs were released or leaked into (lie tar and water and have bear transported around the globe.

　　How do mercury and PCBs end up in fish and the food supply? When they arc released into the air, they attach themselves to particles（微粒）.These particles settle on the ground and in the water and are eventually eater by micro-organisms. Small fish cat the micro-organisms, and large fish eat the small fish and on up the food chain.

　　Because they can negatively affect your health, the U.S. Eavirotunental Protectioc Agency advises that kids younger than 15 years old avoid fish that cortain high levels of mercury and PCBs. These include shark, swordfish, king rrnackerel, and tilefish.

　　There are also many types of fish that are good for you, but arc in danger of being wiped out because of ovcrfishing. Sonic are being fished in the wild so much that they cannot reproduce enough to survive.Others re being farmed in ways that are not environmentally friendly. These fish include red snapper.Atlantic salmon, bluefnn tuna. and king crab.

　　Despite these problems, there are several fish that are both healthy and sustainable (可持续的), such as Alaskan salmon, American catfish, Pacific cod, and several fans-raised fish and shellfish.

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