2018年2月21日 星期三

BBC事實查核:塑料垃圾該焚燒還是掩埋

http://www.bbc.com/zhongwen/trad/science-43131714?
BBC事實查核:塑料垃圾該焚燒還是掩埋
羅傑·哈拉賓(Roger Harrabin)BBC 環境事務分析員

2018年 2月 20日

......對那些很難循環再生的塑料垃圾,我們是燒呢,還是埋?

焚燒

「焚燒派」這麼說:塑料是從石油和天然氣提煉生產的,焚燒的時候會產生大量熱能。
乍看,把塑料垃圾放到焚燒爐裏燒,然後用產生的熱能來發電,似乎合情合理。
如果焚燒爐能把這個過程中剩餘的熱量搜集起來,用於辦公室和家庭供暖,利用效率豈非更高。
以這種方式焚燒塑料垃圾,目前在有些地方代替了燒煤或石油之類產生污染的燃料。
英國拉格比(Rugby)選區保守黨下院議員馬克·珀塞(Mark Pawsey)是議會包裝製造業跨黨派小組主席。他在下院表示,「廢物被用於產生熱能,讓我的選區裏的水泥廠得以生產水泥。
」我的感覺是,對包裝材料熱能價值的這種利用,遠勝於把它送到垃圾填埋場去。「
他的觀點得到此類焚燒爐的運營商的支持。他們的組織叫環境服務協會(Environmental Services Association,ESA)。
該協會會長雅各布·黑勒(Jacob Hayler)告訴我們:」通過焚燒來回收不可再生廢物的能量,要好過把它們送到垃圾填埋場。」
他援引政府文件,英國能源數據解析(Digest of UK Energy Statistics, DUKES)說,2016年「廢物能源」(Energy from Waste, EfW)消耗的垃圾相當於替代了250萬噸原始化石燃油。
黑勒說,總體而言,焚燒的溫室氣體排放量低於垃圾填埋。
這麼說,焚燒塑料很有道理。但是,事情並不那麼簡單。
因為,這些數據來自不分類的垃圾的焚燒,而不是光燒塑料。
普通家庭的生活垃圾在填埋場確實會產生溫室氣體,導致地球升溫,除非把這些填埋場氣體收集起來。
但這不適用於塑料,因為塑料是一種特別穩定的材料。它們不會在填埋場的地下分解,所以不會產生溫室氣體排放。
實際上,「掩埋派」也是振振有詞。
志願者在倫敦泰晤士河畔撿塑料瓶並點數。圖片版權PA
Image caption志願者在倫敦泰晤士河畔撿塑料瓶。英國環境部表示,必須停止輸出塑料垃圾的做法。

「掩埋派」

焚燒塑料會產生有毒有害氣體,如果焚燒爐效率不高,這些氣體會進入環境。據信現代焚燒爐基本上解決了這個問題。
但是,氣候變化也是需要考慮的一個問題。
據諮詢公司 Eunomia 計算,在用於發電的焚燒爐裏燒塑料,產生熱能的效率是25%,而新型燃氣火電站的效率是55%。
該公司的多米尼克·霍格(Dominic Hogg)告訴BBC:「在燒煤發電逐漸淘汰後,焚燒未分類垃圾發電將成為碳排放密度最高的發電方式。
」如果政府希望減少碳排放,那(燒垃圾)就沒有道理,除非政府採取激進的措施來減少未分類垃圾中的塑料數量。「
環保組織還擔心,如果因為中國拒收洋塑料垃圾導致塑料垃圾增多,而英國必須建更多的焚燒爐來應對,那會製造出新的需求:本來應該循環再生的塑料廢物也被用來餵焚燒爐。
英國政府似乎被這一派觀點說服了。環境部次長特蕾西·科菲(Therese Coffey)在議會下院聲明:」從環境的角度考慮,一般而言埋塑料比燒塑料好。「

