美研究「草脫淨」威脅雄性動物性發展 | 台灣環境資訊協會-環境資訊中心

美研究「草脫淨」威脅雄性動物性發展

2010年08月31日
摘譯自2010年8月25日ENS美國,北卡州,三角研究園區報導;林可麗編譯;范仕穎審校

在玉米田噴灑農藥的情形。一項由美國聯邦政府科學家進行的新研究結果顯示,在出生前暴露於低劑量的除草劑「草脫淨」(atrazine)下的雄鼠,跟沒有暴露在草脫淨下的雄鼠比較下,有較高的可能發展出攝護腺發炎以及出現性晚熟的症狀。

草脫淨是美國最常用的農業用殺草劑之一,在美國每年有超過3萬6千公噸的草脫淨被噴灑在像玉米跟甘蔗這類的農作物田裡,用來控制闊葉跟尖葉雜草的生長。大約40種知名農藥的殺草劑都使用草脫淨作為成分之一。

但是草脫淨跟其副產品都是在環境中具持久性的內分泌干擾素(環境荷爾蒙),會進入人類使用的地表水跟地下水中。

芬頓博士(Suzanne Fenton),圖片來源:NIEHS。這份了解草脫淨如何影響雄鼠的研究,由美國國家衛生研究院國家環境衛生科學機構的與史坦克博士(Jason Stanko)共同主持。這組科學家以接近草脫淨的飲用水法定標準濃度對雄鼠進行實驗。草脫淨在飲用水中最高的污染容許濃度是3ppb(ppb:十億分之一)。

生殖內分泌學家芬頓博士說,「我們沒有預料到在這麼低的濃度下也會有這些影響。」2009年的時候,美國環保署對草脫淨開始一項全面性的新評估計畫,用來研究草脫淨對人體的影響。在2010年9月研究計畫結束時,美國環保署說他們將會決定是否需要修正現在草脫淨的風險評估,並且決定是否需要進行更嚴格的管制以保護大眾健康。

這是自1990年初期開始美國環保署第三次對草脫淨進行評估。前兩次審查評估美國環保署判定草脫淨對人體不會造成重大影響。最近的一次評估審查了6千份相關研究資料以及8萬筆的公共意見後,在2006年完成。

研究人員發現攝護腺發炎的比例在控制組雄鼠中為48%,出生前暴露於混和草脫淨跟分解後產物下的的雄性後代則攝護腺發炎比率則升至81%。草脫淨劑量越多,發炎情形就越嚴重。

研究論文的作者之一,美國國家環境衛生科學研究機構病理學家,也是獸醫的馬拉奇博士說,「值得注意的是攝護腺發炎隨著時間有好轉的跡象,也就是說這些影響也許不會是永久性的。」

科學家也發現了暴露在草脫淨下的動物有性晚熟的跡象。

這項新的研究是芬頓第二篇以動物受低劑量草脫淨與其代謝產物混和物影響的第二篇研究論文。

芬頓是2007年一篇研究論文的資深作者,論文探討了低劑量的草脫淨混和物延緩了同胎出生的哺乳類動物雌鼠發展,當初實驗用的對象跟現在實驗的老鼠是同胎出生的。

芬頓指出這些研究發現可能不僅僅只和草脫淨有關,而是與其他殺草劑中發現的chlorotriazine家族有關,包括普拔根(propazine)以及草滅淨(simazine)。這三種殺草劑會製造出相同的分解產物。

芬頓說需要進行更多的研究來了解chlorotriazine與其在哺乳類動物體內以及攝護腺組織內的代謝機制。

草脫淨在歐洲已經被禁用,即使是製造商Syngenta的原產地瑞士。

Atrazine Threat to Male Sexual Development Revealed
RESEARCH TRIANGLE PARK, North Carolina, August 25, 2010 (ENS)

Male rats exposed before birth to low doses of the weedkiller atrazine are more likely to develop prostate inflammation and to go through puberty later than non-exposed animals, finds a new study conducted by federal government scientists.

One of the most common agricultural herbicides in the United States, some 80 million pounds of atrazine are applied across the country every year to control broadleaf and grassy weeds in crops such as corn and sugar cane. It is the main ingredient in about 40 name-brand herbicides.

But atrazine and its byproducts are known to be endocrine disrupters that are persistent in the environment, making their way into both surface water and groundwater supplies.

This study on how atrazine affects male rats was led by Suzanne Fenton, PhD, and Jason Stanko, PhD, of the National Institute of Environmental Health Sciences, part of the National Institutes of Health. The scientists tested male rats using atrazine concentrations close to the regulated levels in drinking water sources.

The current maximum contamination level of atrazine allowed in drinking water is three parts per billion. "We didn't expect to see these kinds of effects at such low levels," said Dr. Fenton, a reproductive endocrinologist.

In 2009, the EPA began a comprehensive new evaluation of atrazine to determine its effects on humans. At the end of this process, in September 2010, the agency has said it will decide whether to revise its current risk assessment of atrazine and whether new restrictions are necessary to better protect public health.

This is the third time since the early 1990s the EPA has evaluated atrazine. In each of the two previous reviews the EPA ruled in atrazine's favor, most recently in 2006 after considering 6,000 studies and 80,000 public comments.

The researchers found that the incidence of prostate inflammation went from 48 percent in the control group of rats to 81 percent in the male offspring who were exposed to a mixture of atrazine and its breakdown products before birth. The severity of the inflammation increased with the strength of the doses.

"It was noteworthy that the prostate inflammation decreased over time, suggesting the effects may not be permanent," said David Malarkey, DVM, PhD, an NIEHS pathologist and co-author on the paper.

The scientists also found that puberty was delayed in the animals who exposed to atrazine.

This new study is Fenton's second paper showing low dose effects of atrazine metabolite mixtures.

Fenton was the senior author on a 2007 paper which demonstrated low doses of the atrazine mix delayed mammary development in female siblings from the same rat litters used in this current study.

Fenton points out that these findings may extend beyond atrazine alone, and may be relevant to other herbicides found in the same chlorotriazine family, including propazine and simazine. All three of the herbicides create the same set of breakdown products.

Fenton says more research is needed to understand the mechanism of action of the chlorotriazines and their metabolites on mammary and prostate tissue.

Atrazine has been banned in Europe, even in Switzerland, the home of manufacturer Syngenta.

全文及圖片詳見:ENS報導