北极汞污染严重 气温上升或可以拯救北极熊？

As polar bears are forced onto land, they're feeding on animals with less mercury—reducing their levels of the toxic pollutant. Christopher Intagliata reports.

北极熊被迫迁移到陆上，它们捕食的动物体内汞含量更少——这就降低了它们摄入的有毒污染物的量。克里斯托弗˙因塔利亚塔报道。

As climate change warms the Arctic, sea ice there is disappearing at record rates—sea ice that polar bears prefer to prowl. As a result, some bears are spending more time on solid land. And are thus switching up their diets, too. Instead of the ringed seals they ate out on the ice, the bears are foraging on bowhead whale carcasses, up on the beach.

随着气候变化，北极变暖，海冰正在以空前的速度消失，而这些海冰正是北极熊们喜爱的活动之地。海冰的消失导致一些北极熊在陆地上活动的时间增加，这也改变了它们的饮食习惯。这些北极熊以前在海冰上捕食环斑海豹，而现在它们觅食的是被冲到海岸上来的弓头鲸尸体。

So what does this mean for them?

那么这对它们来说意味着什么?

"It's sort of good news/bad news." Melissa McKinney, an ecotoxicologist at the University of Connecticut. The bad news is that the bears are losing vital habitat. But the silver lining is that bears decamping to land have lower levels of toxic mercury due to their changes in diet.

“这可以说既是个好消息又是个坏消息。”康涅狄格大学生态毒理学家梅丽莎˙麦金尼(Melissa McKinney)说。坏消息是北极熊们正在不断失去至关重要的栖息地。但是我们还是能看到一线希望：由于饮食习惯的改变，撤到陆地上的北极熊体内的汞含量降低了。

McKinney and her team studied hair samples from one polar bear population in Alaska, from 2004 to 2011. In that time they saw a 65 percent in the bears' mercury levels—to concentrations below the known threshold for negative biological effects. And it looks like the different diet may be the reason.

从2004年到2011年，麦金尼和她的团队研究了阿拉斯加的一个北极熊群体的毛发样本。他们发现北极熊体内的汞含量在这个时间段降低了65%——现在它们体内的汞含量浓度已经低于负面生物学效应的阈值。而原因很可能就是饮食的改变。

Bowhead whales feed on plankton, while ringed seals eat fish and other animals in which mercury has had the chance to accumulate. "So if polar bears are feeding on prey items that are lower in the food chain, then they're likely experiencing a less mercury-contaminated food source than they would be otherwise."

弓头鲸以浮游生物为生，而环斑海豹则捕食鱼和其他体内有汞积累的动物。“所以，如果北极熊捕食那些处于食物链较底端的生物，那么它们接触到的食物源所受到的汞污染可能更少。

The bears that feed on whales are also in better condition—higher body-mass index. And being well fed means their bodies don't need to break down fat and muscle energy stores, where a lot of whatever mercury they have consumed is locked up. The study is in the journal Environmental Science and Technology. [Melissa A. McKinney et al., Ecological Change Drives a Decline in Mercury Concentrations in Southern Beaufort Sea Polar Bears]

这些捕食鲸类的北极熊的身体状况也更好——它们有更高的身体质量指数。吃得很好意味着它们的身体不需要分解脂肪，而且肌肉能量能够被储存下来，这样它们摄入的大量汞就能被固定住。这项研究发表在期刊《环境科学与技术》上。[Melissa A. McKinney et al., Ecological Change Drives a Decline in Mercury Concentrations in Southern Beaufort Sea Polar Bears]

“We see polar bears as a sentinel of climate change. And I think it's really important for us to remember that, either positively or negatively, climate change can shape the risks that are posed by other environmental stressors—in this case toxic pollutants." Of course, it would be better to stop the warming and have less mercury in the environment. But the takeaway here is that climate change has multiple effects that go beyond disappearing ice.

“我们把北极熊视为气候变化的一个指示。我认为我们必须记住一点，气候变化会对由其他环境压力造成的风险产生正面或者负面的影响——这个事件中的风险因素便是毒素污染。“诚然，如果既能阻止气候变暖，又能降低环境中的汞含量就更好了。但是目前的关键问题是，气候变化造成的多重影响远不只是海冰消失。

—Christopher Intagliata

延伸阅读：

北极汞污染源还是人 《自然》：人类活动排放气态汞进入大气