攔截碳排放

確實,我們可以再進一步,來論證把塑料垃圾埋在填埋場是一種成本低廉的碳捕集和儲存方式。
數十年來,政府一直在承諾要開發能夠搜集火電站碳排放並將它們注入地下岩層的發電廠。
掩埋塑料也能取得同樣的效果,把不需要的碳鎖住,而成本卻只是一個零頭。
英國綠色和平組織的艾麗娜·珀麗薩諾(Elena Polisano)對此勉強表示同意。
她告訴BBC:「我們應該做的是,按這個順序,減少、重覆利用、循環再生。
」到了需要決定垃圾該焚燒還是掩埋的階段,我們應該已經是失敗多次了。
「但是,跟任由這些失敗以有毒氣體的形式在大氣中擴散相比,控制失敗還是更安全。」
這個問題看上去很學術,但對於英國政府卻很實際,尤其是因為環境大臣正在凖備新的垃圾處理計劃,而且還聲稱英國必須「停止離岸處理垃圾」。

2018年2月17日 星期六

BBC試驗:椰子油 好

Is coconut oil a superfood?

Michael Mosley
Image captionMichael Mosley investigates coconut oil claims
Sales of coconut oil are rocketing, propelled by celebrity endorsements and claims that drinking the stuff will cure everything from bad breath to digestive disorders.
Actress Angelina Jolie-Pitt is said to have a tablespoon or so with her breakfast most mornings, while model Miranda Kerr says she not only adds it to salads and smoothies, but she cooks with it and splashes it on her skin as well.
The health claims that swirl around coconut oil are treated with a great deal of scepticism by scientists.
If anything coconut oil is seen, in the scientific community, as an unhealthy fat. It is very high in saturated fat (86%), even more so than butter (51%) or lard (39%).
The reason that foods rich in saturated fats are frowned on is because eating them causes a rise in blood levels of LDL (low density lipoprotein).
LDL is known as "bad cholesterol" because high levels are linked with increased risk of heart disease.
On the other hand, saturated fats - which are particularly bad for you - also tend to raise HDL, "good" cholesterol, which has the opposite effect. It is possible that a particular food can raise overall cholesterol levels, yet still be heart-friendly.

Cholesterol check

So is coconut oil a cholesterol-busting wonder food, as some claim, or is this all dangerous hype?
Despite all the sound and fury that surrounds coconut oil there have been surprisingly few human studies carried out to test specific health claims.
So for the current BBC2 series of Trust Me I'm a Doctor, we thought we should help organise a trial.
The Trust Me team started by contacting Prof Kay-Tee Khaw and Prof Nita Forouhi, both eminent Cambridge academics.
With their help we recruited 94 volunteers, aged 50-75 and with no history of diabetes or heart disease, and designed a study to assess what effect eating different types of fat would have on their cholesterol levels.
We began by randomly allocating our volunteers to one of three groups. Every day for four weeks, the first was asked to eat 50g of extra virgin coconut oil - that's about three tablespoons full.
Chart showing how much saturated fat is in different food?
The second group was asked to consume the same amount of extra virgin olive oil.
Olive oil is a key element of the Mediterranean diet, which is widely seen as being extremely healthy.
And the third was asked to eat 50g of unsalted butter a day. Again, that adds up to just over three tablespoons.
The volunteers were told that they could consume these fats in whatever way they pleased, as long as they did so every day for the whole four weeks.
They were also warned that, because they were consuming an extra 450 calories a day, they might well put on some weight.
Before our volunteers started on their new high-fat regime we took blood samples to get baseline measurements, focusing mainly on their levels of LDL (the "bad" cholesterol) and HDL (the "good" cholesterol)
The importance of these two measures is that your heart attack risk is best calculated, not by looking at your total cholesterol score, but your total cholesterol divided by your HDL score. NHS Choices suggests that this figure should be below four.
So what happened? As expected the butter eaters saw an average rise in their LDL levels of about 10%, which was almost matched by a 5% rise in their HDL levels
Those consuming olive oil saw a small reduction, albeit a non-significant drop, in LDL cholesterol, and a 5% rise in HDL. So olive oil lived up to its heart-friendly reputation.

Premature?

But the big surprise was the coconut oil. Not only was there no rise in LDL levels, which was what we were expecting, but there was a particularly large rise in HDL, the "good" cholesterol, up by 15%
On the face of it that would suggest that the people consuming the coconut oil had actually reduced their risk of developing heart disease or stroke.
CoconutsImage copyrightGETTY IMAGES
Image captionCoconut oil is high in saturated fat
I asked Prof Khaw, who was clearly surprised by these results, why she thought it had happened
"I have no real idea," she candidly replied. "Perhaps it is because the main saturated fat in coconut oil is lauric acid and lauric acid may have different biological impacts on blood lipids to other fatty acids. The evidence for that comes mainly from animals, so it was fascinating to see this effect in free-living humans."
So should we be hailing coconut oil as a health food?
"I think decisions to eat particular oils depend on more than just the health effects", she said. "This is just one study and it would be irresponsible to suggest changing dietary advice based on one study, however well conducted."
This was a very short-term study and compared to olive oil, research on coconut oil is at an early stage.
So the claims about coconut oil being a superfood are premature.
But if, like me, you enjoy putting coconut in your curries, there seems no very good reason to stop.



BBC試驗:椰子油是超級食品還是心臟病殺手?

  • 2018年 1月 9日
椰子油可以食用,也可以美容。圖片版權GETTY IMAGES
Image caption椰子油可以食用,也可以美容。
最近椰子油的銷量猛增,這可能與名人效應有關。據稱,椰子油包治百病,從口臭到消化不良。
據說,著名好萊塢影星安吉麗娜·朱莉幾乎每天早晨都在早餐中吃一湯匙椰子油。
她還在烹調中使用椰子油,並用椰子油來護膚。
椰子油真這麼神奇嗎?許多科學家都對椰子油的健康療效持懷疑態度。
不僅如此,科學界還把椰子油看作是壞脂肪,因為它富含飽和脂肪(86%),遠遠高於黃油(51%)以及豬油(39%)。
因此BBC"相信我,我是醫生"節目小組決定做一個實驗,看看椰子油真的是超級食品還是垃圾食品?
人們吃了富含飽和脂肪的食品後會導致血液中壞膽固醇(LDL)的上升。

膽固醇與心臟病

如果人體中的壞膽固醇含量高則會增加心臟病的風險。
但是,另一方面雖然飽和脂肪對健康有害,然而它也能增加人體中好膽固醇(HDL)的水平。好膽固醇可以保護心臟。
換句話說,有些食品可以讓膽固醇的總含量增加,但同時仍然對心臟有利。

椰子油試驗

儘管椰子油據說具有種種神奇妙處,但卻沒有什麼可信的人體試驗來測試它的效果。
因此我們決定來做這個實驗。"相信我,我是醫生"節目小組邀請了94名年齡在50-75歲之間的志願者。他們必須沒有糖尿病和心臟病史。
我們決定測試一下不同脂肪對志願者膽固醇水平的影響。
我們把志願者分為3組,第一組連續4周每天都要吃50克的高質椰子油;第二組連續4周每天吃同樣數量的高質橄欖油;第三組志願者吃的是未加鹽的黃油。
廣泛認為橄欖油是健康食品,它也是地中海飲食中的一個重要元素。
在志願者開始試驗前,我們先採了他們血樣,特別是他們體內的LDL和HDL的水平。
因為這兩項指標對心臟病風險指數最重要,特別是總膽固醇除以好膽固醇得出的比例,這一數字最好在4以下。
結果令人吃驚
試驗的結果顯示,吃黃油的志願者壞膽固醇水平上升了大約10%,好膽固醇上升了5%。
橄欖油志願者的壞膽固醇水平略有下降,好膽固醇水平上升了5%。
但最令人吃驚的則是吃椰子油的這組試驗者,不但他們體內的壞膽固醇水平沒有上升,他們好膽固醇水平激增了15%。
表面上看,食用椰子油的人群實際上降低了患心臟病或是中風的危險。
橄欖油圖片版權GETTY IMAGES
Image caption普遍認為橄欖油是健康食品。
參與該試驗項目的醫生們也對這一結果感到意外。
Khaw教授說,也許椰子油中所含的飽和脂肪主要是月桂酸,而月桂酸對血脂的影響同其它脂肪酸不一樣。
這是否意味著我們可以把椰子油看作是一種健康食品呢?
Khaw教授認為,這畢竟只是一次試驗的結果而已。選用何種脂肪油不單單要僅從健康方面考慮,如果僅憑借一次試驗的結果來建議人們改變飲食習慣則顯得有點不負責任。
此外,這只是一次短期的試驗,而且試驗還處於早期階段。
也許,現在就稱椰子油是超級食品還有點不太成熟。
但是,如果你像我一樣喜歡在咖喱菜餚中加點椰子油,那就大膽地加吧。